The lipids of pulmonary surfactant: dynamics and interactions with proteins

Cathepsin H: molecular characteristics and clues to function and mechanism

Cathepsin H (CatH) is a lysosomal cysteine protease with a unique aminopeptidase activity that is extensively expressed in the lung, pancreas, thymus, kidney, liver, skin, and brain. Owing to its specific enzymatic activity, CatH has critical effects on the regulation of biological behaviours of cancer cells and pathological processes in brain diseases. Moreover, a neutral pH level is optimal for CatH activity, so it is expected to be active in the extra-lysosomal and extracellular space. In the present review, we describe the expression, maturation, and enzymatic properties of CatH, and summarize the available experimental evidence that mechanistically links CatH to various physiological and pathological processes. Finally, we discuss the challenges and potentials of CatH inhibitors in CatH-induced disease therapy.

Plasmalogen-Based Liquid Crystalline Multiphase Structures Involving Docosapentaenoyl Derivatives Inspired by Biological Cubic Membranes

Structural properties of plasmenyl-glycerophospholipids (plasmalogens) have been scarcely studied for plasmalogens with long polyunsaturated fatty acid (PUFA) chains, despite of their significance for the organization and functions of the cellular membranes. Elaboration of supramolecular assemblies involving PUFA-chain plasmalogens in nanostructured mixtures with lyotropic lipids may accelerate the development of nanomedicines for certain severe pathologies (e.g., peroxisomal disorders, cardiometabolic impairments, and neurodegenerative Alzheimer's and Parkinson's diseases). Here, we investigate the spontaneous self-assembly of bioinspired, custom-produced docosapentaenoyl (DPA) plasmenyl (ether) and ester phospholipids in aqueous environment (pH 7) by synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). A coexistence of a liquid crystalline primitive cubic Im3m phase and an inverted hexagonal (H_II) phase is observed for the DPA-ethanolamine plasmalogen (C16:1p-22:5n6 PE) derivative. A double-diamond cubic Pn3m phase is formed in mixed assemblies of the phosphoethanolamine plasmalogen (C16:1p-22:5n6 PE) and monoolein (MO), whereas a coexistence of cubic and lamellar liquid crystalline phases is established for the DPA-plasmenyl phosphocholine (C16:1p-22:5n6 PC)/MO mixture at ambient temperature. The DPA-diacyl phosphoinositol (22:5n6-22:5n6 PI) ester lipid displays a propensity for a lamellar phase formation. Double membrane vesicles and multilamellar onion topologies with inhomogeneous distribution of interfacial curvature are formed upon incorporation of the phosphoethanolamine plasmalogen (C16:1p-22:5n6 PE) into dioleoylphosphocholine (DOPC) bilayers. Nanoparticulate formulations of plasmalogen-loaded cubosomes, hexosomes, and various multiphase cubosome- and hexosome-derived architectures and mixed type nano-objects (e.g., oil droplet-embedding vesicles or core-shell particles with soft corona) are produced with PUFA-chain phospholipids and lipophilic antioxidant-containing membrane compositions that are characterized by synchrotron SAXS and cryo-TEM imaging. The obtained multiphase nanostructures reflect the changes in the membrane curvature induced by the inclusion of DPA-based PE and PC plasmalogens, as well as DPA-PI ester derivative, and open new opportunities for exploration of these bioinspired nanoassemblies.

Differential Sex-Dependent Regulation of the Alveolar Macrophage miRNome of SP-A2 and co-ex (SP-A1/SP-A2) and Sex Differences Attenuation after 18 h of Ozone Exposure

Background: Human SP-A1 and SP-A2, encoded by SFTPA1 and SFTPA2, and their genetic variants differentially impact alveolar macrophage (AM) functions and regulation, including the miRNome. We investigated whether miRNome differences previously observed between AM from SP-A2 and SP-A1/SP-A2 mice are due to continued qualitative differences or a delayed response of mice carrying a single gene. Methods: Human transgenic (hTG) mice, carrying SP-A2 or both SP-A genes, and SP-A-KO mice were exposed to filtered air (FA) or ozone (O₃)_. AM miRNA levels, target gene expression, and pathways determined 18 h after O₃ exposure. RESULTS: We found (a) differences in miRNome due to sex, SP-A genotype, and exposure; (b) miRNome of both sexes was largely downregulated by O₃, and co-ex had fewer changed (≥2-fold) miRNAs than either group; (c) the number and direction of the expression of genes with significant changes in males and females in co-ex are almost the opposite of those in SP-A2; (d) the same pathways were found in the studied groups; and (e) O₃ exposure attenuated sex differences with a higher number of genotype-dependent and genotype-independent miRNAs common in both sexes after O₃ exposure. Conclusion: Qualitative differences between SP-A2 and co-ex persist 18 h post-O₃, and O₃ attenuates sex differences.

Lipid-Protein and Protein-Protein Interactions in the Pulmonary Surfactant System and Their Role in Lung Homeostasis

Pulmonary surfactant is a lipid/protein complex synthesized by the alveolar epithelium and secreted into the airspaces, where it coats and protects the large respiratory air–liquid interface. Surfactant, assembled as a complex network of membranous structures, integrates elements in charge of reducing surface tension to a minimum along the breathing cycle, thus maintaining a large surface open to gas exchange and also protecting the lung and the body from the entrance of a myriad of potentially pathogenic entities. Different molecules in the surfactant establish a multivalent crosstalk with the epithelium, the immune system and the lung microbiota, constituting a crucial platform to sustain homeostasis, under health and disease. This review summarizes some of the most important molecules and interactions within lung surfactant and how multiple lipid–protein and protein–protein interactions contribute to the proper maintenance of an operative respiratory surface.

Alveolar Dynamics and Beyond - The Importance of Surfactant Protein C and Cholesterol in Lung Homeostasis and Fibrosis

Surfactant protein C (SP-C) is an important player in enhancing the interfacial adsorption of lung surfactant lipid films to the alveolar air-liquid interface. Doing so, surface tension drops down enough to stabilize alveoli and the lung, reducing the work of breathing. In addition, it has been shown that SP-C counteracts the deleterious effect of high amounts of cholesterol in the surfactant lipid films. On its side, cholesterol is a well-known modulator of the biophysical properties of biological membranes and it has been proven that it activates the inflammasome pathways in the lung. Even though the molecular mechanism is not known, there are evidences suggesting that these two molecules may interplay with each other in order to keep the proper function of the lung. This review focuses in the role of SP-C and cholesterol in the development of lung fibrosis and the potential pathways in which impairment of both molecules leads to aberrant lung repair, and therefore impaired alveolar dynamics. From molecular to cellular mechanisms to evidences in animal models and human diseases. The evidences revised here highlight a potential SP-C/cholesterol axis as target for the treatment of lung fibrosis.

Protocols for Enzymatic Fluorometric Assays to Quantify Phospholipid Classes

Phospholipids, consisting of a hydrophilic head group and two hydrophobic acyl chains, are essential for the structures of cell membranes, plasma lipoproteins, biliary mixed micelles, pulmonary surfactants, and extracellular vesicles. Beyond their structural roles, phospholipids have important roles in numerous biological processes. Thus, abnormalities in the metabolism and transport of phospholipids are involved in many diseases, including dyslipidemia, atherosclerosis, cholestasis, drug-induced liver injury, neurological diseases, autoimmune diseases, respiratory diseases, myopathies, and cancers. To further clarify the physiological, pathological, and molecular mechanisms and to identify disease biomarkers, we have recently developed enzymatic fluorometric assays for quantifying all major phospholipid classes, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, phosphatidylinositol, phosphatidylglycerol + cardiolipin, and sphingomyelin. These assays are specific, sensitive, simple, and high-throughput, and will be applicable to cells, intracellular organelles, tissues, fluids, lipoproteins, and extracellular vesicles. In this review, we present the detailed protocols for the enzymatic fluorometric measurements of phospholipid classes in cultured cells.

Differential Impact of Co-expressed SP-A1/SP-A2 Protein on AM miRNome; Sex Differences

In humans there are two surfactant protein A (SP-A) functional genes SFTPA1 and SFTPA2 encoding innate immune molecules, SP-A1 and SP-A2, respectively, with numerous genetic variants each. SP-A interacts and regulates many of the functions of alveolar macrophages (AM). It is shown that SP-A variants differ in their ability to regulate the AM miRNome in response to oxidative stress (OxS). Because humans have both SP-A gene products, we were interested to determine the combined effect of co-expressed SP-A1/SP-A2 (co-ex) in response to ozone (O₃) induced OxS on AM miRNome. Human transgenic (hTG) mice, carrying both SP-A1/SP-A2 (6A²/1A⁰, co-ex) and SP-A- KO were utilized. The hTG and KO mice were exposed to filtered air (FA) or O₃ and miRNA levels were measured after AM isolation with or without normalization to KO. We found: (i) The AM miRNome of co-ex males and females in response to OxS to be largely downregulated after normalization to KO, but after Bonferroni multiple comparison analysis only in females the AM miRNome remained significantly different compared to control (FA); (ii) The targets of the significantly changed miRNAs were downregulated in females and upregulated in males; (iii) Several of the validated mRNA targets were involved in pro-inflammatory response, anti-apoptosis, cell cycle, cellular growth and proliferation; (iv) The AM of SP-A2 male, shown, previously to have major effect on the male AM miRNome in response to OxS, shared similarities with the co-ex, namely in pathways involved in the pro-inflammatory response and anti-apoptosis but also exhibited differences with the cell-cycle, growth, and proliferation pathway being involved in co-ex and ROS homeostasis in SP-A2 male. We speculate that the presence of both gene products vs. single gene products differentially impact the AM responses in males and females in response to OxS.

Phospholipid regulation of innate immunity and respiratory viral infection

Toll-like receptors (TLRs) coupled to intracellular signaling cascades function as central elements of innate immunity that control transcription of numerous pro-inflammatory genes. Two minor anionic phospholipids present in the pulmonary surfactant complex, palmitoyl-oleoyl-phosphatidylglycerol (POPG) and phosphatidylinositol (PI), antagonize the cognate ligand activation of TLRs 2 and 4. The lipids block recognition of activating ligands by the TLRs, either directly or via the TLR4 coreceptors CD14 and MD2. Antagonism of TLR activation results in inhibition of the initiating step of the pro-inflammatory signaling pathways. Evidence for this mechanism of action comes from direct binding studies between CD14 and MD2 with POPG and PI. Additional evidence for this mechanism of antagonism also comes from monitoring the reduction of protein phosphorylation events that characterize the intracellular signaling by activated TLRs. The pathogenesis of respiratory syncytial virus (RSV) and influenza A virus (IAV) have been linked to TLR4 activation, and we examined the action of POPG and PI as potential antagonists of the pathology of these viruses. Surprisingly, POPG and PI dramatically curtail infection, in addition to inhibiting inflammatory sequelae associated with RSV and IAV infections. The mechanism of action by the lipids is disruption of virus particle binding to host cell plasma membrane receptors, required for viral uptake. The antagonism of activation of TLRs and virus binding to the alveolar epithelium by resident constituents of the pulmonary surfactant system suggests that POPG and PI function in homeostasis, to prevent inflammatory processes that result in reductions in gas exchange within the alveolar compartment.

The biology of the ABCA3 lipid transporter in lung health and disease

The lipid transporter, ATP-binding cassette class A3 (ABCA3), is a highly conserved multi-membrane-spanning protein that plays a critical role in the regulation of pulmonary surfactant homeostasis. Mutations in ABCA3 have been increasingly recognized as one of the causes of inherited pulmonary diseases. These monogenic disorders produce familial lung abnormalities with pathological presentations ranging from neonatal surfactant-deficiency-induced respiratory failure to childhood or adult diffuse parenchymal lung diseases for which specific treatment modalities remain limited. More than 200 ABCA3 mutations have been reported to date with approximately three quarters of patients presenting as compound heterozygotes. Recent advances in our understanding of the molecular basis underlying normal ABCA3 biosynthesis and processing and of the mechanisms of alveolar epithelial cell dysregulation caused by the expression of its mutant forms are beginning to emerge. These insights and the role of environmental factors and modifier genes are discussed in the context of the considerable variability in disease presentation observed in patients with identical ABCA3 gene mutations. Moreover, the opportunities afforded by an enhanced understanding of ABCA3 biology for targeted therapeutic strategies are addressed.

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

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

Interfacial behavior of pulmonary surfactant preparations containing egg yolk lecithin

Mammalian lungs are covered with lipid-protein complexes or pulmonary surfactants. In this work, which aimed towards the less expensive production of artificial pulmonary surfactants, we produced surfactants composed of egg yolk lecithin (eggPC), palmitic acid, and hexadecanol (= 0.30/0.35/0.35, mol/mol/mol ) containing different amounts of Hel 13-5 (NH2-KLLKLLLKLWLKLLKLLL-COOH) as a substitute for the proteins in native pulmonary surfactants. Surface pressure (π)-molecular area (A) and surface potential (DV)-A isotherms of the mixtures were measured via the Wilhelmy and ionizing (241)Am electrode methods, respectively. The interactions between the lipid components and Hel 13-5 led to variations in the surface pressure caused by the expulsion of fluid components from the surface. Furthermore, the π-A and DV-A isotherms featured large hysteresis loops for the surfactant that contained a small amount of Hel 13-5 during compression and successive expansion cycling. To elucidate the morphology, the phase behavior was visualized in situ at the air-water interface by means of fluorescence microscopy; the images suggested less effective interactions between Hel 13-5 and the unsaturated PC in eggPC despite the similarity of their monolayer properties.

In vitro exposure of proteins to ozone

An in vitro system has been developed to expose proteins to ozone. The system is designed to deliver consistent and accurate levels of ozone over a range of concentrations (between 0.1 and >/=10 ppm) with extended exposure times (24 h or longer) in a humidified environment (100%). In the experiment presented in this article, ozone concentrations between 0.1 and 2.0 ppm were used. Ozone was generated by an electrical discharge ozonizer to ensure stability; it was continually monitored by an ultraviolet ozone analyzer and was precisely controlled by mass flow controllers, which gave reproducible results between runs. Humidity was closely regulated in the system to allow small amounts of protein solutions (50 muL or less) to be exposed without significant changes (<0.2%) in sample volume. The degree of surfactant protein-A (SP-A) oxidation by ozone was measured between runs to demonstrate the reproducibility of the system. A detailed description of the system is given, and protein oxidation detection methods and their limitations are discussed. Using these methods, we were able to assess oxidation of SP-A that apparently occurred prior to its isolation from the lung by bronchoalveolar lavage. This in vitro system allowed us to expose small amounts of protein to ozone in a simple, highly controlled, and reproducible manner.

Surfactant phospholipid metabolism

Pulmonary surfactant is essential for life and is composed of a complex lipoprotein-like mixture that lines the inner surface of the lung to prevent alveolar collapse at the end of expiration. The molecular composition of surfactant depends on highly integrated and regulated processes involving its biosynthesis, remodeling, degradation, and intracellular trafficking. Despite its multicomponent composition, the study of surfactant phospholipid metabolism has focused on two predominant components, disaturated phosphatidylcholine that confers surface-tension lowering activities, and phosphatidylglycerol, recently implicated in innate immune defense. Future studies providing a better understanding of the molecular control and physiological relevance of minor surfactant lipid components are needed. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

A correlative approach at characterizing nanoparticle mobility and interactions after cellular uptake

The interactions of nanoparticles with human cells are of large interest in the context of nanomaterial safety. Here, we use live cell imaging and image-based fluorescence correlation methods to determine colocalization of 88 nm and 32 nm silica nanoparticles with endocytotic vesicles derived from the cytoplasmic membrane and lysosomes, as well as to quantify intracellular mobility of internalized particles, in contrast to particle number quantification by counting techniques. In our study, A549 cells are used as a model for human type II alveolar epithelial cells. We present data supporting endocytotic uptake of the particles and subsequent active transport to the perinuclear region. The presence of particles in lamellar bodies is proposed as a potential exocytosis route.

Influence of hydrophobic alkylated gold nanoparticles on the phase behavior of monolayers of DPPC and clinical lung surfactant

The effect of hydrophobic alkylated gold nanoparticles (Au NPs) on the phase behavior and structure of Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) and Survanta, a naturally derived commercial pulmonary surfactant that contains DPPC as the main lipid component and hydrophobic surfactant proteins SP-B and SP-C, has been investigated in connection with the potential implication of inorganic NPs in pulmonary surfactant dysfunction. Hexadecanethiolate-capped Au NPs (C(16)SAu NPs) with an average core diameter of 2 nm have been incorporated into DPPC monolayers in concentrations ranging from 0.1 to 0.5 mol %. Concentrations of up to 0.2 mol % in DPPC and 16 wt % in Survanta do not affect the monolayer phase behavior at 20 °C, as evidenced by surface pressure-area (π-A) and ellipsometric isotherms. The monolayer structure at the air/water interface was imaged as a function of the surface pressure by Brewster angle microscopy (BAM). In the liquid-expanded/liquid-condensed phase coexistence region of DPPC, the presence of 0.2 mol % C(16)SAu NPs causes the formation of many small, circular, condensed lipid domains, in contrast to the characteristic larger multilobes formed by pure lipid. Condensed domains of similar size and shape to those of DPPC with 0.2 mol % C(16)SAu NPs are formed by compressing Survanta, and these are not affected by the C(16)SAu NPs. Atomic force microscopy images of Langmuir-Schaefer-deposited films support the BAM observations and reveal, moreover, that at high surface pressures (i.e., 35 and 45 mN m(-1)) the C(16)SAu NPs form honeycomb-like aggregates around the polygonal condensed DPPC domains. In the Survanta monolayers, the C(16)SAu NPs were found to accumulate together with the proteins in the liquid-expanded phase around the circular condensed lipid domains. In conclusion, the presence of hydrophobic C(16)SAu NPs in amounts that do not influence the π-A isotherm alters the nucleation, growth, and morphology of the condensed domains in monolayers of DPPC but not of those of Survanta. Systematic investigations of the effect of the interaction of chemically defined NPs with the lipid and protein components of lung surfactant on the physicochemical properties of surfactant films are pertinent to understanding how inhaled NPs impact pulmonary function.

Compatible solutes: ectoine and hydroxyectoine improve functional nanostructures in artificial lung surfactants

Ectoine and hydroxyectoine belong to the family of compatible solutes and are among the most abundant osmolytes in nature. These compatible solutes protect biomolecules from extreme conditions and maintain their native function. In the present study, we have investigated the effect of ectoine and hydroxyectoine on the domain structures of artificial lung surfactant films consisting of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG) and the lung surfactant specific surfactant protein C (SP-C) in a molar ratio of 80:20:0.4. The pressure-area isotherms are found to be almost unchanged by both compatible solutes. The topology of the fluid domains shown by scanning force microscopy, which is thought to be responsible for the biophysical behavior under compression, however, is modified giving rise to the assumption that ectoine and hydroxyectoine are favorable for a proper lung surfactant function. This is further evidenced by the analysis of the insertion kinetics of lipid vesicles into the lipid-peptide monolayer, which is clearly enhanced in the presence of both compatible solutes. Thus, we could show that ectoine and hydroxyectoine enhance the function of lung surfactant in a simple model system, which might provide an additional rationale to inhalative therapy.

Impaired lipid metabolism in idiopathic pulmonary alveolar proteinosis

BACKGROUND

It is well known that lipids abnormally accumulate in the alveoli during idiopathic pulmonary alveolar proteinosis (PAP). It is unclear, however, whether lipids also abnormally accumulate in serum. This study investigated the serum lipid panels in idiopathic PAP patients and explored the relationships between serum levels and the severity of idiopathic PAP.

METHODS AND RESULTS

Clinical data including the level of serum lipids were evaluated in 33 non-diabetic idiopathic PAP patients and 157 healthy volunteers. Serum levels of triglyceride were higher in PAP patients than in healthy subjects (median: 192.00 mg/dl (P25: 104.36, P75: 219.00) vs 119.56 mg/dl (P25: 78.81, P75: 193.03), P < 0.05), while high-density lipoprotein cholesterol (HDL-C) levels were lower in patients than in the control group (42.50 ± 10.30 vs 51.34 ± 12.06 mg/dl, P < 0.01). Forced expiratory volume in one second and forced vital capacity in hypertriglyceridemia patients were lower than those in patients with normal triglyceride. Serum LDL-C and HDL-C ratio correlated negatively with PaO2 (r = -0.403, P < 0.05) and positively with lactate dehydrogenase (r = 0.381, P < 0.05).

CONCLUSIONS

PAP associates with high triglyceride and low HDL levels in the serum, and these lipids provide potential intervention strategy for treatment.

Fluorocarbon-hybrid pulmonary surfactants for replacement therapy--a Langmuir monolayer study

Effective additives to pulmonary surfactant (PS) preparations for therapy of respiratory distress syndrome (RDS) are being intensively sought. We report here the investigation of the effects of partially fluorinated amphiphiles (PFA) on the surface behavior of a model PS formulation. When small amounts of a partially fluorinated alcohol C(8)F(17)C(m)H(2m)OH (F8HmOH, m = 5 and 11) are added to the PS model preparation (a dipalmitoylphosphatidylcholine (DPPC)/Hel 13-5 peptide mixture) considered here, the effectiveness of the latter in in vitro pulmonary functions is enhanced. The mechanism for the improved efficacy depends on the hydrophobic chain length of the added PFA molecules. The shorter PFA, F8H5OH, when incorporated in the monolayer of the PS model preparation, promotes a disordered liquid-expanded (LE) phase upon lateral compression (fluidization). In contrast, the addition of the longer PFA, F8H11OH, reduces the disordered LE/ordered liquid-condensed (LC) phase transition pressure and promotes the growth of ordered domains (solidification). Furthermore, compression-expansion cycles suggest that F8H5OH, when incorporated in the PS model preparation, undergoes an irreversible elimination into the subphase, whereas F8H11OH enhances the squeeze-out phenomenon of the SP-B mimicking peptide, which is important in pulmonary functions and is related to the formation of a solid-like monolayer at the surface and of a surface reservoir just below the surface. F8H11OH particularly reinforces the effectiveness of DPPC in terms of minimum reachable surface tension, and of preservation of the integrated hysteresis area between compression and expansion isotherms, the two latter parameters being generally accepted indices for assessing PS efficacy. We suggest that PFA amphiphiles may be useful potential additives for synthetic PS preparations destined for treatment of RDS in premature infants and in adults.

Pulmonary surfactant pathophysiology: current models and open questions

Pulmonary surfactant is an essential lipid-protein complex that stabilizes the respiratory units (alveoli) involved in gas exchange. Quantitative or qualitative derangements in surfactant are associated with severe respiratory pathologies. The integrated regulation of surfactant synthesis, secretion, and metabolism is critical for air breathing and, ultimately, survival. The goal of this review is to summarize our current understanding and highlight important knowledge gaps in surfactant homeostatic mechanisms.

Early subcutaneous administration of etanercept (Enbrel) prevents from hyperoxia-induced lung injury

Both hyperoxia-induced proapoptotic sensitization of alveolar type II cells (TII cells) and high-stretch mechanical ventilation induced pulmonary inflammation are tumor necrosis factor alpha (TNFalpha) mediated. Therefore, binding of free TNFalpha should protect from TNFalpha-mediated acute lung injury and ameliorate the subsequently developing chronic lung disease. Here, the authors show that a single subcutaneous pretreatment of rat with etanercept, a recombinant p75 TNF receptor 2 human immunoglobulin G1 (IgG1) construct, inhibits the hyperoxia-induced and TNFalpha-mediated increase in the expression of TNFalpha receptor, the activation of caspase 3 in TII cells, and, as an early indicator of lung injury, the capillary-alveolar leakage and granulocyte number in lung lavage. The authors assume that subcutaneous administration of etanercept might be suitable to prevent acute lung injury and its sequelae induced by hyperoxic ventilation of premature neonates and critically ill patients.

Identification of the amino acid sequence that targets peroxiredoxin 6 to lysosome-like structures of lung epithelial cells

Peroxiredoxin 6 (Prdx6), an enzyme with glutathione peroxidase and PLA2 (aiPLA2) activities, is highly expressed in respiratory epithelium, where it participates in phospholipid turnover and antioxidant defense. Prdx6 has been localized by immunocytochemistry and subcellular fractionation to acidic organelles (lung lamellar bodies and lysosomes) and cytosol. On the basis of their pH optima, we have postulated that protein subcellular localization determines the balance between the two activities of Prdx6. Using green fluorescent protein-labeled protein expression in alveolar epithelial cell lines, we showed Prdx6 localization to organellar structures resembling lamellar bodies in mouse lung epithelial (MLE-12) cells and lysosomes in A549 cells. Localization within lamellar bodies/lysosomes was in the luminal compartment. Targeting to lysosome-like organelles was abolished by the deletion of amino acids 31-40 from the Prdx6 NH2-terminal region; deletion of the COOH-terminal region had no effect. A green fluorescent protein-labeled peptide containing only amino acids 31-40 showed lysosomal targeting that was abolished by mutation of S32 or G34 within the peptide. Studies with mutated protein indicated that lipid binding was not necessary for Prdx6 targeting. This peptide sequence has no homology to known organellar targeting motifs. These studies indicate that the localization of Prdx6 in acidic organelles and consequent PLA2 activity depend on a novel 10-aa peptide located at positions 31-40 of the protein.

Molecular dynamics simulation study of a pulmonary surfactant film interacting with a carbonaceous nanoparticle

This article reports an all-atom molecular dynamics simulation to study a model pulmonary surfactant film interacting with a carbonaceous nanoparticle. The pulmonary surfactant is modeled as a dipalmitoylphosphatidylcholine monolayer with a peptide consisting of the first 25 residues from surfactant protein B. The nanoparticle model with a chemical formula C188H53 was generated using a computational code for combustion conditions. The nanoparticle has a carbon cage structure reminiscent of the buckyballs with open ends. A series of molecular-scale structural and dynamical properties of the surfactant film in the absence and presence of nanoparticle are analyzed, including radial distribution functions, mean-square displacements of lipids and nanoparticle, chain tilt angle, and the surfactant protein B peptide helix tilt angle. The results show that the nanoparticle affects the structure and packing of the lipids and peptide in the film, and it appears that the nanoparticle and peptide repel each other. The ability of the nanoparticle to translocate the surfactant film is one of the most important predictions of this study. The potential of mean force for dragging the particle through the film provides such information. The reported potential of mean force suggests that the nanoparticle can easily penetrate the monolayer but further translocation to the water phase is energetically prohibitive. The implication is that nanoparticles can interact with the lung surfactant, as supported by recent experimental data by Bakshi et al.

Lipids including cholesteryl linoleate and cholesteryl arachidonate contribute to the inherent antibacterial activity of human nasal fluid

Mucosal surfaces provide first-line defense against microbial invasion through their complex secretions. The antimicrobial activities of proteins in these secretions have been well delineated, but the contributions of lipids to mucosal defense have not been defined. We found that normal human nasal fluid contains all major lipid classes (in micrograms per milliliter), as well as lipoproteins and apolipoprotein A-I. The predominant less polar lipids were myristic, palmitic, palmitoleic, stearic, oleic, and linoleic acid, cholesterol, and cholesteryl palmitate, cholesteryl linoleate, and cholesteryl arachidonate. Normal human bronchioepithelial cell secretions exhibited a similar lipid composition. Removal of less-polar lipids significantly decreased the inherent antibacterial activity of nasal fluid against Pseudomonas aeruginosa, which was in part restored after replenishing the lipids. Furthermore, lipids extracted from nasal fluid exerted direct antibacterial activity in synergism with the antimicrobial human neutrophil peptide HNP-2 and liposomal formulations of cholesteryl linoleate and cholesteryl arachidonate were active against P. aeruginosa at physiological concentrations as found in nasal fluid and exerted inhibitory activity against other Gram-negative and Gram-positive bacteria. These data suggest that host-derived lipids contribute to mucosal defense. The emerging concept of host-derived antimicrobial lipids unveils novel roads to a better understanding of the immunology of infectious diseases.

Influence of lipid saturation grade and headgroup charge: a refined lung surfactant adsorption model

Rapid adsorption of surfactant material to the air/liquid interface of the lung is essential for maintaining normal lung function. The detailed mechanism of this process, however, remains unclear. In this study, we elucidate the influence of lipid saturation grade and headgroup charge of surface layer lipids on surfactant protein (SP)-induced vesicle insertion into monolayers spread at the air/water interface of a film balance. We used dipalmitoylphosphatidlycholine (DPPC),1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) as monolayer lipids doped with either hydrophobic surfactant-specific protein SP-B or SP-C (0.2 and 0.4 mol %, respectively). Vesicles consisting of DPPC/DPPG (4:1, mol ratio) were injected into a stirred subphase to quantify adsorption kinetics. Based on kinetic film balance and fluorescence measurements, a refined model describing distinct steps of vesicle adsorption to surfactant monolayers is presented. First, in a protein-independent step, lipids from vesicles bridged to the interfacial film by Ca(2+) ions are inserted into defects of a disordered monolayer at low surface pressures. Second, in a SP-facilitated step, active material insertion involving an SP-B- or SP-C-induced flip-flop of lipids occurs at higher surface pressures. Negatively charged lipids obviously influence the threshold pressures at which this second protein-mediated adsorption mechanism takes place.

The model of the action mechanism of SP-C in the lung surfactant monolayers

The action mechanism of surfactant protein C (SP-C) in the lung surfactant monolayers is studied. On the basis of the SP-C molecular structure, a detailed interaction model is developed to describe the interaction of phospholipids/SP-C in the lung surfactant monolayers. It is supposed that: (1) in an alveolus monolayer, SP-C molecules are surrounded by phosphatidylglycerol (PG). When the monolayer is compressed, SP-C molecules can promote PG molecules to be squeezed out; (2) during compressing of the monolayer, unsaturated-PG molecules form a collapse pit firstly when liquid-expanded state (LE) components achieve the collapse pressure. Then, SP-C's alpha-helix is attracted by the collapse pit and both alpha-helix and PG molecules are squeezed out speedily. Finally, the squeezed-out matters can form a lipid-protein aggregation in the subphase. The lipid-protein aggregation, in the centre of which, there is the hydrophobic alpha-helix section surrounded by PG molecules; (3) during the monolayer expanding, because of the increasing of the monolayer's surface tension, the structure of the lipid-protein aggregation is disturbed and reinserts into the surface of the monolayer rapidly. On the basis of analyzing the energies change of the squeeze-out process, a mathematical model is obtained to calculate the squeezed-out number of DPPG molecules when a SP-C molecule squeezes out in a monolayer. According to the model, it is concluded that SP-C has the capability to promote the squeeze-out and the reinsertion of most of PG component in an alveolus monolayer, the prediction data agree well with the experimental data.

Interfacial organizations of gel phospholipid and cholesterol in bovine lung surfactant films

Pulmonary surfactants stabilize the lung by way of reducing surface tension at the air-lung interface of the alveolus. 31P NMR, thin-layer chromatography, and electrospray ionization mass spectroscopy of bovine lipid extract surfactant (BLES) confirmed dipalmitoylphosphatidylcholine (DPPC) to be the major phospholipid species, with significant amounts of palmitoyl-oleoylphosphatidylcholine, palmitoyl-myristoylphosphatidylcholine, and palmitoyl-oleoylphosphatidylglycerol. BLES and DPPC spread at the air-water interface were studied through surface pressure area, fluorescence, and Brewster angle microscopy measurements. Langmuir-Blodgett films of monomolecular films, deposited on mica, were characterized by atomic force microscopy. BLES films displayed shape, size, and vertical height profiles distinct from those of DPPC alone. Calcium ions in the subphase altered BLES film domain structure. The addition of cholesterol (4 mol %) resulted in the destabilization of compressed BLES films at higher surface pressures (>40 mN m-1) and the formation of multilayered structures, apparently consisting of stacked monolayers. The studies suggested potential roles for individual surfactant lipid components in supramolecular arrangements, which could be the contributing factors in pulmonary surfactant to attain low surface tension at the air-water interface.

Peroxiredoxins in the lung with emphasis on peroxiredoxin VI

All six mammalian peroxiredoxins are expressed in the lung. Peroxiredoxin (Prx) VI is the isoform expressed at the highest level and its lung expression exceeds that for other organs. The predominant location of Prx VI is the cytosol and acidic organelles of Clara cells of the conducting airways and type II epithelial cells and macrophages in the alveoli. Prx I and VI show developmental induction of transcription at birth. PrxVI shares structural homology with other peroxiredoxins exhibiting a thioredoxin fold and a conserved catalytic Cys residue in the N-terminus of the protein. This enzyme is highly inducible by oxidative stress in both the neonatal and adult lung consistent with a role in antioxidant defense. Prx VI has several properties that distinguish its peroxidase activity from other peroxiredoxins: it can reduce phospholipid hydroperoxides in addition to other organic hydroperoxides and H2O2; the electron donor that serves to reduce the oxidized peroxidatic cysteine is not thioredoxin but GSH; instead of homodimerization, heterodimerization with pi-glutathione S-transferase is required for regeneration of the active enzyme. Prx VI also expresses a phospholipase A2 activity that is Ca2+-independent, maximal at acidic pH, and dependent on a serine-based catalytic triad and nucleophilic elbow at the surface of the protein. Models of altered Prx VI expression at the cellular, organ and whole animal levels have demonstrated that Prx VI functions as an important anti-oxidant enzyme with levels of protection that exceed those ascribed to GSH peroxidase (GPx1). The phospholipase A2 activity plays an important role in lung surfactant homeostasis and is responsible for the bulk of the degradation of internalized phosphatidylcholine and its resynthesis by the reacylation pathway. Expression of peroxiredoxins is elevated in several lung diseases including lung cancer, mesothelioma and sarcoidosis, although the mechanism for these alterations is not known. The unique properties of Prx VI enable it to play an important role in lung cell function.

Alteration of the Pulmonary Surfactant System in Full-Term Infants with Hereditary ABCA3 Deficiency

RATIONALE

ABCA3 mutations are known to cause fatal surfactant deficiency.

OBJECTIVE

We studied ABCA3 protein expression in full-term newborns with unexplained respiratory distress syndrome (URDS) as well as the relevance of ABCA3 mutations for surfactant homeostasis.

METHODS

Lung tissue of infants with URDS was analyzed for the expression of ABCA3 in type II pneumocytes. Coding exons of the ABCA3 gene were sequenced. Surfactant protein expression was studied by immunohistochemistry, immunoelectron microscopy, and Western blotting.

RESULTS

ABCA3 protein expression was found to be greatly reduced or absent in 10 of 14 infants with URDS. Direct sequencing revealed distinct ABCA3 mutations clustering within vulnerable domains of the ABCA3 protein. A strong expression of precursors of surfactant protein B (pro-SP-B) but only low levels and aggregates of mature surfactant protein B (SP-B) within electron-dense bodies in type II pneumocytes were found. Within the matrix of electron-dense bodies, we detected precursors of SP-C (pro-SP-C) and cathepsin D. SP-A was localized in small intracellular vesicles, but not in electron-dense bodies. SP-A and pro-SP-B were shown to accumulate in the intraalveolar space, whereas mature SP-B and SP-C were reduced or absent, respectively.

CONCLUSION

Our data provide evidence that ABCA3 mutations are associated not only with a deficiency of ABCA3 but also with an abnormal processing and routing of SP-B and SP-C, leading to severe alterations of surfactant homeostasis and respiratory distress syndrome. To identify infants with hereditary ABCA3 deficiency, we suggest a combined diagnostic approach including immunohistochemical, ultrastructural, and mutation analysis.

Improved anti-oxidant activity of superoxide dismutase by direct chemical modification

Chemically modified derivatives of superoxide dismutase (SOD), i.e., cationized (Cat-SOD) and mannosylated SOD (Man-SOD), were designed to improve an ability of SOD to suppress reactive oxygen species (ROS)-mediated injury in the alveolar epithelium. To evaluate their effectiveness, an in vitro model of paraquat poisoning was developed with primary cultured rabbit alveolar type II cells. Despite a 5.6-fold higher cellular association than native SOD, Man-SOD did not protect cell injury due to paraquat following evaluation by MTT assay. In contrast, Cat-SOD exhibited a 140-fold higher cellular association than native SOD and greatly suppressed paraquat-induced cell injury, as well as lipid peroxidation. Incubation with 300 U/ml Cat-SOD for 2 h increased intracellular SOD activity 5.3-fold. The increase in intracellular SOD activity was significantly inhibited in the presence of cytochalasin B, an endocytosis inhibitor. Internalization of Cat-SOD was also confirmed by confocal laser scanning fluorescein microscopy. In addition, the protective effect of Cat-SOD against paraquat-induced cell injury was completely abolished by the presence of cytochalasin B. In conclusion, this study demonstrated that cationization of SOD greatly enhances its intracellular delivery and, as a consequence, produces a significant protective effect against ROS-mediated injury of the alveolar epithelium.

Probing perturbation of bovine lung surfactant extracts by albumin using DSC and 2H-NMR

Lung surfactant (LS), a lipid-protein mixture, forms films at the lung air-water interface and prevents alveolar collapse at end expiration. In lung disease and injury, the surface activity of LS is inhibited by leakage of serum proteins such as albumin into the alveolar hypophase. Multilamellar vesicular dispersions of a clinically used replacement, bovine lipid extract surfactant (BLES), to which (2% by weight) chain-perdeuterated dipalmitoylphosphatidycholine (DPPG mixtures-d(62)) had been added, were studied using deuterium-NMR spectroscopy ((2)H-NMR) and differential scanning calorimetry (DSC). DSC scans of BLES showed a broad gel to liquid-crystalline phase transition between 10-35 degrees C, with a temperature of maximum heat flow (T(max)) around 27 degrees C. Incorporation of the DPPC-d(62) into BLES-reconstituted vesicles did not alter the T(max) or the transition range as observed by DSC or the hydrocarbon stretching modes of the lipids observed using infrared spectroscopy. Transition enthalpy change and (2)H-NMR order parameter profiles were not significantly altered by addition of calcium and cholesterol to BLES. (2)H-NMR spectra of the DPPC-d(62) probes in these samples were characteristic of a single average lipid environment at all temperatures. This suggested either continuous ordering of the bilayer through the transition during cooling or averaging of the DPPC-d(62) environment by rapid diffusion between small domains on a short timescale relative to that characteristic of the (2)H-NMR experiment. Addition of 10% by weight of soluble bovine serum albumin (1:0.1, BLES/albumin, dry wt/wt) broadened the transition slightly and resulted in the superposition of (2)H-NMR spectral features characteristic of coexisting fluid and ordered phases. This suggests the persistence of phase-separated domains throughout the transition regime (5-35 degrees C) of BLES with albumin. The study suggests albumin can cause segregation of protein bound-lipid domains in surfactant at NMR timescales (10(-5) s). Persistent phase separation at physiological temperature may provide for a basis for loss of surface activity of surfactant in dysfunction and disease.

Rare SP-A alleles and the SP-A1-6A4 allele associate with risk for lung carcinoma

Next to cigarette smoking, genetic factors may contribute to lung cancer risk. Pulmonary surfactant components may mediate response to inhaled carcinogenic substances and/or play a role in lung function and inflammation. We studied associations between surfactant protein (SP) genetic variants and risk in lung cancer subgroups. Samples (n=308) were genotyped for SP-A1, -A2, -B, and -D marker alleles. These included 99 patients with small cell lung carcinoma (SCLC, n=31), or non-SCLC (NSCLC, n=68) consisting of squamous cell carcinoma (SCC, n=35), and adenocarcinoma (AC) (n=23); controls (n=99) matched by age, sex, and smoking status (clinical control) to SCLC and NSCLC; and 110 healthy individuals (population control). We found (a) no significant marker associations with SCLC, (b) rare SP-A2 (1A9) and SP-A1 (6A11) alleles associate with NSCLC risk when compared with population control, (c) the same alleles (1A9, 6A11) associate with risk for AC when compared with population (6A11) or clinical control (1A9), and (d) the SP-A1-6A4 allele (found in approximately 10% of the population) associates with SCC, when compared with population or clinical control. A correlation between SP-A variants and lung cancer susceptibility appears to exist, indicating that SP-A alleles may be useful markers of lung cancer risk.

Altered lung phospholipid metabolism in mice with targeted deletion of lysosomal-type phospholipase A2

Lung surfactant dipalmitoylphosphatidylcholine (DPPC) is endocytosed by alveolar epithelial cells and degraded by lysosomal-type phospholipase A2 (aiPLA2). This enzyme is identical to peroxiredoxin 6 (Prdx6), a bifunctional protein with PLA2 and GSH peroxidase activities. Lung phospholipid was studied in Prdx6 knockout (Prdx6-/-) mice. The normalized content of total phospholipid, phosphatidylcholine (PC), and disaturated phosphatidylcholine (DSPC) in bronchoalveolar lavage fluid, lung lamellar bodies, and lung homogenate was unchanged with age in wild-type mice but increased progressively in Prdx6-/- animals. Degradation of internalized [3H]DPPC in isolated mouse lungs after endotracheal instillation of unilamellar liposomes labeled with [3H]DPPC was significantly decreased at 2 h in Prdx6-/- mice (13.6 +/- 0.3% vs. 26.8 +/- 0.8% in the wild type), reflected by decreased dpm in the lysophosphatidylcholine and the unsaturated PC fractions. Incorporation of [14C]palmitate into DSPC at 24 h after intravenous injection was decreased by 73% in lamellar bodies and by 54% in alveolar lavage surfactant in Prdx6-/- mice, whereas incorporation of [3H]choline was decreased only slightly. Phospholipid metabolism in Prdx6-/- lungs was similar to that in wild-type lungs treated with MJ33, an inhibitor of aiPLA2 activity. These results confirm an important role for Prdx6 in lung surfactant DPPC degradation and synthesis by the reacylation pathway.

Inhibition of TNFalpha in vivo prevents hyperoxia-mediated activation of caspase 3 in type II cells

Background

The mechanisms during the initial phase of oxygen toxicity leading to pulmonary tissue damage are incompletely known. Increase of tumour necrosis factor alpha (TNFalpha) represents one of the first pulmonary responses to hyperoxia. We hypothesised that, in the initial phase of hyperoxia, TNFalpha activates the caspase cascade in type II pneumocytes (TIIcells).

Methods

Lung sections or freshly isolated TIIcells of control and hyperoxic treated rats (48 hrs) were used for the determination of TNFalpha (ELISA), TNF-receptor 1 (Western blot) and activity of caspases 8, 3, and 9 (colorimetrically). NF-kappaB activation was determined by EMSA, by increase of the p65 subunit in the nuclear fraction, and by immunocytochemistry using a monoclonal anti-NF-kappaB-antibody which selectively stained the activated, nuclear form of NF-kappa B. Apoptotic markers in lung tissue sections (TUNEL) and in TIIcells (cell death detection ELISA, Bax, Bcl-2, mitochondrial membrane potential, and late and early apoptotic cells) were measured using commercially available kits.

Results

In vivo, hyperoxia activated NF-kappaB and increased the expression of TNFalpha, TNF-receptor 1 and the activity of caspase 8 and 3 in freshly isolated TIIcells. Intratracheal application of anti-TNFalpha antibodies prevented the increase of TNFRI and of caspase 3 activity. Under hyperoxia, there was neither a significant change of cytosolic cytochrome C or of caspase 9 activity, nor an increase in apoptosis of TIIcells. Hyperoxia-induced activation of caspase 3 gradually decreased over two days of normoxia without increasing apoptosis. Therefore, activation of caspase 3 is a temporary effect in sublethal hyperoxia and did not mark the "point of no return" in TIIcells.

Conclusion

In the initiation phase of pulmonary oxygen toxicity, an increase of TNFalpha and its receptor TNFR1 leads to the activation of caspase 8 and 3 in TIIcells. Together with the hyperoxic induced increase of Bax and the decrease of the mitochondrial membrane potential, activation of caspase 3 can be seen as sensitisation for apoptosis. Eliminating the TNFalpha effect in vivo by anti-TNFalpha antibodies prevents the pro-apoptotic sensitisation of TIIcells.

Serum cholestenoic acid as a potential marker of pulmonary cholesterol homeostasis: increased levels in patients with pulmonary alveolar proteinosis

The conversion of cholesterol into the more polar metabolites 27-hydroxycholesterol (27-OH) and cholestenoic acid by the cytochrome P450 sterol 27-hydroxylase is a cholesterol-removal mechanism used by almost all cells. Most of the cholestenoic acid present in the circulation originates from the lung, and it has been suggested that sterol 27-hydroxylase is of particular importance for cholesterol homeostasis in this organ. As an example of pulmonary cholesterol accumulation, a known disorder of surfactant homeostasis, pulmonary alveolar proteinosis (PAP), was studied. Analysis of bronchoalveolar lavage fluid from PAP patients revealed a significant accumulation of the cholesterol metabolites cholestenoic acid and 27-OH. This pattern was recapitulated in serum, with a significant increase in the levels of both cholestenoic acid (P=0.003) and 27-OH (P=0.017) in PAP patients compared with healthy controls. Analysis of PAP alveolar macrophages did not reveal a significant change in mRNA expression levels of either sterol 27-hydroxylase or the cholesterol-esterifying enzyme acyl-CoA:cholesterol acyltransferase-1. These results are consistent with the contention that substrate availability, rather than enzyme expression, is the key factor in regulating the production of cholestenoic acid by the lung and that serum cholestenoic acid may be a marker of pulmonary cholesterol homeostasis.

Matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectrometry in lipid and phospholipid research

The interest in the analysis of lipids and phospholipids is continuously increasing due to the importance of these molecules in biochemistry (e.g. in the context of biomembranes and lipid second messengers) as well as in industry. Unfortunately, commonly used methods of lipid analysis are often time-consuming and tedious because they include previous separation and/or derivatization steps. With the development of "soft-ionization techniques" like electrospray ionization (ESI) or matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF), mass spectrometry became also applicable to lipid analysis. The aim of this review is to summarize so far available experiences in MALDI-TOF mass spectrometric analysis of lipids. It will be shown that MALDI-TOF MS can be applied to all known lipid classes and the characteristics of individual lipids will be discussed. Additionally, some selected applications in medicine and biology, e.g. mixture analysis, cell and tissue analysis and the determination of enzyme activities will be described. Advantages and disadvantages of MALDI-TOF MS in comparison to other established lipid analysis methods will be also discussed.

The N-terminal Propeptide of Lung Surfactant Protein C is Necessary for Biosynthesis and Prevents Unfolding of a Metastable α-Helix

The lung surfactant-associated protein C (SP-C) consists mainly of a polyvaline alpha-helix, which is stable in a lipid membrane. However, in agreement with the predicted beta-strand conformation of a polyvaline segment, helical SP-C unfolds and transforms into beta-sheet aggregates and amyloid fibrils within a few days in aqueous organic solvents. SP-C fibril formation and aggregation have been associated with lung disease. Here, we show that in a recently isolated biosynthetic precursor of SP-C (SP-Ci), a 12 residue N-terminal propeptide locks the metastable polyvaline part in a helical conformation. The SP-Ci helix does not aggregate or unfold during several weeks of incubation, as judged by hydrogen/deuterium exchange and mass spectrometry. Hydrogen/deuterium exchange experiments further indicate that the propeptide reduces exchange in parts corresponding to mature SP-C. Finally, in an acidic environment, SP-Ci unfolds and aggregates into amyloid fibrils like SP-C. These data suggest a direct role of the N-terminal propeptide in SP-C biosynthesis.

Analysis of the phospholipid composition of bronchoalveolar lavage (BAL) fluid from man and minipig by MALDI-TOF mass spectrometry in combination with TLC

Surfaces of lungs are covered by the surfactant, an aqueous mixture of different phospholipids (PL) and proteins. Although the surfactant represents a relatively simple mixture of only a few PL (primarily phosphatidylcholine (PC) and phosphatidylglycerol (PG)), reliable methods of routine lipid analysis of the surfactant are still lacking. It will be shown that matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS) represents a suitable technique for the differentiation of the apolar components of the surfactant of different species. Samples of man and minipig are used in this study since both are known to vary in their PL composition. PL of surfactant were separated by thin-layer chromatography (TLC) and the obtained subfractions subjected to MALDI-TOF MS analysis in order to monitor the presence of even minor PL species. It will be shown that besides PG and PC, also phosphatidylethanolamine, -inositol and sphingomyelin can be detected in surfactant of man, whereas only sphingomyelin could be detected in the minipig sample.

The pulmonary surfactant: impact of tobacco smoke and related compounds on surfactant and lung development

Cigarette smoking, one of the most pervasive habits in society, presents many well established health risks. While lung cancer is probably the most common and well documented disease associated with tobacco exposure, it is becoming clear from recent research that many other diseases are causally related to smoking. Whether from direct smoking or inhaling environmental tobacco smoke (ETS), termed secondhand smoke, the cells of the respiratory tissues and the lining pulmonary surfactant are the first body tissues to be directly exposed to the many thousands of toxic chemicals in tobacco. Considering the vast surface area of the lung and the extreme attenuation of the blood-air barrier, it is not surprising that this organ is the primary route for exposure, not just to smoke but to most environmental contaminants. Recent research has shown that the pulmonary surfactant, a complex mixture of phospholipids and proteins, is the first site of defense against particulates or gas components of smoke. However, it is not clear what effect smoke has on the surfactant. Most studies have demonstrated that smoking reduces bronchoalveolar lavage phospholipid levels. Some components of smoke also appear to have a direct detergent-like effect on the surfactant while others appear to alter cycling or secretion. Ultimately these effects are reflected in changes in the dynamics of the surfactant system and, clinically in changes in lung mechanics. Similarly, exposure of the developing fetal lung through maternal smoking results in postnatal alterations in lung mechanics and higher incidents of wheezing and coughing. Direct exposure of developing lung to nicotine induces changes suggestive of fetal stress. Furthermore, identification of nicotinic receptors in fetal lung airways and corresponding increases in airway connective tissue support a possible involvement of nicotine in postnatal asthma development. Finally, at the level of the alveoli of the lung, colocalization of nicotinic receptors and surfactant-specific protein in alveolar cells is suggestive of a role in surfactant metabolism. Further research is needed to determine the mechanistic effects of smoke and its components on surfactant function and, importantly, the effects of smoke components on the developing pulmonary system.

The Impact of Intravenous Fat Emulsion Administration in Acute Lung Injury

The aim of this study was to evaluate the effect of parenteral nutrition containing medium- and long-chain triglycerides on the function of the respiratory system and to investigate mechanisms involved in this process. We studied 13 patients with acute respiratory distress syndrome (ARDS), 8 receiving lipid and 5 placebo, and 6 without ARDS, receiving lipid. Bronchoalveolar lavage (BAL) was performed before and 1 hour after administration of lipid or placebo. In patients with ARDS, lipid administration resulted in deterioration of oxygenation (Pa(O(2))/FI(O(2)): from 129 +/- 37 to 95 +/- 42), compliance of respiratory system (from 39.2 +/- 12 to 33.1 +/- 9.2 ml/cm H(2)O), and pulmonary vascular resistance (from 258 +/- 47 to 321 +/- 58 dyne x s x cm(-5)). In the BAL fluid of the same group, an increase in total protein and phospholipid concentrations, phospholipase activities, platelet-activating factor and neutrophils, as well as alterations in BAL lipid profile were observed. No significant changes were observed in the control or in the ARDS-Placebo groups. In conclusion, this study indicates that administration of medium- and long-chain triglycerides in patients with ARDS causes alterations in lung function and hemodynamics. Inflammatory cells, possibly activated by lipids, release phospholipase A(2) and platelet-activating factor, enhancing edema formation, inflammation, and surfactant alterations.

Rab3D and actin reveal distinct lamellar body subpopulations in alveolar epithelial type II cells

Rab3D is a small GTP-binding protein associated with secretory vesicles in various exocrine and endocrine cells, where it has been implicated in regulated exocytosis. Data obtained previously in pancreas have suggested that rab3D is involved in the coating of secretory granules with filamentous actin. In the present study we employed Western blot analysis, immunofluorescence, and immunoelectron microscopy to examine the distribution of rab3D in rat lung. Rab3D immunoreactivity was detected in bronchiolar Clara cells and alveolar epithelial type II (AET-II) cells. In both cell types, rab3D displayed preferential localization to secretory vesicles that were identified using specific antibodies against Clara Cell Secretory Protein and p180 lamellar body protein, respectively. Interestingly, rab3D was associated with only 24% of the lamellar bodies in AET-II cells. Rab3D-positive lamellar bodies were typically in close proximity of the apical plasma membrane, where exocytosis occurs. Another subpopulation of lamellar bodies, constituting only 2%, was not only rab3D-positive but could also be labeled with the filamentous-actin probe phalloidin. A third subpopulation, constituting 9%, displayed actin coating without rab3D staining. We propose that these three lamellar body subpopulations represent consecutive intermediates along the regulated exocytotic pathway, implying that rab3D release and actin coating are intimately linked processes.

Phospholipid metabolism in lung surfactant

Pulmonary surfactant is a mixture of lipids, mostly phospholipids, and proteins that allows for breathing with minimal effort. The current chapter discusses the metabolism of the phospholipids of this material. Surfactant phospholipids are synthesized in the type II epithelial cells of the lung. The lipids and surfactant proteins are assembled in intracellular storage organelles, called lamellar bodies, and are subsequently secreted into the alveolar space. Within this extracellular space surfactant undergoes several transformations. First the lamellar bodies unravel to form a highly organized lattice-like lipid:protein structure tubular myelin. Second, the organized structures, in particular tubular myelin, adsorb to form a lipid at the air-liquid interface of the alveoli. It is, in fact, this surface tension reducing film that is responsible for the physiological role of surfactant, to prevent lung collapse and allow ease of inflation. Third, the surface film is converted to a small vesicular form. Finally, these small vesicles are taken-up by the type II cells for recycling and degradation and by alveolar macrophages for degradation.

Chemokines Accumulate in the Lungs of Rats with Severe Pulmonary Embolism Induced by Polystyrene Microspheres

Pulmonary thromboembolism (PEm) is a serious and life threatening disease and the most common cause of acute pulmonary vascular occlusion. Even following successful treatment of PEm, many patients experience long-term disability due to diminished heart and lung function. Considerable damage to the lungs presumably occurs due to reperfusion injury following anti-occlusive treatments for PEm and the resulting chronic inflammatory state in the lung vasculature. We have used a rat model of irreversible PEm to ask whether pulmonary vascular occlusion in the absence of reperfusion is itself sufficient to induce an inflammatory response in lungs. By adjusting the severity of the vascular occlusion, we were able to generate hypertensive and nonhypertensive PEm, and then examine lung tissue for expression of CXC and C-C chemokine genes and bronchoalveolar lavage (BAL) fluid for the presence of chemokine proteins. Hypertensive and nonhypertensive PEm resulted in increased expression of both CXC and C-C chemokines genes in lung tissues. Hypertensive PEm was also associated with a 50-100-fold increase in protein content in lung BAL fluid, which included the CXC chemokines cytokine-induced neutrophil chemoattractant and macrophage-inflammatory protein 2. The presence of chemokines in BALs was reflected by a potent neutrophil chemotactic activity in in vitro chemotaxis assays. Abs to cytokine-induced neutrophil chemoattractant blocked the in vitro neutrophil chemotactic activity of BAL by 44%. Our results indicate that the ischemia and hypertension associated with PEm are sufficient to induce expression of proinflammatory mediators such as chemokines, and establish a proinflammatory environment in the ischemic lung even before reperfusion.