New Findings
What is the central question of this study?
It is reported that polymorphism of the gene for pulmonary surfactant‐associated protein B (SFTPB) is associated with chronic obstructive ...pulmonary disease (COPD): what are the function and mechanism of action of SFTPB in COPD?
What is the main finding and its importance?
Under stimulation of the risk factors of COPD, SFTPB expression is decreased, which may be involved in the formation of COPD. The progress of COPD induces an inflammatory response and reduces SFTPB expression. Levels of prostaglandin‐endoperoxide synthase‐2 (PTGS2) and inflammatory responses are changed by SFTPB, which indicates that SFTPB promotes the progression of COPD by PTGS2 and inflammation.
Pulmonary surfactant‐associated protein B (SFTPB) is a critical protein for lung homeostasis, and polymorphism of its gene is associated with chronic obstructive pulmonary disease (COPD). However, few studies have so far confirmed the functional involvement of SFTPB in COPD. Serum SFTPB and inflammatory cytokine levels were measured in 54 patients with acute exacerbation of COPD and 29 healthy controls. A549 cells were induced using 10% cigarette smoke extract (CSE) and treated with dexamethasone to investigate the effect of inflammation on SFTPB expression, and the effect of SFTPB overexpression and silencing on inflammatory cytokines was measured using real‐time PCR and enzyme‐linked immunosorbent assay. SFTPB expression was assessed in mouse lung tissues using immunofluorescence. Serum levels of SFTPB were significantly lower in COPD patients than in controls (P = 0.009). Conversely, levels of interleukin (IL)‐6 and prostaglandin‐endoperoxide synthase‐2 (PTGS2) were increased in COPD patients (IL‐6: P = 0.006; PTGS2: P = 0.043). After CSE treatment, SFTPB mRNA and protein levels were significantly decreased compared to controls (mRNA: P = 0.002; protein: P = 0.011), while IL‐6, IL‐8 and PTGS2 were elevated. Dexamethasone treatment increased SFTPB levels. Following overexpression of SFTPB in A549 cells, mRNA and protein levels of IL‐6, IL‐8 and PTGS2 were significantly reduced, while gene silencing induced the opposite effect. SFTPB levels were significantly reduced in the lung tissue of a mouse model of COPD compared to controls. Reduced SFTPB levels may induce PTGS2 and inflammatory responses in COPD and SFTPB could be a key protein for evaluation of COPD progression.
The glucagon-like peptide-1 receptor (GLP-1R) is found in a variety of tissues outside of the pancreas. For example, GLP-1R is expressed in the lung, where it has been implicated in the regulation of ...the lipid fraction of surfactants, suggesting it fulfills an important role in lung function. Here, we show that GLP-1R expression is strongly up-regulated immediately after birth in neonatal rats, particular in male offspring. Moreover, administering long half-life GLP-1R agonists to the mother from gestational day 14 to birth (exendin-4 or liraglutide) increased surfactant protein (SP)-A and SP-B mRNA expression and the amount of SPs in the amniotic fluid at the end of pregnancy. These effects were similar or more potent to those induced by the glucocorticoid dexamethasone, which also increased GLP-1R expression in fetuses just before delivery. Lir increased fetal SP-A and GLP-1R expression in control rats and in a nitrofen-induced model of lung hypoplasia. Moreover, lung size increased in controls after Lir administration, which also prevented the decrease in lung weight and the poor neonatal survival of the offspring from nitrofen-treated dams, effects that were not produced by dexamethasone. Taken together, our results demonstrate the importance of the GLP-1 system in regulating SP production and lung development.
There is clear evidence that environmental exposures and genetic predisposition contribute to the pathogenesis of idiopathic pulmonary fibrosis (IPF). Cigarette smoking increases the risk of ...developing IPF several-fold, as do other exposures such as metal-fume and wood-dust exposure. Occupations that increase the risk of IPF are agricultural work, hairdressing, and stone polishing, supporting the role of environmental exposure in disease pathogenesis. Genetic predisposition to IPF is evident from its familial aggregation and the fact that pulmonary fibrosis develops in several rare genetic disorders. Mutations in surfactant proteins lead to pulmonary fibrosis and are associated with endoplasmic reticulum stress in alveolar type II epithelial cells. Mutations in telomerase have been found in several families with IPF, and shortened telomeres are found in sporadic cases of IPF. A common variant in mucin 5B predisposes to both familial and sporadic IPF and is present in the majority of cases, indicating sporadic IPF occurs in those with genetic predisposition.
Purpose
Acute respiratory distress syndrome (ARDS) is a major cause of hypoxemic respiratory failure in adults. In ARDS extensive inflammation and leakage of fluid into the alveoli lead to ...dysregulation of pulmonary surfactant metabolism and function. Altered surfactant synthesis, secretion, and breakdown contribute to the clinical features of decreased lung compliance and alveolar collapse. Lung function in ARDS could potentially be restored with surfactant replacement therapy, and synthetic surfactants with modified peptide analogues may better withstand inactivation in ARDS alveoli than natural surfactants.
Methods
This study aimed to investigate the activity in vitro and the bolus effect (200 mg phospholipids/kg) of synthetic surfactant CHF5633 with analogues of SP‐B and SP‐C, or natural surfactant Poractant alfa (Curosurf
®
, both preparations Chiesi Farmaceutici S.p.A.) in a severe ARDS model (the ratio of partial pressure arterial oxygen and fraction of inspired oxygen,
P/F
ratio ≤ 13.3 kPa) induced by hydrochloric acid instillation followed by injurious ventilation in adult New Zealand rabbits. The animals were ventilated for 4 h after surfactant treatment and the respiratory parameters, histological appearance of lung parenchyma and levels of inflammation, oxidative stress, surfactant dysfunction, and endothelial damage were evaluated.
Results
Both surfactant preparations yielded comparable improvements in lung function parameters, reductions in lung injury score, pro-inflammatory cytokines levels, and lung edema formation compared to untreated controls.
Conclusions
This study indicates that surfactant replacement therapy with CHF5633 improves lung function and lung architecture, and attenuates inflammation in severe ARDS in adult rabbits similarly to Poractant alfa. Clinical trials have so far not yielded conclusive results, but exogenous surfactant may be a valid supportive treatment for patients with ARDS given its anti-inflammatory and lung-protective effects.
Pulmonary surfactant is a mixture of lipids and proteins, consisting of 90% phospholipid, and 10% protein by weight, found predominantly in pulmonary alveoli of vertebrate lungs. Two minor components ...of pulmonary surfactant phospholipids, phosphatidylglycerol (PG) and phosphatidylinositol (PI), are present within the alveoli at very high concentrations, and exert anti-inflammatory effects by regulating multiple Toll like receptors (TLR2/1, TLR4, and TLR2/6) by antagonizing cognate ligand-dependent activation. POPG also attenuates LPS-induced lung injury in vivo. In addition, these lipids bind directly to RSV and influenza A viruses (IAVs) and block interaction between host cells and virions, and thereby prevent viral replication in vitro. POPG and PI also inhibit RSV and IAV infection in vivo, in mice and ferrets. The lipids markedly inhibit SARS-CoV-2 infection in vitro. These findings suggest that both POPG and PI have strong potential to be applied as both prophylaxis and post-infection treatments for problematic respiratory viral infections.
Anionic Pulmonary Surfactant Phospholipids Antagonize Activation of Toll Like Receptors and Inhibit Infection by Respiratory Viruses.
The two major pulmonary surfactant anionic phospholipids (PI and POPG) act as decoy ligands for TLR-receptors and influenza A viruses and RSV. The lipids inhibit SARS-CoV-2 replication. Display omitted
•Pulmonary surfactant phospholipids, PG and PI inhibit activation of multiple TLRs.•The lipids inhibit proinflammatory cytokine production and protect the tissue.•PG and PI have potent anti-viral effects against RSV, influenza A and SARS-CoV-2.•Both POPG and PI significantly inhibit SARS-CoV-2 replication in vitro.•The lipids have strong potential as anti-inflammatory and anti-viral agents.
Acute respiratory distress syndrome (ARDS) is associated with diffuse inflammation, alveolar epithelial damage, and leakage of plasma proteins into the alveolar space, which together contribute to ...inactivation of pulmonary surfactant and respiratory failure. Exogenous surfactant delivery is therefore considered to hold potential for ARDS treatment, but clinical trials with natural derived surfactant or synthetic surfactant containing a surfactant protein C (SP‐C) analogue have been negative. Synthetic surfactant CHF5633, containing analogues of SP‐B and SP‐C, may be effective against ARDS. The aim here was to compare treatment effects of CHF5633 and animal‐derived surfactant poractant alfa in animal model of ARDS. ARDS was induced in adult New Zealand rabbits by mild lung lavages followed by injurious ventilation until respiratory failure (P/F ratio <26.7 kPa). The animals were then treated with intratracheal bolus of 200 mg/kg CHF5633 or poractant alfa (Curosurf®), or air as control. The animals were subsequently ventilated for an additional 4 hr and respiratory parameters were recorded regularly. Postmortem, histological analysis, degree of lung edema, and levels of the cytokines TNFα, IL‐6, and IL‐8 in lung homogenates were evaluated. Both surfactant preparations improved lung function, reduced the levels of pro‐inflammatory cytokines, and degree of lung edema to very similar degrees versus the controls. No significant differences in any of the analyzed parameters were observed between the CHF5633‐ and poractant alfa‐treated groups. This study indicates that single dose of CHF5633 improves lung function and attenuates inflammation as effectively as poractant alfa in experimental ARDS caused by injurious ventilation.
Pulmonary surfactant is a lipid-protein complex that lowers surface tension at the respiratory air-liquid interface, stabilizing the lungs against physical forces tending to collapse alveoli. ...Dysfunction of surfactant is associated with respiratory pathologies such as acute respiratory distress syndrome or meconium aspiration syndrome where naturally occurring surfactant-inhibitory agents such as serum, meconium, or cholesterol reach the lung. We analyzed the effect of hyaluronan (HA) on the structure and surface behavior of pulmonary surfactant to understand the mechanism for HA-promoted surfactant protection in the presence of inhibitory agents. In particular, we found that HA affects structural properties such as the aggregation state of surfactant membranes and the size, distribution, and order/packing of phase-segregated lipid domains. These effects do not require a direct interaction between surfactant complexes and HA and are accompanied by a compositional reorganization of large surfactant complexes that become enriched with saturated phospholipid species. HA-exposed surfactant reaches very high efficiency in terms of rapid and spontaneous adsorption of surfactant phospholipids at the air-liquid interface and shows significantly improved resistance to inactivation by serum or cholesterol. We propose that physical effects pertaining to the formation of a meshwork of interpenetrating HA polymer chains are responsible for the changes in surfactant structure and composition that enhance surfactant function and, thus, resistance to inactivation. The higher resistance of HA-exposed surfactant to inactivation persists even after removal of the polymer, suggesting that transient exposure of surfactant to polymers like HA could be a promising strategy for the production of more efficient therapeutic surfactant preparations.
Background: Pulmonary surfactant is inactivated under pathological conditions, making clinical surfactants fail in respiratory therapies.
Results: Exposure to a hyaluronan meshwork modifies the structure and composition of surfactant.
Conclusion: Transient exposure of surfactant to hyaluronan leads to a higher resistance to inactivation.
Significance: Understanding the effects of polymers as additives in surfactant will allow the development of new therapeutic options.
Pulmonary alveolar proteinosis (PAP) is characterized by filling of the alveolar spaces by lipoprotein-rich material of ill-defined composition, and is caused by molecularly different and often rare ...diseases that occur from birth to old age.
To perform a quantitative lipidomic analysis of lipids and the surfactant proteins A, B, and C in lavage fluids from patients with proteinosis of different causes in comparison with healthy control subjects.
During the last two decades, we have collected BAL samples from patients with PAP due to autoantibodies against granulocyte-macrophage colony-stimulating factor; genetic mutations in CSF2RA (colony-stimulating factor 2 receptor α-subunit), MARS (methionyl aminoacyl-tRNA synthetase), FARSB (phenylalanine-tRNA synthetase, β-subunit), and NPC2 (Niemann-Pick disease type C2); and secondary to myeloid leukemia. Their lipid composition was quantified.
Free cholesterol was largely increased by 60-fold and cholesteryl esters were increased by 24-fold. There was an excessive, more than 130-fold increase in ceramide and other sphingolipids. In particular, the long-chain ceramides d18:1/20:0 and d18:1/24:0 were elevated and likely contributed to the proapoptotic environment observed in PAP. Cellular debris lipids such as phosphatidylethanolamine and phosphatidylserine were only moderately increased, by four- to sevenfold. The surfactant lipid class phosphatidylcholine expanded 17-fold, lysophosphatidylcholine expanded 54-fold, and the surfactant proteins A, B, and C expanded 144-, 4-, and 17-fold, respectively. These changes did not differ among the various diseases that cause PAP.
This insight into the alveolar lipidome may provide monitoring tools and lead to new therapeutic strategies for PAP.
Lung surfactant (LS) is an essential system supporting the respiratory function. Cholesterol can be deleterious for LS function, a condition that is reversed by the presence of the lipopeptide SP-C. ...In this work, the structure of LS-mimicking membranes has been analyzed under the combined effect of SP-C and cholesterol by deuterium NMR and phosphorus NMR and by electron spin resonance. Our results show that SP-C induces phase segregation at 37°C, resulting in an ordered phase with spectral features resembling an interdigitated state enriched in dipalmitoylphosphatidylcholine, a liquid-crystalline bilayer phase, and an extremely mobile phase consistent with small vesicles or micelles. In the presence of cholesterol, POPC and POPG motion seem to be more hindered by SP-C than dipalmitoylphosphatidylcholine. The use of deuterated cholesterol did not show signs of specific interactions that could be attributed to SP-C or to the other hydrophobic surfactant protein SP-B. Palmitoylation of SP-C had an indirect effect on the extent of protein-lipid perturbations by stabilizing SP-C structure, and seemed to be important to maximize differences among the lipids participating in each phase. These results shed some light on how SP-C-induced lipid perturbations can alter membrane structure to sustain LS functionality at the air-liquid interface.
Limited supply and complicated manufacturing procedure of animal-derived surfactants make the development of synthetic surfactants warranted. The synthesis of surfactant protein (SP)-B and SP-C is ...complicated and several analogues have been developed. Mini-BLeu is an analogue that corresponds to the first and last helix of SP-B joined by a loop and linked by 2 disulphide bridges. SP-C33Leu is an SP-C analogue that can be cost-efficiently produced, but no such analogue has yet been described for SP-B.
To design short SP-B analogues which lack disulphide bridges, are easy to produce and are efficacious in a preterm rabbit fetus model of neonatal RDS.
Synthetic surfactants were prepared by adding 2 or 8% (w/w) of synthetic variants of Mini-B27, similar to Mini-BLeu but with a short loop, or different peptides covering helix 1 of SP-B to 2% (w/w) of SP-C33Leu in 80 mg/mL of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/egg yolk phosphatidylcholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol, 50: 40: 10 (by weight). Premature newborn rabbit fetuses were treated with 200 mg/kg of the surfactant preparations and ventilated with defined pressures for 30 min without positive end-expiratory pressure. Tidal volumes were registered during the experiments and lung gas volumes were measured at the end of the ventilation period.
Synthetic surfactant containing the Mini-B27 analogue with 2 disulphides gives similar lung gas volumes as treatment with an animal-derived surfactant preparation, but all other SP-B analogues gave lower lung gas volumes. All synthetic surfactants studied gave no significant differences in compliances except the surfactant containing the Mini-B27 analogue without cysteines that performed somewhat better at 30 min.
The helix-loop-helix SP-B analogues tested in this study require the presence of 2 disulphide bridges for optimal activity in a rabbit RDS model.
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