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Surfacen®, a clinical preparation of exogenous pulmonary surfactant, and pulmonary surfactant protein A (SP-A) were evaluated in relation to their in vitro effect on the growth of a clinical isolate of Streptococcus pneumoniae. The bacterium was incubated in a normal saline solution for 5 h at 37°C, together with Surfacen® and SP-A. Surfacen® showed antibacterial activity against the clinical isolate of Streptococcus pneumonia at 10 or 25 mg/ml with one logarithm of reduction of the bacterial growth; also SP-A had the same effect at concentrations of 0.25, 0.5 or 1 mg/ml. Porcine SP-A addition at the highest Surfacen® concentration (25 mg/ml) showed a higher antibacterial activity by reducing two logarithms of bacterial growth. [ABSTRACT FROM AUTHOR]

Abstract: Hyperpolarized 83Kr has previously been demonstrated to enable MRI contrast that is sensitive to the chemical composition of the surface in a porous model system. Methodological advances have lead to a substantial increase in the 83Kr hyperpolarization and the resulting signal intensity. Using the improved methodology for spin exchange optical pumping of isotopically enriched 83Kr, internal anatomical details of ex vivo rodent lung were resolved with hyperpolarized 83Kr MRI after krypton inhalation. Different 83Kr relaxation times were found between the main bronchi and the parenchymal regions in ex vivo rat lungs. The T1 weighted hyperpolarized 83Kr MRI provided a first demonstration of surface quadrupolar relaxation (SQUARE) pulmonary MRI contrast. [Copyright &y& Elsevier]

Dipalmitoylphosphatidylcholine, (DP-PtdCho), the major phospholipid component of lung surfactant is biosynthesized via a de novo pathway, the last step of which is catalyzed by CDP-choline:cholinephosphotransferase (CPT) and two remodeling steps: a deacylation and a reacylation one, catalyzed by an acidic, Ca-independent phospholipase A ( aiPLA) and a lyso-phosphatidylcholine acyltransferase (LPCAT), respectively. The aim of our study was to investigate whether a low magnitude, non-injurious static mode of mechanical stretch can induce phosphatidylcholine (PtdCho) biosynthesis and its remodeling to DP-PtdCho in the A549 cell-line, a model of alveolar type II cells. The deformation of A549 cells did not cause any release of lactate dehydrogenase, or phospholipids into the cell culture supernatants. An increase in PtdCho levels was observed after 1 h of static stretching, especially among the DP-PtdCho molecular species, as indicated by targeted lipidomics approach and site-directed fatty acyl-chain analysis. Moreover, although sphingomyelin (CerPCho) levels were unaffected, the DP-PtdCho/CerPCho ratio increased. Induction was observed in CPT, LPCAT and aiPLA enzymatic activities and gene expression. Finally, incubation of the cells with MJ33 suppressed aiPLA activity and DP-PtdCho production. Our data suggest that mild static mechanical stretch can promote the biosynthesis of PtdCho and its remodeling to DP-PtdCho in lung epithelial cells. Thus, low magnitude stretch could contribute to protective mechanisms rather than to injurious ones. [ABSTRACT FROM AUTHOR]

Abstract: Pulmonary inhalation chemotherapeutic drug delivery offers many advantages for lung cancer patients in comparison to conventional systemic chemotherapy. Inhalable particles are advantageous in their ability to deliver drug deep in the lung by utilizing optimally sized particles and higher local drug dose delivery. In this work, spray-dried and co-spray dried inhalable lung surfactant-mimic PEGylated lipopolymers as microparticulate/nanoparticulate dry powders containing paclitaxel were rationally designed via organic solution advanced spray drying (no water) in closed-mode from dilute concentration feed solution. Dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine poly(ethylene glycol) (DPPE-PEG) with varying PEG chain length were mixed with varying amounts of paclitaxel in methanol to produce co-spray dried microparticles and nanoparticles. Scanning electron microscopy showed the spherical particle morphology of the inhalable particles. Thermal analysis and X-ray powder diffraction confirmed the retention of the phospholipid bilayer structure in the solid-state following spray drying, the degree of solid-state molecular order, and solid-state phase transition behavior. The residual water content of the particles was very low as quantified analytically Karl Fisher titration. The amount of paclitaxel loaded into the particles was quantified which indicated high encapsulation efficiencies (43–99%). Dry powder aerosol dispersion performance was measured in vitro using the Next Generation Impactor™ (NGI™) coupled with the Handihaler® dry powder inhaler device and showed mass median aerodynamic diameters in the range of 3.4–7μm. These results demonstrate that this novel microparticulate/nanoparticulate chemotherapeutic PEGylated phospholipid dry powder inhalation aerosol platform has great potential in lung cancer drug delivery. [Copyright &y& Elsevier]

Surfactants in current clinical use are largely ineffective in treating acute lung injury (ALI)/ acute respiratory distress syndrome. In part, this ineffectiveness is due to inactivation of surfactant by serum leakage into the alveoli. Previously, we reported that adding hyaluronan and some nonionic polymers to synthetic lipids combined with native SP-B and SP-C enhanced surface activity. In this study, we first tested two therapeutic lung surfactants and then retested after adding hyaluronan, polyethylene glycol or dextran alone or in two-polymer combinations including hyaluronan in the absence or presence of serum. Surface activities were measured in a modified bubble surfactometer. Results indicate that the inhibition threshold (defined as the amount of serum required to produce a minimum surface tension above 10 mN/m after 5 minutes of cycling) was 35 times higher with hyaluronan plus dextran added to Infasurf than with Infasurf alone, and better than all other mixtures tested. The threshold for Survanta with hyaluronan plus polyethylene glycol was 7 times higher than Survanta alone. We next tested selected surfactant mixtures in an animal model that mimicked ALI. All measurements of lung function showed significant improvement ( P ≤ .05) with hyaluronan, or with hyaluronan and dextran added to Infasurf compared to Infasurf alone. Also, for these two groups, lung function was still improving at the end of the experiment. We conclude that certain polymers added to clinical surfactants can greatly increase resistance to inactivation in vitro, while in vivo, both Infasurf mixtures containing hyaluronan tended to normalize measures of lung function unlike other mixtures tested. [ABSTRACT FROM AUTHOR]

Surfactant complex and its individual components decrease surface tension, silence inflammatory responses, bind and destroy air-borne microbes, facilitate phagocytosis by alveolar macrophages and bind endogenous and exogenous molecules. Surfactant components generally decrease harmful inflammatory responses. New exogenous surfactants and new indications for surfactant therapy remain to be studied. At term the pool of human surfactant from developing airways extends to the amniotic cavity and to the gastrointestinal tract. Preterm labor-inducing inflammatory ligands (interleukin-1 or lipopolysaccharide) cause a robust induction of surfactant complex and lower the risk of respiratory distress syndrome (RDS). The effect of antenatal glucocorticoid therapy is complementary. According to transgenic experiments or genetic evidence in humans, surfactant proteins A, D or C (SP-A, SP-D, SP-C), expressed in fetal tissue, influence the onset of term or preterm labor. After birth, the surface tension-reducing and the inflammation-silencing effects of exogenous and endogenous surfactant are complementary. Surfactant proteins influence the genetic predisposition of RDS, bronchopulmonary dysplasia (BPD) and airway infections in early infancy. Moderate to severe BPD has a strong genetic predisposition. Deleterious mutations of SP-B, ABCA3 or SP-C cause congenital interstitial lung disease that mimics the phenotype of established severe BPD. I propose that lung surfactant protects both the fetus and the newborn. Surfactant ameliorates inflammatory responses that are harmful to the mother, fetus and infant. In chorioamnionitis, inflammatory ligands are carried from the fetal membranes to the alveolar space via amniotic fluid and developing airways. They induce surfactant synthesis and secretion. Surfactant ameliorates severe inflammatory responses in fetal compartments and promotes spontaneous preterm birth. Copyright © 2013 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Langmuir monolayers of Cholesterol (Chol) and a mixture of Chol with 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), at a ratio of 17:83 in weight, spread on pure water and on silica nanoparticle dispersions, have been investigated measuring the compression isotherms as well as the surface pressure response to harmonic area variation of the monolayer. Aim of this study was to evaluate the effects of the interaction of silica nanoparticles with Chol and the conditions for the incorporation in the monolayer. In previous works on different kind of lipid monolayers, it has been shown that hydrophilic silica nanoparticles dispersed in the sub-phase may transfer into the monolayer, driven by the interaction with the lipid molecules that make them partially hydrophobic. The results here obtained indicate that also for Chol and Chol–DPPC mixtures the presence of silica nanoparticles may have important effects on the phase behaviour and structural properties of the monolayer. As confirmed by complementary structural characterisations, BAM, AFM and ellipsometry, the principal effect of the nanoparticle incorporation is the disruption of the monolayer packing, owing to the alteration of the cohesive interactions of lipid components. [Copyright &y& Elsevier]

Abstract: Pulmonary surfactant model peptide, Hel 13–5, in binary and ternary lipid mixtures has been characterized employing the polarization–modulation infrared reflection–absorption spectroscopy (PM-IRRAS) in situ at the air–water interface for a monolayer state and the polarized ATR-FTIR for a bilayer film. In the bilayer form, Hel 13–5 predominantly adopts an α-helical secondary structure in the lipid mixtures. It had been made clear from CD measurements that the Hel 13–5 structure is mainly in the α-helical form in aqueous solutions. In the monolayer state, however, the secondary structure of Hel 13–5 exhibits an interconversion of the α-helix into β-sheet with increasing surface pressures. The difference in the secondary structure is attributed to formation of a surface-associated reservoir just below the surface monolayer. The reservoir formation is a key function of pulmonary surfactants and is induced by a squeeze-out of the fluid components in their monolayers. Compression and expansion cycles of the monolayers generate a hysteresis in molecular orientation of the lipid monolayer as well as in peptide structure. The formation and deformation of reservoirs are, in common, deeply related to the hysteresis behavior. Thus, the transition of peptide structures across the interface is a quite important matter to clarify the role and its mechanism of the reservoirs in pulmonary functions. The present study primarily reveals roles of the anionic lipids in control of the peptide secondary structure. Accordingly, it is demonstrated that they prevent the protein structure transition from α-helix into β-sheet by incorporating the peptide during the squeeze-out event. [Copyright &y& Elsevier]

A54145 factor D (A5D) is a cyclic lipopeptide antibiotic that shares several structural and mechanistic features with the clinically important antibiotic daptomycin, such as their requirement for calcium and phosphatidylglycerol (PG) for activity. Studies by others have suggested that daptomycin's activity is strongly inhibited by lung surfactant while A5D's activity is not. This finding has inspired efforts, albeit unsuccessful, to develop an A5D analogue that is highly active in the presence of lung surfactant and can be used for treating community acquired pneumonia (CAP). Here we demonstrate that A5D, like daptomycin, has a strong preference for the 1,2-diacyl- sn -glycero-3-phospho-1'- sn -glycerol stereoisomer (2 R ,2' S configuration) of PG. This PG stereoisomer was determined to be the only stereoisomer of PG in lung surfactant. Both antibiotics are completely antagonized by approximately 1-2 mol equiv of 2 R ,2' S -PG. Studies performed in the presence of lung surfactant revealed that the antagonism of these peptides by surfactant is mainly due to their interaction with PG and that A5D is not significantly less susceptible to inhibition by lung surfactant than daptomycin.

The influence of five different types of aluminosilicate nanoparticles (NPs) on the dynamic surface activity of model pulmonary surfactant (PS) (Survanta) was studied experimentally using oscillating bubble tensiometry. Bentonite, halloysite and montmorillonite (MM) NPs, which are used as fillers of polymer composites, were characterized regarding the size distribution, morphology and surface area. Particle doses applied in the studies were estimated based on the inhalation rate and duration, taking into account the expected aerosol concentration and deposition efficiency after penetration of NPs into the alveolar region. The results indicate that aluminosilicate NPs at concentrations in the pulmonary liquid above 0.1 mg cm−3 are capable of promoting alterations of the original dynamic biophysical activity of the PS. This effect is indicated by deviation of the minimum surface tension, stability index and the size of surface tension hysteresis. Such response is dependent on the type of NPs present in the system and is stronger when particle concentration increases. It is suggested that interactions between NPs and the PS must be related to the surfactant adsorption on the suspended particles, while in the case of surface-modified clay NPs the additional washout of surface-active components may be expected. It is speculated that observed changes in surface properties of the surfactant may be associated with undesired health effects following extensive inhalation of aluminosilicate NPs in the workplace. [ABSTRACT FROM AUTHOR]

Abstract: It is now established that the surface activity of the clinically used lung surfactant is reduced by serum proteins and can be restored by adding the hydrophilic polymers. The mechanisms of lung surfactant inactivation by serum proteins and restoring effect by the hydrophilic polymers remain not completely understood. In this paper the state and rheological dilatational properties of surface films formed from clinical lung surfactant Exosurf, Survanta, Curosurf and Alveofact in the presence of serum albumin (BSA) and hydrophilic polymers polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and Dextran were studied. The obtained results suggest that the lung surfactant and BSA mixtures spread at air–water interface form a DPPC/BSA mixed monolayers with lower content of DPPC. The presence of hydrophilic polymers PVP, PEG and Dextran restore the DPPC content in the surface film. The effectiveness of the DPPC spreading and formation of better compacted film increases in order Exosurf, Survanta, Curosurf, Alveofact. The obtained results are in accordance with the generally admitted ideas about the mechanisms of serum protein inactivation and restoring effect of hydrophilic polymers based on the previously studies of the lung surfactant adsorption rate. [Copyright &y& Elsevier]

Abstract: Microbubbles are micrometer-size gaseous particles suspended in water, and they are often stabilized by a lipid monolayer shell. Natural microbubbles are found in freshwater and saltwater systems, and engineered microbubbles have a variety of applications in food sciences, biotechnology and medicine. Lipid-coated microbubbles are found to have remarkable stability and mechanical behavior owing to the resistance of the lipid monolayer encapsulation to collapse. The purpose of this review is to tie in recent observations of lipid-coated microbubble dissolution and gas exchange with current literature on the physics of lipid monolayer collapse in the context of lung surfactant. Based on this analysis, we conclude that microbubble shells collapse through the nucleation of microscopic folds, which then catalyze the formation and aggregation of new folds, leading to macroscopic folding events. This process results in a cyclic behavior of crumple-to-smooth transitions, which can be modulated through lipid composition. Eventually, the microbubbles stabilize at 1–2μm diameter, regardless of initial size or lipid composition, and various mechanisms for this stabilization are postulated. Our ultimate goal is to inspire the reader to consider lipid monolayer collapse as the main long-term stabilizing mechanism for lipid-coated microbubbles, and to stimulate the use of microbubbles as a platform for studying monolayer collapse phenomena. [Copyright &y& Elsevier]

Abstract: Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and mixtures of DOPC with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), at a ratio of 37:63 in weight, spread on pure water and on silica nanoparticle dispersions, have been investigated using a combination of thermodynamic, surface rheology, BAM and AFM diagnostics. The compression surface pressure isotherms were determined in a Langmuir trough as well as the surface pressure response to harmonic area variation of the monolayer. Composite layers were obtained at selected thermodynamic states by transfer from the fluid interface to solid substrates and then analysed by AFM diagnostics. Aim of this study was to evaluate the effect of the incorporation of silica nanoparticles on the phase behaviour and structural properties of these monolayers. In fact, as shown in previous works on similar lipid systems, the hydrophilic silica nanoparticles dispersed in the sub-phase are transferred into the monolayer due to the interaction with lipid molecules which makes them partially hydrophobic. The results here obtained indicate that the appreciable influence of silica nanoparticles, previously observed for DPPC alone, is also important for DOPC and DOPC–DPPC mixture. Moreover, as confirmed by the AFM results on the deposited layers, these effects are mainly due to the disruption of the molecular packing and to the modification of the miscibility between the two lipid components. [Copyright &y& Elsevier]

Abstract: Background: We previously demonstrated that donor treatment with inhaled hydrogen protects lung grafts from cold ischemia/reperfusion (I/R) injury during lung transplantation. To elucidate the mechanisms underlying hydrogen’s protective effects, we conducted a gene array analysis to identify changes in gene expression associated with hydrogen treatment. Methods: Donor rats were exposed to mechanical ventilation with 98% oxygen and 2% nitrogen or 2% hydrogen for 3h before harvest; lung grafts were stored for 4h in cold Perfadex. Affymetrix gene array analysis of mRNA transcripts was performed on the lung tissue prior to implantation. Results: Pretreatment of donor lungs with hydrogen altered the expression of 229 genes represented on the array (182 upregulated; 47 downregulated). Hydrogen treatment induced several lung surfactant-related genes, ATP synthase genes and stress-response genes. The intracellular surfactant pool, tissue adenosine triphosphate (ATP) levels and heat shock protein 70 (HSP70) expression increased in the hydrogen-treated grafts. Hydrogen treatment also induced the transcription factors C/EBPα and C/EBPβ, which are known regulators of surfactant-related genes. Conclusion: Donor ventilation with hydrogen significantly increases expression of surfactant-related molecules, ATP synthases and stress-response molecules in lung grafts. The induction of these molecules may underlie hydrogen’s protective effects against I/R injury during transplantation. [Copyright &y& Elsevier]

Lung surfactant is crucial for reducing the surface tension of alveolar space, thus preventing the alveoli from collapse. Lung surfactant is synthesized in alveolar epithelial type II cells and stored in lamellar bodies before being released via the fusion of lamellar bodies with the apical plasma membrane. SNAREs (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptors) play an essential role in membrane fusion. We have previously demonstrated the requirement of t-SNARE (target SNARE) proteins, syntaxin 2 and SNAP-23 ( N-ethylmaleimide-sensitive factor-attachment protein 23), in regulated surfactant secretion. Here, we characterized the distribution of VAMPs (vesicle-associated membrane proteins) in rat lung and alveolar type II cells. VAMP-2, −3 and −8 are shown in type II cells at both mRNA and protein levels. VAMP-2 and −8 were enriched in LB (lamellar body) fraction. Immunochemistry studies indicated that VAMP-2 was co-localized with the LB marker protein, LB-180. Functionally, the cytoplasmic domain of VAMP-2, but not VAMP-8 inhibited surfactant secretion in type II cells. We suggest that VAMP-2 is the v-SNARE (vesicle SNARE) involved in regulated surfactant secretion. [ABSTRACT FROM AUTHOR]

The hydrophobic lung surfactant protein, SP-B, is essential for survival. Cycling of lung volume during respiration requires a surface-active lipid-protein layer at the alveolar air-water interface. SP-B may contribute to surfactant layer maintenance and renewal by facilitating contact and transfer between the surface layer and bilayer reservoirs of surfactant material. However, only small effects of SP-B on phospholipid orientational order in model systems have been reported. In this study, N-terminal (SP-B) and C-terminal (SP-B) helices of SP-B, either linked as Mini-B or unlinked but present in equal amounts, were incorporated into either model phospholipid mixtures or into bovine lipid extract surfactant in the form of vesicle dispersions or mechanically oriented bilayer samples. Deuterium and phosphorus nuclear magnetic resonance (NMR) were used to characterize effects of these peptides on phospholipid chain orientational order, headgroup orientation, and the response of lipid-peptide mixtures to mechanical orientation by mica plates. Only small effects on chain orientational order or headgroup orientation, in either vesicle or mechanically oriented samples, were seen. In mechanically constrained samples, however, Mini-B and its component helices did have specific effects on the propensity of lipid-peptide mixtures to form unoriented bilayer populations which do not exchange with the oriented fraction on the timescale of the NMR experiment. Modification of local bilayer orientation, even in the presence of mechanical constraint, may be relevant to the transfer of material from bilayer reservoirs to a flat surface-active layer, a process that likely requires contact facilitated by the formation of highly curved protrusions. [ABSTRACT FROM AUTHOR]

It has been proposed that during human evolution, development of obligate bipedalism, narrow birth canal cross-sectional area and the large brain have forced an adjustment in duration of pregnancy (scaling of gestational age; Plunkett 2011). Children compared to other mammals are born with proportionally small brains (compared to adult brains), suggesting shortening of pregnancy duration during recent evolution. Prevalence of both obstructed delivery and premature birth is still exceptionally high. In near term infants, functional maturity and viability is high, and gene variants predisposing to respiratory distress syndrome (RDS) are rare. Advanced antenatal and neonatal treatment practices during the new era of medicine allowed survival of also very preterm infants (gestation <32 weeks). Genetic factors may play a major role in predisposing these infants to common pulmonary (bronchopulmonary dysplasia [BPD]; RDS) and intracerebral (intraventricular hemorrhage [IVH], cerebral palsy [CP]) diseases. Fetal genes also influence the susceptibility to preterm labor and premature birth. Specific genes associating with diseases in preterm infants may also contribute to the susceptibility to preterm birth. Understanding and applying the knowledge of genetic interactions in normal and abnormal perinatal-neonatal development requires large, well-structured population cohorts, studies involving the whole genome and international interdisciplinary collaboration. [ABSTRACT FROM AUTHOR]

Abstract: Efficient downregulation of gene expression depends on the uptake, intracellular distribution and efficient release of siRNA from their carrier. Therefore, the cellular uptake behavior and mechanism and intracellular localization of siRNA-loaded biodegradable nanoparticles were investigated. A biodegradable polymer, composed of poly(vinyl alcohol) (PVA) modified with diamine moieties and grafted with PLGA, abbreviated as DEAPA-PVA-g-PLGA, was used for the preparation of siRNA-loaded nanoparticles by solvent displacement. Particle sizes and morphology were determined by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The dependence of particle uptake into H1299-EGFP cells (lung cancer cells expressing green fluorescent protein) on both incubation time and temperature was studied by flow cytometry. Inhibition experiments focusing on clathrin- or caveolae-mediated uptake or uptake by macropinocytosis were performed. The intracellular localization was investigated by confocal laser scanning microscopy. The GFP knockdown efficiency was determined in vitro to establish the potential of the nanoparticles for the downregulation of gene expression. Nanoparticles with diameters of 120–180nm were successfully generated. In contrast to the uptake of standard PEI-polyplexes, which increased continuously over a period of 4h, nanoparticle uptake was complete within 2h. A decrease in particle uptake at 4°C (in comparison with 37°C) suggests an active uptake process. Inhibition experiments revealed the predominance of clathrin-mediated uptake for siRNA-loaded nanoparticles. The siRNA-loaded nanoparticles could be clearly located within cells, mainly in intracellular vesicles. Particle uptake could be increased by the addition of lung surfactant to the formulation. Bioactivity in terms of successful GFP knockdown in vitro was demonstrated and could be further optimized by the use of surfactant-modified particles. In conclusion, a high and rapid cellular uptake was shown for siRNA-loaded nanoparticles. Cell internalization is based on an energy-dependent and predominantly clathrin-mediated process. Particle localization in endosomes and lysosomes was demonstrated. Evidence for the efficient delivery of bioactive siRNA and specific GFP knockdown provides a solid basis for the application of DEAPA-PVA-g-PLGA-based particles for gene silencing in vivo. [Copyright &y& Elsevier]

The article offers information on a study related to the measurement of phospholipid concentration, protein concentration and surface tension of bronchoalveolar lavage fluid (BALF) used in surfactant assessment in rats by intratracheal instillation of nickel oxide and titanium dioxide. According to the study, submicron sized particles of nickel oxide with smaller median diameters potentially have a stronger biological effect than micron size particles.

Abstract: Stable isotope labelling of lipid precursors coupled with mass spectrometry-based lipidomic analyses and determination of isotope enrichment in substrate, intermediate and product pools provide the parameters needed to determine absolute flux rates through lipid pathways in vivo. Here, as an illustration of the power of such analyses we investigated lung phosphatidylcholine (PC) synthesis in Surfactant Protein-D (SP-D) null mice. These animals develop emphysema, foamy alveolar macrophages and an alveolar lipoproteinosis with increasing age. We used the incorporation of methyl-9-[2H] choline chloride coupled with ESI-MS/MS to quantify absolute rates of lung surfactant PC synthesis and secretion in an SP-D−/− mouse model, together with an analysis of the molecular specificity of lung PC synthesis. PC synthetic rates were comparable in control (0.52μmol/lung/h) and SP-D−/− (0.69μmol/lung/h) mice, as were rates of surfactant PC secretion (29.8 and 30.6nmol/lung/h, respectively). Increased lung PC in the SP-D−/− mouse was due to impaired catabolism, with a rate of accumulation of 0.057μmol/lung/h. The relatively low rates of surfactant PC secretion compared with total lung PC synthesis were compatible with a suggested ABCA1-mediated basolateral lipid efflux from alveolar type II epithelial cells. Finally, PC molecular species analysis suggested that a proportion of newly synthesised PC is secreted rapidly into the lung air spaces in both control and SP-D−/− mice before significant PC acyl remodelling occurs. [Copyright &y& Elsevier]

Abstract: The interfacial behavior of the newly designed Fluorocarbon Hydrocarbon Cationic Lipid (FHCL or CH3(CH2)17N+(C2H5)2(CH2)3(CF2)7CF3I−) and its mixtures with a phospholipid (DPPC, Dipalmitoylphosphatidylcholine) at different mole fractions were investigated. This new molecule was synthesized to mimic the selected properties of lung surfactant, which is a natural lipid–protein mixture which is known to play important roles in the process of respiration, by considering the structure/function relation of lung surfactant protein (SP-C). Each segment in the molecular structure was selected to affect the molecular level interaction at the interface whereas the keeping the overall structure as simple as possible. The surface pressure area isotherms obtained for the mixtures of DPPC/FHCL indicated that there was repulsive interaction between DPPC and FHCL molecules. Due to the molecular level interaction, specifically at mole fraction 0.3, the isotherm obtained from that mixture resembled the isotherm obtained from the DPPC monolayer in the presence of SP-C. High elasticity of the interface was one of the important parameters for the respiration process, therefore, shear and dilatational elasticities of two-component systems were determined and they were found to be similar to the case where SP-C protein is present. Fluorescence microscopy images were taken in order to investigate the monolayer in details. The FHCL was able to fluidize the DPPC monolayer even at high surface pressures effectively. In addition, the cyclic compression–expansion isotherms were obtained to understand the spreading and re-spreading ability of the pure FHCL and the mixed DPPC/FHCL monolayers. At a specific mole fraction, X FHCL =0.3, the mixture exhibited good hysteresis in area, compressibility, recruitment index and re-spreading ability at the interface. All these results point out that FHCL can fulfill the selected features of the lung surfactant that are attributed to the presence of SP-C protein when mixed with DPPC, even if the molecular structure of the FHCL is quite simple. [Copyright &y& Elsevier]

Abstract: The purpose of this review is to provide insight into the biophysical properties and functions of tear fluid and lung surfactant – two similar fluids covering the epithelium of two distinctive organs. Both fluids form a layer-like structure that essentially comprise of an aqueous layer next to the epithelium and an anterior lipid layer at the air-water interface. The aqueous layers contain soluble proteins and metabolites, and they are responsible for the host defence system and nutrition of the organ. However, many proteins also interact with the lipid layer and are important for the surface-active function of the fluid film. The lipid layer of lung surfactant comprises mainly of phospholipids, especially phosphatidylcholines, and only small amounts of non-polar lipids, mainly cholesterol. In contrast, tear fluid lipid layer comprises of a mixture of polar and non-polar lipids. However, the relative proportion and the spectrum of different polar and non-polar lipids seem to be more extensive in tear fluid than in lung surfactant. The differing lipid compositions generate distinctive lipid layer structures. Despite the structural differences, these lipid layers decrease the surface tension of the air-water interface. The structure of the tear film lipid layer also minimises the evaporation of the tear fluid. In lung surfactant surface activity is crucial for the function of the organ, as the lipid layer prevents the collapse of the lung alveoli during the compression-expansion cycle of breathing. Similarly the tear film experiences a compression-expansion cycle during blinking. The dynamics of this cycle have been studied to a lesser extent and are not as clear as those of lung surfactant. The common structure and properties suggest a similar behaviour under rapid compression–expansion for both fluids. [Copyright &y& Elsevier]

Abstract: The efficiency of pulmonary surfactant to stabilize the respiratory surface depends critically on the ability of surfactant to form highly packed films at the air–liquid interface. In the present study we have compared the packing and hydration properties of lipids in native pulmonary surfactant and in several surfactant models by analyzing the pressure and temperature dependence of the fluorescence emission of the LAURDAN (1-[6-(dimethylamino)-2-naphthyl]dodecan-1-one) probe incorporated into surfactant interfacial films or free-standing membranes. In interfacial films, compression-driven changes in the fluorescence of LAURDAN, evaluated from the generalized polarization function (GPF), correlated with changes in packing monitored by surface pressure. Compression isotherms and GPF profiles of films formed by native surfactant or its organic extract were compared at 25 or 37°C to those of films made of dipalmitoylphosphatidylcholine (DPPC), palmitoyloleoylphosphatidylcholine (POPC), DPPC/phosphatidylglycerol (PG) (7:3, w/w), or the mixture DPPC/POPC/palmitoyloleoylphosphatidylglycerol (POPG)/cholesterol (Chol) (50:25:15.10), which simulates the lipid composition of surfactant. In general terms, compression of surfactant films at 25°C leads to LAURDAN GPF values close to those obtained from pure DPPC monolayers, suggesting that compressed surfactant films reach a dehydrated state of the lipid surface, which is similar to that achieved in DPPC monolayers. However, at 37°C, the highest GPF values were achieved in films made of full surfactant organic extract or the mixture DPPC/POPC/POPG/Chol, suggesting a potentially important role of cholesterol to ensure maximal packing/dehydration under physiological constraints. Native surfactant films reached high pressures at 37°C while maintaining relatively low GPF, suggesting that the complex three-dimensional structures formed by whole surfactant might withstand the highest pressures without necessarily achieving full dehydration of the lipid environments sensed by LAURDAN. Finally, comparison of the thermotropic profiles of LAURDAN GPF in surfactant model bilayers and monolayers of analogous composition shows that the fluorophore probes an environment that is in average intrinsically more hydrated at the interface than inserted into free-standing bilayers, particularly at 37°C. This effect suggests that the dependence of membrane and surfactant events on the balance of polar/non-polar interactions could differ in bilayer and monolayer models, and might be affected differently by the access of water molecules to confined or free-standing lipid structures. [Copyright &y& Elsevier]

To develop a rapid method for diagnosing lung maturity at birth with the purpose of administering surfactant early to infants with immature lungs and to spare infants with mature lungs from this treatment. Lamellar body counts (LBC) on gastric aspirates from 191 newborns were counted in the platelet window in automatic blood cell counters. A preliminary study was performed on 108 aspirates from 2000 in infants with <32 weeks' gestation. Furthermore, 83 aspirates from 2004 to 2005 in infants with <30 weeks' gestation were analysed. Lamellar bodies in gastric aspirate were identified by electron microscopy. Seventy of the aspirates from 2004 to 2005 were analysed with a Sysmex XE-2100 (Sysmex, Holbæk, Næstved, Odense and Rigshospitalet, Denmark) counter. Twenty-four of these infants developed moderate to severe respiratory distress syndrome (RDS). The best cut-off value was 8000/μL with a sensitivity of 75% and a specificity of 72%. Forty-four of the 70 aspirates from 2004 to 2005 were analysed by Sysmex, Advia 120 and Cell-Dyn 4000. Thirteen other aspirates from 2004 to 05 were analysed by Sysmex and Coulter Counter LH755. Using Advia and Coulter the results were similar to Sysmex, but LBC obtained with Cell-Dyn were not correlated with the development of RDS. Lamellar body counts on gastric aspirate is a promising tool for prediction of development of RDS in infants of <30 weeks` gestation. [ABSTRACT FROM AUTHOR]

Abstract: Functionality, structure and composition of the adsorbed films of bovine lipid extract surfactant (BLES), in the absence and presence of bovine serum albumin (BSA), at the air–buffer interface was characterized through surface tension, atomic force microscopy and time of flight secondary ion mass spectrometric methods. Gel and fluid domains of BLES films were found to be altered significantly in the presence of BSA. Differential scanning calorimetric studies on BLES dispersions in presence of BSA revealed that the perturbations of the lipid bilayer structures were significant only at higher amount of BSA. FTIR studies on the BLES dispersions in buffer solution revealed that BSA could affect the lipid head-group hydrations in bilayer as well as the methylene and methyl vibration modes of fatty acyl chains of the phospholipids present in BLES. Serum albumin could perturb the film structure at pathophysiological concentration while higher amount of BSA was required in perturbing the bilayer structures. The studies suggest a connected perturbed bilayer to monolayer transition model for surfactant inactivation at the alveolar–air interface in dysfunctional surfactants. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to investigate whether early phase of acute respiratory distress syndrome (ARDS) is associated with changes in immune response, either systemic or localized to the lung. ARDS and control mechanically ventilated patients, as well as healthy volunteers were studied. Alveolar macrophages (AMΦ) and blood monocytes (BM) were treated ex vivo with lipopolysaccharide (LPS), interferon-γ (IFNγ), and surfactant. Phospholipase A2 (PLA2) activity and TLR4 expression were evaluated as markers of cell response. AMΦ from ARDS patients did not respond upon treatment with either LPS or IFN-γ by inducing PLA2 production. On the contrary, upon stimulation, in control patients the intracellular PLA2, (mainly cPLA2) levels were increased, but secretion of PLA2 (mainly sPLA2-IIA) was observed only after treatment with LPS. Surfactant suppressed PLA2 production in cells from both groups of patients. Increased relative changes of total PLA2 activity and an upregulation of TLR4 expression upon stimulation was observed in BM from primary ARDS, control patients and healthy volunteers. In BM from secondary ARDS patients, however, no PLA2 induction was observed, with a concomitant down-regulation of TLR4 expression. Cytosolic PLA2, its activated form, p-cPLA2, and sPLA2-IIA were the predominant PLA2 types within the cells, while extracellularly only sPLA2-IIA was identified. These results support the concept of down-regulated innate immunity in early ARDS that is compartmentalized in primary and systemic in secondary ARDS. PLA2 isoforms could serve as markers of the immunity status in ARDS. Finally, our data highlight the role of surfactant in controlling inflammation. [Copyright &y& Elsevier]

Abstract: Hydrophobic lung surfactant proteins B and C (SP-B and SP-C) are critical for normal respiration in vertebrates, and each comprises specific structural attributes that enable the surface-tension-reducing ability of the lipid–protein mixture in lung surfactant. The difficulty in obtaining pure SP-B and SP-C on a large scale has hindered efforts to develop a non-animal-derived surfactant replacement therapy for respiratory distress. Although peptide-based SP-C mimics exhibit similar activity to the natural protein, helical peptide-based mimics of SP-B benefit from dimeric structures. To determine if in vitro surface activity improvements in a mixed lipid film could be garnered without creating a dimerized structural motif, a helical and cationic peptoid-based SP-B mimic was modified by SP-C-like N-terminus alkylation with octadecylamine. “Hybridized” mono- and dialkylated peptoids significantly decreased the maximum surface tension of the lipid film during cycling on the pulsating bubble surfactometer relative to the unalkylated variant. Peptoids were localized in the fluid phase of giant unilamellar vesicle lipid bilayers, as has been described for SP-B and SP-C. Using Langmuir–Wilhelmy surface balance epifluorescence imaging (FM) and atomic force microscopy (AFM), only lipid-alkylated peptoid films revealed micro- and nanostructures closely resembling films containing SP-B. AFM images of lipid-alkylated peptoid films showed gel condensed-phase domains surrounded by a distinct phase containing “nanosilo” structures believed to enhance re-spreading of submonolayer material. N-terminus alkylation may be a simple, effective method for increasing lipid affinity and surface activity of single-helix SP-B mimics. [Copyright &y& Elsevier]

Abstract: In situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) at the air–water interface has been used to determine secondary structure of the pulmonary surfactant model peptide, Hel 13-5, in the absence and the presence of phospholipid monolayers. Herein, fully saturated phospholipids of DPPC and DPPG are utilized to understand the effect of specific interaction between anionic DPPG and cationic Hel 13-5 on the peptide secondary structure. The spectrum frequency in the amide region (1500–1700cm−1) obtained from PM-IRRAS has been confirmed by comparing with that from ATR-FTIR for the corresponding bulk films. The PM-IRRAS spectra of single Hel 13-5 monolayers indicate the α-helical contour in the amide region, which coincides with the result from CD measurements in aqueous solutions. In the presence of phospholipid monolayers, however, Hel 13-5 changes its conformation from the α-helix to the extended β-sheet as surface pressure increases upon compression at the interface, and this interconversion is found to be irreversible even during expansion process of monolayers. Furthermore, it is notable that the electrostatic interaction between DPPG and Hel 13-5 inhibits to some extent the interconversion to the β-sheet during compression. These features are completely different from the bulk behavior, which demonstrates different roles of native proteins in the bulk phase and at the interface for pulmonary functions. In addition, the conformational variation of Hel 13-5 does not indicate close correlation with surface activity, which is common characteristic even for reversible hysteresis curves in pulmonary surfactant systems. This suggests that the secondary structure of native proteins is not strongly related to the surface activity during respiration. This work contributes to secondary structure determination of Hel 13-5 in the phospholipid domains in situ at the air–water interface and will provide insight into the molecular and physiological mechanism for SP-B and SP-C actions across the interface. [Copyright &y& Elsevier]

Abstract: Peroxiredoxins (Prx) are enzymes that catalyze the reduction of hydrogen peroxide and alkyl hydroperoxides. Prxs are ubiquitous enzymes with representatives found in Bacteria, Archaea and Eukarya. Many 1-cysteine peroxiredoxins (1-CysPrx) are dual-function enzyme with both peroxidase and acidic Ca2+-independent phospholipase A2 (aiPLA2) activities. The functions proposed for 1-CysPrx/aiPLA2 include the protection of cell membrane phospholipids against oxidative damage (peroxidation) and the metabolism (hydrolysis) of phospholipids, such as those of lung surfactant. The peroxidase active site motif PVCTTE of 1-CysPrx contains the conserved catalytic cysteine residue, and the esterase (lipase) motif GXSXG of the enzyme contains the conserved catalytic serine residue. In addition to the classic lipase motif GXSXG, various 1-CysPrx/aiPLA2s have closely related variant putative lipase motifs containing the catalytic serine residue. The PLA2 moieties are prevalent and highly homologous in vertebrate and bacterial 1-CysPrx/aiPLA2s that is consistent with a high degree evolutional conservation of the enzyme. [Copyright &y& Elsevier]

Abstract: The lateral organization of domain structures is an extremely significant aspect of biomembrane research. Chemical imaging by mass spectrometry with its recent advancement in sensitivity and lateral resolution has become a highly promising tool in biological research. In this review, we focus briefly on the instrumentation, working principle and important concepts related to time-of-flight secondary ion mass spectrometry followed by an overview of lipid/protein fragmentation patterns and chemical mapping. The key issues addressed are the applications of time-of-flight secondary ion mass spectrometry in biological membrane research. Additionally, we briefly review our recent investigations based on time-of-flight secondary ion mass spectrometry to unravel the lateral distribution of lipids and surfactant proteins in lung surfactant model systems as an example that highlights the importance of fluidity and ionic conditions on lipid phase behavior and lipid–protein interactions. [Copyright &y& Elsevier]

Abstract: Lung surfactant protein B (SP-B) is a lipophilic protein critical to lung function at ambient pressure. KL4 is a 21-residue peptide which has successfully replaced SP-B in clinical trials of synthetic lung surfactants. CD and FTIR measurements indicate KL4 is helical in a lipid bilayer environment, but its exact secondary structure and orientation within the bilayer remain controversial. To investigate the partitioning and dynamics of KL4 in phospholipid bilayers, we introduced CD3-enriched leucines at four positions along the peptide to serve as probes of side chain dynamics via 2H solid-state NMR. The chosen labels allow distinction between models of helical secondary structure as well as between a transmembrane orientation or partitioning in the plane of the lipid leaflets. Leucine side chains are also sensitive to helix packing interactions in peptides that oligomerize. The partitioning and orientation of KL4 in DPPC/POPG and POPC/POPG phospholipid bilayers, as inferred from the leucine side chain dynamics, is consistent with monomeric KL4 lying in the plane of the bilayers and adopting an unusual helical structure which confers amphipathicity and allows partitioning into the lipid hydrophobic interior. At physiologic temperatures, the partitioning depth and dynamics of the peptide are dependent on the degree of saturation present in the lipids. The deeper partitioning of KL4 relative to antimicrobial amphipathic α-helices leads to negative membrane curvature strain as evidenced by the formation of hexagonal phase structures in a POPE/POPG phospholipid mixture on addition of KL4. The unusual secondary structure of KL4 and its ability to differentially partition into lipid lamellae containing varying levels of saturation suggest a mechanism for its role in restoring lung compliance. [Copyright &y& Elsevier]

Surfactant protein-A (SP-A) plays an important role in the clearance of surfactant from the lung alveolar space and in the regulation of surfactant secretion and uptake by type II pneumocytes in culture. Two pathways are important for the endocytosis of surfactant by type II cells and the intact lung, a receptor-mediated clathrin-dependent pathway and a non-clathrin, actin-mediated pathway. The critical role of the clathrin/receptor-mediated pathway in normal mice is supported by the finding that SP-A gene-targeted mice use the actin-dependent pathway to maintain normal clearance of surfactant. Addition of SP-A to the surfactant of the SP-A null mice “rescued” the phenotype, further emphasizing the essential role of the SP-A/receptor-mediated process in surfactant turnover. This review presents an overview of the structure of SP-A and its function in surfactant turnover. The evidence that the interaction of SP-A with type II cells is a receptor-mediated process is presented. A newly identified receptor for SP-A, P63/CKAP4, is described in detail, with elucidation of the specific structural features of this 63 kDa, nonglycosylated, highly coiled, transmembrane protein. The compelling evidence that P63 functions as a receptor for SP-A on type II cells is summarized. Regulation of P63 receptor density on the surface of pneumocytes may be a novel approach for the regulation of surfactant homeostasis by the lung. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Phospholipases A2 (PLA2) catalyse the cleavage of fatty acids esterified at the sn-2 position of glycerophospholipids. In acute lung injury-acute respiratory distress syndrome (ALI-ARDS) several distinct isoenzymes appear in lung cells and fluid. Some are capable to trigger molecular events leading to enhanced inflammation and lung damage and others have a role in lung surfactant recycling preserving lung function: Secreted forms (groups sPLA2-IIA, -V, -X) can directly hydrolyze surfactant phospholipids. Cytosolic PLA2 (cPLA2-IVA) requiring Ca2+ has a preference for arachidonate, the precursor of eicosanoids which participate in the inflammatory response in the lung. Ca2+-independent intracellular PLA2s (iPLA2) take part in surfactant phospholipids turnover within alveolar cells. Acidic Ca2+-independent PLA2 (aiPLA2), of lysosomal origin, has additionally antioxidant properties, (peroxiredoxin VI activity), and participates in the formation of dipalmitoyl-phosphatidylcholine in lung surfactant. PAF-AH degrades PAF, a potent mediator of inflammation, and oxidatively fragmented phospholipids but also leads to toxic metabolites. Therefore, the regulation of PLA2 isoforms could be a valuable approach for ARDS treatment. [Copyright &y& Elsevier]

Human Neutrophil Elastase (HNE) is one of the main proteases secreted into the alveolar space by infiltrated neutrophils during several inflammatory lung diseases such as cystic fibrosis, acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Consequently, a number of therapeutic approaches based on the specific inhibition of HNE are currently under investigation. The present work reviews the physiopathological role of HNE in ALI/ARDS and its relationship to the pulmonary surfactant system, as well as the clinical potential of protease inhibitors in this setting. In spite of the complex physiopathology of these diseases, the available evidence points to a direct link between HNE and ALI/ARDS, with increased local concentrations of this protease in animal models of ALI as well as in patients. Furthermore, the unbalanced ratio of protease/endogenous inhibitors characteristic of these disorders has led to the pharmacological and clinical evaluation of HNE inhibitors, examining their addition to currently available exogenous surfactant with promising results. [ABSTRACT FROM AUTHOR]

In the context of several lung diseases such as cystic fibrosis, acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), several proteases are released from infiltrate neutrophils on alveolar space, where the human neutrophil elastase (HNE) play a major role. Based on this concept, therapeutic approaches have been developed in order to inhibit the elastolytic activity. In this sense, this article summarizes, first, some pathophysiological functions of neutrophil elastase in ALI/ARDS and their relationship with the lung surfactant and the potential therapeutic use of elastase inhibitors as well. The results show that although the pathophysiology of ALI/ARDS is complex, several evidences shows a direct relationship between neutrophil elastase and ALI, where is observed a increasing of protease concentration in ALI animal model as well as in patients. On the other hand, due to unbalance protease/endogenous inhibitors, the pharmacological assays and the clinical application of neutrophil elastase inhibitors are being researched with promising results. [ABSTRACT FROM AUTHOR]

Abstract: Dipalmitoyl phosphatidylcholine (DPPC) is the most abundant phospholipid in lung surfactant, primarily responsible for the reduction of surface tension to near 0mN/m during expiration. In addition, DPPC liposomes are also used for drug delivery. In this study, the effects of hydrochloric acid, nitric acid and sulphuric acid on various properties of DPPC was investigated. The surface pressure versus area isotherms of DPPC monolayers at different concentrations of acid were obtained using a Langmuir–Blodgett trough. Distinct changes in the shapes of DPPC isotherms were observed in presence of acid. The lift off area for DPPC control at pH 7.4 was 58Å2. The lift off area for DPPC was 105, 100 and 95Å2 at concentration of 15.5×10−2 mol/dm3 of nitric acid, sulphuric acid and hydrochloric acid respectively. Collapse plateaus were longest in presence of nitric acid compared to hydrochloric acid and sulphuric acid. The nitric acid treated liposomes showed improved adsorption as evidenced by lower surface tension values achieved within 1s at concentrations ranging from 3.1×10−6 to 15.5×10−4 mol/dm3 having pH 6.2–2.9. The inhibitory concentrations of nitric acid which significantly increased the average surface tension values achieved within 1s were 3.1×10−3 to 15.5×10−2 mol/dm3 (pH 2.6–1.0). The sulphuric acid treated liposomes showed improved adsorption at concentrations of 3.1×10−6 to 3.1×10−2 mol/dm3 (pH 6.1–1.7). The adsorption was significantly inhibited at pH 1.4–0.4 achieved with sulphuric acid. The HCl-treated liposomes showed an improved adsorption at concentrations ranging from 3.1×10−6 to 15.5×10−2 mol/dm3 (pH 6.4–1.3). The average surface pressure value achieved within 1s at inhibitory concentration of 3.1×10−1 mol/dm3 of HCl at a pH of 0.83 was 10.1±2.2mN/m. Acids did not affect the compressibility of DPPC. Increased leakage of calcein from DPPC liposomes at decreasing pH suggested increased permeability of DPPC liposomes under acidic conditions. The results of this study may have implications for pH dependent drug delivery in acidic conditions as well as for lung surfactant dysfunction in acid lung injury. [Copyright &y& Elsevier]

Microplastics (MPs), as pollutants of environmental concern, are correlated with increased risk of various respiratory diseases. Nevertheless, whether or not MPs have adverse influences on the interfacial properties of lung surfactant (LS), and its effect on the generation of reactive oxygen species are poorly understood. In the present study, natural LS extracted from porcine lungs was used to investigate the interaction with polystyrene as a representative MPs. The results showed that the phase behavior, surface tension, and membrane structure of the LS were altered in the presence of polystyrene. Adsorption experiments demonstrated that in the mixed system of polystyrene and LS (the main active ingredients are phospholipids and proteins), adsorption of phospholipid components by polystyrene was notably higher than that of proteins. Moreover, polystyrene can accelerate the conversion between ascorbic acid and deoxyascorbic acid, thereby producing hydrogen peroxide (HOOH) in simulated lung fluid (containing LS) and further giving rise to an increase in the content of hydroxyl radicals (•OH). This work provides new insight into the potential hazard of MPs in human respiratory system, which is helpful for deeply understanding the unfavorable physicochemical effects of MPs exposure and the role of inhaled MPs on lung health. [Display omitted] • Inhaled polystyrene can adsorb phospholipids and proteins in lung surfactant (LS). • Polystyrene impacted the phase behavior, surface tension, and microstructure of LS. • Hydroxyl radicals can be formed in simulated lung fluid in the presence of polystyrene. • Polystyrene can drive ascorbic acid to produce HOOH and further generate hydroxyl radicals. [ABSTRACT FROM AUTHOR]

Abstract: Due to their large specific surface area, the potential of nanoparticles to be highly reactive and to induce oxidative stress is particularly high. In addition, some types of nanoparticles contain transition metals as trace impurities which are known to generate reactive oxygen species (ROS) in biological systems. This study investigates the potential of two types of single-walled carbon nanotube samples, nanoparticulate carbon black and crocidolite asbestos to induce ROS in lung epithelial cells in vitro. Carbon nanotube and carbon black samples were used as produced, without further purification or processing, in order to best mimic occupational exposure by inhalation of airborne dust particles derived from carbon nanomaterial production. Intracellular ROS were measured following short-term exposure of primary bronchial epithelial cells (NHBE) and A549 alveolar epithelial carcinoma cells using the redox sensitive probe carboxydichlorofluorescin (carboxy-DCFDA). The oxidative potential of agglomerated nanomaterial samples was compared following dispersion in cell culture medium with and without foetal calf serum (FCS) supplement. In addition, samples were dispersed in dipalmitoylphosphatidylcholine (DPPC), the major component of lung surfactant. It could be illustrated that in vitro exposure of lung epithelial cells to carbon nanomaterial samples results only in moderate or low oxidative stress under the exposure conditions employed. However, cell responses are strongly dependent on the vehicle used for dispersion. Whereas the presence of DPPC increased intracellular ROS formation, FCS seemed to protect the cells from oxidative insult. [Copyright &y& Elsevier]

Airborne nanoplastics can be inhaled to threaten human health, but research on the inhaled nanoplastic toxicity is in its infancy, and interaction mechanisms are largely unknown. By means of molecular dynamics simulation, we employed spherical nanoplastics of different materials and aging properties to predict and elucidate nanoplastic transformations in alveolar fluid and impacts on the lung surfactant (LS) film at the alveolar air-water interface. Results showed spontaneous adsorption of LS molecules on nanoplastics of 10 nm in diameter, and the adsorption layer can be defined as coronas, which increased the particle size, reduced and equalized the surface hydrophobicity, and endowed nanoplastics with negative surface charges. Nanoplastics of polypropylene and polyvinylchloride materials were dissolved by LS, which could increase bioavailability of polymers and toxic additives. Aging properties represented by the nanoplastic size, polymer's molecular weight and surface chemistry altered nanoplastic transformations through modulating competition between polymer-LS and polymer-polymer interactions. Upon transferred to the alveolar air-water interface through vesicle fusion, nanoplastics could interfere with the normal biophysical function of LS through disrupting the LS ultrastructure and fluidity, and prompting collapse of the LS film. These results provide new molecular level insights into fate and toxicity of airborne nanoplastics in human respiratory system. [Display omitted] • Nanoplastics of five materials and three aging properties are prepared. • LS molecules spontaneously adsorb on nanoplastics to form LS coronas. • Nanoplastics of polypropylene and polyvinylchloride materials are dissolved by LS. • Aging properties alter transformations via modulating competitive interactions. • Dissolved nanoplastics interfere with the normal biophysical function of LS. [ABSTRACT FROM AUTHOR]

Abstract: Single-walled carbon nanotubes have gained enormous popularity due to a variety of potential applications which will ultimately lead to increased human and environmental exposure to these nanoparticles. This study was carried out in order to evaluate the inflammatory response of immortalised and primary human lung epithelial cells (A549 and NHBE) to single-walled carbon nanotube samples (SWCNT). Special focus was placed on the mediating role of lung surfactant on particle toxicity. The toxicity of SWCNT dispersed in cell culture medium was compared to that of nanotubes dispersed in dipalmitoylphosphatidylcholine (DPPC, the main component of lung lining fluid). Exposure was carried out for 6 to 48 h with the latter time-point showing the most significant responses. Moreover, exposure was performed in the presence of the pro-inflammatory stimulus tumour necrosis factor-α (TNF-α) in order to mimic exposure of stimulated cells, as would occur during infection. Endpoints evaluated included cell viability, proliferation and the analysis of inflammatory mediators such as interleukin (IL)-8, IL-6, TNF-α and macrophage chemoattractant protein-1 (MCP-1). Crocidolite asbestos was included as a well characterised, toxic fibre control. The results of this study showed that HiPco SWCNT samples suppress inflammatory responses of A549 and NHBE cells. This was also true for TNF-α stimulated cells. The use of DPPC improved the degree of SWCNT dispersion in A549 medium and in turn, leads to increased particle toxicity, however, it was not shown to modify NHBE cell responses. [Copyright &y& Elsevier]

Abstract: In pulmonary tuberculosis, Mycobacterium tuberculosis lies in close physical proximity to alveolar surfactant. Cell walls of the mycobacteria contain loosely bound, detachable surface-active lipids. In this study, the effect of mycolic acid (MA), the most abundant mycobacterial cell wall lipid, on the surface activity of phospholipid mixtures from lung surfactant was investigated using Langmuir monolayers and atomic force microscopy (AFM). In the presence of mycolic acid, all the surfactant lipid mixtures attained high minimum surface tensions (between 20 and 40 mN/m) and decreased surface compressibility moduli <50 mN/m. AFM images showed that the smooth surface topography of surfactant lipid monolayers was altered with addition of MA. Aggregates with diverse heights of at least two layer thicknesses were found in the presence of mycolic acid. Mycolic acids could aggregate within surfactant lipid monolayers and result in disturbed monolayer surface activity. The extent of the effect of mycolic acid depended on the initial state of the monolayer, with fluid films of DPPC–POPC and DPPC–CHOL being least affected. The results imply inhibitory effects of mycolic acid toward lung surfactant lipids and could be a mechanism of lung surfactant dysfunction in pulmonary tuberculosis. [Copyright &y& Elsevier]

Abstract: The effect of the buffer composition and the preparation protocol on the dynamic surface tension (DST) and vesicle sizes of aqueous dipalmitoylphosphatidylcholine (DPPC) dispersions was studied. Four isotonic buffers were used in preparing DPPC dispersions at physiological conditions for possible biological applications: (1) a standard PBS solution; (2) the above PBS with 1mM CaCl2; (3) PBS with one tenth the previous standard phosphate salt concentrations and 2.5mM CaCl2; and (4) 150mM NaCl with 2.5mM CaCl2 and 10mM HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid). Two protocols, with a new method and an old method (Bangham method), were used in preparing the DPPC dispersions. The DPPC dispersions prepared with the new method contained mostly vesicles and were quite stable at 25 or 37°C. Dynamic light scattering (DLS) and spectroturbidimetry (ST) results showed that the DPPC vesicle sizes in buffer (4) were much smaller than those in the other buffers. When the DPPC dispersions were prepared with the new method, the diameter of the DPPC particles was smaller than those with the old method. The DPPC vesicles with the new method were more stable than those with the other method. The DPPC dispersions of 1000ppm at 37°C with the new method produced, at pulsating area conditions at 20 cycles per minute, low tension minima (γ min), lower than 10mN/m, in buffers (1), (2), and (4). With buffer (4) the DSTs were lower and were achieved faster than with the other buffers. A minimum concentration of 1000 or 250ppm DPPC was needed to produce DSTs lower than 10mN/m within 10min or less, with buffer (2) or (4), respectively. IRRAS results suggest that DPPC in buffer (2) or (4) forms a close-packed monolayer at the interface. These results have implications for designing efficient protocols of lipid dispersion preparation and lung surfactant replacement formulations in treating respiratory disease. [Copyright &y& Elsevier]

Abstract: Lung surfactant protein B (SP-B) is critical to minimizing surface tension in the alveoli. The C-terminus of SP-B, residues 59–80, has much of the surface activity of the full protein and serves as a template for the development of synthetic surfactant replacements. The molecular mechanisms responsible for its ability to restore lung compliance were investigated with circular dichroism, differential scanning calorimetry, and 31P and 2H solid-state NMR spectroscopy. SP-B59–80 forms an amphipathic helix which alters lipid organization and acyl chain dynamics in fluid lamellar phase 4:1 DPPC:POPG and 3:1 POPC:POPG MLVs. At higher levels of SP-B59–80 in the POPC:POPG lipid system a transition to a nonlamellar phase is observed while DPPC:POPG mixtures remain in a lamellar phase. Deuterium NMR shows an increase in acyl chain order in DPPC:POPG MLVs on addition of SP-B59–80; in POPC:POPG MLVs, acyl chain order parameters decrease. Our results indicate SP-B59–80 penetrates deeply into DPPC:POPG bilayers and binds more peripherally to POPC:POPG bilayers. Similar behavior has been observed for KL4, a peptide mimetic of SP-B which was originally designed using SP-B59–80 as a template and has been clinically demonstrated to be successful in treating respiratory distress syndrome. The ability of these helical peptides to differentially partition into lipid lamellae based on their degree of monounsaturation and subsequent changes in lipid dynamics suggest a mechanism for lipid organization and trafficking within the dynamic lung environment. [Copyright &y& Elsevier]

Abstract: It is known that Brazilian chrysotile is rapidly removed from the lungs, but quantitative studies about the influence of lung surfactants on chrysotile dissolution have not been investigated. In this work, the chemical behavior of chrysotile and its dissolution in the presence of dipalmitoylphosphatidylcholine (DPPC) were investigated in physiological conditions. The dissolution was investigated through quantification of magnesium and silicon released by chrysotile. At 37°C, the magnesium concentration is similar to control (without DPPC), which is about 2.0×10−4 molL−1, meaning that the dissolution process is not affected by the presence of this surfactant. The same was observed for silicon. The silicon concentration released by chrysotile is similar in all media tested. It is known that the dissolution mechanisms of brucite and tridymite layers are different. From our results, we propose that under physiological conditions, the mechanism of brucite dissolution is based on its interaction with hydrogen ions and that the mechanism of tridymite dissolution is based on a hydrolysis process. [Copyright &y& Elsevier]

Lipid monolayers at an air-water interface can be compressed laterally and reach high surface density. Beyond a certain threshold, they become unstable and collapse. Lipid monolayer collapse plays an important role in the regulation of surface tension at the air-liquid interface in the lungs. Although the structures of lipid aggregates formed upon collapse can be characterized experimentally, the mechanism leading to these structures is not fully understood. We investigate the molecular mechanism of monolayer collapse using molecular dynamics simulations. Upon lateral compression, the collapse begins with buckling of the monolayer, followed by folding of the buckle into a bilayer in the water phase. Folding leads to an increase in the monolayer surface tension, which reaches the equilibrium spreading value. Immediately after their formation, the bilayer folds have a flat semielliptical shape, in agreement with theoretical predictions. The folds undergo further transformation and form either flat circular bilayers or vesicles. The transformation pathway depends on macroscopic parameters of the system: the bending modulus, the line tension at the monolayer-bilayer connection, and the line tension at the bilayer perimeter. These parameters are determined by the system composition and temperature. Coexistence of the monolayer with lipid aggregates is favorable at lower tensions of the monolayer-bilayer connection. Transformation into a vesicle reduces the energy of the fold perimeter and is facilitated for softer bilayers, e.g., those with a higher content of unsaturated lipids, or at higher temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Thin liquid films composed of usual surface-active substances have well-developed theory and variety of applications for a long time. Recently the accumulated knowledge on thin liquid films composed of lipid–protein mixture, lung surfactant, or its constituents has been successfully applied to a number of problems in biology and medicine, e.g. as a new and adequate model system for studying the structure, stability, molecular interactions and lateral mobility in the surfactant layer on the alveolar surface. [Copyright &y& Elsevier]

When a two-dimensional (2D) film is compressed to its stability limit, it explores the third dimension via collapse. Understanding this 2D-to-3D transition is of great importance as it provides insight into the origin of defects in thin films. This review draws attention to a reversible folding collapse first discovered in model lung surfac- tant systems and explores the driving forces for this mechanism. The mode of collapse can be tuned by varying the mechanical properties of the film. I present a continuum elastic theory that captures the on- set of the observed folding instability and use digital image analysis to analyxe the folding dynamics. This article further explores factors that determine the maximum surface pressure a mixed monolayer can sustain and explains the observed phenomenon using the prin- ciple of rigidity percolation. The folding transition observed in lipid monolayers described here has also been observed in other systems, including monolayers of nanoparticles. [ABSTRACT FROM AUTHOR]