Synergistic Action of Antimicrobial Lung Proteins against Klebsiella pneumoniae

As key components of innate immunity, lung antimicrobial proteins play a critical role in warding off invading respiratory pathogens. Lung surfactant protein A (SP-A) exerts synergistic antimicrobial activity with the N-terminal segment of the SP-B proprotein (SP-B^N) against Klebsiella pneumoniae K2 in vivo. However, the factors that govern SP-A/SP-B^N antimicrobial activity are still unclear. The aim of this study was to identify the mechanisms by which SP-A and SP-B^N act synergistically against K. pneumoniae, which is resistant to either protein alone. The effect of these proteins on K. pneumoniae was studied by membrane permeabilization and depolarization assays and transmission electron microscopy. Their effects on model membranes of the outer and inner bacterial membranes were analyzed by differential scanning calorimetry and membrane leakage assays. Our results indicate that the SP-A/SP-B^N complex alters the ultrastructure of K. pneumoniae by binding to lipopolysaccharide molecules present in the outer membrane, forming packing defects in the membrane that may favor the translocation of both proteins to the periplasmic space. The SP-A/SP-B^N complex depolarized and permeabilized the inner membrane, perhaps through the induction of toroidal pores. We conclude that the synergistic antimicrobial activity of SP-A/SP-B^N is based on the capability of this complex, but not either protein alone, to alter the integrity of bacterial membranes.

Phospholipid packing and hydration in pulmonary surfactant membranes and films as sensed by LAURDAN

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.

“Hydrophobic” Surfactant Apoproteins and Augmentation of Phospholipid Recycling

A 10,000-11,000 molecular weight apoprotein was isolated from an ethanol-ether extract of rat lung surfactant and purified by silicic acid chromatography. The protein (Apo Et) significantly augmented the uptake of phospholipids in liposomal form by cultured rat granular pneumocytes by a time-dependent process that varied with protein concentration and liposome composition. The protein had no effect on cell viability and showed no phospholipase activity. The mechanism for this augmented phospholipid uptake is not known but could be due to an alteration of physical form of the phospholipids by the protein or to a receptor-mediated uptake of phospholipids. This protein may prove to be a physiologically important regulator of the recycling of lung surfactant phospholipids.

PROTEIN INHIBITION OF SURFACTANT DURING MECHANICAL VENTILATION OF ISOLATED RAT LUNGS

This study tested the hypothesis that material leaking into the airspace from the vasculature during ventilation interferes with surfactant function and contributes to decreases in lung compliance. Rats were euthanized and the lungs were isolated either with or without flushing of the vasculature, followed by mechanical ventilation and analysis of lung compliance and lung lavage analysis. Flushed lungs had higher lung compliance compared to the non-flushed lungs. This was associated with lower protein concentrations and improved surfactant activity. It is concluded that during mechanical ventilation, leakage of proteins results in surfactant inhibition and thereby contribute to decreased lung compliance.

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.

Inhibition of breathing after surfactant depletion is achieved at a higher arterial PCO2 during ventilation with liquid than with gas

Background

Inhibition of phrenic nerve activity (PNA) can be achieved when alveolar ventilation is adequate and when stretching of lung tissue stimulates mechanoreceptors to inhibit inspiratory activity. During mechanical ventilation under different lung conditions, inhibition of PNA can provide a physiological setting at which ventilatory parameters can be compared and related to arterial blood gases and pH.

Objective

To study lung mechanics and gas exchange at inhibition of PNA during controlled gas ventilation (GV) and during partial liquid ventilation (PLV) before and after lung lavage.

Methods

Nine anaesthetised, mechanically ventilated young cats (age 3.8 ± 0.5 months, weight 2.3 ± 0.1 kg) (mean ± SD) were studied with stepwise increases in peak inspiratory pressure (PIP) until total inhibition of PNA was attained before lavage (with GV) and after lavage (GV and PLV). Tidal volume (V_t), PIP, oesophageal pressure and arterial blood gases were measured at inhibition of PNA. One way repeated measures analysis of variance and Student Newman Keuls-tests were used for statistical analysis.

Results

During GV, inhibition of PNA occurred at lower PIP, transpulmonary pressure (Ptp) and Vt before than after lung lavage. After lavage, inhibition of inspiratory activity was achieved at the same PIP, Ptp and Vt during GV and PLV, but occurred at a higher PaCO₂ during PLV. After lavage compliance at inhibition was almost the same during GV and PLV and resistance was lower during GV than during PLV.

Conclusion

Inhibition of inspiratory activity occurs at a higher PaCO₂ during PLV than during GV in cats with surfactant-depleted lungs. This could indicate that PLV induces better recruitment of mechanoreceptors than GV.

Inhaled nitric oxide affects endogenous surfactant in experimental lung transplantation

BACKGROUND

Inhalation of nitric oxide (NO) has been proposed as a therapy to improve lung transplantation outcome. We investigated the effect that inhaled NO has on the surfactant system in the context of ischemia-reperfusion injury.

METHODS

Single left-lung transplantation was performed in weight-matched pairs of Landrace pigs. A double-lung block from the donor animal was flushed with University of Wisconsin solution at 4 degrees C followed by immersion in cold University of Wisconsin solution for 22 hr. The left donor lung was transplanted into the recipient. Recipients were divided into two groups: (1) treated with inhaled NO (40 ppm) (n=6) immediately after initiating lung reperfusion and (2) without treatment (n=6). Lung function was measured during 2 hr of reperfusion. Surfactant components in small and large aggregates, isolated from cell-free bronchoalveolar lavages, and surfactant function were measured.

RESULTS

NO inhalation significantly decreased arterial oxygenation. With respect to the surfactant system, NO inhalation worsened the surfactant adsorption rate to an air-liquid interface and affected levels of hydrophobic surfactant proteins (SPs), SP-B and SP-C, and phospholipids, which decreased in large surfactant aggregates but not in small surfactant aggregates. SP-A was reduced in large surfactant aggregates of transplanted lungs from both untreated and NO-treated groups.

CONCLUSION

A decreased level of SP-A, SP-B, and SP-C in large surfactant aggregates of transplanted lungs treated with NO is a marker of lung injury. We conclude that treatment with inhaled NO after lung transplantation is deleterious for the surfactant system and causes a parallel worsening of arterial oxygenation.

Pulmonary surfactant protein A isolation as a by-product of porcine pulmonary surfactant production

A pulmonary surfactant reduces surface tension at the air/liquid interface of the alveoli and stabilizes alveoli at low lung volumes. Surfactant deficiency and dysfunction were shown to be present in a number of pulmonary diseases, and surfactant replacement therapy is the common clinical conduct. The hydrophilic SP-A (surfactant protein A) is absent when solvent extraction was used during exogenous surfactant production. Addition of SP-A to the surfactant preparation increases the surface activity and completely counteracts inhibition by blood proteins. SP-A recognizes and binds to carbohydrate structures on the surfaces of pathogenic micro-organisms, and acts as opsonins or cross-linking molecules by binding to a variety of cells that participate in the pulmonary immune response. The purification procedure yielded 206 mg of high-purity SP-A/kg of porcine lung, as judged by gel filtration, SDS/PAGE and Western blotting. The electrophoretic profiles obtained showed that pure SP-A consists of proteins of wide molecular mass in the range 26-36 kDa and a dimer in the range 56-60 kDa. The Western-blot results displayed the same band pattern profile after incubating the membrane using a commercially available polyclonal anti-SP-A antibody produced in goat. Gel-filtration experiments confirmed the molecular mass of SP-A in 10 mM NaCl solution. The isolated SP-A showed mannose-binding ability, representative of its functionality.

Surface activity of a synthetic lung surfactant containing a phospholipase-resistant phosphonolipid analog of dipalmitoyl phosphatidylcholine

Surface activity and sensitivity to inhibition from phospholipase A2 (PLA2), lysophosphatidylcholine (LPC), and serum albumin were studied for a synthetic C16:0 diether phosphonolipid (DEPN-8) combined with 1.5% by weight of mixed hydrophobic surfactant proteins (SP)-B/C purified from calf lung surfactant extract (CLSE). Pure DEPN-8 had better adsorption and film respreading than the major lung surfactant phospholipid dipalmitoyl phosphatidylcholine and reached minimum surface tensions <1 mN/m under dynamic compression on the Wilhelmy balance and on a pulsating bubble surfactometer (37 degrees C, 20 cycles/min, 50% area compression). DEPN-8 + 1.5% SP-B/C exhibited even greater adsorption and had overall dynamic surface tension lowering equal to CLSE on the bubble. In addition, films of DEPN-8 + 1.5% SP-B/C on the Wilhelmy balance had better respreading than CLSE after seven (but not two) cycles of compression-expansion at 23 degrees C. DEPN-8 is structurally resistant to degradation by PLA2, and DEPN-8 + 1.5% SP-B/C maintained high adsorption and dynamic surface activity in the presence of this enzyme. Incubation of CLSE with PLA2 led to chemical degradation, generation of LPC, and reduced surface activity. DEPN-8 + 1.5% SP-B/C was also more resistant than CLSE to direct biophysical inhibition by LPC, and the two were similar in their sensitivity to biophysical inhibition by serum albumin. These findings indicate that synthetic surfactants containing DEPN-8 combined with surfactant proteins or related synthetic peptides have potential utility for treating surfactant dysfunction in inflammatory lung injury.

[Purification of porcine pulmonary surfactant by CO2 supercritical fluid extraction]

OBJECTIVE

To develop a supercritical fluid extraction (SFE) method for purifying porcine pulmonary surfactant.

METHOD

An orthogonal design with 4 factors and 4 levels was used to optimize the SFE conditions.

RESULTS

The best extraction conditions were established as the following: pressure 30 MPa, temperature 50 degrees Celsius, dynamic extraction for 4 h with 0.2 ml ethanol as the modifier.

CONCLUSION

The new method for purifying porcine pulmonary surfactant by SFE-CO2 can cause drastic reduction of organic solvents, being convenient to use and effective to purify.

Surfactant strengthens the inhibitory effect of C-reactive protein on human lung macrophage cytokine release

In this study we investigated the effect of acute-phase levels of C-reactive protein (CRP) on cytokine production by pulmonary macrophages in the presence or absence of pulmonary surfactant. Both human alveolar and interstitial macrophages as well as human surfactant were obtained from multiple organ donor lungs. Precultured macrophages were stimulated with LPS alone or together with IFN-gamma in the presence or absence of CRP, surfactant, and combinations. Releases of TNF-alpha and of IL-1beta to the medium were determined. We found that CRP could modulate lung inflammation in humans by decreasing the production of proinflammatory cytokines by both alveolar and interstitial macrophages stimulated with LPS alone or together with IFN-gamma. The potential interaction between CRP and surfactant phospholipids did not overcome the effect of either CRP or surfactant on TNF-alpha and IL-1beta release by lung macrophages. On the contrary, CRP and pulmonary surfactant together had a greater inhibitory effect than either alone on the release of proinflammatory cytokines by lung macrophages.

Porcine surfactant protein D is N-glycosylated in its carbohydrate recognition domain and is assembled into differently charged oligomers

Surfactant protein D (SP-D) belongs to a subgroup of mammalian collagenous Ca(2+)-dependent lectins known as the collectins. It is thought to play a significant role in the innate immune response against microorganisms within the lungs and at other mucosal surfaces. This report documents the isolation and characterization of SP-D purified from porcine lung lavage using mannan affinity chromatography and gel filtration. Ultrastructural analysis shows both dodecameric and higher order oligomeric complexes of SP-D. The molecular mass of monomeric porcine SP-D (50 kD) is larger than that of SP-D from humans (43 kD). The difference in mass is due to the presence of an Asparagine-linked glycosylation in the carbohydrate recognition domain of porcine SP-D, which is absent in SP-D of other species investigated so far. Analysis of this carbohydrate moiety indicates that it is a highly heterogeneous, complex type oligosaccharide which is sialylated. The heterogeneity of oligosaccharide sialylation results in the existence of many differently charged porcine SP-D isoforms. The removal of the carbohydrate moiety reduces the inhibitory effect of porcine SP-D on influenza A virus haemagglutination. Therefore, the carbohydrate moiety may influence interactions with pathogens.

Expression of surfactant protein D in the human gastric mucosa and during Helicobacter pylori infection

Helicobacter pylori establishes persistent infection of gastric mucosa with diverse clinical outcomes. The innate immune molecule surfactant protein D (SP-D) binds selectively to microorganisms, inducing aggregation and phagocytosis. In this study, we demonstrated the expression of SP-D in gastric mucosa by reverse transcription-PCR and immunohistochemical analysis. SP-D is present at the luminal surface and within the gastric pits, with maximal expression at the surface. Levels of expression are significantly increased in H. pylori-associated gastritis compared to those in the normal mucosa. Immunofluorescence microscopy was used to demonstrate binding and agglutination of H. pylori by SP-D in a lectin-specific manner. These activities resulted in a 50% reduction in the motility of H. pylori, as judged on the basis of curvilinear velocity measured by using a Hobson BacTracker. Lipopolysaccharides extracted from three H. pylori strains were shown to bind SP-D in a concentration-dependent manner, and there was marked variation in the avidity of binding among the strains. SP-D may therefore play a significant role in the innate immune response to H. pylori infection.

Synthesis, purification and surface activities of the human pulmonary surfactant protein-C (SP-C) analogue, SP-CL16 (6-28)

We previously reported that a human analogue of pulmonary surfactant protein-C (SP-C), SP-CL16 (6-28), with 23 residues (Fig. 1) was the most active analogue in a reconstituted lipid mixture and had the shortest chain among the poly-leucine-analogues examined. In the present study, we examined a new method of preparing this analogue, that is, stepwise solid-phase synthesis employing the Fmoc method followed by centrifugal partition chromatography (CPC) using an n-hexane/CH3OH/H2O/trifluoroacetic acid (TFA) (1000: 1000:1:2, v/v) solvent system according to the descending method. The synthetic peptides were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry in search of activity to improve the in vitro surface activity of a ternary lipid mixture composed of dipalmitoylphosphatidylcholine, egg-phosphatidylglycerol and palmitic acid (75:25:10, w/w) in a Langmuir-Wilhelmy surface balance. SP-CL16 (6-28) seemed comparable in surface activity with Surfacten (Surfactant-TA), a modified surfactant preparation which has been used for the treatment of respiratory distress syndrome.

High-yield purification of lung surfactant proteins sp-b and sp-c and the effects on surface activity

Several protocols for purification of milligram quantities of lung surfactant proteins (SP)-B and SP-C were studied for separation efficiency and surface activity of the isolated proteins recombined with synthetic phospholipids (SPL). SP-B and SP-C were obtained from calf lung surfactant extract by C8 chromatography with isocratic elution by either of three solvent systems: 7:1:0.4 MeOH/CHCl(3)/5% 0.1 M HCl (solvent A), 7:1 MeOH/CHCl(3)+ 0.1% TFA (solvent B), and 7:1:0.4 MeOH/CHCl(3)/H(2)O + 0.1% TFA (solvent C). Solvents A and C yielded pure apoprotein in a single pass, with estimated total protein recoveries of >85 and >90%, respectively. Solvent B was less effective in purifying SP-B and SP-C, had a lower recovery efficiency, and gave isolates with less surface activity. Mixtures of SPL plus SP-B eluted with solvents A and C adsorbed to equilibrium surface tensions of 21-22 mN/m and reached minimum surface tensions <1 mN/m during dynamic cycling. Mixtures of SPL with SP-C obtained with solvents A and C had equilibrium surface tensions of 26-27 mN/m and minimum dynamic values of 2-7 mN/m. The ability to obtain milligrams of virtually lipid-free SP-B and SP-C in a single column pass will facilitate research on their biological, structural, and biophysical properties.

Selective labeling of pulmonary surfactant protein SP-C in organic solution

Pulmonary surfactant protein SP-C has been isolated from porcine lungs and treated with dansyl isothiocyanate in chloroform:methanol 2:1 (v/v) solutions,under conditions optimized to introduce a single dansyl group covalently attached to the N-terminalamine group of the protein without loss of its native thioesther-linked palmitic chains. The resulting derivative Dans-SP-C conserves the secondary structure of native SP-C as well as the ability to promote interfacial adsorption of DPPC suspensions and to affect the thermotropic behavior of DPPC bilayers. This derivative can be used to characterize lipid-protein and protein-protein interactions of a native-like SP-C in lipid/protein complexes.

Surface activity in vitro: role of surfactant proteins

Pattle, who provided some of the initial direct evidence for the presence of pulmonary surfactant in the lung, was also the first to show surfactant was susceptible to proteases such as trypsin. Pattle concluded surfactant was a lipoprotein. Our group has investigated the roles of the surfactant proteins (SP-) SP-A, SP-B, and SP-C using a captive bubble tensiometer. These studies show that SP-C>SP-B>SP-A in enhancing surfactant lipid adsorption (film formation) to the equilibrium surface tension of approximately 22-25 mN/m from the 70 mN/m of saline at 37 degrees C. In addition to enhancing adsorption, surfactant proteins can stabilize surfactant films so that lateral compression induced through surface area reduction results in the lowering of surface tension (gamma) from approximately 25 mN/m (equilibrium) to values near 0 mN/m. These low tensions, which are required to stabilize alveoli during expiration, are thought to arise through exclusion of fluid phospholipids from the surface monolayer, resulting in an enrichment in the gel phase component dipalmitoylphosphatidylcholine (DPPC). The results are consistent with DPPC enrichment occurring through two mechanisms, selective DPPC adsorption and preferential squeeze-out of fluid components such as unsaturated phosphatidylcholine (PC) and phosphatidylglycerol (PG) from the monolayer. Evidence for selective DPPC adsorption arises from experiments showing that the surface area reductions required to achieve gamma near 0 mN/m with DPPC/PG samples containing SP-B or SP-A plus SP-B films were less than those predicted for a pure squeeze-out mechanism. Surface activity improves during quasi-static or dynamic compression-expansion cycles, indicating the squeeze-out mechanism also occurs. Although SP-C was not as effective as SP-B in promoting selective DPPC adsorption, this protein is more effective in promoting the reinsertion of lipids forced out of the surface monolayer following overcompression at low gamma values. Addition of SP-A to samples containing SP-B but not SP-C limits the increase in gamma(max) during expansion. It is concluded that the surfactant apoproteins possess distinct overlapping functions. SP-B is effective in selective DPPC insertion during monolayer formation and in PG squeeze-out during monolayer compression. SP-A can promote adsorption during film formation, particularly in the presence of SP-B. SP-C appears to have a superior role to SP-B in formation of the surfactant reservoir and in reinsertion of collapse phase lipids.

[Expression and characterization of human pulmonary surfactant-associated protein A1 in Saccharomyces cerevisiae]

The cDNA encoding pulmonary surfactant-associated protein A1 (SP-A1) derived from healthy adult's lung was cloned into the pVT102U/alpha, expression vector of Saccharomyces cerevisiae, which contains the yeast alpha-factor signal sequence, leading to the secretion of expressed protein, and then transformed into Saccharomyces cerevisiae S-78 (leu2, ura3, rep4) by electroporation. After 2-3 days culture in adequate pH, the expressed SP-A1 accumulated up to 400 mg/L in supernatant. The pure proteins were obtained by Sephadex G-25, G-75, Sepharose 4B. The expressed recombinant products, 62 kD and 32 kD, reacted to specific antibody using ELISA and Western blot. The SP-A1 protein expressed in Saccharomyces cerevisiae was efficient in enhancing the phagocytosis of E. coli J5 by alveolar macrophages.

Lipid analysis of bronchoalveolar lavage fluid (BAL) by MALDI-TOF mass spectrometry and 31P NMR spectroscopy

Despite the high clinical relevance, only the cellular moiety of bronchoalveolar lavage (BAL) has been intensively investigated and is used for diagnosis purposes. On the other hand, the cell-free fluid is, by far, less characterized. Although this fluid represents a relatively simple mixture of only a few different phospholipids (mainly phosphatidylcholine, phosphatidylglycerol and cholesterol), methods for the routine analysis of these fluids are still lacking. In the present investigation we have applied, for the first time, MALDI-TOF mass spectrometry, as well as 31P NMR spectroscopy to the analysis of organic extracts of bronchoalveolar lavage fluids. BAL from different mammals (rat, minipig, rabbit and man) were investigated and, for means of comparison, organic extracts of lung tissue were also examined. Both applied methods provide fast and reliable information on the lipid composition of the bronchoalveolar lavage. However, despite of its comparably low sensitivity, 31P NMR spectroscopy detects all phospholipid species in a single experiment and with the same sensitivity, whereas MALDI-TOF fails in the detection of phosphatidylethanolamine in the presence of higher quantities of phosphatidylcholine. In contrast, MALDI-TOF mass spectrometry is more suitable for the detection of cholesterol and the determination of the fatty acid composition of the individual phospholipids, especially lysolipids. It will be shown that all BALs exhibit significant, species-dependent differences that mainly concern the content of phosphatidylglycerol and lyso-phosphatidylcholine. It is concluded that both methods are suitable tools in lipid research due to the (in comparison to alternative methods) simplicity of performance.

Concentration-dependent, temperature-dependent non-Newtonian viscosity of lung surfactant dispersions

The bulk shear viscosities of aqueous dispersions of lavaged calf lung surfactant (LS) and its chloroform:methanol extract (CLSE) were measured as a function of concentration, shear rate and temperature. At 10-mg phospholipid per milliliter, dispersions of LS and vortexed CLSE in 0.15 M NaCl (saline) had low viscosities near 1 cp over a range of shear rates from 225 to 1125 s(-1). Lung surfactant viscosity increased with phospholipid concentration and became strongly non-Newtonian with higher values at low shear rates. At 37 degrees C and 40 mg/ml, LS and vortexed CLSE in saline had viscosities of 38 and 34 cp (77 s(-1)) and 12 and 7 cp (770 s(-1)), respectively. Viscosity values for LS and CLSE were dependent on temperature and, at fixed shear, were lower at 23 degrees C than at 37 or 10 degrees C. Hysteresis was also present in viscosity measurements depending on whether shear rate was successively increased or decreased during study. Addition of 5 mM Ca(2+) at 37 degrees C markedly reduced CLSE viscosity at all shear rates and decreased LS viscosity at low shear rates. Dispersion by sonication rather than vortexing increased the viscosity of CLSE at fixed shear, while synthetic phospholipids dispersed by either method had low, relatively Newtonian viscosities. The complex viscous behavior of dispersions of LS and CLSE in saline results from their heterogeneous aggregated microstructure of phospholipids and apoproteins. Viscosity is influenced not only by the aggregate surface area under shear, but also by phospholipid-apoprotein interactions and aggregate structure/deformability. Similar complexities likely affect the viscosities of biologically-derived exogenous surfactant preparations administered to patients in clinical surfactant therapy.

Human surfactant protein a suppresses T cell-dependent inflammation and attenuates the manifestations of idiopathic pneumonia syndrome in mice

We have previously shown an association between growth factor-induced upregulation of surfactant protein (SP)-A and suppression of alveolar inflammation in our murine model of donor T cell-dependent lung dysfunction after bone-marrow transplantation, referred to as idiopathic pneumonia syndrome (IPS). We hypothesized that SP-A protects the lung in vivo from IPS injury by downregulation of alveolar inflammation. Human SP-A (100 microg), purified by n-butanol extraction or preparative isoelectric focusing, was transtracheally instilled on Day 4 after BMT during a time of in vivo donor T-cell activation. At 48 h after treatment, immunohistochemical staining of lung sections showed that SP-A did not alter T cell- dependent cellular infiltration. However, macrophages from SP-A-instilled mice were less injured and spontaneously produced less tumor necrosis factor-alpha than did cells from buffer-instilled mice. Although exogenous SP-A did not significantly alter bronchoalveolar lavage fluid (BALF) high levels of total protein (TP), an inverse correlation between BALF SP-A and TP concentrations (r = -0.65; P = 0.02) was observed in SP-A-treated but not in buffer-instilled mice. The only difference between the effects of the two sources of SP-A was that butanol-extracted SP-A, but not isoelectric focusing-purified SP-A, suppressed the interferon-gamma/nitric oxide pathway. We conclude that SP-A downregulates T cell-dependent alveolar inflammation by multiple pathways leading to decreased IPS injury.

Effects of Stachybotrys chartarum on surfactant convertase activity in juvenile mice

We have shown recently that alveolar type II cells are sensitive to exposure to Stachybotrys chartarum spores, both in vitro and in an in vivo juvenile mouse model. In mice, this sensitivity is manifest in part as a significant increase in the newly secreted, biologically active, heavy aggregate form of alveolar surfactant (H) and the accumulation of the lighter, "metabolically used", biologically inactive alveolar surfactant forms (L(vivo)) in the interalveolar space. Conversion of the heavy, surface-active alveolar surfactant to the light metabolically used, nonsurface active forms is believed to involve the activity of an enzyme, namely convertase, which is thought to be derived from lamellar bodies (LB) in alveolar type II cells. The purpose of this study was to evaluate the effects of S. chartarum spores on mouse H and LB convertase activity by measuring their rates of conversion to L(vivo) using the in vitro surface area cycling technique. It was determined whether there were concurrent changes in the protein and phospholipid concentrations of the raw bronchoalveolar lavage fluid (RL) and LB fractions that could be correlated with changes in convertase activity. Conversions of H to L(vivo) in untreated control mice and saline-, isosatratoxin F-, and Cladosporium cladosporioides-exposed mice were not significantly different (p > 0.05). However, conversion from H to L(vivo) in the mice exposed to S. chartarum spores was significantly higher than all other treatment groups (p < 0.001). LB to L(vivo) conversions in untreated and saline-exposed mice were not significantly different, although they were significantly higher than the H to L(vivo) conversions in these two animal treatment groups (p < 0.005), which supports the position that LB is a source of convertase activity in animals. LB to L(vivo) conversion from C. cladosporioides-, isosatrotoxin F-, and S. chartarum-exposed mice were all significantly depressed (p < 0.003) compared to the LB to L(vivo) conversion values obtained from untreated and saline-exposed mice. Protein concentrations in RL, H, L(vivo), and LB from mice exposed to S. chartarum spores were significantly elevated compared to those from the other treatment groups (p < 0.001). Protein concentration in H isolated from C. cladosporioides-exposed mice was also significantly elevated above untreated and saline control animal levels. Phospholipid concentrations in H isolated from S. chartarum-exposed mice were significantly elevated compared to those from other treatment groups, while LB phospholipid concentrations were significantly increased compared to saline and untreated control animal groups. These results show that S. chartarum spores significantly alter convertase activity in both the H and LB surfactant fractions in juvenile mice and that these changes can be related to changes in protein and phospholipid concentrations in alveolar lavage fractions. As surfactant promotes lung stability by reducing the surface tension of the air-alveolar interface, these results further support our position that inhalation exposure to S. chartarum spores in exposed individuals may lead to altered surfactant metabolism, and possibly to lung dysfunction through diminished alveolar surfactant surface tension attributes, and lung stability.

Immunohistochemical investigation of pulmonary surfactant-associated protein A in fatal poisoning

To evaluate the immunohistochemical distribution of pulmonary surfactant-associated protein A (SP-A) in fatal poisoning in relation to the effects of drugs and poisons on respiratory function, 42 forensic autopsy cases were examined by scoring the staining intensity. The highest scores of SP-A staining, with dense granular deposits (aggregates) in the intra-alveolar space, were observed in fatalities from pancuronium bromide (muscle relaxant) injection and petroleum (butane) gas inhalation. Poisoning with organophosphate pesticides and arsenic (ingestion) showed a second grade SP-A score. However, The SP-A scores were relatively low in ethanol and sedative-hypnotic intoxication. Carbon monoxide intoxication showed a varied degree of SP-A score, and the aggregated SP-A score tended to be higher in cases of lower blood carboxyhemoglobin concentration. A varied SP-A score was also observed in methamphetamine fatalities, in which the score was relatively low in cases with a higher serum drug level. Increase of SP-A was not always associated with the intra-alveolar effusion or hemorrhages. The above-described observations suggested that the immunohistochemical score of SP-A may be a possible indication for intensity and duration of drug/poison-dependent respiratory distress.

Surfactant proteins in bronchoalveolar lavage fluid of horses: assay technique and changes following road transport

An enzyme-linked immunosorbent assay (ELISA) was developed for equine surfactant proteins SP-A and SP-D in bronchoalveolar lavage fluid (BALF). Anti-equine SP-A or SP-D monoclonal antibodies (mAb) were produced by hybridoma technology, purified by the antibody purification reagent, and analysed by Western blotting analysis. The immunoreaction (two-site sandwich ELISA) with a mAb, peroxidase-labelled mAb and BALF sample was carried out simultaneously and analytical recovery and precision were assayed. Six mAb for SP-A and four mAb for SP-D were successfully cloned in limiting dilution to monoclonality. These mAb were reacted with equine SP-A or SP-D on Western blotting analysis. For SP-A, a combination of solid-phase TA08 and horseradish peroxidase (HRP)-conjugated WA28 was found to be more sensitive than other combinations, gave a good dose response and was capable of measuring 0.78 to 100 ng of protein/ml. For SP-D, a combination of solid-phase TD13 and HRP-conjugated WD19 was found to be more sensitive than other combinations, had a good dose response and was capable of measuring 0.78 to 200 ng of protein/ml. The assay was used to determine the effect of 41 hours of road transport on the concentrations of SP-A and SP-D in the BALF of 30 horses. The concentrations of SP-A and SP-D decreased by 55 per cent and 36 per cent, respectively, decreases similar to the decrease in phosphatidylglycerol concentration previously reported by the authors.

Structural characterisation of human proteinosis surfactant protein A

Human surfactant protein-A (SP-A) has been purified from a proteinosis patient and characterised by a combination of automated Edman degradation and mass spectrometry. The complete protein sequence was characterised. The major part of SP-A was shown to consist of SP-A2 gene product, and only a small amount of SP-A1 gene product was shown to be present. A cysteine extension to the N-terminal was indicated by sequence data, but was not definitely proven. All proline residues in the Y position of Gly-X-Y in the collagen-like region were at least partially modified to hydroxy-proline, but no lysine residues were found to be modified. A complex N-linked glycosylation was found on Asn-187 showing great heterogeneity as variants from a mono-antennary to penta-antennary glycosylation with varying amounts of attached pentose were identified. The disulfide bridges in the carbohydrate recognition domain were identified to be in the 1-4, 2-3 pattern common for collectins. Interchain disulfide bridges were discovered between two Cys-48 residues and cysteine residues in the N-terminal region. However, the exact disulfide bridge connections within the bouquet-like ultrastructure could not be established.

Very low surfactant protein C contents in newborn Belgian White and Blue calves with respiratory distress syndrome

We have studied a respiratory distress syndrome (RDS) occurring in newborn calves of the Belgian White and Blue (BWB) breed that represents the large majority of beef cattle in Belgium. Pulmonary surfactant isolated from 14 BWB newborn calves that died from RDS and from 7 healthy controls was analysed for composition and surface activity. An extremely low content or, in some instances, an absence of surfactant protein C (SP-C) was detected in the RDS samples by Western blotting and differential amino acid analysis [0.03+/-0.01% (w/w) relative to total phospholipids, compared with 0.39+/-0.06% for healthy controls (means+/-S.E.M., P < 0.001)]. The contents of surfactant protein B (SP-B) were similar in RDS and control samples. The crude surfactant samples isolated from RDS calves had higher ratios of total protein to total phospholipid, altered phospholipid profiles and lower SP-A contents. Both crude and organic extracts of RDS surfactant samples showed increased dynamic surface tension compared with healthy controls when evaluated with a pulsating-bubble surfactometer. The addition of purified SP-C to organic extracts of RDS surfactant samples lowered surface tension. Strongly decreased levels of mature SP-C associated with fatal RDS and altered surface activity in vitro have, to the best of our knowledge, not been previously reported. The mechanisms underlying RDS and the decrease in SP-C in BWB calves remain to be established.

Influence of modified natural or synthetic surfactant preparations on growth of bacteria causing infections in the neonatal period

Connatal bacterial pneumonia is common in neonates. Animal studies and initial clinical reports indicate that surfactant dysfunction is involved in the pathophysiology of severe neonatal pneumonia. Since respiratory distress syndrome and connatal pneumonia may be difficult to differentiate in the first hours of life, neonates with respiratory failure due to bacterial infections might receive surfactant. Under such conditions surfactant components might be catabolized by bacteria and promote bacterial growth. We therefore investigated the influence of three modified natural (Curosurf, Alveofact, and Survanta) and two synthetic (Exosurf and Pumactant) surfactant preparations on the growth of bacteria frequently cultured from blood or tracheal aspirate fluid in the first days of life. Group B streptococci (GBS), Staphyloccocus aureus, and Escherichia coli were incubated in a nutrient-free medium (normal saline) for 5 h at 37 degrees C, together with different surfactants at concentrations of 0, 1, 10, and 20 mg/ml. With the exception of E. coli, incubation in saline alone led to a variable decrease in CFU. In the presence of Alveofact, Exosurf, and Pumactant the decline in bacterial numbers was less marked than in saline alone. Curosurf was bactericidal in a dose-dependent fashion for GBS and had a strong negative impact on the growth of a GBS subtype that lacked the polysaccharide capsule. In contrast, Survanta (10 and 20 mg/ml) significantly promoted the growth of E. coli, indicating that surfactant components may actually serve as nutrients. We conclude that bacterial growth in different surfactant preparations is influenced by microbial species and the composition and dose of the surfactant. Further studies are necessary to elucidate the mechanisms behind our findings and to evaluate the effects of surfactant on bacterial growth in vivo.

Pulmonary surfactant is altered during mechanical ventilation of isolated rat lung

OBJECTIVE

To test the hypothesis that the lung injury induced by certain mechanical ventilation strategies is associated with changes in the pulmonary surfactant system.

DESIGN

Analysis of the pulmonary surfactant system from isolated rat lungs after one of four different ventilatory strategies.

SETTING

A research laboratory at a university.

SUBJECTS

A total of 45 Sprague-Dawley rats.

INTERVENTIONS

Isolated lungs were randomized to either no ventilation (0-TIME) or to ventilation at 40 breaths/min in a humidified 37 degrees C chamber for either 30 mins or 120 mins with one of the following four strategies: a) control (CON, 7 mL/kg, 3 cm H2O positive end-expiratory pressure); b) medium volume, zero end-expiratory pressure (MVZP, 15 mL/kg, 0 cm H2O end-expiratory pressure); c) medium volume, high positive end-expiratory pressure (MVHP, 15 mL/kg, 9 cm H2O positive end-expiratory pressure); and d) high volume, zero end-expiratory pressure (HVZP, 40 mL/kg, 0 cm H2O end-expiratory pressure).

MEASUREMENTS

Pressure-volume curves were determined before and after the ventilation period, after which the lungs were lavaged for surfactant analysis.

MAIN RESULTS

Compared with 0-TIME, 30 mins of ventilation with the HVZP strategy or 120 mins of ventilation with CON and MVZP strategies caused a significant decrease in compliance. Groups showing a decreased compliance had significant increases in the amount of surfactant, surfactant large aggregates, and total lavage protein compared with 0-TIME.

CONCLUSIONS

A short period of injurious mechanical ventilation can cause a decrease in lung compliance that is associated with a large influx of proteins into the alveolar space and with alterations of the pulmonary surfactant system. The changes of surfactant in these experiments are different from those seen in acute lung injury, indicating that they may represent an initial response to mechanical ventilation.

Lipopeptide preparation and analysis

Lipophilic peptides and proteins present specific problems during preparation and analysis which require the use of modified methodology. This chapter discusses some of the methods that have been employed in the isolation and structural studies of the pulmonary surfactant-associated proteins B and C (SP-B and SP-C), other proteins with lipid-like physicochemical properties, and the SP-B precursor. In particular, methods for separation and analysis of peptide/lipid mixtures, high-resolution separation of lipopeptides, analysis of fatty acylated peptides, and secondary and tertiary structure analysis of lipopeptides are discussed.

Lung surfactant protein A provides a route of entry for respiratory syncytial virus into host cells

Lung surfactant protein A (SP-A) has a central role in host defense mediated by the interaction of surface carbohydrates of inhaled pathogens with the lectin domains of SP-A. Respiratory syncytial virus (RSV), the most important viral pathogen of neonates and infants, encodes a highly glycosylated attachment protein, G. Binding studies were performed with G-protein from RSV (human, A2 strain) and human SP-A. The effect of SP-A on the interaction between RSV and host cells was determined by two methods: an infectivity study with monolayers of Hep-2C cells and by interleukin-8 (IL-8) release from buffy coat (BC) cells. SP-A binds to RSV G-protein in a concentration-dependent manner that is inhibitable by both ethylenediamine tetraacetic acid (EDTA) and mannan, indicating that binding is through the carbohydrate recognition domain of the SP-A and a carbohydrate moiety of the G-protein. The level of RSV infection of Hep-2C cells increases with increasing concentrations of SP-A. The amount of IL-8 released by BC cells in the presence of RSV is increased with SP-A concentrations of 2.9 microg/mL or greater. Our results show that SP-A enhances the attachment of RSV and subsequent entry into host cells. The effect of SP-A on viral uptake by epithelial cells and macrophage may determine both innate and adaptive immune responses to RSV.

Self-aggregation of surfactant protein A

Environmental factors of physiological relevance such as pH, calcium, ionic strength, and temperature can affect the state of self-aggregation of surfactant protein A (SP-A). We have studied the secondary structure of different SP-A aggregates and analyzed their fluorescence characteristics. (a) We found that self-aggregation of SP-A can be Ca(2+)-dependent. The concentration of Ca(2+) needed for half-maximal self-association (K(a)(Ca)()2+) depended on the presence of salts. Thus, at low ionic strength, K(a)(Ca)()2+ was 2.3 mM, whereas at physiological ionic strength, K(a)(Ca)()2+ was 2.35 microM. Circular dichroism and fluorescence measurements of Ca(2+)-dependent SP-A aggregates indicated that those protein aggregates formed in the absence of NaCl are structurally different from those formed in its presence. (b) We found that self-aggregation of SP-A can be pH-dependent. Self-aggregation of SP-A induced by H(+) was highly influenced by the presence of salts, which reduced the extent of self-association of the protein. The presence of both salts and Ca(2+) attenuated even more the effects of acidic media on SP-A self-aggregation. (c) We found that self-aggregation of SP-A can be temperature-dependent. At 20 degrees C, SP-A underwent self-aggregation at physiological but not at low ionic strength, in the presence of EDTA. All of these aggregates were dissociated by either adding EDTA (a), increasing the pH to neutral pH (b), or increasing the temperature to 37 degrees C (c). Dissociation of Ca(2+)-induced protein aggregates at low ionic strength was accompanied by an irreversible loss of both SP-A secondary structure and SP-A-dependent lipid aggregation properties. On the other hand, temperature-dependent experiments indicated that a structurally intact collagen-like domain was required for either Ca(2+)- or Ca(2+)/Na(+)-induced SP-A self-aggregation but not for H(+)-induced protein aggregation.

Surfactant protein A exhibits inhibitory effect on eosinophils IL-8 production

Eosinophils are believed to be one of the important sources of cytokines such as IL-8 at the site of allergic inflammation. It has been demonstrated that pulmonary surfactant protein A (SP-A) plays a potential role in modifying inflammation and the immune function. To verify the regulating effect of SP-A on eosinophil cytokine generation, we studied the effect of SP-A by determining of IL-8 production and expression stimulated with sIgA or PMA. SP-A purified from surfactant recovered from patients with alveolar proteinosis was added to eosinophils isolated by the negative selection method with immunomagnetic beads, and cultured for 24 h. The concentrations of IL-8 in the cell-free supernatants and cell lysates were then measured by ELISA. We also used a semiquantitative reverse transcriptase-polymerase chain reaction assay to detect the effect of SP-A on IL-8 mRNA expression. SP-A inhibited the secretion of IL-8 in a dose-dependent fashion. Suppression of IL-8 production by SP-A was significantly inhibited by SP-A antibody (PE10). SP-A also attenuated expression of IL-8 mRNA in eosinophils. These results indicate that SP-A might have the potential role to modify allergic inflammation by inhibiting IL-8 expression and production from eosinophils.

Intracellular localization of processing events in human surfactant protein B biosynthesis

Surfactant protein B (SP-B) is essential to the function of pulmonary surfactant and to alveolar type 2 cell phenotype. Human SP-B is the 79-amino acid product of extensive post-translational processing of a 381-amino acid preproprotein. Processing involves modification of the primary translation product from 39 to 42 kDa and at least 3 subsequent proteolytic cleavages to produce the mature 8-kDa SP-B. To examine the intracellular sites of SP-B processing, we carried out immunofluorescence cytochemistry and inhibitor studies on human fetal lung in explant culture and isolated type 2 cells in monolayer culture using polyclonal antibodies to human SP-B(8) (Phe(201)-Met(279)) and specific epitopes within the N- (NFProx, Ser(145)-Leu(160); NFlank Gln(186)-Gln(200)) and C-terminal (CFlank, Gly(284)-Ser(304)) propeptides of pro-SP-B. Fluorescence immunocytochemistry using epitope-specific antisera showed colocalization of pro-SP-B with the endoplasmic reticulum resident protein BiP. The 25-kDa intermediate was partially endo H-sensitive, colocalized with the medial Golgi resident protein MG160, and shifted into the endoplasmic reticulum in the presence of brefeldin A, which interferes with anterograde transport from endoplasmic reticulum to Golgi. The 9-kDa intermediate colocalized in part with MG160 but not with Lamp-1, a transmembrane protein resident in late endosomes and lamellar bodies. Brefeldin A induced a loss of colocalization between MG160 and NFlank, shifting NFlank immunostaining to a juxtanuclear tubular array. In pulse-chase studies, brefeldin A blocked all processing of 42-kDa pro-SP-B whereas similar studies using monensin blocked the final N-terminal processing event of 9 to 8 kDa SP-B. We conclude that: 1) the first enzymatic cleavage of pro-SP-B to the 25-kDa intermediate is in the brefeldin A-sensitive, medial Golgi; 2) cleavage of the 25-kDa intermediate to a 9-kDa form is a trans-Golgi event that is slowed but not blocked by monensin; 3) the final cleavage of 9 to 8 kDa SP-B is a monensin-sensitive, post-Golgi event occurring prior to transfer of SP-B to lamellar bodies.

Quantitative analysis of hydrophobic pulmonary surfactant proteins by high-performance liquid chromatography with light-scattering detection

A new method for the separation and quantification of two hydrophobic lung surfactant proteins (SPs) is described. It is based on size-exclusion chromatography using the apolar stationary phase butyl silicagel with a pore size of 30 nm and isocratic elution with chloroform, methanol and trifluoroacetic acid. The samples were prepared from sheep lung lavage fluid by centrifugation and fractional extraction with butanol and chloroform-methanol. The chromatograms show three peaks in the elution order SP-B, SP-C and lipids. A small peak ahead of SP-B, which disappeared after reduction with 2-mercaptoethanol, was oligomeric SP-B. The response of the evaporative light-scattering detector was non-linear. For preparative high-performance liquid chromatography ultraviolet detection at 279 nm is recommended.

Structural characterization of human and bovine lung surfactant protein D

Human and bovine surfactant proteins D (SP-D) were purified from late amniotic fluid and bronchioalveolar lavage on the basis of its Ca(2+)-dependent affinity for maltose. The molecular mass of a trimeric subunit was determined by matrix-assisted laser desorption ionization MS to lie in the range 115-125 kDa for human SP-D and 110-123 kDa for bovine SP-D. A single polypeptide chain was determined at 37-41 and 36-40 kDa for the human and bovine species respectively. The major parts of the primary structures of both SP-D molecules were determined by a combination of MS and Edman degradation. The heterogeneity in SP-D was caused mainly by a high number of post-translational modifications in the collagen-like region. Proline and lysine residues were partly hydroxylated and lysine residues were further O-glycosylated with the disaccharide galactose-glucose. A partly occupied N-linked glycosylation site was characterized in human SP-D. The carbohydrate was determined as a complex type bi-antennary structure, with a small content of mono-antennary and tri-antennary structures. No sialic acid residues were present on the glycan, but some had an attached fucose and/or an N-acetylglucosamine residue linked to the core. Bovine SP-D was determined as having a similar structure.

Multiple mechanisms of lung surfactant inhibition

We studied the mechanisms by which C16:0 lysophosphatidylcholine (LPC) and albumin inhibit the surface activity of calf lung surfactant extract (CLSE) by using a pulsating bubble apparatus with a specialized hypophase exchange system, plus adsorption and Wilhelmy balance measurements. In the absence of inhibitors, CLSE (1 mg phospholipid/mL) reached minimum surface tension (gamma(min)) < 1 mN/m within 5 min of bubble pulsation at 20 cycles/min at 37 degrees C. Mixtures of CLSE:LPC had impaired surface activity depending on LPC content: gamma(min) was raised to 5 mN/m by 14 wt % LPC, to 15 mN/m by 25-30 wt% LPC, and to >20 mN/m (67 wt % LPC), even at high CLSE concentrations (3 and 6 mg phospholipid/mL). In contrast, inhibition of CLSE by albumin was more easily abolished when surfactant concentration was raised. Mixtures of albumin (3 mg/mL) and CLSE (1 mg phospholipid/mL) had gamma(min) >20 mN/m, but normal values of gamma(min) < 1 mN/m were reached at higher CLSE concentration (3 mg phospholipid/mL) even when albumin concentration was increased 8-fold to 24 mg/mL. In hypophase exchange studies, LPC, but not albumin, was able to penetrate preformed CLSE surface films and raise gamma(min) CLSE surface films with gamma(min) < 1 mN/m were isolated by an initial hypophase exchange with saline, and a second exchange with an LPC-containing hypophase raised gamma(min) to approximately 10 mN/m. CLSE surface films retained the ability to reach gamma(min) < 1 mN/m in analogous hypophase exchange studies with albumin. The ability of LPC to penetrate surface films of CLSE, although albumin could not, was also demonstrated in adsorption experiments in a Teflon dish, where diffusion was minimized by subphase stirring. Wilhelmy balance experiments also demonstrated that LPC could mix and interact with CLSE or dipalmitoyl phosphatidylcholine in solvent-spread surface films. The ability of LPC or other cell membrane lipids to penetrate interfacial films and raise gamma(min) even at high surfactant concentration may increase their inhibitory actions during acute lung injury.

Biophysical characterization and modeling of lung surfactant components

The present study characterizes the dynamic interfacial properties of calf lung surfactant (CLS) and samples reconstituted in a stepwise fashion from phospholipid (PL), hydrophobic apoprotein (HA), surfactant apoprotein A (SP-A), and neutral lipid fractions. Dipalmitoylphosphatidylcholine (DPPC), the major PL component of surfactant, was examined for comparison. Surface tension was measured over a range of oscillation frequencies (1-100 cycles/min) and bulk phase concentrations (0.01-1 mg/ml) by using a pulsating bubble surfactometer. Distinct differences in behavior were seen between samples. These differences were interpreted by using a previously validated model of surfactant adsorption kinetics that describes function in terms of 1) adsorption rate coefficient (k1), 2) desorption rate coefficient (k2), 3) minimum equilibrium surface tension (gamma*), 4) minimum surface tension at film collapse (gammamin), and 5) change in surface tension with interfacial area for gamma < gamma* (m2). Results show that DPPC and PL have k1 and k2 values several orders of magnitude lower than CLS. PL had a gammamin of 19-20 dyn/cm, significantly greater than CLS (nearly zero). Addition of the HA to PL restored dynamic interfacial behavior to nearly that of CLS. However, m2 remained at a reduced level. Addition of the SP-A to PL + HA restored m2 to a level similar to that of CLS. No further improvement in function occurred with the addition of the neutral lipid. These results support prior studies that show addition of HA to the PL markedly increases adsorption and film stability. However, SP-A is required to completely normalize dynamic behavior.

Biophysical activity of an artificial surfactant containing an analogue of surfactant protein (SP)-C and native SP-B

Natural surfactant preparations containing phospholipids and the hydrophobic surfactant proteins B and C (SP-B and SP-C) are effective in the treatment of respiratory distress syndrome in premature infants. The limited supply, and the risk of infectious agents and immunological reactions have promoted the evaluation of synthetic peptides in surfactant preparations. However, the folding of synthetic SP-C into an alpha-helix is inefficient and alpha-helical SP-C analogues with Val-->Leu substitutions form oligomers. In order to circumvent these problems we have synthesized an SP-C analogue, named SP-C(LKS), which differs from SP-C mainly by the exchange of most of the Val residues in positions 16-28 with Leu residues to promote an alpha-helical conformation, and by the introduction of Lys residues at positions 17, 22 and 27 in order to locate positive charges around the helical circumference and thereby avoid self polymerization. CD spectroscopy showed a spectrum typical for alpha-helical peptides and SDS/PAGE disclosed a single band. The biophysical activity of artificial surfactant preparations containing SP-C(LKS) and phospholipids, with and without native SP-B, was measured using a Wilhelmy balance and a pulsating bubble surfactometer. SP-C(LKS) (3%, w/w) in a mixture of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/phosphatidylglycerol/palmitic acid (68:22:9, by wt.) suspended in 150 mM NaCl, showed rapid spreading at the air-liquid interface and produced a surface tension of <1 mN/m at minimum bubble size (gammamin) and 42 mN/m at maximum bubble size (gammamax) in the pulsating bubble surfactometer. The addition of 2% (w/w) SP-B to the preparation reduced the maximum surface tension to 33-35 mN/m, i.e. both gammamin and gammamax values were similar to those of natural surfactant preparations. Optimal in vitro characteristics were also obtained from a preparation containing SP-C(LKS), SP-B, DPPC and phosphatidylglycerol, i.e. when palmitic acid was omitted from the lipid mixture. SP-B containing surfactant preparations made up in Hepes buffer at pH 6.9, instead of in 150 mM NaCl, had similar biophysical activity provided that palmitic acid was omitted, but decreased activity in the presence of palmitic acid.

Damage to surfactant-specific protein in acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) develops in association with many serious medical disorders. Mortality is at least 40%, and there is no specific therapy. A massive influx of activated neutrophils, which damage pulmonary vascular endothelium and alveolar epithelium, leads to alveolar oedema and pulmonary surfactant dysfunction. In-vitro studies show that neutrophil elastase can cleave surfactant-specific proteins and impair surfactant function. If this happens in vivo in ARDS, the response to surfactant therapy will be limited.

METHODS

Samples of pulmonary surfactant were obtained from the lungs of 18 patients with ARDS and six healthy controls by bronchoalveolar lavage. We separated proteins in these samples according to molecular weight by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). We then used western blotting with monoclonal antibody E8 to detect the major surfactant-specific protein A (SP-A).

FINDINGS

By contrast with controls, 14 of 18 patients had evidence of in-vivo damage to SP-A that resembled damage caused to SP-A when it is cleaved by neutrophil elastase. Controls showed a single band of normal dimers at 66 kDa, whereas 14 of 18 patients showed multiple bands at 66 kDa, 55 kDA, and 30-36 kDa, and six showed additional bands at 36-40 kDa.

INTERPRETATION

Direct damage to surfactant-specific proteins occurs in lungs of patients with ARDS, probably by proteolysis. Trials of protein-containing therapeutic surfactant are in progress in ARDS, and our results indicate that the frequent failure to maintain response may result from continuing damage to surfactant by products of activated neutrophils. A combination of surfactant and antiprotease therapy may improve therapeutic prospects.

Sulfuric acid aerosol induces changes in alveolar surface tension in the guinea pig but not in the rat

The purpose of this study was to investigate the effects of an acid aerosol, at high concentration, on the surface properties of the extracellular fluid lining the airways and alveolae. Guinea pigs and rats were exposed to 43 mg/m3 and 94 mg/m3 of sulfuric acid aerosol mass median aerodynamic diameter (MMAD) 0.9 micron or water aerosol (control), respectively, for 4 hours in an exposure chamber. Surfactant material was extracted from bronchoalveolar lavage fluid (BAL) by centrifugation, and phospholipid, protein, and cell concentrations measured. The extract was reconstituted to 300 micrograms/mL of phospholipid, and its surface properties assessed with a captive bubble surfactometer. The minimum surface tension for the acid-exposed guinea pig BAL was 12.1 +/- 8.48 (mean +/- SD) mN/m, which was significantly higher than the control group, 2.0 +/- 0.43 (mean +/- SD) or the acid-exposed rats, 1.29 +/- 0.11 (mean +/- SD). The change in film area obtained by compressing the film from equilibrium surface tension (25 mN/m) to its minimum value (gamma min) was 62.9 +/- 13.83 (mean +/- SD)% for acid-exposed guinea pigs, compared to 16.3 +/- 5.77 (mean +/- SD)% for the control guinea pigs. The most sensitive index of surfactant inhibition was found to be the maximum film compressibility (Cmax) of the compression isotherm. This index was 119 times greater for the acid-exposed guinea pigs compared to control animals. These abnormalities were associated with an elevation of total protein (0.95 +/- 0.33 [mean +/- SD] mg/mL compared to 0.13 +/- 0.03 [mean +/- SD] mg/mL in controls) and polymorphonuclear leucocytes in the BAL. There was no change in total phospholipids. By contrast BAL retrieved from rats exposed to approximately twice the concentration of acid aerosol showed no cellular nor biochemical abnormalities and its surface tension properties were normal. We conclude that the abnormalities of surfactant activity in the acid-exposed guinea pigs result from the cellular and humoral responses of acute lung injury rather than a direct effect of acid.

Glycoprotein-340 binds surfactant protein-A (SP-A) and stimulates alveolar macrophage migration in an SP-A-independent manner

Glycoprotein-340 (gp-340) was first identified as a surfactant protein (SP)-D-binding molecule purified from lung lavage of patients with alveolar proteinosis (Holmskov, et al., J. Biol. Chem. 1997;272:13743). In purifying SP-A from proteinosis lavage, we isolated a protein that copurifies with SP-A and SP-D and that was later found by protein sequencing to be gp-340. We have shown that soluble gp-340 binds SP-A in a calcium-dependent manner independent of the lectin activity of SP-A. To examine the functional significance of this interaction, we tested the ability of soluble gp-340 to block SP-A binding to and stimulation of the chemotaxis of alveolar macrophages. We found that gp-340 does not affect the binding of SP-A to alveolar macrophages over a wide range of SP-A concentrations, nor does it inhibit the ability of SP-A to stimulate macrophage chemotaxis. We also found that gp-340 alone stimulates the random migration (chemokinesis) of alveolar macrophages in a manner independent of SP-A-stimulated chemotaxis. These results suggest that gp-340 is not a cell-surface receptor necessary for SP-A stimulation of chemotaxis, and show that gp-340 can directly affect macrophage function.

Effects of endotoxin on surfactant protein A and D stimulation of NO production by alveolar macrophages

Surfactant protein (SP) A and SP-D affect numerous functions of immune cells including enhancing phagocytosis of bacteria and production of reactive species. Previous studies have shown that SP-A and SP-D bind to a variety of bacteria and to the lipopolysaccharide (LPS) components of their cell walls. In addition, purified preparations of SPs often contain endotoxin. The goals of this study were 1) to evaluate the effects of SP-A and SP-D and complexes of SPs and LPS on the production of nitric oxide metabolites by rat alveolar macrophages and 2) to evaluate methods for the removal of endotoxin with optimal recovery of SP. Incubation of SP-A or SP-D with polymyxin, 100 mM N-octyl-beta-D-glucopyranoside, and 2 mM EDTA followed by dialysis was the most effective method of those tested for reducing endotoxin levels. Commonly used storage buffers for SP-D, but not for SP-A, inhibited the detection of endotoxin. There was a correlation between the endotoxin content of the SP-A and SP-D preparations and their ability to stimulate production of nitrite by alveolar macrophages. SP-A and SP-D treated as described above to remove endotoxin did not stimulate nitrite production. These studies suggest that the functions of SP-A and SP-D are affected by endotoxin and illustrate the importance of monitoring SP preparations for endotoxin contamination.

Purification and biochemical characterization of equine pulmonary surfactant protein D

OBJECTIVE

To characterize surfactant protein D (SP-D) isolated from bronchoalveolar lavage fluid (BALF) of healthy horses.

SAMPLE POPULATION

BALF from 10 Thoroughbreds (5 males, 5 females; 26 to 40 months old) without history or clinical signs of respiratory tract disease.

PROCEDURE

BALF was obtained and centrifuged at 33,000 X g. The supernatant was applied to a mannose-Sepharose 6B affinity column in the presence of calcium, and the bound protein fraction was analyzed by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblot analysis; amino acid composition was determined and partial sequencing was done. Phospholipid binding and liposome aggregation assay were performed, using purified proteins.

RESULTS

The protein isolated by use of mannose affinity matrices was SP-D. It bound carbohydrates and phosphatidylinositol, which are the characteristic features of SP-D isolated from other animal species. Amino acid analysis and partial primary sequence of the isolated protein indicated high homology with rat and human SP-D. Furthermore, immunoblot analysis indicated that equine SP-D reacted with human and rat SP-D-specific antibodies.

CONCLUSION AND CLINICAL RELEVANCE

SP-D exists in equine lungs; its measurement may be useful in evaluating equine lung disease.

Purification and biochemical characterization of pulmonary surfactant protein A of horses

OBJECTIVE

To characterize surfactant protein isolated from bronchoalveolar lavage fluids of healthy horses.

ANIMALS

10 Thoroughbreds (5 males, 5 females; 26 to 40 months old) that did not have a history or clinical signs of respiratory tract disease.

PROCEDURE

Bronchoalveolar lavage fluid (BALF) was obtained and centrifuged at 33,000 X g. Lipid was removed from precipitated fractions by means of extraction with 1-butanol, and organic solvent-insoluble protein precipitates were dialyzed against Tris buffer. The suspension was centrifuged, and supernatant was placed in a mannose-Sepharose affinity column, with calcium. The bound protein fraction was analyzed by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western immunoblot analysis, and amino acid sequencing. A liposome-aggregation assay was also performed, using purified proteins.

RESULTS

Protein isolated by use of mannose-affinity matrices was identified as surfactant protein A (SP-A). It had carbohydrate-binding and phospholipid-aggregation properties characteristic of SP-A isolated from other animal species. The partial primary sequence of the isolated protein had high homology with rat and human SP-A. Furthermore, the equine SP-A reacted with anti-human and anti-rat SP-A specific antibodies.

CONCLUSION

Analysis of these findings indicated the existence of SP-A in pulmonary tissues of horses.

CLINICAL RELEVANCE

Measurement of SP-A concentrations may be useful for clinicians evaluating pulmonary disease of horses.

Neutral lipids induce critical behavior in interfacial monolayers of pulmonary surfactant

We have shown previously that lateral compression of pulmonary surfactant monolayers initially induces separation of two phases but that these remix when the films become more dense (1). In the studies reported here, we used fluorescence microscopy to examine the role of the different surfactant constituents in the remixing of the separated phases. Subfractions containing only the purified phospholipids (PPL), the surfactant proteins and phospholipids (SP&PL), and the neutral and phospholipids (N&PL) were obtained by chromatographic separation of the components in extracted calf surfactant (calf lung surfactant extract, CLSE). Compression of the different monolayers produced nonfluorescent domains that emerged for temperatures between 20 and 41 degreesC at similar surface pressures 6-8 mN/m higher than values observed for dipalmitoyl phosphatidylcholine (DPPC), the most prevalent component of pulmonary surfactant. Comparison of the different preparations showed that the neutral lipid increased the total nonfluorescent area at surface pressures up to 25 mN/m but dispersed that total area among a larger number of smaller domains. The surfactant proteins also produced smaller domains, but they had the opposite effect of decreasing the total nonfluorescent area. Only the neutral lipids caused remixing. In images from static monolayers, the domains for N&PL dropped from a maximum of 26 +/- 3% of the interface at 25 mN/m to 4 +/- 2% at 30 mN/m, similar to the previously reported behavior for CLSE. During continuous compression through a narrow range of pressure and molecular area, in N&PL, CLSE, and mixtures of PPL with 10% cholesterol, domains became highly distorted immediately prior to remixing. The characteristic transition in shape and abrupt termination of phase coexistence indicate that the remixing caused by the neutral lipids occurs at or close to a critical point.

An endogenous peptide isolated from the gut, NK-lysin, stimulates insulin secretion without changes in cytosolic free Ca2+ concentration

We have recently isolated and cloned a novel endogenous peptide from pig intestine, NK-lysin (NKL). In the present study we show that NKL (1-100 nM) potently and reversibly stimulates insulin secretion in rat pancreatic islets and in the beta-cell line HIT T15. This effect of NKL was not accompanied by changes in cytoplasmic free calcium concentration. The stimulatory activity of NKL on insulin release was also observed in permeabilized islets under Ca2+-clamped conditions. Preincubation of HIT T15 cells with NKL for 1 h or 24 h did not influence cell viability. Possible mechanisms of insulinotropic activity of NKL are discussed.

Surfactant proteins A and D: disease markers

The abundant and restricted expression of surfactant proteins SP-A and SP-D within the lung makes these collectins specific markers for lung diseases. The measurement of SP-A and SP-D in amniotic fluids and tracheal aspirates reflects lung maturity and the production level of the lung surfactant in infants with respiratory distress syndrome (RDS). The SP-A concentrations in bronchoalveolar lavage (BAL) fluids are significantly decreased in patients with acute respiratory distress syndrome (ARDS) and also in patients at risk to develop ARDS. The prominent increase of these proteins in BAL fluids and sputum is diagnostic for pulmonary alveolar proteinosis (PAP). The concentrations of SP-A and SP-D in BAL fluids from patients with idiopathic pulmonary fibrosis (IPF) and interstitial pneumonia with collagen vascular diseases (IPCD) are rather lower than those in healthy controls and the SP-A/phospholipid ratio may be a useful marker of survival prediction. SP-A and SP-D appear in the circulation in specific lung diseases. Their serum concentrations significantly increase in patients with PAP, IPF and IPCD. The successive monitoring of serum levels of SP-A and SP-D may predict the disease activity. The serum SP-A levels increase in patients with ARDS. SP-A is also a marker for lung adenocarcinomas and can be used to differentiate lung adenocarcinomas from other types and metastatic cancers from other origins, and to detect metastasis of lung adenocarcinomas.

Interactions of surfactant protein D with pathogens, allergens and phagocytes

Surfactant protein D (SP-D) is considered to play an important role in innate immunity in the lungs by binding, via its multiple C-type lectin domains, to carbohydrate structures present on a range of viruses, bacteria, yeasts and fungi. The resulting agglutination of the target pathogens provides host defence which can be further enhanced by killing and clearance mechanisms mediated by phagocytic cells which carry receptors for SP-D. Recent findings suggest that SP-D, and the structurally related lung surfactant protein A (SP-A), may also modulate allergic reactions by binding certain glycosylated allergens. The finding of SP-D at a variety of other sites besides the lungs, such as the gastric mucosae, is suggestive that it may play a general protective role in several secretions.

Interactions of surfactant protein A with epithelial cells and phagocytes

Surfactant protein A (SP-A) has been shown to bind to and regulate the functions of both alveolar type II cells and immune cells including alveolar macrophages. The interaction of SP-A with type II cells has been shown in vitro to inhibit lipid secretion and to promote the uptake of lipid by these cells and these observations led to the hypothesis that SP-A plays an important role in regulating surfactant turnover and metabolism. The finding that mice made deficient in SP-A by homologous recombination (SP-A -/- mice) have relatively normal surfactant pool sizes has raised the possibility that either redundant mechanisms function in vivo to keep pool sizes normal in the absence of SP-A or that the in vitro findings are not significant in the context of the whole, unstressed animal. The interaction of SP-A with immune cells has been shown to affect a variety of responses which, in general, function to promote host defense against infection. Although SP-A receptors have been identified, additional studies will be required to elucidate the mechanism of interaction of SP-A with these cells and the relative importance of the different receptors in SP-A mediated regulation of cell function.