Lung surfactant

The Genetic Basis, Lung Involvement, and Therapeutic Options in Niemann-Pick Disease: A Comprehensive Review

Niemann-Pick Disease (NPD) is a rare autosomal recessive disease belonging to lysosomal storage disorders. Three types of NPD have been described: NPD type A, B, and C. NPD type A and B are caused by mutations in the gene SMPD1 coding for sphingomyelin phosphodiesterase 1, with a consequent lack of acid sphingomyelinase activity. These diseases have been thus classified as acid sphingomyelinase deficiencies (ASMDs). NPD type C is a neurologic disorder due to mutations in the genes NPC1 or NPC2, causing a defect of cholesterol trafficking and esterification. Although all three types of NPD can manifest with pulmonary involvement, lung disease occurs more frequently in NPD type B, typically with interstitial lung disease, recurrent pulmonary infections, and respiratory failure. In this sense, bronchoscopy with broncho-alveolar lavage or biopsy together with high-resolution computed tomography are fundamental diagnostic tools. Although several efforts have been made to find an effective therapy for NPD, to date, only limited therapeutic options are available. Enzyme replacement therapy with Olipudase α is the first and only approved disease-modifying therapy for patients with ASMD. A lung transplant and hematopoietic stem cell transplantation are also described for ASMD in the literature. The only approved disease-modifying therapy in NPD type C is miglustat, a substrate-reduction treatment. The aim of this review was to delineate a state of the art on the genetic basis and lung involvement in NPD, focusing on clinical manifestations, radiologic and histopathologic characteristics of the disease, and available therapeutic options, with a gaze on future therapeutic strategies.

Pulmonary involvement in Niemann-Pick C type 1

Niemann-Pick disease type C (NPC) is a lysosomal storage disorder caused by mutations in either NPC-1 or NPC-2 genes, resulting in abnormal intracellular cholesterol trafficking. The estimated prevalence of NPC disease is 1: 120,000-150,000. Lung involvement has been described in only few patients with NPC, mostly NPC2. We describe a series of 12 patients, originating from six families all homozygotes to the p.R404Q (c.1211G > A) mutation of NPC1 gene; nine of them had significant pulmonary manifestations. All patients were followed in our medical center. Nine of the patients had pulmonary involvement, with recurrent pneumonia as the first manifestation in most, followed by recurrent wheezing episodes and subsequent development of interstitial lung disease with chronic need for oxygen support. Seven patients were reported of having interstitial disease by various imaging modalities.Conclusion: Pulmonary involvement in NPC1 is more common than previously reported. It is characterized as primary obstructive and restrictive lung disease and not only as part of neurologic sequel of NPC. It can lead to respiratory insufficiency and death from respiratory failure. What is Known: • Lung involvement has been described in only few patients with NPC. • Most reported NPC cases with pulmonary involvement were of NPC2. What is New: • Pulmonary involvement in NPC1 is more common than previously reported. • Pulmonary involvement in NPC1 should be considered as part of the disease and be thoroughly assessed and managed.

Targeted Metabolomics Identifies Pharmacodynamic Biomarkers for BIO 300 Mitigation of Radiation-Induced Lung Injury

PURPOSE

Biomarkers serve a number of purposes during drug development including defining the natural history of injury/disease, serving as a secondary endpoint or trigger for intervention, and/or aiding in the selection of an effective dose in humans. BIO 300 is a patent-protected pharmaceutical formulation of nanoparticles of synthetic genistein being developed by Humanetics Corporation. The primary goal of this metabolomic discovery experiment was to identify biomarkers that correlate with radiation-induced lung injury and BIO 300 efficacy for mitigating tissue damage based upon the primary endpoint of survival.

METHODS

High-throughput targeted metabolomics of lung tissue from male C57L/J mice exposed to 12.5 Gy whole thorax lung irradiation, treated daily with 400 mg/kg BIO 300 for either 2 weeks or 6 weeks starting 24 h post radiation exposure, were assayed at 180 d post-radiation to identify potential biomarkers.

RESULTS

A panel of lung metabolites that are responsive to radiation and able to distinguish an efficacious treatment schedule of BIO 300 from a non-efficacious treatment schedule in terms of 180 d survival were identified.

CONCLUSIONS

These metabolites represent potential biomarkers that could be further validated for use in drug development of BIO 300 and in the translation of dose from animal to human.

Clearance in vivo of instilled [h]cholesterol from the rat lung

Phospholipids and lung surfactant proteins are known to be recycled within the lung alveolus mainly by uptake into type II epithelial cells that secrete lipid-enriched lung surfactant. Dipalmitoyl phosphatidylcholine (DPPC) is the major component of lung surfactant lipids and cholesterol is the second most abundant. However, cholesterol turnover in vivo has not been measured and it is not known how long steroidal compounds persist in the lung in intact animals. Here we report on experiments in which radiolabeled cholesterol was instilled into the lungs of rats, then at various postinstillation periods, radioactive sterols in lavage fluid, and in postlavage whole lungs were measured in individual animals. Radioactive sterols in the lungs remained high for a week and were still detectable 46 days later. The clearance rate during the initial postinstillation week was approximately 10% per day. Both radioactive free and esterified sterols were recovered from bronchoalveolar lavage fluid and postlavage lungs.

Surfactant lipids regulate LPS-induced interleukin-8 production in A549 lung epithelial cells by inhibiting translocation of TLR4 into lipid raft domains

In addition to providing mechanical stability, growing evidence suggests that surfactant lipid components can modulate inflammatory responses in the lung. However, little is known of the molecular mechanisms involved in the immunomodulatory action of surfactant lipids. This study investigates the effect of the lipid-rich surfactant preparations Survanta, Curosurf, and the major surfactant phospholipid dipalmitoylphosphatidylcholine (DPPC) on interleukin-8 (IL-8) gene and protein expression in human A549 lung epithelial cells using immunoassay and PCR techniques. To examine potential mechanisms of the surfactant lipid effects, Toll-like receptor 4 (TLR4) expression was analyzed by flow cytometry, and membrane lipid raft domains were separated by density gradient ultracentrifugation and analyzed by immunoblotting with anti-TLR4 antibody. The lipid-rich surfactant preparations Survanta, Curosurf, and DPPC, at physiological concentrations, significantly downregulated lipopolysaccharide (LPS)-induced IL-8 expression in A549 cells both at the mRNA and protein levels. The surfactant preparations did not affect the cell surface expression of TLR4 or the binding of LPS to the cells. However, LPS treatment induced translocation of TLR4 into membrane lipid raft microdomains, and this translocation was inhibited by incubation of the cells with the surfactant lipid. This study provides important mechanistic details of the immune-modulating action of pulmonary surfactant lipids.

Pentastomids and the tetrapod lung

Pentastomids comprise a highly specialized taxon of arthropod-like parasites that probably became adapted to the lungs of amphibians and reptiles early in their long evolutionary history. Few other macroparasites exploit this particular niche. Pentastomids are often large, long-lived and yet they cause little observable pathology in lungs, despite being haematophagous. The lungs of all tetrapods are lined with pulmonary surfactant, a remarkable biological material consisting of a complex mixture of phospholipids, neutral lipids and proteins that has the unique ability to disperse over the air-liquid lining of the lung. In the lower tetrapods it acts as an anti-glue preventing adhesion of respiratory surfaces when lungs collapse during swallowing prey or upon expiration. In mammals, pulmonary surfactant also plays a critical role regulating the activity of alveolar macrophages, the predominant phagocytes of the lower airways and alveoli. This review outlines the evidence suggesting that lung-dwelling pentastomids, and also nymphs encysted in the tissues of mammalian intermediate hosts, evade immune surveillance and reduce inflammation by coating the chitinous cuticle with a their own stage-specific surfactant. The lipid composition of surfactant derived from lung instars of the pentastomid Porocephalus crotali cultured in vitro is very similar to that recovered from the lung of its snake host. Pentastomid surfactant, visualised as lamellate droplets within sub-parietal cells, is delivered to the cuticle via chitin-lined efferent ducts that erupt at a surface density of < 400 mm-2. The fidelity of the system, which ensures that every part of the cuticle surface is membrane-coated, testifies to its strategic importance. Two other extensive glands discharge membrane-associated (hydrophobic ?) proteins onto the hooks and head; some have been purified and partly characterized but their role in minimising inflammatory responses is, as yet, undetermined.

DPPC regulates COX-2 expression in monocytes via phosphorylation of CREB

The major phospholipid in pulmonary surfactant dipalmitoyl phosphatidylcholine (DPPC) has been shown to modulate inflammatory responses. Using human monocytes, this study demonstrates that DPPC significantly increased PGE(2) (P<0.05) production by 2.5-fold when compared to untreated monocyte controls. Mechanistically, this effect was concomitant with an increase in COX-2 expression which was abrogated in the presence of a COX-2 inhibitor. The regulation of COX-2 expression was independent of NF-kappaB activity. Further, DPPC increased the phosphorylation of the cyclic AMP response element binding protein (CREB; an important nuclear transcription factor important in regulating COX-2 expression). In addition, we also show that changing the fatty acid groups of PC (e.g. using l-alpha-phosphatidylcholine beta-arachidonoyl-gamma-palmitoyl (PAPC)) has a profound effect on the regulation of COX-2 expression and CREB activation. This study provides new evidence for the anti-inflammatory activity of DPPC and that this activity is at least in part mediated via CREB activation of COX-2.

Structural characterization of the monolayer-multilayer transition in a pulmonary surfactant model: IR studies of films transferred at continuously varying surface pressures

The four-component system acyl chain perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC)/1,2-dipalmitoylphosphatidylglycerol/ (DPPG)/pulmonary surfactant protein SP-C/cholesterol provides a useful model for in vitro biophysical studies of the reversible monolayer to multilayer transition that occurs during compression <--> expansion cycles in the lung. Monolayer films of this mixture (with chain perdeuterated DPPC-d62) at the air/water interface have been transferred to solid substrates under conditions of continuously varying surface pressure, an approach termed COVASP (continuously varying surface pressures) (Langmuir 2007, 23, 4958). The thermodynamic properties of the Langmuir films have been examined with pressure-area isotherms, while the molecular properties of the film constituents in the transferred films in the monolayer and multilayer phases have been examined with IR spectroscopy. Quantitative intensity measurements of the DPPC-d62, DPPG, and SP-C components in each phase reveal that the DPPG and SP-C constituents are relatively enriched in the multilayer compared with the DPPC-d62, although all three species are present in both phases. Some molecular structure information is available from the surface-pressure-induced variation in IR parameters. The DPPC-d62 exhibits slightly increased conformational order in the multilayer phase as detected from decreases in the CD2 stretching frequencies upon compression, while the lipid phosphate residues become dehydrated, as deduced from increases in the 1245 cm-1 symmetric PO2- stretching frequency. A small increase is observed in the protein amide I frequency; possible interpretations of these changes are presented. The current observations are compared with ideas contained in the "squeeze-out hypothesis" (Handbook of Physiology, The Respiratory System; American Physiological Society Press: Bethesda, MD, 1986; Vol. III, p 247) and in the "liquid crystalline collapse" model (Biophys. J. 2003, 84, 3792). Within the limitation of the current procedures, the data contain elements from both these descriptions of the monolayer transformation. Extensions and possible limitations of the COVASP-IR method are discussed.

STAT3 regulates ABCA3 expression and influences lamellar body formation in alveolar type II cells

ATP-Binding Cassette A3 (ABCA3) is a lamellar body associated lipid transport protein required for normal synthesis and storage of pulmonary surfactant in type II cells in the alveoli. In this study, we demonstrate that STAT3, activated by IL-6, regulates ABCA3 expression in vivo and in vitro. ABCA3 mRNA and immunostaining were decreased in adult mouse lungs in which STAT3 was deleted from the respiratory epithelium (Stat3(Delta/Delta) mice). Consistent with the role of STAT3, intratracheal IL-6 induced ABCA3 expression in vivo. Decreased ABCA3 and abnormalities in the formation of lamellar bodies, the intracellular site of surfactant lipid storage, were observed in Stat3(Delta/Delta) mice. Expression of SREBP1a and 1c, SCAP, ABCA3, and AKT mRNAs was inhibited by deletion of Stat3 in type II cells isolated from Stat3(Delta/Delta) mice. The activities of PI3K and AKT were required for normal Abca3 gene expression in vitro. AKT activation induced SREBP expression and increased the activity of the Abca3 promoter in vitro, consistent with the role of STAT3 signaling, at least in part via SREBP, in the regulation of ABCA3. ABCA3 expression is regulated by IL-6 in a pathway that includes STAT3, PI3K, AKT, SCAP, and SREBP. Activation of STAT3 after exposure to IL-6 enhances ABCA3 expression, which, in turn, influences pulmonary surfactant homeostasis.

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

BACKGROUND

Extensive biochemical and biophysical changes of the pulmonary surfactant system occur in the acute respiratory distress syndrome (ARDS).

METHODS

The effect of intrabronchial administration of a recombinant surfactant protein C-based surfactant preparation (Venticute) on gas exchange, surfactant composition and function was investigated in 31 patients with ARDS in a randomised controlled phase I/II clinical pilot trial. Bronchoalveolar lavage fluids for surfactant analysis were obtained 3 h before and 48 and 120 h after the first surfactant application. Potentially deleterious effects of surfactant neutral lipids in patients with ARDS were also identified.

RESULTS

Before treatment all patients had marked abnormalities in the surfactant phospholipid and protein composition. In response to surfactant treatment, gas exchange improved and surfactant phospholipid and protein content were almost normalised. Alveolar surface activity was dramatically impaired before treatment and only partially improved after surfactant administration. Further analysis of the bronchoalveolar lavage fluids revealed a twofold increase in neutral lipid content and altered neutral lipid profile in patients with ARDS compared with healthy controls. These differences persisted even after administration of large amounts of Venticute. Supplementation of Venticute or natural surfactant with a synthetic neutral lipid preparation, mimicking the profile in ARDS, caused a dose-dependent deterioration of surface activity in vitro.

CONCLUSION

Intrabronchial surfactant treatment improves gas exchange in ARDS, but the efficacy may be limited by increased concentration and altered neutral lipid profile in surfactant under these conditions.

Ischemic and endotoxin pre-conditioning reduce lung reperfusion injury-induced surfactant alterations

BACKGROUND

Pulmonary ischemia/reperfusion injury represents a common clinical phenomenon after lung transplantation, pulmonary embolism, and cardiac surgery with extracorporeal circulation. We investigated the influence of ischemic and endotoxin pre-conditioning on gas exchange and surfactant properties in a canine model of ischemia/reperfusion injury.

METHODS

Twenty-six foxhounds underwent 3 hours of warm ischemia of the left lung, followed by 8 hours of reperfusion. Ischemic pre-conditioning was performed for either 5 minutes (IPC-5) or by 2 10-minute ischemic periods (IPC-10), before ischemia. For endotoxin pre-conditioning, dogs were pre-treated by a daily intravenous application of increasing amounts of endotoxin for 6 days. No pre-conditioning was performed in the controls. Bronchoalveolar lavage was performed before ischemia/reperfusion injury (baseline) and after the 8-hour reperfusion period in the non-injured right and in the reperfused left lung. Bronchoalveolar lavage fluids were analyzed for the phospholipid-protein ratio, the content of large surfactant aggregates, the phospholipid and neutral lipid profile, the surfactant protein (SP) content, and for biophysical activity.

RESULTS

Severe surfactant alterations were observed in the ischemia/reperfusion-injured left lung, with increased protein concentrations and depressed concentrations of large surface aggregates, SP-B, dipalmitoylated phosphatidylcholine, and phosphatidylglycerol. Endotoxin pre-conditioning and IPC-5 were both capable of greatly preventing the ischemia/reperfusion injury-related deterioration of surfactant properties. IPC-10 exerted no effects. Endotoxin pre-conditioning and IPC-5, but not IPC-10, also prevented loss of gas exchange.

CONCLUSIONS

Ischemic and endotoxin pre-conditioning may protect against impairment of gas exchange in ischemia/reperfusion injury by restoring physiological surfactant properties.

Regulation of platelet-activating factor synthesis in human monocytes by dipalmitoyl phosphatidylcholine

Platelet-activating factor (PAF) has a major role in inflammatory responses within the lung. This study investigates the effect of pulmonary surfactant on the synthesis of PAF in human monocytic cells. The pulmonary surfactant preparation Curosurf significantly inhibited lipopolysaccharide (LPS)-stimulated PAF biosynthesis (P<0.01) in a human monocytic cell line, Mono mac-6 (MM6), as determined by (3)H PAF scintillation-proximity assay. The inhibitory properties of surfactant were determined to be associated, at least in part, with the 1,2-dipalmitoyl phosphatidylcholine (DPPC) component of surfactant. DPPC alone also inhibited LPS-stimulated PAF biosynthesis in human peripheral blood monocytes. DPPC treatment did not affect LPS-stimulated phospholipase A(2) activity in MM6 cell lysates. However, DPPC significantly inhibited LPS-stimulated coenzyme A (CoA)-independent transacylase and acetyl CoA:lyso-PAF acetyltransferase activity. DPPC treatment of MM6 cells decreased plasma membrane fluidity as demonstrated by electron paramagnetic resonance spectroscopy coupled with spin labeling. Taken together, these findings indicate that pulmonary surfactant, particularly the DPPC component, can inhibit LPS-stimulated PAF production via perturbation of the cell membrane, which inhibits the activity of specific membrane-associated enzymes involved in PAF biosynthesis.

Role of platelet-activating factor in phosphatidylcholine secretion in primary cultures of rat type II pneumocytes

This study was designed to investigate the effect of platelet-activating factor (PAF) in the secretory response of type II pneumocytes, that are involved in the synthesis and secretion of the pulmonary surfactant. PAF increased phosphatidylcholine secretion in a concentration-dependent manner in the 10(-5) - 10(-10) M range, with a maximum phosphatidylcholine secretion of up to 3.3 fold the basal values (3.4 +/- 0.3% phosphatidylcholine secreted). This effect was prevented by the synthetic PAF-receptor antagonist WEB 2086. A study of the mechanism through which PAF exerts its stimulatory effect was carried out adding different agents that are well known stimulants of phosphatidylcholine secretion. Thus, PAF increased the TPA- and terbutaline-stimulated phosphatidylcholine secretion, that are PKC and PKA activators respectively, suggesting the involvement of both protein kinases in the process. This involvement was further supported by the use of inhibitors of protein kinases and by the stimulation of cAMP production in type II pneumocytes incubated with PAF.

Analysis of lung surfactant model systems with time-of-flight secondary ion mass spectrometry

An often-used model lung surfactant containing dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and the surfactant protein C (SP-C) was analyzed as Langmuir-Blodgett film by spatially resolved time-of-flight secondary ion mass spectrometry (TOF-SIMS) to directly visualize the formation and composition of domains. Binary lipid and lipid/SP-C systems were probed for comparison. TOF-SIMS spectra revealed positive secondary ions (SI) characteristic for DPPC and SP-C, but not for DPPG. SI mapping results in images with domain structures in DPPC/DPPG and DPPG/SP-C, but not in DPPC/SP-C films. We are able to distinguish between the fluid and condensed areas probably due to a matrix effect. These findings correspond with other imaging techniques, fluorescence light microscopy (FLM), scanning force microscopy (SFM), and silver decoration. The ternary mixture DPPC/DPPG/SP-C transferred from the collapse region exhibited SP-C-rich domains surrounding pure lipid areas. The results obtained are in full accordance with our earlier SFM picture of layered protrusions that serve as a compressed reservoir for surfactant material during expansion. Our study demonstrates once more that SP-C plays a unique role in the respiration process.

Inhibitors of sterol biosynthesis and amphotericin B reduce the viability of pneumocystis carinii f. sp. carinii

Pneumocystis carinii synthesizes sterols with a double bond at C-7 of the sterol nucleus and an alkyl group with one or two carbons at C-24 of the side chain. Also, some human-derived Pneumocystis carinii f. sp. hominis strains contain lanosterol derivatives with an alkyl group at C-24. These unique sterols have not been found in other pathogens of mammalian lungs. Thus, P. carinii may have important differences in its susceptibility to drugs known to block reactions in ergosterol biosynthesis in other fungi. In the present study, inhibitors of 3-hydroxy-3-methyglutaryl coenzyme A reductase, squalene synthase, squalene epoxidase, squalene epoxide-lanosterol cyclase, lanosterol demethylase, Delta(8) to Delta(7) isomerase, and S-adenosylmethionine:sterol methyltransferase were tested for their effects on P. carinii viability as determined by quantitation of cellular ATP levels in a population of organisms. Compounds within each category varied in inhibitory effect; the most effective included drugs targeted at squalene synthase, squalene epoxide-lanosterol cyclase, and Delta(8) to Delta(7) isomerase. Some drugs that are potent against ergosterol-synthesizing fungi had little effect against P. carinii, suggesting that substrates and/or enzymes in P. carinii sterol biosynthetic reactions are distinct. Amphotericin B is ineffective in clearing P. carinii infections at clinical doses; however, this drug apparently binds to sterols and causes permeability changes in P. carinii membranes, since it reduced cellular ATP levels in a dose-dependent fashion.

C27 to C32 sterols found in Pneumocystis, an opportunistic pathogen of immunocompromised mammals

Pneumocystis carinii is the paradigm of opportunistic infections in immunocompromised mammals. Prior to the acquired immunodeficiency syndrome (AIDS) pandemic and the use of immunosuppressive therapy in organ transplant and cancer patients, P. carinii was regarded as a curiosity, rarely observed clinically. Interest in this organism exploded when it was identified as the agent of P. carinii pneumonia (PcP), the direct cause of death among many AIDS patients. Aggressive prophylaxis has decreased the number of acute PcP cases, but it remains among the most prevalent opportunistic infections found within this patient population. The taxonomic assignment of P. carinii has long been argued; molecular genetics data now demonstrate that it is a fungus. Several antimycotic drugs are targeted against ergosterol or its biosynthesis, but these are not as effective against PcP as they are against other fungal infections. This can now be explained in part by the identification of the sterols of P. carinii. The organism lacks ergosterol but contains distinct C28 and C29 delta7 24-alkylsterols. Also, 24-methylenelanost-8-en-3beta-ol (C31) and pneumocysterol, (24Z)-ethylidenelanost-8-en-3beta-ol (C32) were recently identified in organisms infecting humans. Together, the delta7 24-alkylsterols and pneumocysterol are regarded as signature lipids of the pathogen that can be useful for the diagnosis of PcP, since no other lung pathogen is known to contain them. Cholesterol (C27), the dominant sterol component in P. carinii, is probably totally scavenged from the host. De novo synthesis of sterols has been demonstrated by the presence of lovastatin-sensitive 3-hydroxy-3-methylglutaryl-CoA reductase activity, the incorporation of radiolabeled mevalonate and squalene into P. carinii sterols, and the reduction in cellular ATP in cells treated with inhibitors of enzymes in sterol biosynthesis.

Involvement of calcium in the stimulation of phosphatidylcholine secretion in primary cultures of rat type II pneumocytes by Escherichia coli lipopolysaccharide

The purpose of this study was to evaluate the mechanism by which Escherichia coli lipopolysaccharide stimulates the secretion of phosphatidylcholine in primary cultures of rat type II pneumocytes. The stimulatory effect of lipopolysaccharide on phosphatidylcholine secretion was additive to those of terbutaline and TPA (protein kinase A and C activators respectively) and this effect was not suppressed by inhibitors of both protein kinases. On the other hand, lipopolysaccharide did not modify the increase on phosphatidylcholine secretion induced by the endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin, and enhanced slightly the calcium-ionophore A23187 stimulated phosphatidylcholine secretion. In addition, the stimulatory effect of lipopolysaccharide was suppressed by BAPTA, an intracellular Ca2+ chelator, and KN-62, a specific inhibitor of Ca2+-calmodulin-dependent protein kinase. These results, together with the lipopolysaccharide-mediated increase in the cytosolic [Ca2+], suggest that stimulation of phosphatidylcholine secretion by lipopolysaccharide in type II pneumocytes occurs by a calcium-dependent transduction mechanism via Ca2+-calmodulin-dependent protein kinase activation.

The inflammatory cytokines tumor necrosis factor alpha and interleukin-1beta stimulate phosphatidylcholine secretion in primary cultures of rat type II pneumocytes

Tumor necrosis factor alpha and interleukin-1beta increase surfactant secretion in type II pneumocytes in a time- and dose-dependent manner. This stimulatory effect was additive to that of lipopolysaccharide, suggesting that cytokines and lipopolysaccharide may exert their actions through different signal transduction pathways. Tumor necrosis factor alpha and interleukin-1beta did not modify the increase on phosphatidylcholine secretion induced by the direct protein kinase C activator tetradecanoylphorbol 13-acetate, whereas this effect was inhibited by the protein kinase C inhibitors bisindolylmaleimide (2 x 10(-6) M) and 1-(5-isoquinolinylsulphonyl)-2-methyl piperazone (10(-4) M). In addition, the stimulatory effect of tumor necrosis factor alpha and interleukin-1beta was not suppressed by the intracellular Ca2+ chelator BAPTA (5 x 10(-6) M) or by KN-62 (3 x 10(-5) M), a specific inhibitor of Ca2+-calmodulin-dependent protein kinase. These results suggest that tumor necrosis factor alpha or interleukin-1beta stimulate phosphatidylcholine secretion via protein kinase C activation in a Ca2+-independent manner.

The structure of a model pulmonary surfactant as revealed by scanning force microscopy

The structures formed by a pulmonary surfactant model system of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and recombinant surfactant-associated protein C (SP-C) were studied using scanning force microscopy (SFM) on Langmuir-Blodgett films. The films appeared to be phase separated, in agreement with earlier investigations by fluorescence light microscopy. There were smooth polygonal patches of mostly lipid, surrounded by a corrugated rim rich in SP-C. When the films were compressed beyond the equilibrium surface pressure, the protein-rich phase mediated the formation of layered protrusions. The height of these multilamellar structures embodied equidistant steps slightly higher than a DPPC double layer in the gel phase. At the air-water interface too, a high compressibility at low surface tension was indicative of the exclusion of matter. The exclusion process proved to be fully reversible. The present study demonstrates that some of the matter of the model pulmonary surfactant can move in and out of the active monolayer. The SFM images revealed a lipid-protein complex that was responsible for the reversible exclusion of double-layer structures. This mechanism may be important in the natural system too, to keep the surface tension of the alveolar air/water interface constantly low over the range of area encountered upon breathing.

Characterizations of neutral lipid fatty acids and cis-9,10-epoxy octadecanoic acid in Pneumocystis carinii carinii

Pneumocystis carinii causes pneumonitis in immunodeficient individuals and is a prevalent opportunistic infection of patients with AIDS. This pathogen resides extracellularly in the hypophase lining the alveolar epithelium, which is highly enriched in lung surfactant lipids. Procedures yielding highly pure organism preparations that enable reliable biochemical analyses of organisms isolated from the lungs of infected laboratory animals have been developed. The results of the present study revealed that the fatty acid profiles of total lipids, the neutral lipid traction, and individual neutral lipid classes of lungs from normal and immunosuppressed rats as well as P. carinii were grossly similar, although some quantitative differences were detected. One qualitative exception found was the detection in P. carinii of the rare fatty acid cis-9,10-epoxy stearic acid, which was not detected in the lipids of rat lungs. The detection of this fatty acid in P. carinii may also have important taxonomic implications. Unlike phospholipids, many of the fatty acids of nonmembrane neutral lipids may be utilized by P. carinii for other cellular functions, such as stored reserves for energy production and precursors for organism-specific membrane lipids. The present study represents the first report of detailed fatty acid analyses of individual neutral lipid classes of this important opportunistic pathogen.

Composition of Pneumocystis carinii neutral lipids and identification of coenzyme Q10 as the major ubiquinone homolog

The lipids of purified preparations of Pneumocystis carinii carinii freshly isolated from infected rats were analyzed and compared with those of whole lungs from normal and methylprednisolone-immunosuppressed uninfected rats. In this study, the neutral lipid fraction was examined in detail; the relative concentrations of individual classes making up this fraction were quantified. Of particular interest was the nature of the organism's ubiquinone (coenzyme Q, CoQ) fraction because atovaquone, a hydroxynaphtho-quinone (566C80) analog of ubiquinone, is efficacious in the treatment of P. carinii pneumonia. The ubiquinone concentration in both P. carinii and lung tissues was relatively low compared to that present in rat heart and liver tissues. Two homologs were identified in the organism: CoQ10 was the predominant homolog with lesser amounts of CoQ9 present. In contrast, the lungs of normal and immunosuppressed uninfected rats had CoQ9 and lesser amounts of CoQ8, but no detectable CoQ10. Furthermore, radiolabeled mevalonic acid was incorporated in vitro into the ubiquinone fraction of P. carinii indicating that the organism has the de novo branch of the isoprenoid biosynthetic pathway leading to polyprenyl formation. Hence, it was concluded that CoQ10 (if not both CoQ10 and CoQ9) in P. carinii was not scavenged from the host but was synthesized by the organism. Although lung tissues contained substantial free fatty acids, the organism was enriched in these lipids. The high concentration of free fatty acids and relatively low level of triglycerides in P. carinii suggest that fatty acids may represent major carbon sources for ATP production by the organism.

Fatty acid composition of the major phospholipids of Pneumocystic carinii: comparison with those in the lungs of normal and methylprednisolone-immunosuppressed rats

Large numbers of viable organisms can be isolated from the corticosteroid-immunosuppressed rat model of Pneumocystis carinii pneumonia. With the development of purification protocols that provide organism preparations of high purity, meaningful lipid biochemical analyses of this important opportunistic pathogen can now be conducted. The phospholipid class composition of the pathogen was reported earlier, together with observations of changes that occur in the rat lungs in response to methylprednisolone immunosuppression treatment. In this report, analyses of the effects of corticosteroids on the fatty acid compositions of the major lung phospholipids, individually isolated and purified by thin-layer chromatography, were elucidated and quantified by gas-liquid chromatography. In response to methylprednisolone, there was a relative increase in palmitate and there were decreases in several unsaturated fatty acids of the rat whole-lung total polar lipids leading to a doubling of the saturation index. Reciprocal changes in the relative concentrations of palmitate and stearate in phosphatidylethanolamine, phosphatidylinositol, lysophosphatidylcholine, and cardiolipin were observed, suggesting that there is tight control of acylation of these phospholipids in the lung. Detailed phospholipid fatty acid analyses were also performed with mixed life cycle stages of P. carinii organisms. The most abundant phospholipids, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, had much higher concentrations of oleic acid and lower concentrations of palmitate in P. carinii than in lung tissue. Sphingomyelin in lung tissue and P. carinii differed from the glycerophospholipids by the presence of high levels of saturated C(22) and C(24) fatty acids. This study represents the most comprehensive fatty acid analysis of rat lung phospholipids and the changes that occur in response to corticosteroid treatment. It is the first report about the fatty acids of individual phospholipids of the opportunistic protist P. carinii carinii.

Inhibition of pulmonary surfactant biophysical activity by cationic polyamino acids

PURPOSE

The purpose of this study is to investigate the interaction of cationic polyamino acids, polylysine and polyarginine, with rat pulmonary surfactant at the air/water interface.

METHODS

Surface pressure measurements of rat pulmonary surfactant in the presence and absence of polyamino acids were carried out in both dynamic and static modes.

RESULTS

In dynamic cycle studies, compression and expansion of adsorbed surfactant films in the presence of the cationic polyamino acids resulted in a delayed attainment of the plateau surface pressure. In area studies of spread surfactant films at constant surface pressure, cationic polyamino acids in the subphase resulted in an increase in film area. Increased film area was also observed when a polyamino acid was injected beneath films of dipalmitoyl-phosphatidylcholine/phosphatidylglycerol. In the presence of the cationic polyamino acids, the equilibrium surface pressure (at constant film area) of pulmonary surfactant was elevated in a concentration- and molecular weight-dependent manner.

CONCLUSIONS

These data indicate that the model cationic peptides interact with surfactant lipid, possibly electrostatically with phosphatidylglycerol. It is concluded that the surface activity of pulmonary surfactant is significantly inhibited by the presence of the polycations, possibly by the formation of a mixed lipid/polyamino acid film.

Effect of Escherichia coli lipopolysaccharide on surfactant secretion in primary cultures of rat type II pneumocytes

The purpose of this study is to evaluate the effect of the Escherichia coli lipopolysaccharide on the secretion of phosphatidylcholine, the principal component of pulmonary surfactant, in primary cultures of rat alveolar type II pneumocytes. Lipopolysaccharide stimulated phosphatidylcholine secretion in a time- and dose-dependent manner. At a concentration of 200 micrograms/ml, lipopolysaccharide stimulated the release of phosphatidylcholine 4-fold over the basal secretory rate, and the concentration producing half the maximal response was 20 micrograms/ml. The stimulatory effect of lipopolysaccharide on phosphatidylcholine secretion was additive to that of the protein kinase C activator TPA, which is a potent stimulator of surfactant secretion. Lipopolysaccharide did not activate protein kinase C, which suggests that stimulation of phosphatidylcholine secretion by the endotoxin was through a mechanism independent of protein kinase C activation.

Exclusion of SP-C, but not SP-B, by gel phase palmitoyl lipids

The interactions of the hydrophobic pulmonary surfactant proteins, SP-C and SP-B, with lipid bilayers were assessed by fluorescence energy transfer. SP-C and SP-B were labeled with the fluorescent probe, succinimidyl nitrobenzoxadiazolyl amino hexanoate (NBD). Fluorescence energy transfer from NBD-SP-C and NBD-SP-B to four distinct indocarbocyanine probes (CnDiI) was utilized to determine the association of the surfactant proteins with various lipid acyl chains. In lipid mixtures including DPPC and DPPG, SP-C was associated with shorter chain and unsaturated lipids below the bulk lipid phase transition. Longer chain saturated CnDiI were excluded from SP-C aggregates. In contrast, SP-B demonstrated little acyl chain preference. The association of SP-C with shorter chain and unsaturated lipids below the bulk phase transition is interpreted to arise from a mismatch in the length of the hydrophobic region of the SP-C alpha-helix relative to the length of the hydrophobic region of dipalmitoyl lipids in the gel phase.

Phospholipid composition of Pneumocystis carinii carinii and effects of methylprednisolone immunosuppression on rat lung lipids

The phospholipid class composition of Pneumocystis carinii carinii freshly isolated from infected lungs generally resembled that of the host lung, suggesting that the parasite scavenges lung alveolar lipids. However, subtle quantitative differences were demonstrated, indicating that the pathogen has the metabolic capacity to de novo synthesize, or at least tailor, its lipids. The concentration of phosphatidylcholine, the major lung surfactant lipid, in the organism was lower than that in lungs of normal and immunosuppressed uninfected rats, and the concentration of phosphatidylinositol was higher. Phosphonolipids were not detected in the organism by chemical analysis and nuclear magnetic resonance spectrometry. The immunosuppressive regimen alone caused increases in both surfactant protein A and the lipid content of the whole lung. The lungs of rats that were subjected to corticosteroid immunosuppression and had heavy parasite loads had dramatically elevated surfactant protein A levels, whereas the lipid contents of these lungs were not different from lipid contents in whole lungs of immunosuppressed uninfected rats. P. carinii was found to concentrate lipids, indicating that a large amount of the lipids in the whole infected rat lung was within the parasites residing in the organ. These observations have important implications relevant to the use of corticosteroid therapy for P. carinii pneumonitis.

Analysis of dipalmitoyl phosphatidylcholine in amniotic fluid by enzymatic hydrolysis and high-performance thin-layer chromatography reflectance spectrodensitometry

A novel test for the determination of dipalmitoyl phosphatidylcholine (DPPC) in amniotic fluid (AF) as free dipalmitoylglycerol (DPG), is described. Aliquots of amniotic fluid were hydrolyzed with Bacilus cereus phospholipase C, and the resulting diglycerides analyzed by AgNO3-modified high-performance thin-layer chromatography (HPTLC)-reflectance spectrodensitometry. This HPTLC system provided resolution of DPG and palmitoylpalmitoleoylglycerol (POG) from other 1,2-diglycerides and cholesterol. The turn-around analysis time for triplicate aliquots of amniotic fluid was 40 min. Recoveries ranged between 90 and 98%. In summary, this method provides a quantitative, specific, highly reproducible, and fast turn-around means of analysis of DPPC in amniotic fluid.

Fatty acid composition of lung, macrophage and surfactant phospholipids after short-term enteral feeding with n-3 lipids

Utilization of enteral feeding modalities may prove clinically relevant for rapid modulation of lung phospholipid polyunsaturated fatty acids (PUFA) that serve as substrates for the formation of vasoactive dienoic eicosanoids. We compared the effects of short-term enteral feeding with formulations enriched with either fish (n-3) or corn (n-6) oil PUFA on the fatty acid composition of rat lung, alveolar macrophage and surfactant phospholipids. The diets were infused continuously for 72 h through a surgically placed gastroduodenal feeding catheter by a syringe pump. The n-3 PUFA derived from the fish oil enriched diet were readily incorporated into the phospholipid membranes of the alveolar macrophages, lung tissue and pulmonary surfactant. The relative percentages of the n-3 PUFA were significantly higher and individual and total n-6 PUFA significantly lower in the macrophage, lung and surfactant phospholipids from the n-3-supplemented rats in comparison with those present in the rats infused enterally with the n-6 diet or untreated, chow-fed rats (baseline). In contrast, there was a significant increase in linoleic acid (18:2n-6) without modification of arachidonic acid (20:4n-6) in the alveolar macrophages, lung tissue and surfactant from rats enterally receiving the n-6 diet relative to levels measured in the rats at baseline. The results suggest that short-term continuous delivery of n-3-enriched enteral preparations can foster rapid modification of membrane phospholipid PUFA composition of lung tissue, alveolar macrophages and lung surfactant.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the presence of "metabolic sterols" in Pneumocystis: identification and initial characterization of Pneumocystis carinii sterols

Mixed life cycle stages of rat-derived Pneumocystis carinii were isolated from host lungs and their sterols were compared with those present in lungs from normal and immunosuppressed uninfected rats. Gas-liquid chromatography consistently detected, resolved, and quantified 9, 10, and 20 sterol components in the total nonsaponifiable neutral lipid fraction of lungs from normal rats, lungs from immunosuppressed uninfected rats, and P. carinii preparations, respectively. In all samples, cholesterol was the most abundant sterol present, comprising 97%, 93%, and 78% of total sterols in lungs from normal rats, lungs from immunosuppressed uninfected rats, and P. carinii, respectively. Tentative identifications of several rat lung and P. carinii minor sterols were made based on gas-liquid chromatogram retention times and fragmentation patterns from mass spectral analyses. Campesterol (ergost-5-en-3-ol), cholest-5-en-3-one, and beta-sitosterol (stigmast-5-en-3-ol) were among the minor components present in both types of lung controls, and were also components of P. carinii sterols. In contrast to lung controls, the sterols of P. carinii were enriched in C28 and C29 sterols with one or two double bonds, and a hydroxyl group at C-3 (ergost-5-en-3-ol, ergost-7-en-3-ol, ergosta-dien-3-ol, stigmast-5-en-3-ol, stigmast-7-en-3-ol and stigmasta-dien-3-ol). Steryl esters of P. carinii, probably stored in cytoplasmic lipid droplets, were dominated by those present in the host lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of Pneumocystis carinii preparations developed for lipid analysis

Pneumocystis carinii organisms were isolated from viral antibody-negative rats that had been infected by intratracheal intubation of organism preparations tested negative for common bacteria and fungi. Infection scores of lungs from infected animals at the time of parasite isolation was > 5 (100-1,000 organisms/oil immersion field). Electron microscopy of heavily infected lungs revealed that the pathogens adhered to Type I pneumocytes and to each other, resulting in obstructions up to several cell layers thick, which extended into the alveolar lumen. Protocols for purifying the organisms were developed to optimize separation from each other and from host cells, and to optimize preparation purity, recovery efficiency, and organism viability. The study tested mucolytic agents, sieving, various centrifugation speeds, lysis of host cells by osmotic shock and filtration through membranes of different pore diameter. Final preparations contained no intact host cells as determined by light microscopy. Only minor amounts (< 5%) of host debris were detected by electron microscopy. Most organisms and their pellicles were ultrastructurally intact but no longer adhered to one another. The final preparation was characterized biochemically by quantitation of the specific lung surfactant marker surfactant protein A, which indicated > 99.5% purity. The total non-P. carinii protein in the final preparation (< 6%, depending on the level of infection) was estimated by the protein content of pelletable material resulting from processing uninfected lungs in an identical manner. Elimination of free cholesterol and phospholipids from host lung tissue was monitored during the purification process. Exogenous stigmasterol, added as an extracellular marker, decreased during the purification process and was undetectable in the final organism preparation. Yields of 10(8)-10(9) organisms/rat were routinely obtained. Viability, assessed by the calcein acetoxymethyl ester-propidium iodide assay, was 80-95%.

Alveolar surfactant and adult respiratory distress syndrome. Pathogenetic role and therapeutic prospects

The adult respiratory distress syndrome (ARDS) is characterized by extended inflammatory processes in the lung microvascular, interstitial, and alveolar compartments, resulting in vasomotor disturbances, plasma leakage, cell injury, and complex gas exchange disturbances. Abnormalities in the alveolar surfactant system have long been implicated in the pathogenetic sequelae of this life-threatening syndrome. This hypothesis is supported by similarities in pulmonary failure between patients with ARDS and preterm babies with infant respiratory distress syndrome, known to be triggered primarily by lack of surfactant material. Mechanisms of surfactant alterations in ARDS include: (a) lack of surface-active compounds (phospholipids, apoproteins) due to reduced generation/release by diseased pneumocytes or to increased loss of material (this feature includes changes in the relative composition of the surfactant phospholipid and/or apoprotein profiles); (b) inhibition of surfactant function by plasma protein leakage (inhibitory potencies of different plasma proteins have been defined); (c) "incorporation" of surfactant phospholipids and apoproteins into polymerizing fibrin upon hyaline membrane formation; and (d) damage/inhibition of surfactant compounds by inflammatory mediators (proteases, oxidants, nonsurfactant lipids). Alterations in alveolar surfactant function may well contribute to a variety of pathophysiological key events encountered in ARDS. These include decrease in compliance, ventilation-perfusion mismatch including shunt flow due to altered gas flow distribution (atelectasis, partial alveolar collapse, small airway collapse), and lung edema formation. Moreover, more speculative at the present time, surfactant abnormalities may add to a reduction in alveolar host defense competence and an upregulation of inflammatory events under conditions of ARDS. Persistent atelectasis of surfactant-deficient and in particular fibrin-loaded alveoli may represent a key event to trigger fibroblast proliferation and fibrosis in late ARDS ("collapse induration"). Overall, the presently available data on surfactant abnormalities in ARDS lend credit to therapeutic trials with transbronchial surfactant administration. In addition to the classical goals of replacement therapy defined for preterm infants (rapid improvement in lung compliance and gas exchange), this approach will have to consider its impact on host defense competence and inflammatory and proliferative processes when applied in adults with respiratory failure.

The surfactant system of the adult lung: physiology and clinical perspectives

Pulmonary surfactant is synthesized and secreted by alveolar type II cells and constitutes an important component of the alveolar lining fluid. It comprises a unique mixture of phospholipids and surfactant-specific proteins. More than 30 years after its first biochemical characterization, knowledge of the composition and functions of the surfactant complex has grown considerably. Its classically known role is to decrease surface tension in alveolar air spaces to a degree that facilitates adequate ventilation of the peripheral lung. More recently, other important surfactant functions have come into view. Probably most notable among these, surfactant has been demonstrated to enhance local pulmonary defense mechanisms and to modulate immune responses in the alveolar milieu. These findings have prompted interest in the role and the possible alterations of the surfactant system in a variety of lung diseases and in environmental impacts on the lung. However, only a limited number of studies investigating surfactant changes in human lung disease have hitherto been published. Preliminary results suggest that surfactant analyses, e.g., from bronchoalveolar lavage fluids, may reveal quantitative and qualitative abnormalities of the surfactant system in human lung disorders. It is hypothesized that in the future, surfactant studies may become one of our clinical tools to evaluate the activity and severity of peripheral lung diseases. In certain disorders they may also gain diagnostic significance. Further clinical studies will be necessary to investigate the potential therapeutic benefits of surfactant substitution and the usefulness of pharmacologic manipulation of the secretory activity of alveolar type II cells in pulmonary medicine.

Effects of lung surfactant proteolipid SP-C on the organization of model membrane lipids: a fluorescence study

Lipid-protein interactions of pulmonary surfactant-associated protein SP-C in model DPPC/DPPG and DPPC/DPPG/eggPC vesicles were studied using steady-state and time-resolved fluorescence measurements of two fluorescent phospholipid probes, NBD-PC and NBD-PG. These fluorescent probes were utilized to determine SP-C-induced lipid perturbations near the bilayer surface, and to investigate possible lipid headgroup-specific interactions of SP-C. The presence of SP-C in DPPC/DPPG membrane vesicles resulted in (1) a dramatic increase in steady-state anisotropy of NBD-PC and NBD-PG at gel phase temperatures, (2) a broadening of the gel-fluid phase transition, (3) a decrease in self-quenching of NBD-PC and NBD-PG probes, and (4) a slight increase in steady-state anisotropy of NBD-PG at fluid phase temperatures. Time-resolved measurements, as well as steady-state intensity measurements indicate that incorporation of SP-C into DPPC/DPPG or DPPC/DPPG/eggPC vesicles results in a increase in the fraction of the long-lifetime species of NBD-PC. The results presented here indicate that SP-C orders the membrane bilayer surface, disrupts acyl chain packing, and may increase the lateral pressure within the bilayer.

The effect of lung surfactant apolipoproteins B/C on the chemical shift anisotropy of sn-2-[1-13C]dipalmitoylphosphatidylcholine

Nuclear magnetic resonance spectroscopy has been used to investigate the effect of the lung surfactant apolipoproteins B/C on dipalmitoylphosphatidylcholine to address the mechanism by which the adsorption rate of phospholipids from the bulk to the air/water interface is enhanced. Apolipoproteins B/C were isolated from bovine lung and separated from associated lipids by lipophilic Sephadex column chromatography. Amino acid analysis indicated the presence of both apolipoproteins B and C. The 13C chemical shift anisotropy of DPPC was determined as a function of temperature. Previous workers (Wittebort et al., Biochemistry, 20 (1981) 3487-3502) have concluded that the observed magnitude of the chemical shift anisotropy of the carbonyl group of the sn-2 acyl chain in pure DPPC is a result of rapid rotation about an axis along the length of the phospholipid both in the gel and liquid crystalline state. The orientation of the carbonyl group with respect to the axis of diffusion, however, undergoes an approximately 25-30 degrees shift in passage from the gel to liquid crystalline state, with the intermediate, rippled (P beta') state composed of an exchange between these two orientations. The presence of physiological concentrations SP-B/C reduced the width of the anisotropy of DPPC below but had no effect on lipids above the main phase transition temperature. This suggests that SP-B/C has a general effect on the entire assembly of lipids. The temperature of the onset of the orientational change is lowered indicating a portion of the lipids are affected by the lung surfactant apolipoproteins.

The lung lectin surfactant protein A aggregates phospholipid vesicles via a novel mechanism

Surfactant protein A (SP-A), a lung-specific glycoprotein, consists of an N-terminal collagen-like domain and a C-terminal domain with a sequence similar to that of several Ca2(+)-dependent lectins. SP-A induces a rapid Ca2(+)-dependent aggregation of phospholipid vesicles. We report here that vesicle aggregation is mediated by Ca2(+)-induced interactions between carbohydrate-binding domains and oligosaccharide moieties of SP-A. This novel mechanism of membrane interactions may be relevant to the formation of the membrane lattice of tubular myelin, an extracellular form of surfactant.

Surface properties and sensitivity to protein-inhibition of a recombinant apoprotein C-based phospholipid mixture in vitro--comparison to natural surfactant

Surfactant alterations due to protein leakage are implicated in the pathogenesis of the adult respiratory distress syndrome. In the present study, surface properties of a palmitic acid containing phospholipid mixture (DPPC: PG: PA/68.5:22.5:9) supplemented with 2% recombinant human surfactant apoprotein C (PLM-Crec) were compared to those of the lipids alone (PLM) and to those of calf lung surfactant extract (CLSE). Experiments were performed in a Wilhelmy balance and in a pulsating bubble surfactometer. Adsorption facilities and dynamic surface tension-lowering properties of the surfactants alone, their sensitivity to the inhibitory effect of fibrinogen (fbg), and their capacity to restore surface properties of fbg-inhibited CLSE were investigated. PLM revealed limited surface activity, was very sensitive to inhibition by fbg and had moderate effect on the surface properties of fbg-inhibited CLSE. In contrast, PLM-Crec and CLSE revealed similar excellent adsorption kinetics and dynamic surface tension lowering properties. Higher percentage of SP-C within the synthetic mixture (up to 10%) or additional admixture of human purified or recombinant SP-A (up to 10%) did not further improve these surface properties. However, PLM-Crec was markedly more sensitive to inactivation by fbg than CLSE. The surface activity of fbg-inhibited CLSE was fully restored by additional admixture of CLSE or PLM-Crec in both the Wilhelmy and the bubble system, with slight superiority of the natural surfactant extract. We conclude that the surface properties of PLM-Crec are clearly superior to those of the apoprotein-free lipid mixture and are similar to those of the natural surfactant extract CLSE. PLM-Crec is markedly more sensitive to inhibition by fibrinogen than CLSE, but possesses nearly equivalent efficacy in restoring the surface properties of fbg-inhibited CLSE as compared to the natural material.

Tumor necrosis factor-alpha inhibits expression of pulmonary surfactant protein

Tumor necrosis factor-alpha (TNF-alpha) decreased the expression of pulmonary surfactant proteins SP-A and SP-B in human pulmonary adenocarcinoma cell lines. The effect of TNF alpha on SP-A content and mRNA in the pulmonary adenocarcinoma cell line, H441-4, was concentration and time dependent. TNF alpha decreased the cellular content of SP-A to less than 10% of control 48 h after addition. TNF alpha decreased de novo synthesis of SP-A and decreased the accumulation of SP-A in media. SP-A mRNA was decreased within 12 h of addition of TNF alpha, with nearly complete loss of SP-A mRNA observed after 24 h. Inhibitory effects of TNF alpha on SP-A mRNA were dose-related with nearly complete inhibition of SP-A mRNA caused by 25 ng/ml TNF alpha. The effects of TNF alpha on SP-A were distinct from the effects of interferon gamma which increased SP-A content approximately twofold in H441-4 cells. TNF alpha also decreased the content of SP-B mRNA. In contrast to the inhibitory effect of TNF alpha on SP-A and SP-B mRNA, TNF alpha increased mRNA encoding human manganese superoxide dismutase (Mn-SOD). TNF alpha did not inhibit growth, alter cell viability or beta-actin mRNA in either cell line. These in vitro studies demonstrate the marked pretranslational inhibitory effects of the cytokine, TNF alpha, on the expression of pulmonary surfactant proteins, SP-A and SP-B. The results support the concept that macrophage-derived cytokines may control surfactant protein expression.

A biophysical study of abscisic acid interaction with membrane phospholipid components

Molecular area/surface pressure Langmuir isotherms of amphiphilic dipalmitoylphosphatidylcholine (DPPC) monolayers indicated that abscisic acid (ABA) has a marked rigidifying effect, expressed as reduction of molecular area and increase of monolayer collapse point. Moreover, ABA markedly increased aqueous droplet hydrophobicity, as indicated by a concentration-dependent increase of contact angle when placed on a hydrocarbon chain surface; no such effects were obtained on either amphiphilic or octadecyltrichlorosilane surfaces. A combination of TLC and mass spectometry revealed the presence of DPPC in Vicia faba and Commelina communis guard-cell protoplast membranes. ABA also increased plasma membrane rigidity as evidenced by probing with lipid specific membrane probes, namely diphenylhexatriene and its trimethyl derivative. Regarded together the results suggest a specific site of ABA binding to DPPC. The linkage between senescence and stomatal closure is discussed in the light of the new data presented here. It is suggested that DPPC in guard-cell membranes may have a physical role in preventing collapse and/or bursting. In this connection an analogy is drawn with pulmonary mechanisms.

Fatty acids stimulate phosphatidylcholine synthesis and CTP:choline-phosphate cytidylyltransferase in type II pneumocytes isolated from adult rat lung

The regulation by cyclic AMP and fatty acids of phosphatidylcholine (PC) synthesis in rat alveolar type II cells was studied. In contrast with results with hepatocytes, cyclic AMP and its potent chlorophenylthio analogue had no inhibitory effect on [Me-14C]choline incorporation into PC in pulse-chase studies with alveolar type II cells. The inclusion of the fatty acids palmitate, oleate or linoleate in the chase incubation medium stimulated the incorporation of [Me-14C]choline into PC by type II cells. The effect of palmitate, which was more pronounced than that of the other fatty acids, appeared to be concentration-dependent. Increased [Me-14C]choline incorporation into PC was paralleled by an accelerated disappearance of the radiolabel from choline phosphate, which is consistent with an activation of CTP:choline-phosphate cytidylyltransferase. This enzyme is considered to be rate-limiting in the synthesis of PC de novo by type II cells. As fatty acids are also substrate for PC synthesis, their effect could also be due to compensation for a fatty acid deficiency. To test this possibility, fatty acid synthesis in the type II cells was stimulated by addition of lactate. Even then, an additional stimulation of PC synthesis by palmitate was observed, which supports the regulatory influence of exogenous fatty acids. Incubation of type II cells in the presence of 0.2 mM-palmitate resulted in a 45% increase in the membrane-bound CTP:choline-phosphate cytidylyltransferase activity, whereas the soluble activity remained unchanged. Choline kinase activity in the soluble fraction increased by 48%. However, the increase in choline kinase is unlikely to be responsible for the increased metabolic flux through the choline phosphate pathway, because there is a relatively large pool of choline phosphate in type II cells. Therefore it is suggested that the microsomal CTP:choline-phosphate cytidylyltransferase is the form of this enzyme which is active in surfactant PC synthesis, and possibly has a regulatory role in this pathway.