Patients with ARDS show improvement but not normalisation of alveolar surface activity with surfactant treatment: putative role of neutral lipids

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.

HUB genes transcriptionally regulate lipid metabolism in alveolar type II cells under LPS stimulation

Objective

Alveolar type II (ATII) cells produce pulmonary surfactant (PS) essential for maintaining lung function. The aberration or depletion of PS can cause alveolar collapse, a hallmark of acute respiratory distress syndrome (ARDS). However, the intricacies underlying these changes remain unclear. This study aimed to elucidate the mechanisms underlying PS perturbations in ATII cells using transcriptional RNA-seq, offering insights into the pathogenesis of ARDS.

Methods

ATII cells were identified using immunofluorescence targeting surface-active protein C. We used 24-h lipopolysaccharide (LPS)-induced ATII cells as an ARDS cell model. The efficacy of the injury model was gauged by detecting the presence of tumour necrosis factor-α and interleukin-6. RNA-seq analysis was performed to investigate the dynamics of PS deviation in unaltered and LPS-exposed ATII cells.

Results

Whole-transcriptome sequencing revealed that LPS-stimulated ATII cells showed significantly increased transcription of genes, including Lss, Nsdhl, Hmgcs1, Mvd, Cyp51, Idi1, Acss2, Insig1, and Hsd17b7, which play key roles in regulating cholesterol biosynthesis. We further verified gene levels using real-time quantitative PCR, and the results showed that the mRNA expression of these genes increased, which was consistent with the RNA-seq results.

Conclusion

Our study revealed pivotal transcriptional shifts in ATII cells after LPS exposure, particularly in nine key lipid and cholesterol metabolism genes. This altered expression might disrupt the lipid balance, ultimately affecting PS function. This finding deepens our understanding of the aetiology of ARDS and may lead to new therapeutic directions.

Molecular Impact of Conventional and Electronic Cigarettes on Pulmonary Surfactant

The alveolar epithelium is covered by a non-cellular layer consisting of an aqueous hypophase topped by pulmonary surfactant, a lipo-protein mixture with surface-active properties. Exposure to cigarette smoke (CS) affects lung physiology and is linked to the development of several diseases. The macroscopic effects of CS are determined by several types of cell and molecular dysfunction, which, among other consequences, lead to surfactant alterations. The purpose of this review is to summarize the published studies aimed at uncovering the effects of CS on both the lipid and protein constituents of surfactant, discussing the molecular mechanisms involved in surfactant homeostasis that are altered by CS. Although surfactant homeostasis has been the topic of several studies and some molecular pathways can be deduced from an analysis of the literature, it remains evident that many aspects of the mechanisms of action of CS on surfactant homeostasis deserve further investigation.

Pulmonary surfactant and COVID-19: A new synthesis

Chapter 1

COVID-19 pathogenesis poses paradoxes difficult to explain with traditional physiology. For instance, since type II pneumocytes are considered the primary cellular target of SARS-CoV-2; as these produce pulmonary surfactant (PS), the possibility that insufficient PS plays a role in COVID-19 pathogenesis has been raised. However, the opposite of predicted high alveolar surface tension is found in many early COVID-19 patients: paradoxically normal lung volumes and high compliance occur, with profound hypoxemia. That 'COVID anomaly' was quickly rationalised by invoking traditional vascular mechanisms-mainly because of surprisingly preserved alveolar surface in early hypoxemic cases. However, that quick rejection of alveolar damage only occurred because the actual mechanism of gas exchange has long been presumed to be non-problematic, due to diffusion through the alveolar surface. On the contrary, we provide physical chemical evidence that gas exchange occurs by an process of expansion and contraction of the three-dimensional structures of PS and its associated proteins. This view explains anomalous observations from the level of cryo-TEM to whole individuals. It encompasses results from premature infants to the deepest diving seals. Once understood, the COVID anomaly dissolves and is straightforwardly explained as covert viral damage to the 3D structure of PS, with direct treatment implications. As a natural experiment, the SARS-CoV-2 virus itself has helped us to simplify and clarify not only the nature of dyspnea and its relationship to pulmonary compliance, but also the fine detail of the PS including such features as water channels which had heretofore been entirely unexpected.

Chapter 2

For a long time, physical, colloid and surface chemistry have not intersected with physiology and cell biology as much as we might have hoped. The reasons are starting to become clear. The discipline of physical chemistry suffered from serious unrecognised omissions that rendered it ineffective. These foundational defects included omission of specific ion molecular forces and hydration effects. The discipline lacked a predictive theory of self-assembly of lipids and proteins. Worse, theory omitted any role for dissolved gases, O2, N2, CO2, and their existence as stable nanobubbles above physiological salt concentration. Recent developments have gone some way to explaining the foam-like lung surfactant structures and function. It delivers O2/N2 as nanobubbles, and efflux of CO2, and H2O nanobubbles at the alveolar surface. Knowledge of pulmonary surfactant structure allows an explanation of the mechanism of corona virus entry, and differences in infectivity of different variants. CO2 nanobubbles, resulting from metabolism passing through the molecular frit provided by the glycocalyx of venous tissue, forms the previously unexplained foam which is the endothelial surface layer. CO2 nanobubbles turn out to be lethal to viruses, providing a plausible explanation for the origin of 'Long COVID'. Circulating nanobubbles, stable above physiological 0.17 M salt drive various enzyme-like activities and chemical reactions. Awareness of the microstructure of Pulmonary Surfactant and that nanobubbles of (O2/N2) and CO2 are integral to respiratory and circulatory physiology provides new insights to the COVID-19 and other pathogen activity.

A recipe for a good clinical pulmonary surfactant

The lives of thousands premature babies have been saved along the last thirty years thanks to the establishment and consolidation of pulmonary surfactant replacement therapies (SRT). It took some time to close the gap between the identification of the biophysical and molecular causes of the high mortality associated with respiratory distress syndrome in very premature babies and the development of a proper therapy. Closing the gap required the elucidation of some key questions defining the structure–function relationships in surfactant as well as the particular role of the different molecular components assembled into the surfactant system. On the other hand, the application of SRT as part of treatments targeting other devastating respiratory pathologies, in babies and adults, is depending on further extensive research still required before enough amounts of good humanized clinical surfactants will be available. This review summarizes our current concepts on the compositional and structural determinants defining pulmonary surfactant activity, the principles behind the development of efficient natural animal-derived or recombinant or synthetic therapeutic surfactants, as well as a the most promising lines of research that are already opening new perspectives in the application of tailored surfactant therapies to treat important yet unresolved respiratory pathologies.

Mechanobiology of Pulmonary Diseases: A Review of Engineering Tools to Understand Lung Mechanotransduction

Cells within the lung micro-environment are continuously subjected to dynamic mechanical stimuli which are converted into biochemical signaling events in a process known as mechanotransduction. In pulmonary diseases, the abrogated mechanical conditions modify the homeostatic signaling which influences cellular phenotype and disease progression. The use of in vitro models has significantly expanded our understanding of lung mechanotransduction mechanisms. However, our ability to match complex facets of the lung including three-dimensionality, multicellular interactions, and multiple simultaneous forces is limited and it has proven difficult to replicate and control these factors in vitro. The goal of this review is to (a) outline the anatomy of the pulmonary system and the mechanical stimuli that reside therein, (b) describe how disease impacts the mechanical micro-environment of the lung, and (c) summarize how existing in vitro models have contributed to our current understanding of pulmonary mechanotransduction. We also highlight critical needs in the pulmonary mechanotransduction field with an emphasis on next-generation devices that can simulate the complex mechanical and cellular environment of the lung. This review provides a comprehensive basis for understanding the current state of knowledge in pulmonary mechanotransduction and identifying the areas for future research.

Lipid-based therapies against SARS-CoV-2 infection

Viruses have evolved to manipulate host lipid metabolism to benefit their replication cycle. Enveloped viruses, including coronaviruses, use host lipids in various stages of the viral life cycle, particularly in the formation of replication compartments and envelopes. Host lipids are utilised by the virus in receptor binding, viral fusion and entry, as well as viral replication. Association of dyslipidaemia with the pathological development of Covid‐19 raises the possibility that exploitation of host lipid metabolism might have therapeutic benefit against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). In this review, promising host lipid targets are discussed along with potential inhibitors. In addition, specific host lipids are involved in the inflammatory responses due to viral infection, so lipid supplementation represents another potential strategy to counteract the severity of viral infection. Furthermore, switching the lipid metabolism through a ketogenic diet is another potential way of limiting the effects of viral infection. Taken together, restricting the access of host lipids to the virus, either by using lipid inhibitors or supplementation with exogenous lipids, might significantly limit SARS‐CoV‐2 infection and/or severity.

An adverse outcome pathway for lung surfactant function inhibition leading to decreased lung function

Inhaled substances, such as consumer products, chemicals at the workplace, and nanoparticles, can affect the lung function in several ways. In this paper, we explore the adverse outcome pathway (AOP) that starts when inhaled substances that reach the alveoli inhibit the function of the lung surfactant, and leads to decreased lung function. Lung surfactant covers the inner surface of the alveoli, and regulates the surface tension at the air-liquid interface during breathing. The inhibition of the lung surfactant function leads to alveolar collapse because of the resulting high surface tension at the end of expiration. The collapsed alveoli can be re-opened by inspiration, but this re-opening causes shear stress on cells covering the alveoli. This can damage the alveolar-capillary membrane integrity, allowing blood components to enter the alveolar airspace. Blood components, such as albumin, can interact with the lung surfactant and further inhibit its function. The collapse of the alveoli is responsible for a decrease in the surface area available for blood oxygenation, and it reduces the volume of air that can be inhaled and exhaled. These different key events lead to decreased lung function, characterized by clinical signs of respiratory toxicity and reduced blood oxygenation. Here we present the weight of evidence that supports the AOP, and we give an overview of the methods available in vitro and in vivo to measure each key event of the pathway, and how this AOP can potentially be used in screening for inhalation toxicity.

Molecular and biophysical mechanisms behind the enhancement of lung surfactant function during controlled therapeutic hypothermia

Therapeutic hypothermia (TH) enhances pulmonary surfactant performance in vivo by molecular mechanisms still unknown. Here, the interfacial structure and the composition of lung surfactant films have been analysed in vitro under TH as well as the molecular basis of its improved performance both under physiological and inhibitory conditions. The biophysical activity of a purified porcine surfactant was tested under slow and breathing-like dynamics by constrained drop surfactometry (CDS) and in the captive bubble surfactometer (CBS) at both 33 and 37 °C. Additionally, the temperature-dependent surfactant activity was also analysed upon inhibition by plasma and subsequent restoration by further surfactant supplementation. Interfacial performance was correlated with lateral structure and lipid composition of films made of native surfactant. Lipid/protein mixtures designed as models to mimic different surfactant contexts were also studied. The capability of surfactant to drastically reduce surface tension was enhanced at 33 °C. Larger DPPC-enriched domains and lower percentages of less active lipids were detected in surfactant films exposed to TH-like conditions. Surfactant resistance to plasma inhibition was boosted and restoration therapies were more effective at 33 °C. This may explain the improved respiratory outcomes observed in cooled patients with acute respiratory distress syndrome and opens new opportunities in the treatment of acute lung injury.

Surfactant Injury in the Early Phase of Severe Meconium Aspiration Syndrome

No in vivo data are available regarding the effect of meconium on human surfactant in the early stages of severe meconium aspiration syndrome (MAS). In the present study, we sought to characterize the changes in surfactant composition, function, and structure during the early phase of meconium injury. We designed a translational prospective cohort study of nonbronchoscopic BAL of neonates with severe MAS (n = 14) or no lung disease (n = 18). Surfactant lipids were analyzed by liquid chromatography-high-resolution mass spectrometry. Secretory phospholipase A₂ subtypes IB, V, and X and SP-A (surfactant protein A) were assayed by ELISA. SP-B and SP-C were analyzed by Western blotting under both nonreducing and reducing conditions. Surfactant function was assessed by adsorption test and captive bubble surfactometry, and lung aeration was evaluated by semiquantitative lung ultrasound. Surfactant nanostructure was studied using cryo-EM and atomic force microscopy. Several changes in phospholipid subclasses were detected during MAS. Lysophosphatidylcholine species released by phospholipase A₂ hydrolysis were increased. SP-B and SP-C were significantly increased together with some shorter immature forms of SP-B. Surfactant function was impaired and correlated with poor lung aeration. Surfactant nanostructure was significantly damaged in terms of vesicle size, tridimensional complexity, and compactness. Various alterations of surfactant phospholipids and proteins were detected in the early phase of severe meconium aspiration and were due to hydrolysis and inflammation and a defensive response. This impairs both surfactant structure and function, finally resulting in reduced lung aeration. These findings support the development of new surfactant protection and antiinflammatory strategies for severe MAS.

Alveolar lipids in pulmonary disease. A review

Lung lipid metabolism participates both in infant and adult pulmonary disease. The lung is composed by multiple cell types with specialized functions and coordinately acting to meet specific physiologic requirements. The alveoli are the niche of the most active lipid metabolic cell in the lung, the type 2 cell (T2C). T2C synthesize surfactant lipids that are an absolute requirement for respiration, including dipalmitoylphosphatidylcholine. After its synthesis and secretion into the alveoli, surfactant is recycled by the T2C or degraded by the alveolar macrophages (AM). Surfactant biosynthesis and recycling is tightly regulated, and dysregulation of this pathway occurs in many pulmonary disease processes. Alveolar lipids can participate in the development of pulmonary disease from their extracellular location in the lumen of the alveoli, and from their intracellular location in T2C or AM. External insults like smoke and pollution can disturb surfactant homeostasis and result in either surfactant insufficiency or accumulation. But disruption of surfactant homeostasis is also observed in many chronic adult diseases, including chronic obstructive pulmonary disease (COPD), and others. Sustained damage to the T2C is one of the postulated causes of idiopathic pulmonary fibrosis (IPF), and surfactant homeostasis is disrupted during fibrotic conditions. Similarly, surfactant homeostasis is impacted during acute respiratory distress syndrome (ARDS) and infections. Bioactive lipids like eicosanoids and sphingolipids also participate in chronic lung disease and in respiratory infections. We review the most recent knowledge on alveolar lipids and their essential metabolic and signaling functions during homeostasis and during some of the most commonly observed pulmonary diseases.

Synthetic surfactant with a recombinant surfactant protein C analogue improves lung function and attenuates inflammation in a model of acute respiratory distress syndrome in adult rabbits

AIM

In acute respiratory distress syndrome (ARDS) damaged alveolar epithelium, leakage of plasma proteins into the alveolar space and inactivation of pulmonary surfactant lead to respiratory dysfunction. Lung function could potentially be restored with exogenous surfactant therapy, but clinical trials have so far been disappointing. These negative results may be explained by inactivation and/or too low doses of the administered surfactant. Surfactant based on a recombinant surfactant protein C analogue (rSP-C33Leu) is easy to produce and in this study we compared its effects on lung function and inflammation with a commercial surfactant preparation in an adult rabbit model of ARDS.

METHODS

ARDS was induced in adult New Zealand rabbits by mild lung-lavages followed by injurious ventilation (V_T 20 m/kg body weight) until P/F ratio < 26.7 kPa. The animals were treated with two intratracheal boluses of 2.5 mL/kg of 2% rSP-C33Leu in DPPC/egg PC/POPG, 50:40:10 or poractant alfa (Curosurf®), both surfactants containing 80 mg phospholipids/mL, or air as control. The animals were subsequently ventilated (V_T 8-9 m/kg body weight) for an additional 3 h and lung function parameters were recorded. Histological appearance of the lungs, degree of lung oedema and levels of the cytokines TNFα IL-6 and IL-8 in lung homogenates were evaluated.

RESULTS

Both surfactant preparations improved lung function vs. the control group and also reduced inflammation scores, production of pro-inflammatory cytokines, and formation of lung oedema to similar degrees. Poractant alfa improved compliance at 1 h, P/F ratio and PaO₂ at 1.5 h compared to rSP-C33Leu surfactant.

CONCLUSION

This study indicates that treatment of experimental ARDS with synthetic lung surfactant based on rSP-C33Leu improves lung function and attenuates inflammation.

Pharmacological agents for adults with acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a life-threatening condition caused by direct or indirect injury to the lungs. Despite improvements in clinical management (for example, lung protection strategies), mortality in this patient group is at approximately 40%. This is an update of a previous version of this review, last published in 2004.

OBJECTIVES

To evaluate the effectiveness of pharmacological agents in adults with ARDS on mortality, mechanical ventilation, and fitness to return to work at 12 months.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, and CINAHL on 10 December 2018. We searched clinical trials registers and grey literature, and handsearched reference lists of included studies and related reviews.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing pharmacological agents with control (placebo or standard therapy) to treat adults with established ARDS. We excluded trials of nitric oxide, inhaled prostacyclins, partial liquid ventilation, neuromuscular blocking agents, fluid and nutritional interventions and medical oxygen. We excluded studies published earlier than 2000, because of changes to lung protection strategies for people with ARDS since this date.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion, extracted data, and assessed risks of bias. We assessed the certainty of evidence with GRADE.

MAIN RESULTS

We included 48 RCTs with 6299 participants who had ARDS; two included only participants with mild ARDS (also called acute lung injury). Most studies included causes of ARDS that were both direct and indirect injuries. We noted differences between studies, for example the time of administration or the size of dose, and because of unclear reporting we were uncertain whether all studies had used equivalent lung protection strategies.We included five types of agents as the primary comparisons in the review: corticosteroids, surfactants, N-acetylcysteine, statins, and beta-agonists. We included 15 additional agents (sivelestat, mesenchymal stem cells, ulinastatin, anisodimine, angiotensin-converting enzyme (ACE) inhibitor, recombinant human ACE2 (palifermin), AP301, granulocyte-macrophage colony stimulating factor (GM-CSF), levosimendan, prostacyclins, lisofylline, ketaconazole, nitroglycerins, L-2-oxothiazolidine-4-carboxylic acid (OTZ), and penehyclidine hydrochloride).We used GRADE to downgrade outcomes for imprecision (because of few studies and few participants), for study limitations (e.g. high risks of bias) and for inconsistency (e.g. differences between study data).Corticosteroids versus placebo or standard therapyCorticosteroids may reduce all-cause mortality within three months by 86 per 1000 patients (with as many as 161 fewer to 19 more deaths); however, the 95% confidence interval (CI) includes the possibility of both increased and reduced deaths (risk ratio (RR) 0.77, 95% CI 0.57 to 1.05; 6 studies, 574 participants; low-certainty evidence). Due to the very low-certainty evidence, we are uncertain whether corticosteroids make little or no difference to late all-cause mortality (later than three months) (RR 0.99, 95% CI 0.64 to 1.52; 1 study, 180 participants), or to the duration of mechanical ventilation (mean difference (MD) -4.30, 95% CI -9.72 to 1.12; 3 studies, 277 participants). We found that ventilator-free days up to day 28 (VFD) may be improved with corticosteroids (MD 4.09, 95% CI 1.74 to 6.44; 4 studies, 494 participants; low-certainty evidence). No studies reported adverse events leading to discontinuation of study medication, or fitness to return to work at 12 months (FTR).Surfactants versus placebo or standard therapyWe are uncertain whether surfactants make little or no difference to early mortality (RR 1.08, 95% CI 0.91 to 1.29; 9 studies, 1338 participants), or whether they reduce late all-cause mortality (RR 1.28, 95% CI 1.01 to 1.61; 1 study, 418 participants). Similarly, we are uncertain whether surfactants reduce the duration of mechanical ventilation (MD -2.50, 95% CI -4.95 to -0.05; 1 study, 16 participants), make little or no difference to VFD (MD -0.39, 95% CI -2.49 to 1.72; 2 studies, 344 participants), or to adverse events leading to discontinuation of study medication (RR 0.50, 95% CI 0.17 to 1.44; 2 studies, 88 participants). We are uncertain of these effects because we assessed them as very low-certainty. No studies reported FTR.N-aceytylcysteine versus placeboWe are uncertain whether N-acetylcysteine makes little or no difference to early mortality, because we assessed this as very low-certainty evidence (RR 0.64, 95% CI 0.32 to 1.30; 1 study, 36 participants). No studies reported late all-cause mortality, duration of mechanical ventilation, VFD, adverse events leading to study drug discontinuation, or FTR.Statins versus placeboStatins probably make little or no difference to early mortality (RR 0.99, 95% CI 0.78 to 1.26; 3 studies, 1344 participants; moderate-certainty evidence) or to VFD (MD 0.40, 95% CI -0.71 to 1.52; 3 studies, 1342 participants; moderate-certainty evidence). Statins may make little or no difference to duration of mechanical ventilation (MD 2.70, 95% CI -3.55 to 8.95; 1 study, 60 participants; low-certainty evidence). We could not include data for adverse events leading to study drug discontinuation in one study because it was unclearly reported. No studies reported late all-cause mortality or FTR.Beta-agonists versus placebo controlBeta-blockers probably slightly increase early mortality by 40 per 1000 patients (with as many as 119 more or 25 fewer deaths); however, the 95% CI includes the possibility of an increase as well as a reduction in mortality (RR 1.14, 95% CI 0.91 to 1.42; 3 studies, 646 participants; moderate-certainty evidence). Due to the very low-certainty evidence, we are uncertain whether beta-agonists increase VFD (MD -2.20, 95% CI -3.68 to -0.71; 3 studies, 646 participants), or make little or no difference to adverse events leading to study drug discontinuation (one study reported little or no difference between groups, and one study reported more events in the beta-agonist group). No studies reported late all-cause mortality, duration of mechanical ventilation, or FTR.

AUTHORS' CONCLUSIONS

We found insufficient evidence to determine with certainty whether corticosteroids, surfactants, N-acetylcysteine, statins, or beta-agonists were effective at reducing mortality in people with ARDS, or duration of mechanical ventilation, or increasing ventilator-free days. Three studies awaiting classification may alter the conclusions of this review. As the potential long-term consequences of ARDS are important to survivors, future research should incorporate a longer follow-up to measure the impacts on quality of life.

Human pluripotent stem cell-derived alveolar epithelial cells are alternatives for in vitro pulmotoxicity assessment

Human pluripotent stem cell (hPSC)-derived alveolar epithelial cells (AECs) provide new opportunities for understanding lung development and the treatment of pulmonary diseases. However, toxicity assessments using hPSC-AECs have not been undertaken. In this study, we generated functional AECs from hPSCs and evaluated their inflammatory and apoptotic responses to cadmium (Cd) exposure (1, 5, and 10 μM) for 24 h compared with the human bronchial epithelial cell line (BEAS-2B) and primary AECs as controls. Our data showed that Cd (10 μM) treatment induced substantial inflammatory responses and apoptosis in BEAS-2B cells, but not in both hPSC-AECs and primary AECs. Interestingly, conditioned medium from AEC cultures significantly alleviated apoptotic and inflammatory responses to Cd exposure in BEAS-2B cells. Using cytokine arrays, several potential factors secreted from hPSC-AECs and primary AECs were detected and may be involved in reducing Cd-induced cytotoxicity. We also observed higher expression of surfactant proteins B and C in both hPSC-AECs and primary AECs, which may contribute to protection against Cd-induced cytotoxicity. These results suggested that hPSC-AECs phenotypically and functionally resemble primary AECs and could be more biologically relevant alternatives for evaluating the pathological contribution of confirmed or potential pulmotoxic materials included in smoking and microdust.

Inhibition and counterinhibition of Surfacen, a clinical lung surfactant of natural origin

Inactivation of pulmonary surfactant by different components such as serum, cholesterol or meconium contributes to severe respiratory pathologies through destabilization and collapse of airspaces. Recent studies have analyzed in detail how the interfacial properties of natural surfactant purified from animal lungs are altered as a consequence of its exposure to serum proteins or meconium-mobilized cholesterol. It has been also demonstrated that pre-exposure of surfactant to polymers such as hyaluronic acid provides resistance to inactivation by multiple inhibitory agents. In the current work, we have extended these studies to the analysis of Surfacen, a clinical surfactant currently in use to rescue premature babies suffering or at risk of respiratory distress due to congenital lack of surfactant. This surfactant is also strongly inhibited by both meconium and serum when tested in the captive bubble surfactometer (CBS) under conditions mimicking respiratory dynamics. As it occurs with native surfactant, Surfacen is markedly protected from inhibition by pre-exposure to hyaluronic acid, confirming that clinical surfactants can be improved to treat pathologies associated with strongly deactivating contexts, such as those associated with lung injury and inflammation. Remarkably, we found that, under physiologically-mimicking conditions, a cholesterol-free clinical surfactant such as Surfacen is less susceptible to inhibition by cholesterol-mobilizing environments than cholesterol-containing natural surfactant, as a consequence of a markedly reduced susceptibility to incorporation of exogenous cholesterol.

The clinical practice guideline for the management of ARDS in Japan

BACKGROUND

The Japanese Society of Respiratory Care Medicine and the Japanese Society of Intensive Care Medicine provide here a clinical practice guideline for the management of adult patients with ARDS in the ICU.

METHOD

The guideline was developed applying the GRADE system for performing robust systematic reviews with plausible recommendations. The guideline consists of 13 clinical questions mainly regarding ventilator settings and drug therapies (the last question includes 11 medications that are not approved for clinical use in Japan).

RESULTS

The recommendations for adult patients with ARDS include: we suggest against early tracheostomy (GRADE 2C), we suggest using NPPV for early respiratory management (GRADE 2C), we recommend the use of low tidal volumes at 6-8 mL/kg (GRADE 1B), we suggest setting the plateau pressure at 30cmH20 or less (GRADE2B), we suggest using PEEP within the range of plateau pressures less than or equal to 30cmH2O, without compromising hemodynamics (Grade 2B), and using higher PEEP levels in patients with moderate to severe ARDS (Grade 2B), we suggest using protocolized methods for liberation from mechanical ventilation (Grade 2D), we suggest prone positioning especially in patients with moderate to severe respiratory dysfunction (GRADE 2C), we suggest against the use of high frequency oscillation (GRADE 2C), we suggest the use of neuromuscular blocking agents in patients requiring mechanical ventilation under certain circumstances (GRADE 2B), we suggest fluid restriction in the management of ARDS (GRADE 2A), we do not suggest the use of neutrophil elastase inhibitors (GRADE 2D), we suggest the administration of steroids, equivalent to methylprednisolone 1-2mg/kg/ day (GRADE 2A), and we do not recommend other medications for the treatment of adult patients with ARDS (GRADE1B; inhaled/intravenous β2 stimulants, prostaglandin E1, activated protein C, ketoconazole, and lisofylline, GRADE 1C; inhaled nitric oxide, GRADE 1D; surfactant, GRADE 2B; granulocyte macrophage colony-stimulating factor, N-acetylcysteine, GRADE 2C; Statin.).

CONCLUSIONS

This article was translated from the Japanese version originally published as the ARDS clinical practice guidelines 2016 by the committee of ARDS clinical practice guideline (Tokyo, 2016, 293p, available from http://www.jsicm.org/ARDSGL/ARDSGL2016.pdf). The original article, written for Japanese healthcare providers, provides points of view that are different from those in other countries.

Effect of Lung Surfactant Protein SP-C and SP-C-Promoted Membrane Fragmentation on Cholesterol Dynamics

To allow breathing and prevent alveolar collapse, lung surfactant (LS) develops a complex membranous system at the respiratory surface. LS is defined by a specific protein and lipid composition, including saturated and unsaturated phospholipid species and cholesterol. Surfactant protein C (SP-C) has been suggested to be an essential element for sustaining the presence of cholesterol in surfactant without functional impairment. In this work, we used a fluorescent sterol-partitioning assay to assess the effect of the surfactant proteins SP-B and SP-C on cholesterol distribution in membranes. Our results suggest that in the LS context, the combined action of SP-B and SP-C appears to facilitate cholesterol dynamics, whereas SP-C does not seem to establish a direct interaction with cholesterol that could increase the partition of free cholesterol into membranes. Interestingly, SP-C exhibits a membrane-fragmentation behavior, leading to the conversion of large unilamellar vesicles into highly curved vesicles ∼25 nm in diameter. Sterol partition was observed to be sensitive to the bending of bilayers, indicating that the effect of SP-C to mobilize cholesterol could be indirectly associated with SP-C-mediated membrane remodeling. Our results suggest a potential role for SP-C in generating small surfactant structures that may participate in cholesterol mobilization and pulmonary surfactant homeostasis at the alveolar interfaces.

The role of multilayers in preventing the premature buckling of the pulmonary surfactant

The pulmonary surfactant is a protein-lipid mixture that spreads into a film at the air-lung interface. The highly-compacted molecules of the film keep the interface from shrinking under the influence of otherwise high surface tension and thus prevent atelectasis. We have previously shown that for the film to withstand a high film pressure without collapsing it needs to assume a specific architecture of a molecular monolayer with islands of stacks of molecular multilayers scattered over the area. Surface activity was assessed in a captive bubble surfactometer (CBS) and the role of cholesterol and oxidation on surfactant function examined. The surfactant film was conceptualized as a plate under pressure. Finite element analysis was used to evaluate the role of the multilayer stacks in preventing buckling of the plate during compression. The model of film topography was constructed from atomic force microscope (AFM) scans of surfactant films and known physical properties of dipalmitoylphosphatidylcholine (DPPC), a major constituent of surfactant, using ANSYS structural-analysis software. We report that multilayer structures increase film stability. In simulation studies, the critical load required to induce surfactant film buckling increased about two-fold in the presence of multilayers. Our in vitro surfactant studies showed that surface topography varied between functional and dysfunctional films. However, the critical factor for film stability was the anchoring of the multilayers. Furthermore, the anchoring of multilayers and mechanical stability of the film was dependent on the presence of hydrophobic surfactant protein-C. The current study expands our understanding of the mechanism of surfactant inactivation in disease.

In vitro and in vivo comparison between poractant alfa and the new generation synthetic surfactant CHF5633

BACKGROUND

CHF5633 is a new generation synthetic surfactant containing both SP-B and SP-C analogues developed for the treatment of respiratory distress syndrome. Here, the optimal dose and its performance in comparison to the animal-derived surfactant poractant alfa were investigated.

METHODS

In vitro surfactant activity was determined by means of the Wilhelmy balance and the capillary surfactometer. The dose-finding study was performed in preterm rabbits with severe surfactant deficiency. CHF5633 doses ranging from 50 to 300 mg/kg were used. Untreated animals and animals treated with 200 mg/kg of poractant alfa were included for comparison.

RESULTS

In vitro, minimum surface tension (γ_min) was decreased from values above 70 to 0 mN/m by both surfactants, and they formed rapidly a film at the air-liquid interface. In vivo studies showed a clear dose-dependent improvement of lung function for CHF5633. The pulmonary effect of CHF5633 200 mg/kg dose was comparable to the pulmonary response elicited by 200 mg/kg of poractant alfa in preterm rabbits.

CONCLUSION

CHF5633 is as efficient as poractant alfa in our in vitro and in vivo settings. A clear dose-dependent improvement of lung function could be observed for CHF5633, with the dose of 200 mg/kg being the most efficient one.

Pulmonary surfactant metabolism in the alveolar airspace: Biogenesis, extracellular conversions, recycling

Pulmonary surfactant is a lipid-protein complex that lines and stabilizes the respiratory interface in the alveoli, allowing for gas exchange during the breathing cycle. At the same time, surfactant constitutes the first line of lung defense against pathogens. This review presents an updated view on the processes involved in biogenesis and intracellular processing of newly synthesized and recycled surfactant components, as well as on the extracellular surfactant transformations before and after the formation of the surface active film at the air-water interface. Special attention is paid to the crucial regulation of surfactant homeostasis, because its disruption is associated with several lung pathologies.

[Critically ill pediatric hemato-oncology patient: What we do is what we should do?]

OBJECTIVE

Primary objective, to describe the management and monitorization of critically ill pediatric hemato-oncology patient (CIPHO) in the Spanish pediatric intensive care units (PICU). Secondary objective, through a literature review, to identify possible areas of improvement.

MATERIAL AND METHODS

Observational transversal descriptive study. An anonymous web-based survey was sent to 324 Spanish pediatric intensivists from April 2011 to May 2011. None of them were pediatric residents.

RESULTS

The survey was answered by 105 intensivists, 59/105 always agreed their treatment with the oncologist. In case of hemodynamic instability, non-invasive blood pressure monitoring is always done by 85/105 and almost always optimized by intra-arterial measuring (85/105) and central venous pressure (70/105). If respiratory failure the use of non-invasive ventilation (NIPPV) is always (36/105) or frequently (60/105) established prior to conventional mechanical ventilation. To replace or withdraw non-invasive ventilation only 44/96 of the respondents to this question use a clinical protocol. Before the instauration of conventional mechanical ventilation the oncological prognosis is considered by 72/105. In case of acute oliguric renal failure the renal replacement techniques are widely used (74/105). The withdrawal of sustaining life support is frequently discussed (75/103) and agreed with the oncologist (91/103) and caregivers (81/103).

CONCLUSIONS

In our study, despite there is not a defined standard-of-care, the respondents showed similar therapeutics and monitorization choices. The use of NIPPV as first respiratory assistance is extended. Prospective, observational and multicenter studies should be developed to establish the results of this management in this population.

Amyloid-β (1-40) restores adhesion properties of pulmonary surfactant, counteracting the effect of cholesterol

A pulmonary surfactant (PS) is a thin lipid-protein film covering the surface of the lung alveoli at the air/liquid interface. The primary purpose of a PS is to control the surface tension of the air/liquid interface and to reduce the work of breathing. High levels of cholesterol in a PS are associated with life-threatening acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Finding therapeutics to counteract the effect of cholesterol in a PS is a matter of contemporary research. In our earlier work, we showed that the addition of amyloid-β (1-40) (Aβ40), the protein implicated in Alzheimer's disease, can reverse the detrimental effects of cholesterol in surfactants by improving multilayer formation and restoring PS surface active properties. We hypothesized that this phenomenon was due to Aβ40 improving adhesion properties of a surfactant. In this work we used atomic force spectroscopy to demonstrate that Aβ40 counteracts the adhesive properties of a PS compromised by high levels of cholesterol in a PS and helps to restore the functionality of a PS.

Cholesterol-mediated surfactant dysfunction is mitigated by surfactant protein A

The ability of pulmonary surfactant to reduce surface tension at the alveolar surface is impaired in various lung diseases. Recent animal studies indicate that elevated levels of cholesterol within surfactant may contribute to its inhibition. It was hypothesized that elevated cholesterol levels within surfactant inhibit human surfactant biophysical function and that these effects can be reversed by surfactant protein A (SP-A). The initial experiment examined the function of surfactant from mechanically ventilated trauma patients in the presence and absence of a cholesterol sequestering agent, methyl-β-cyclodextrin. The results demonstrated improved surface activity when cholesterol was sequestered in vitro using a captive bubble surfactometer (CBS). These results were explored further by reconstitution of surfactant with various concentrations of cholesterol with and without SP-A, and testing of the functionality of these samples in vitro with the CBS and in vivo using surfactant depleted rats. Overall, the results consistently demonstrated that surfactant function was inhibited by levels of cholesterol of 10% (w/w phospholipid) but this inhibition was mitigated by the presence of SP-A. It is concluded that cholesterol-induced surfactant inhibition can actively contribute to physiological impairment of the lungs in mechanically ventilated patients and that SP-A levels may be important to maintain surfactant function in the presence of high cholesterol within surfactant.

Structure-function relationships in pulmonary surfactant membranes: from biophysics to therapy

Pulmonary surfactant is an essential lipid-protein complex to maintain an operative respiratory surface at the mammalian lungs. It reduces surface tension at the alveolar air-liquid interface to stabilise the lungs against physical forces operating along the compression-expansion breathing cycles. At the same time, surfactant integrates elements establishing a primary barrier against the entry of pathogens. Lack or deficiencies of the surfactant system are associated with respiratory pathologies, which treatment often includes supplementation with exogenous materials. The present review summarises current models on the molecular mechanisms of surfactant function, with particular emphasis in its biophysical properties to stabilise the lungs and the molecular alterations connecting impaired surfactant with diseased organs. It also provides a perspective on the current surfactant-based strategies to treat respiratory pathologies. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Effect of serum lipoproteins and cholesterol on an exogenous pulmonary surfactant. ESR analysis of structural changes and their relation with surfactant activity

The study of structural changes in the surfactant may help to understand the mechanisms by which the surfactant is inactivated by serum. Here, we compared the in vitro effects of serum, albumin, lipoproteins (VLDL, LDL, HDL) and cholesterol on the dynamic and structural properties of surfactant suspensions by electronic spin resonance and surface tension measurements. Our results showed that albumin seems to be responsible for macrostructure disaggregation and increased rigidity in the hydrophobic region, but it did not affect surfactant activity. Fluidity in the polar area seems to be critical for proper physiological activity, and the changes induced by serum observed in this area would be generated by HDL or cholesterol, but the amount of cholesterol transferred by serum is not significant. Statistical analysis showed that surfactant activity correlated with the fluidity in the polar area but not with that in the hydrophobic region. We obtained strong evidence that among all the serum components tested, HDL is the one that causes the structural changes that compromise surfactant performance.

Clinical and biological role of secretory phospholipase A2 in acute respiratory distress syndrome infants

INTRODUCTION

Secretory phospholipase A2 is supposed to play a role in acute lung injury but no data are available for pediatric acute respiratory distress syndrome (ARDS). It is not clear which enzyme subtypes are secreted and what the relationships are between enzyme activity, biophysical and biochemical parameters, and clinical outcomes. We aimed to measure the enzyme and identify its subtypes and to study its biochemical and biophysical effect. The secondary aim was to correlate enzyme activity with clinical outcome.

METHODS

Bronchoalveolar lavage was performed in 24 infants with ARDS and 14 controls with no lung disease. Samples were assayed for secretory phospholipase A2 and molecules related to its activity and expression. Western blotting and captive bubble surfactometry were also performed. Clinical data were real time downloaded.

RESULTS

Tumor necrosis factor-α (814 (506-2,499) vs. 287 (111-1,315) pg/mL; P = 0.04), enzyme activity (430 (253-600) vs. 149 (61-387) IU/mL; P = 0.01), free fatty acids (4.3 (2.8-8.6) vs. 2 (0.8-4.6) mM; P = 0.026), and minimum surface tension (25.6 ± 6.1 vs. 18 ± 1.8 mN/m; P = 0.006) were higher in ARDS than in controls. Phospholipids are lower in ARDS than in controls (76.5 (54-100) vs. 1,094 (536-2,907) μg/mL; P = 0.0001). Three enzyme subtypes were identified (-IIA, -V, -X), although in lower quantities in controls; another subtype (-IB) was mainly detected in ARDS. Significant correlations exist between enzyme activity, free fatty acids (ρ = 0.823; P < 0.001), and surface tension (ρ = 0.55; P < 0.028). Correlations also exist with intensive care stay (ρ = 0.54; P = 0.001), PRISM-III24 (ρ = 0.79; P< 0.001), duration of ventilation (ρ = 0.53; P = 0.002), and oxygen therapy (ρ = 0.54; P = 0.001).

CONCLUSIONS

Secretory phospholipase A2 activity is raised in pediatric ARDS and constituted of four subtypes. Enzyme correlates with some inflammatory mediators, surface tension, and major clinical outcomes. Secretory phospholipase A2 may be a clinically relevant target in pediatric ARDS.

Clinical review: Exogenous surfactant therapy for acute lung injury/acute respiratory distress syndrome--where do we go from here?

Acute lung injury and acute respiratory distress syndrome (ARDS) are characterised by severe hypoxemic respiratory failure and poor lung compliance. Despite advances in clinical management, morbidity and mortality remains high. Supportive measures including protective lung ventilation confer a survival advantage in patients with ARDS, but management is otherwise limited by the lack of effective pharmacological therapies. Surfactant dysfunction with quantitative and qualitative abnormalities of both phospholipids and proteins are characteristic of patients with ARDS. Exogenous surfactant replacement in animal models of ARDS and neonatal respiratory distress syndrome shows consistent improvements in gas exchange and survival. However, whilst some adult studies have shown improved oxygenation, no survival benefit has been demonstrated to date. This lack of clinical efficacy may be related to disease heterogeneity (where treatment responders may be obscured by nonresponders), limited understanding of surfactant biology in patients or an absence of therapeutic effect in this population. Crucially, the mechanism of lung injury in neonates is different from that in ARDS: surfactant inhibition by plasma constituents is a typical feature of ARDS, whereas the primary pathology in neonates is the deficiency of surfactant material due to reduced synthesis. Absence of phenotypic characterisation of patients, the lack of an ideal natural surfactant material with adequate surfactant proteins, coupled with uncertainty about optimal timing, dosing and delivery method are some of the limitations of published surfactant replacement clinical trials. Recent advances in stable isotope labelling of surfactant phospholipids coupled with analytical methods using electrospray ionisation mass spectrometry enable highly specific molecular assessment of phospholipid subclasses and synthetic rates that can be utilised for phenotypic characterisation and individualisation of exogenous surfactant replacement therapy. Exploring the clinical benefit of such an approach should be a priority for future ARDS research.

Exogenous surfactant may improve oxygenation but not mortality in adult patients with acute lung injury/acute respiratory distress syndrome: a meta-analysis of 9 clinical trials

OBJECTIVE

To evaluate whether exogenous surfactant therapy may be useful in adult patients with acute lung injury or acute respiratory distress syndrome, using a meta-analysis of published clinical trials.

DESIGN

A comprehensive literature search was performed to identify all randomized clinical trials examining the effects of the treatment of acute lung injury/acute respiratory distress syndrome with exogenous surfactant in adults. The primary outcome measurement was mortality 28 or 30 days after randomization. Secondary outcome measurements included a change in the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen in the first 24 hours or after 120 hours, the number of ventilation-free days, and any adverse effects. The meta-analysis was performed using the Review Manager 5.0.0 system.

PARTICIPANTS

Randomized clinical trials.

INTERVENTION

Meta-analysis of 9 trials.

MEASUREMENTS AND MAIN RESULTS

Nine trials involving 2,575 patients were included in the meta-analysis. The analysis showed that treatment with exogenous pulmonary surfactant does not decrease mortality significantly. There was a significant effect of exogenous surfactant treatment on the change in the partial pressure of arterial oxygen/fraction of inspired oxygen ratio in the first 24 hours but this was lost by 120 hours. The duration of ventilation trended lower in surfactant-treated patients but this was not significant. In addition, surfactant-treated patients had a significantly higher risk of adverse effects.

CONCLUSIONS

An exogenous surfactant may improve oxygenation over the first 24 hours after administration. However, treatment does not improve mortality and oxygenation over ≥120 hours after administration and results in a high rate of adverse effects. Therefore, the present data suggest that an exogenous surfactant cannot be considered an effective adjunctive therapy in patients with acute lung injury/acute respiratory distress syndrome.

Surfactant and its role in the pathobiology of pulmonary infection

Pulmonary surfactant is a complex surface-active substance comprised of key phospholipids and proteins that has many essential functions. Surfactant's unique composition is integrally related to its surface-active properties, its critical role in host defense, and emerging immunomodulatory activities ascribed to surfactant lipids. Together these effector functions provide for lung stability and protection from a barrage of potentially virulent infectious pathogens.

The pharmacology of acute lung injury in sepsis

Acute lung injury (ALI) secondary to sepsis is one of the leading causes of death in sepsis. As such, many pharmacologic and nonpharmacologic strategies have been employed to attenuate its course. Very few of these strategies have proven beneficial. In this paper, we discuss the epidemiology and pathophysiology of ALI, commonly employed pharmacologic and nonpharmacologic treatments, and innovative therapeutic modalities that will likely be the focus of future trials.

Meconium impairs pulmonary surfactant by a combined action of cholesterol and bile acids

Mechanisms for meconium-induced inactivation of pulmonary surfactant as part of the meconium aspiration syndrome in newborn infants, to our knowledge, are not clearly understood. Here we have studied the biophysical mechanisms of how meconium affects surface activity of pulmonary surfactant and whether the membrane-perturbing effects of meconium can be mimicked by exposure of surfactant to a mixture of bile acids and cholesterol. Surface activity of pulmonary surfactant complexes purified from animal lungs was analyzed in the absence and in the presence of meconium in standard surface balances and in a captive bubble surfactometer. We have also evaluated accumulation of surfactant at the air-liquid interface by what we believe to be a novel microtiter plate fluorescent assay, and the effect of meconium components on surfactant membrane fluidity using Laurdan fluorescence thermotropic profiles and differential scanning calorimetry thermograms. Rapid interfacial adsorption, low surface tension upon film compression, efficient film replenishment upon expansion, and thermotropic properties of surfactant complexes are all adversely affected by meconium, and, in a similar manner, they are affected by cholesterol/taurocholate mixtures but not by taurocholate alone. We conclude that inhibition of surfactant by meconium can be mimicked by a bile salt-promoted incorporation of excess cholesterol into surfactant complexes. These results highlight the potential pathogenic role of cholesterol-mobilizing agents as a crucial factor resulting in cholesterol induced alterations of structure and dynamics of surfactant membranes and films.

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.

Palmitoylation of pulmonary surfactant protein SP-C is critical for its functional cooperation with SP-B to sustain compression/expansion dynamics in cholesterol-containing surfactant films

Recent data suggest that a functional cooperation between surfactant proteins SP-B and SP-C may be required to sustain a proper compression-expansion dynamics in the presence of physiological proportions of cholesterol. SP-C is a dually palmitoylated polypeptide of 4.2 kDa, but the role of acylation in SP-C activity is not completely understood. In this work we have compared the behavior of native palmitoylated SP-C and recombinant nonpalmitoylated versions of SP-C produced in bacteria to get a detailed insight into the importance of the palmitic chains to optimize interfacial performance of cholesterol-containing surfactant films. We found that palmitoylation of SP-C is not essential for the protein to promote rapid interfacial adsorption of phospholipids to equilibrium surface tensions (∼22 mN/m), in the presence or absence of cholesterol. However, palmitoylation of SP-C is critical for cholesterol-containing films to reach surface tensions ≤1 mN/m at the highest compression rates assessed in a captive bubble surfactometer, in the presence of SP-B. Interestingly, the ability of SP-C to facilitate reinsertion of phospholipids during expansion was not impaired to the same extent in the absence of palmitoylation, suggesting the existence of palmitoylation-dependent and -independent functions of the protein. We conclude that palmitoylation is key for the functional cooperation of SP-C with SP-B that enables cholesterol-containing surfactant films to reach very low tensions under compression, which could be particularly important in the design of clinical surfactants destined to replacement therapies in pathologies such as acute respiratory distress syndrome.

Investigation of the significance of Oil Red O-positive macrophage excess in bronchoalveolar lavage fluid during HIV infection

OBJECTIVE

To assess the significance of increased levels of Oil Red O-positive macrophages (ORO-PM) in bronchoalveolar lavage fluids (BALFs) from HIV-positive patients.

METHODS

Cytological data for seventy BALF samples from 66 consecutive HIV-infected patients were analysed according to antiretroviral therapy regimen, presence of Pneumocystis jiroveci infection, blood CD4(+) T cell count, HIV-1 viral load and plasma lipid levels. Non-parametric tests were used to compare the values between groups.

RESULTS

The percentages of ORO-PM were high in this group: 40% [6-80] (median [interquartile range]). They were positively correlated with the BALF total cell count, 21% [5-48.5] for <300 cells/mm(3) and 60% [26.5-80] for >300 cells/mm(3) (P<0.01) but inversely correlated with the percentage of BALF lymphocytes, 50% [20-80] for <15% lymphocytes and 11.5% [2-47] for ≥15% lymphocytes (P<0.01). Antiretroviral therapy with or without protease inhibitors, plasma lipid levels, HIV-1 viral load, blood CD4(+) T cell count or presence of a Pneumocystis jiroveci infection were not correlated with the ORO-PM status.

CONCLUSION

Significantly increased numbers of ORO-PM were correlated with high total cell counts and low lymphocyte counts in BALF, irrespective of disease activity or treatment. Extended work on a larger series of patients needs to be conducted.

Recombinant surfactant protein C-based surfactant for patients with severe direct lung injury

RATIONALE

Patients with acute lung injury have impaired function of the lung surfactant system. Prior clinical trials have shown that treatment with exogenous recombinant surfactant protein C (rSP-C)-based surfactant results in improvement in blood oxygenation and have suggested that treatment of patients with severe direct lung injury may decrease mortality.

OBJECTIVES

Determine the clinical benefit of administering an rSP-C-based synthetic surfactant to patients with severe direct lung injury due to pneumonia or aspiration.

METHODS

A prospective randomized blinded study was performed at 161 centers in 22 countries. Patients were randomly allocated to receive usual care plus up to eight doses of rSP-C surfactant administered over 96 hours (n = 419) or only usual care (n = 424).

MEASUREMENTS AND MAIN RESULTS

Mortality to 28 days after treatment, the requirement for mechanical ventilation, and the number of nonpulmonary organ failure-free days were not different between study groups. In contrast to prior studies, there was no improvement in oxygenation in patients receiving surfactant compared with the usual care group. Investigation of the possible reasons underlying the lack of efficacy suggested a partial inactivation of rSP-C surfactant caused by a step of the resuspension process that was introduced with this study.

CONCLUSIONS

In this study, rSP-C-based surfactant was of no clinical benefit to patients with severe direct lung injury. The unexpected lack of improvement in oxygenation, coupled with the results of in vitro tests, suggest that the administered suspension may have had insufficient surface activity to achieve clinical benefit.

Computed tomography assessment of exogenous surfactant-induced lung reaeration in patients with acute lung injury

Introduction

Previous randomized trials failed to demonstrate a decrease in mortality of patients with acute lung injury treated by exogenous surfactant. The aim of this prospective randomized study was to evaluate the effects of exogenous porcine-derived surfactant on pulmonary reaeration and lung tissue in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS).

Methods

Twenty patients with ALI/ARDS were studied (10 treated by surfactant and 10 controls) in whom a spiral thoracic computed tomography scan was acquired before (baseline), 39 hours and 7 days after the first surfactant administration. In the surfactant group, 3 doses of porcine-derived lung surfactant (200 mg/kg/dose) were instilled in both lungs at 0, 12 and 36 hours. Each instillation was followed by recruitment maneuvers. Gas and tissue volumes were measured separately in poorly/nonaerated and normally aerated lung areas before and seven days after the first surfactant administration. Surfactant-induced lung reaeration was defined as an increase in gas volume in poorly/non-aerated lung areas between day seven and baseline compared to the control group.

Results

At day seven, surfactant induced a significant increase in volume of gas in poorly/non-aerated lung areas (320 ± 125 ml versus 135 ± 161 ml in controls, P = 0.01) and a significant increase in volume of tissue in normally aerated lung areas (189 ± 179 ml versus -15 ± 105 ml in controls, P < 0.01). PaO₂/FiO₂ ratio was not different between the surfactant treated group and control group after surfactant replacement.

Conclusions

Intratracheal surfactant replacement induces a significant and prolonged lung reaeration. It also induces a significant increase in lung tissue in normally aerated lung areas, whose mechanisms remain to be elucidated.

Trial registration

NCT00742482.

Pulmonary surfactant protein SP-C counteracts the deleterious effects of cholesterol on the activity of surfactant films under physiologically relevant compression-expansion dynamics

The presence of cholesterol is critical in defining a dynamic lateral structure in pulmonary surfactant membranes. However, an excess of cholesterol has been associated with impaired surface activity of surfactant. It has also been reported that surfactant protein SP-C interacts with cholesterol in lipid/protein interfacial films. In this study, we analyzed the effect of SP-C on the thermodynamic properties of phospholipid membranes containing cholesterol, and the ability of lipid/protein complexes containing cholesterol to form and respread interfacial films capable of producing very low surface tensions upon repetitive compression-expansion cycling. SP-C modulates the effect of cholesterol to reduce the enthalpy associated with the gel-to-liquid-crystalline melting transition in dipalmitoylphosphatidylcholine (DPPC) bilayers, as analyzed by differential scanning calorimetry. The presence of SP-C affects more subtly the effects of cholesterol on the thermotropic properties of ternary membranes, mimicking more closely the lipid composition of native surfactant, where SP-C facilitates the miscibility of the sterol. Incorporation of 1% or 2% SP-C (protein/phospholipid by weight) promotes almost instantaneous adsorption of suspensions of DPPC/palmitoyloleoylphospatidylcholine (POPC)/palmitoyloleoyl-phosphatidylglycerol (POPG) (50:25:15, w/w/w) into the air-liquid interface of a captive bubble, in both the absence and presence of cholesterol. However, cholesterol impairs the ability of SP-C-containing films to achieve very low surface tensions in bubbles subjected to compression-expansion cycling. Cholesterol also substantially impairs the ability of DPPC/POPC/POPG films containing 1% surfactant protein SP-B to mimic the interfacial behavior of native surfactant films, which are characterized by very low minimum surface tensions with only limited area change during compression and practically no compression-expansion hysteresis. However, the simultaneous presence of 2% SP-C practically restores the compression-expansion dynamics of cholesterol- and SP-B-containing films to the efficient behavior shown in the absence of cholesterol. This suggests that cooperation between the two proteins is required for lipid-protein films containing cholesterol to achieve optimal performance under physiologically relevant compression-expansion dynamics.

Chorioamnionitis alters the response to surfactant in preterm infants

OBJECTIVE

To study the association between antenatal exposure to chorioamnionitis and the neonatal response to surfactant.

STUDY DESIGN

Prospective observational cohort of 301 preterm infants of gestational age < or = 32.0 weeks, 146 of whom received surfactant according to standardized criteria. Fraction of inspired oxygen (FiO(2)) requirement (using analysis of variance) and time to extubation (using Kaplan-Meier and Cox regression analyses) were compared between groups based on the presence of histological chorioamnionitis (HC) with or without fetal involvement (HC-, n = 88; HC + F-, n = 25; HC + F+, n = 33) and between infants who developed bronchopulmonary dysplasia (BPD) or died (n = 57) and BPD-free survivors (n = 89). Multiple logistic regression was performed to investigate the association between HC and BPD.

RESULTS

Compared with HC- infants, HC + F+ infants had significantly greater FiO(2) requirement and prolonged time to extubation postsurfactant, not accounted for by differences in gestational age and birth weight. Infants with BPD/death had a strikingly similar pattern of increased FiO(2) requirement postsurfactant. Moreover, in infants who received surfactant, HC + F+ status was associated with increased risk for BPD (odds ratio [OR] = 3.40; 95% confidence interval [CI] = 1.02-11.3; P = .047) and for BPD/death (OR = 2.72; 95% CI = 1.00-7.42; P = .049).

CONCLUSIONS

An impaired surfactant response was observed in preterm infants with severe chorioamnionitis and may be involved in the association between chorioamnionitis, mechanical ventilation, and the development of BPD.

Role of cholesterol in the biophysical dysfunction of surfactant in ventilator-induced lung injury

Mechanical ventilation may lead to an impairment of the endogenous surfactant system, which is one of the mechanisms by which this intervention contributes to the progression of acute lung injury. The most extensively studied mechanism of surfactant dysfunction is serum protein inhibition. However, recent studies indicate that hydrophobic components of surfactant may also contribute. It was hypothesized that elevated levels of cholesterol significantly contribute to surfactant dysfunction in ventilation-induced lung injury. Sprague-Dawley rats ( n = 30) were randomized to either high-tidal volume or low-tidal volume ventilation and monitored for 2 h. Subsequently, the lungs were lavaged, surfactant was isolated, and the biophysical properties of this isolated surfactant were analyzed on a captive bubble surfactometer with and without the removal of cholesterol using methyl-β-cyclodextrin. The results showed lower oxygenation values in the high-tidal volume group during the last 30 min of ventilation compared with the low-tidal volume group. Surfactant obtained from the high-tidal volume animals had a significant impairment in function compared with material from the low-tidal volume group. Removal of cholesterol from the high-tidal volume group improved the ability of the surfactant to reduce the surface tension to low values. Subsequent reconstitution of high-cholesterol values led to an impairment in surface activity. It is concluded that increased levels of cholesterol associated with endogenous surfactant represent a major contributor to the inhibition of surfactant function in ventilation-induced lung injury.

Methyl-beta-cyclodextrin restores the structure and function of pulmonary surfactant films impaired by cholesterol

Pulmonary surfactant, a defined mixture of lipids and proteins, imparts very low surface tension to the lung-air interface by forming an incompressible film. In acute respiratory distress syndrome and other respiratory conditions, this function is impaired by a number of factors, among which is an increase of cholesterol in surfactant. The current study shows in vitro that cholesterol can be extracted from surfactant and function subsequently restored to dysfunctional surfactant films in a dose-dependent manner by methyl-beta-cyclodextrin (MbetaCD). Bovine lipid extract surfactant was supplemented with cholesterol to serve as a model of dysfunctional surfactant. Likewise, when cholesterol in a complex with MbetaCD ("water-soluble cholesterol") was added in aqueous solution, surfactant films were rendered dysfunctional. Atomic force microscopy showed recovery of function by MbetaCD is accompanied by the re-establishment of the native film structure of a lipid monolayer with scattered areas of lipid bilayer stacks, whereas dysfunctional films lacked bilayers. The current study expands upon a recent perspective of surfactant inactivation in disease and suggests a potential treatment.

Mixed DPPC/DPPG monolayers at very high film compression

A drop shape technique using a constrained sessile drop constellation (ADSA-CSD) has been introduced as a superior technique for studying spread films specially at high collapse pressures [Saad et al. Langmuir 2008, 24, 10843-10850]. It has been shown that ADSA-CSD has certain advantages including the need only for small quantities of liquid and insoluble surfactants, the ability to measure very low surface tension values, easier deposition procedure, and leak-proof design. Here, this technique was applied to investigate mixed DPPC/DPPG monolayers to characterize the role of such molecules in maintaining stable film properties and surface activity of lung surfactant preparations. Results of compression isotherms were obtained for different DPPC/DPPG mixture ratios: 90/10, 80/20, 70/30, 60/40, and 50/50 in addition to pure DPPC and pure DPPG at room temperature of 24 degrees C. The ultimate collapse pressure of DPPC/DPPG mixtures was found to be 70.5 mJ/m2 (similar to pure DPPC) for the cases of low DPPG content (up to 20%). Increasing the DPPG content in the mixture (up to 40%) caused a slight decrease in the ultimate collapse pressure. However, further increase of DPPG in the mixture (50% or more) caused a sharp decrease in the ultimate collapse pressure to a value of 59.9 mJ/m2 (similar to pure DPPG). The change in film elasticity was also tracked for the range of mixture ratios studied. The physical reasons for such changes and the interaction between DPPC and DPPG molecules are discussed. The results also show a change in the film hysteresis upon successive compression and expansion cycles for different mixture ratios.

Competitive adsorption: a physical model for lung surfactant inactivation

Charged, surface-active serum proteins can severely reduce or eliminate the adsorption of lung surfactant from the subphase to the alveolar air-liquid interface via a kinetically controlled competitive adsorption process. The decreased surfactant concentration at the interface leads to higher surface tensions during the compression of the interface during breathing. The correspondence between the factors governing colloid stability and competitive adsorption is validated via a new method of measuring surfactant and serum protein adsorption rates to the air-water interface, using quantitative Brewster angle microscopy (BAM). Competitive adsorption from a 10 mg/mL albumin subphase prevents the adsorption of lung surfactant from even high subphase concentrations due to the fast diffusion of the water-soluble proteins to the interface. The formation of an albumin film causes an electrostatic and steric barrier to subsequent surfactant adsorption, which can destroy the necessary properties of functional lung surfactant: low surface tension during compression and rapid respreading after film collapse. Surfactant inactivation is at least partially due to decreased surfactant adsorption; such decreased adsorption due to the presence of serum proteins may play a role in the development and severity of acute respiratory distress syndrome.

Anionic pulmonary surfactant phospholipids inhibit inflammatory responses from alveolar macrophages and U937 cells by binding the lipopolysaccharide-interacting proteins CD14 and MD-2

Lipopolysaccharide (LPS), derived from Gram-negative bacteria, is a major cause of acute lung injury and respiratory distress syndrome. Pulmonary surfactant is secreted as a complex mixture of lipids and proteins onto the alveolar surface of the lung. Surfactant phospholipids are essential in reducing surface tension at the air-liquid interface and preventing alveolar collapse at the end of the respiratory cycle. In the present study, we determined that palmitoyl-oleoyl-phosphatidylglycerol and phosphatidylinositol, which are minor components of pulmonary surfactant, and synthetic dimyristoylphosphatidylglycerol regulated the inflammatory response of alveolar macrophages. The anionic lipids significantly inhibited LPS-induced nitric oxide and tumor necrosis factor-alpha production from rat and human alveolar macrophages and a U937 cell line by reducing the LPS-elicited phosphorylation of multiple intracellular protein kinases. The anionic lipids were also effective at attenuating inflammation when administered intratracheally to mice challenged with LPS. Binding studies revealed high affinity interactions between the palmitoyl-oleoyl-phosphatidylglycerol and the Toll-like receptor 4-interacting proteins CD14 and MD-2. Our data clearly identify important anti-inflammatory properties of the minor surfactant phospholipids at the environmental interface of the lung.

Structure of pulmonary surfactant membranes and films: the role of proteins and lipid-protein interactions

The pulmonary surfactant system constitutes an excellent example of how dynamic membrane polymorphism governs some biological functions through specific lipid-lipid, lipid-protein and protein-protein interactions assembled in highly differentiated cells. Lipid-protein surfactant complexes are assembled in alveolar pneumocytes in the form of tightly packed membranes, which are stored in specialized organelles called lamellar bodies (LB). Upon secretion of LBs, surfactant develops a membrane-based network that covers rapidly and efficiently the whole respiratory surface. This membrane-based surface layer is organized in a way that permits efficient gas exchange while optimizing the encounter of many different molecules and cells at the epithelial surface, in a cross-talk essential to keep the whole organism safe from potential pathogenic invaders. The present review summarizes what is known about the structure of the different forms of surfactant, with special emphasis on current models of the molecular organization of surfactant membrane components. The architecture and the behaviour shown by surfactant structures in vivo are interpreted, to some extent, from the interactions and the properties exhibited by different surfactant models as they have been studied in vitro, particularly addressing the possible role played by surfactant proteins. However, the limitations in structural complexity and biophysical performance of surfactant preparations reconstituted in vitro will be highlighted in particular, to allow for a proper evaluation of the significance of the experimental model systems used so far to study structure-function relationships in surfactant, and to define future challenges in the design and production of more efficient clinical surfactants.

Current perspectives in pulmonary surfactant--inhibition, enhancement and evaluation

Pulmonary surfactant (PS) is a complicated mixture of approximately 90% lipids and 10% proteins. It plays an important role in maintaining normal respiratory mechanics by reducing alveolar surface tension to near-zero values. Supplementing exogenous surfactant to newborns suffering from respiratory distress syndrome (RDS), a leading cause of perinatal mortality, has completely altered neonatal care in industrialized countries. Surfactant therapy has also been applied to the acute respiratory distress syndrome (ARDS) but with only limited success. Biophysical studies suggest that surfactant inhibition is partially responsible for this unsatisfactory performance. This paper reviews the biophysical properties of functional and dysfunctional PS. The biophysical properties of PS are further limited to surface activity, i.e., properties related to highly dynamic and very low surface tensions. Three main perspectives are reviewed. (1) How does PS permit both rapid adsorption and the ability to reach very low surface tensions? (2) How is PS inactivated by different inhibitory substances and how can this inhibition be counteracted? A recent research focus of using water-soluble polymers as additives to enhance the surface activity of clinical PS and to overcome inhibition is extensively discussed. (3) Which in vivo, in situ, and in vitro methods are available for evaluating the surface activity of PS and what are their relative merits? A better understanding of the biophysical properties of functional and dysfunctional PS is important for the further development of surfactant therapy, especially for its potential application in ARDS.