Investigating the Effect of Particle Size on Pulmonary Surfactant Phase Behavior

We study the impact of the addition of particles of a range of sizes on the phase transition behavior of lung surfactant under compression. Charged particles ranging from micro- to nanoscale are deposited on lung surfactant films in a Langmuir trough. Surface area versus surface pressure isotherms and fluorescent microscope observations are utilized to determine changes in the phase transition behavior. We find that the deposition of particles close to 20 nm in diameter significantly impacts the coexistence of the liquid-condensed phase and liquid-expanded phase. This includes morphological changes of the liquid-condensed domains and the elimination of the squeeze-out phase in isotherms. Finally, a drastic increase of the domain fraction of the liquid-condensed phase can be observed for the deposition of 20-nm particles. As the particle size is increased, we observe a return to normal phase behavior. The net result is the observation of a critical particle size that may impact the functionality of the lung surfactant during respiration.     

Investigating the Effect of Particle Size on Pulmonary Surfactant Phase Behavior

We study the impact of the addition of particles of a range of sizes on the phase transition behavior of lung surfactant under compression. Charged particles ranging from micro- to nanoscale are deposited on lung surfactant films in a Langmuir trough. Surface area versus surface pressure isotherms and fluorescent microscope observations are utilized to determine changes in the phase transition behavior. We find that the deposition of particles close to 20 nm in diameter significantly impacts the coexistence of the liquid-condensed phase and liquid-expanded phase. This includes morphological changes of the liquid-condensed domains and the elimination of the squeeze-out phase in isotherms. Finally, a drastic increase of the domain fraction of the liquid-condensed phase can be observed for the deposition of 20-nm particles. As the particle size is increased, we observe a return to normal phase behavior. The net result is the observation of a critical particle size that may impact the functionality of the lung surfactant during respiration.     

Effect of Parenchymal Stiffness on Canine Airway Size with Lung Inflation

Although airway patency is partially maintained by parenchymal tethering, this structural support is often ignored in many discussions of asthma. However, agonists that induce smooth muscle contraction also stiffen the parenchyma, so such parenchymal stiffening may serve as a defense mechanism to prevent airway narrowing or closure. To quantify this effect, specifically how changes in parenchymal stiffness alter airway size at different levels of lung inflation, in the present study, we devised a method to separate the effect of parenchymal stiffening from that of direct airway narrowing. Six anesthetized dogs were studied under four conditions: baseline, after whole lung aerosol histamine challenge, after local airway histamine challenge, and after complete relaxation of the airways. In each of these conditions, we used High resolution Computed Tomography to measure airway size and lung volume at five different airway pressures (0, 12, 25, 32, and 45 cm H₂O). Parenchymal stiffening had a protective effect on airway narrowing, a fact that may be important in the airway response to deep inspiration in asthma. When the parenchyma was stiffened by whole lung aerosol histamine challenge, at every lung volume above FRC, the airways were larger than when they were directly challenged with histamine to the same initial constriction. These results show for the first time that a stiff parenchyma per se minimizes the airway narrowing that occurs with histamine challenge at any lung volume. Thus in clinical asthma, it is not simply increased airway smooth muscle contraction, but perhaps a lack of homogeneous parenchymal stiffening that contributes to the symptomatic airway hyperresponsiveness.     

in Vitro Effect of Lung Surfactant on Alveolar Macrophage Defence Mechanisms Against Cryptococcus Neoformans

The effects of a modified natural porcine surfactant (Curosurf) on phagocytosis and killing of Cryptococcus neoformans by alveolar macrophages and on the production of superoxide anions were investigated in vitro. Attachment and ingestion were evaluated separately by a fluorescent quenching technique. The nitroblue tetrazolium reduction test was used as an indirect measurement of superoxide anion production. Killing was assessed by a colony-forming assay. Surfactant induced increased ingestion of C. neoformans, unopsonized as well as opsonized with fresh serum or anticryptococcal polyclonal IgG. Surfactant had, however, no effect on the attachment or killing of unopsonized or opsonized C. neoformans by the alveolar macrophages. In addition, the enhancement of the oxidative metabolism of the macrophages after stimulation with opsonized yeast was impaired, although the killing was not affected. This study indicates that in vitro Curosurf can influence the alveolar macrophage defence against C. neoformans by enhancing its ingestion and by interacting with the superoxide anions release from alveolar macrophages stimulated with fresh serum or anticryptococcal polyclonal IgG opsonized yeast cells. This revised version was published online in August 2006 with corrections to the Cover Date.     

An Anionic Phospholipid Enables the Hydrophobic Surfactant Proteins to Alter Spontaneous Curvature

The hydrophobic surfactant proteins, SP-B and SP-C, greatly accelerate the adsorption of the surfactant lipids to an air/water interface. Previous studies of factors that affect curvature suggest that vesicles may adsorb via a rate-limiting structure with prominent negative curvature, in which the hydrophilic face of the lipid leaflets is concave. To determine if SP-B and SP-C might promote adsorption by inducing negative curvature, we used small-angle x-ray scattering to test whether the physiological mixture of the two proteins affects the radius of cylindrical monolayers in the inverse hexagonal phase. With dioleoyl phosphatidylethanolamine alone, the proteins had no effect on the hexagonal lattice constant, suggesting that the proteins fail to insert into the cylindrical monolayers. The surfactant lipids also contain ∼10% anionic phospholipids, which might allow incorporation of the cationic proteins. With 10% of the anionic dioleoyl phosphatidylglycerol added to dioleoyl phosphatidylethanolamine, the proteins induced a dose-related decrease in the hexagonal lattice constant. At 30°C, the reduction reached a maximum of 8% relative to the lipids alone at ∼1% (w/w) protein. Variation of NaCl concentration tested whether the effect of the protein represented a strictly electrostatic effect that screening by electrolyte would eliminate. With concentrations up to 3 M NaCl, the dose-related change in the hexagonal lattice constant decreased but persisted. Measurements at different hydrations determined the location of the pivotal plane and proved that the change in the lattice constant produced by the proteins resulted from a shift in spontaneous curvature. These results provide the most direct evidence yet that the surfactant proteins can induce negative curvature in lipid leaflets. This finding supports the model in which the proteins promote adsorption by facilitating the formation of a negatively curved, rate-limiting structure.     

Understanding Human Lung Development through In Vitro Model Systems

An abundance of information about lung development in animal models exists; however, comparatively little is known about lung development in humans. Recent advances using primary human lung tissue combined with the use of human in vitro model systems, such as human pluripotent stem cell-derived tissue, have led to a growing understanding of the mechanisms governing human lung development. They have illuminated key differences between animal models and humans, underscoring the need for continued advancements in modeling human lung development and utilizing human tissue. This review discusses the use of human tissue and the use of human in vitro model systems that have been leveraged to better understand key regulators of human lung development and that have identified uniquely human features of development. This review also examines the implementation and challenges of human model systems and discusses how they can be applied to address knowledge gaps.     

Pulmonary Surfactant Model Systems Catch the Specific Interaction of an Amphiphilic Peptide with Anionic Phospholipid

Interfacial behavior was studied in pulmonary surfactant model systems containing an amphiphilic α-helical peptide (Hel 13-5), which consists of 13 hydrophobic and five hydrophilic amino acid residues. Fully saturated phospholipids of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) were utilized to understand specific interactions between anionic DPPG and cationic Hel 13-5 for pulmonary functions. Surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms of DPPG/Hel 13-5 and DPPC/DPPG (4:1, mol/mol)/Hel 13-5 preparations were measured to obtain basic information on the phase behavior under compression and expansion processes. The interaction leads to a variation in squeeze-out surface pressures against a mole fraction of Hel 13-5, where Hel 13-5 is eliminated from the surface on compression. The phase behavior was visualized by means of Brewster angle microscopy, fluorescence microscopy, and atomic force microscopy. At low surface pressures, the formation of differently ordered domains in size and shape is induced by electrostatic interactions. The domains independently grow upon compression to high surface pressures, especially in the DPPG/Hel 13-5 system. Under the further compression process, protrusion masses are formed in AFM images in the vicinity of squeeze-out pressures. The protrusion masses, which are attributed to the squeezed-out Hel 13-5, grow larger in lateral size with increasing DPPG content in phospholipid compositions. During subsequent expansion up to 35 mN m⁻¹, the protrusions retain their height and lateral diameter for the DPPG/Hel 13-5 system, whereas the protrusions become smaller for the DPPC/Hel 13-5 and DPPC/DPPG/Hel 13-5 systems due to a reentrance of the ejected Hel 13-5 into the surface. In this work we detected for the first time, to our knowledge, a remarkably large hysteresis loop for cyclic ΔV-A isotherms of the binary DPPG/Hel 13-5 preparation. This exciting phenomenon suggests that the specific interaction triggers two completely independent processes for Hel 13-5 during repeated compression and expansion: 1), squeezing-out into the subsolution; and 2), and close packing as a monolayer with DPPG at the interface. These characteristic processes are also strongly supported by atomic force microscopy observations. The data presented here provide complementary information on the mechanism and importance of the specific interaction between the phosphatidylglycerol headgroup and the polarized moiety of native surfactant protein B for biophysical functions of pulmonary surfactants.     

Effect of Sugars, Surfactant, and Tangential Flow Filtration on the Freeze-Drying of Poly(lactic acid) Nanoparticles

Poly(d,l-lactic acid) nanoparticles were freeze-dried in this study. With respect to drying, effect of protective excipients and purification from excess surfactant were evaluated. The nanoparticles were prepared by the nanoprecipitation method with or without a surfactant, poloxamer 188. The particles with the surfactant were used as such or purified by tangential flow filtration. The protective excipients tested were trehalose, sucrose, lactose, glucose, poloxamer 188, and some of their combinations. The best freeze-drying results in terms of nanoparticle survival were achieved with trehalose or sucrose at concentrations 5% and 2% and, on the other hand, with a combination of lactose and glucose. Purification of the nanoparticle dispersion from the excess surfactant prior to the freeze-drying by tangential flow filtration ensured better drying outcome and enabled reduction of the amount of the protective excipients used in the process. The excess surfactant, if not removed, was assumed to interact with the protective excipients decreasing their protective mechanism towards the nanoparticles.     

Relative Cosolute Size Influences the Kinetics of Protein-Protein Interactions

Protein signaling occurs in crowded intracellular environments, and while high concentrations of macromolecules are postulated to modulate protein-protein interactions, analysis of their impact at each step of the reaction pathway has not been systematically addressed. Potential cosolute-induced alterations in target association are particularly important for a signaling molecule like calmodulin (CaM), where competition among >300 targets governs which pathways are selectively activated. To explore how high concentrations of cosolutes influence CaM-target affinity and kinetics, we methodically investigated each step of the CaM-target binding mechanism under crowded or osmolyte-rich environments mimicked by ficoll-70, dextran-10, and sucrose. All cosolutes stabilized compact conformers of CaM and modulated association kinetics by affecting diffusion and rates of conformational change; however, the results showed that differently sized molecules had variable effects to enhance or impede unique steps of the association pathway. On- and off-rates were modulated by all cosolutes in a compensatory fashion, producing little change in steady-state affinity. From this work insights were gained on how high concentrations of inert crowding agents and osmolytes fit into a kinetic framework to describe protein-protein interactions relevant for cellular signaling.     

样本量对云南松幼苗生物量模型构建及预估精度的影响

为探究不同样本量对生物量模型构建及建模精度的影响,以实际调查的20个家系,共615株云南松幼苗为例,通过编写计算机程序建立进行简单随机抽样,构建不同样本量云南松幼苗各器官及单株生物量异速生长方程。利用决定系数（R²）、估计值标准误（SEE）、均方根误差（RMSE）、总相对误差（RS）及平均误差绝对值（MAB）,对模型拟合优度与精度进行比较分析。结果表明：幂函数方程可较好地用于估测云南松幼苗生物量;随着样本量的增加模型精度评估指数MAB呈幂函数形式逐渐减小;当样本数量小于200时MAB较为敏感,模型精度较差,样本量大于200时,其精度随样本量逐渐增加,但变化幅度逐步减小并趋于稳定。因此,根据MAB的变化趋势,样本量达到200时可以构建精度较高且稳定模型。     

KL4 Peptide Induces Reversible Collapse Structures on Multiple Length Scales in Model Lung Surfactant

We investigated the effects of KL₄, a 21-residue amphipathic peptide approximating the overall ratio of positively charged to hydrophobic amino acids in surfactant protein B (SP-B), on the structure and collapse of dipalmitoylphosphatidylcholine and palmitoyl-oleoyl-phosphatidylglycerol monolayers. As reported in prior work on model lung surfactant phospholipid films containing SP-B and SP-B peptides, our experiments show that KL₄ improves surfactant film reversibility during repetitive interfacial cycling in association with the formation of reversible collapse structures on multiple length scales. Emphasis is on exploring a general mechanistic connection between peptide-induced nano- and microscale reversible collapse structures (silos and folds).     

Theory of Optical Coupling Effects Among Surfactant Au Nanoparticles Films

In previous reports, Dalfovo et al. showed experimentally that thin films of Au nanoparticles (NP) with organic coating change their optical properties when exposed to several analytes in the vapor phase (Anal Chem 84:4886–4892 2012; J Phys Chem C 119:5098–5106 2015). This optical behavior was associated with changes in the mean distance between nanoparticles, which resulted in a displacement of their plasmon bands towards blue or red in the presence of toluene (Tol) or ethanol (EtOH) vapors, respectively. In the report by Dalfovo et al. (J Phys Chem C 119:5098–5106 2015), in-situ grazing-incidence small-angle X-ray spectroscopy (GISAXS) was performed to determine changes in the inter-NP distance within the film. In the present work, we perform theoretical calculations to interpret the results obtained by Dalfovo et al. (Anal Chem 84:4886–4892 2012; J Phys Chem C 119:5098–5106 2015). For this purpose, we employ two different theoretical approaches, a quasi-static method (QS) and the Korringa-Kohn-Rostoker method (KKR), in order to describe the plasmon resonance shift as a function of the inter-NP distance changes during exposure to Tol and EtOH vapors. Both theoretical approaches describe qualitatively the behavior observed in previous experimental results that correlate the plasmon resonant wavelength with the inter-NP distance obtained by GISAXS. Our theoretical results show that the plasmon resonant wavelength strongly depends on the ratio between the inter-particle distance and the diameter of the nanoparticles and consequently, these films could be used for optical tuning.

     

Effect of Ageing on the Oxidative Browning of Sugar-Amino Acid Model Systems

Sugar-amino acid model systems were aged for 3 months under anaerobic or aerobic conditions. Subsequently, these aged model systems were stored for 2 weeks at 37°C under aerobic conditions to examine “oxidative browning.” The results obtained were as follows:

1. The oxidative browning of the model systems increased with increase of the ageing period. Fe²⁺ increased the effects of the ageing.

2. The model systems aged under anaerobic conditions darkened more than those aged under aerobic conditions during storage for 2 weeks.

3. An Amadori rearrangement product, 1-deoxy-1-glycino-d-fructcse was isolated from the aged glucose-glycine model system and it caused a marked increase in the rate of the oxidative browning. Therefore, Amadori rearrangement products are considered to be important precursors in the oxidative browning reaction.

     

Isolation and Characterization of Proteins Associated with the Lung Surfactant System

Rabbit lung washings and purified lung surfactant were delipidated without precipitation or loss of protein. This enabled effective study of the proteins by electrophoretic and immunoelectrophoretlc techniques. The lung washings contained secretory immunoglobulin A and several serum proteins. The protein composition of purified lung surfactant was the same as the unfractionated lung washings confirming our previous study which indicated that there is no specific protein associated with surfactant phospholipids obtained by alveolar lavage with isotonic saline.     

Predicting the Size of Silver Nanoparticles from Their Optical Properties

Plasmonics - In this study, localized surface plasmon resonance (LSPR) of the spherical silver nanoparticles (AgNPs) was evaluated based on experimental and theoretical viewpoints. In the...     

Size and Temperature Effects on the Surface Plasmon Resonance in Silver Nanoparticles

The surface plasmon energy in spherical silver nanoparticles embedded in silica host matrix depends on the size and temperature of the nanoparticles. The dependences of the surface plasmon energy were studied for silver nanoparticles in the size range 11?C30?nm and in the temperature interval 293?C650?K. As the size of the nanoparticles decreases or the temperature increases, the surface plasmon resonance shifts to red. When the size of the nanoparticles decreases, the scattering rate of the conduction electrons increases, which results in the nonlinear red shift of the surface plasmon resonance. The red shift with temperature is linear for larger nanoparticles and becomes nonlinear for smaller ones. As the temperature of the nanoparticles increases, the volume thermal expansion of the nanoparticles leads to the red shift of the surface plasmon resonance. The thermal volume expansion coefficient depends on the size and temperature. It increases with a decrease of the nanoparticle size and an increase of the temperature.     

Isolation of Secretory IgA from a Lung Surfactant Fraction

Although dipalmitoyl lecithin, is the essential component of the pulmonary surfactant system that is invoked for alveolar stability, there is no explanation as yet for the origin and role of certain proteins that are found with the phospholipid in pulmonary washings. Aqueous lavages obtained from rabbit lung contain three major proteins, two of which are serum proteins (albumin 60%, γ-globulin 10%), and the third, protein “T” (20%), is described here as pulmonary secretory immunoglobulin A (sIgA). The protein is first recovered quantitatively in the surface activelipid -protein fraction from filtration of pulmonary lavage on Sephadex G-200. The protein is then isolated from the lipid either by filtration on SDS-Sephadex G-200 or by ethanol-ether precipitation. After reductive cleavage with either mercaptoethanol or dithiothreitol and alkylation with iodoacetamide, three protein peaks are obtained from SDS-sephadex G-200 separation. The products of reductive cleavage are analogous to the secretory component (MW～60,000), H-chain (MW～50,000), L-chain (MW～25,000), and J-piece (MW～28,000) of secretory IgA frm colostrum. In inmunodiffusion the lung protein and colostrum sIgA show striking identity lines, as do antibodies to rabbit colostrum and to the lung protein. Amino acid and carbohydrate analyses reveal some differences between the two secretory immunoglobulins. Although this protein has been found together with the phospholipid surfactant of the lung in vitro, the present structural study concludes that the protein is SIgA. Although concurrent immunof luorescence studies showed that this protein is in the alveolar lining layer, we cannot as yet conclude that it belongs to the surfactant system of the lung.