Impact of synthetic surfactant CHF5633 with SP-B and SP-C analogues on lung function and inflammation in rabbit model of acute respiratory distress syndrome

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.

Anti-inflammatory effect of a curcumin-aspirin derivative on Ureaplasma-induced cytokine expressions in neonatal monocytes

One of the major contributors to death in infants is infant respiratory distress syndrome (IRDS). The transition from early acute inflammation to fibrotic hyperplasia is important in the development of IRDS. However, there are no available and effective remedies for suppression of the early inflammation. In this study, the effect of a curcumin-aspirin (C-A) derivative on the expressions of interleukin (IL)-10, IL-8, tumor necrosis factor (TNF)-α, IL-1β, toll-like receptor (TLR)4 and TLR2 was investigated in neonatal monocytes exposed to Ureaplasma parvum. The techniques used were qPCR and flow cytometry. The results revealed that C-A exerted anti-inflammatory effects on stimulated monocytes and significantly suppressed Ureaplasma-stimulated changes in IL-8, TNF-α and IL-1β levels. It did not produce any inflammation or apoptosis in the neonatal cells. Moreover, C-A enhanced IL-10 expression and suppressed the expressions of TLR2 and TLR4, indicating that curcumin-aspirin derivative might hold therapeutic potential for early IRDS.

A Combination of Short and Simple Surfactant Protein B and C Analogues as a New Synthetic Surfactant: In Vitro and Animal Experiments

PURPOSE

Pulmonary surfactants for preterm infants contain mostly animal-derived surfactant proteins (SPs), which are essential for lowering surface tension. We prepared artificial pulmonary surfactants using synthetic human SP analogs and performed in vitro and in vivo experiments.

MATERIALS AND METHODS

We synthesized peptide analogues that resemble human SP-B (RMLPQLVCRLVLRCSMD) and SP-C (CPVHLKRLLLLLLLLLLLLLLLL). Dipalmitoylphosphatidylcholine (DPPC), phosphatidylglycerol (PG), and palmitic acid (PA) were added and mixed in lyophilized to render powdered surfactant. Synsurf-1 was composed of DPPC:PG:PA:SP-B (75:25:10:3, w/w); Synsurf-2 was composed of DPPC:PG:PA:SP-C (75:25:10:3, w/w); and Synsurf-3 was composed of DPPC:PG:PA:SP-B:SP-C (75:25:10:3:3, w/w). We performed in vitro study to compare the physical characteristics using pulsating bubble surfactometer and modified Wilhelmy balance test. Surface spreading and adsorption test of the surfactant preparations were measured. In vivo test was performed using term and preterm rabbit pups. Pressure-volume curves were generated during the deflation phase. Histologic findings were examined.

RESULTS

Pulsating bubble surfactometer readings revealed following minimum and maximum surface tension (mN/m) at 5 minutes: Surfacten® (5.5±0.4, 32.8±1.6), Synsurf-1 (16.7±0.6, 28.7±1.5), Synsurf-2 (7.9±1.0, 33.1±1.6), and Synsurf-3 (7.1±0.8, 34.5±1.0). Surface spreading rates were as follows: Surfacten® (27 mN/m), Synsurf-1 (43 mN/m), Synsurf-2 (27 mN/m), and Synsurf-3 (27 mN/m). Surface adsorption rate results were as follows: Surfacten® (28 mN/m), Synsurf-1 (35 mN/m), Synsurf-2 (29 mN/m), and Synsurf-3 (27 mN/m). The deflation curves were best for Synsurf-3; those for Synsurf-2 were better than those for Surfacten®. Synsurf-1 was the worst surfactant preparation. Microscopic examination showed the largest aerated area of the alveoli in the Synsurf-3 group, followed by Synsurf-1 and Surfacten®; Synsurf-2 was the smallest.

CONCLUSION

Synsurf-3 containing both SP-B and SP-C synthetic analogs showed comparable and better efficacy than commercially used Surfacten® in lowering surface tension, pressure-volume curves, and tissue aerated area of the alveoli.

The new generation synthetic reconstituted surfactant CHF5633 suppresses LPS-induced cytokine responses in human neonatal monocytes

BACKGROUND

New generation synthetic surfactants represent a promising alternative in the treatment of respiratory distress syndrome in preterm infants. CHF5633, a new generation reconstituted agent, has demonstrated biophysical effectiveness in vitro and in vivo. In accordance to several well-known surfactant preparations, we recently demonstrated anti-inflammatory effects on LPS-induced cytokine responses in human adult monocytes. The present study addressed pro- and anti-inflammatory effects of CHF5633 in human cord blood monocytes.

METHODS

Purified neonatal CD14(+) cells, either native or simultaneously stimulated with E. coli LPS, were exposed to CHF5633. TNF-α, IL-1β, IL-8 and IL-10 as well as TLR2 and TLR4 expression were analyzed by means of real-time quantitative PCR and flow cytometry.

RESULTS

CHF5633 did not induce pro-inflammation in native human neonatal monocytes and did not aggravate LPS-induced cytokine responses. Exposure to CHF5633 led to a significant decrease in LPS-induced intracellular TNF-α protein expression, and significantly suppressed LPS-induced mRNA and intracellular protein expression of IL-1β. CHF5633 incubation did not affect cell viability, indicating that the suppressive activity was not due to toxic effects on neonatal monocytes. LPS-induced IL-8, IL-10, TLR2 and TLR4 expression were unaffected.

CONCLUSION

Our data confirm that CHF5633 does not exert unintended pro-apoptotic and pro-inflammatory effects in human neonatal monocytes. CHF5633 rather suppressed LPS-induced TNF-α and IL-1β cytokine responses. Our data add to previous work and may indicate anti-inflammatory features of CHF5633 on LPS-induced monocyte cytokine responses.

Impact of the New Generation Reconstituted Surfactant CHF5633 on Human CD4+ Lymphocytes

Background

Natural surfactant preparations, commonly isolated from porcine or bovine lungs, are used to treat respiratory distress syndrome in preterm infants. Besides biophysical effectiveness, several studies have documented additional immunomodulatory properties. Within the near future, synthetic surfactant preparations may be a promising alternative. CHF5633 is a new generation reconstituted synthetic surfactant preparation with defined composition, containing dipalmitoyl-phosphatidylcholine, palmitoyl-oleoyl-phosphatidylglycerol and synthetic analogs of surfactant protein (SP-) B and SP-C. While its biophysical effectiveness has been demonstrated in vitro and in vivo, possible immunomodulatory abilities are currently unknown.

Aim

The aim of the current study was to define a potential impact of CHF5633 and its single components on pro- and anti-inflammatory cytokine responses in human CD4⁺ lymphocytes.

Methods

Purified human CD4⁺ T cells were activated using anti CD3/CD28 antibodies and exposed to CHF5633, its components, or to the well-known animal-derived surfactant Poractant alfa (Curosurf^®). Proliferative response and cell viability were assessed using flow cytometry and a methylthiazolyldiphenyltetrazolium bromide colorimetric assay. The mRNA expression of IFNγ, IL-2, IL-17A, IL-22, IL-4, and IL-10 was measured by quantitative PCR, while intracellular protein expression was assessed by means of flow cytometry.

Results

Neither CHF5633 nor any of its phospholipid components with or without SP-B or SP-C analogs had any influence on proliferative ability and viability of CD4⁺ lymphocytes under the given conditions. IFNγ, IL-2, IL-17A, IL-22, IL-4, and IL-10 mRNA as well as IFNγ, IL-2, IL-4 and IL-10 protein levels were unaffected in both non-activated and activated CD4⁺ lymphocytes after exposure to CHF5633 or its constituents compared to non-exposed controls. However, in comparison to Curosurf^®, expression levels of anti-inflammatory IL-4 and IL-10 mRNA were significantly increased in CHF5633 exposed CD4⁺ lymphocytes.

Conclusion

For the first time, the immunomodulatory capacity of CHF5633 on CD4⁺ lymphocytes was evaluated. CHF5633 did not show any cytotoxicity on CD4⁺ cells. Moreover, our in vitro data indicate that CHF5633 does not exert unintended pro-inflammatory effects on non-activated and activated CD4⁺ T cells. As far as anti-inflammatory cytokines are concerned, it might lack an overall reductive ability in comparison to animal-derived surfactants, potentially leaving pro- and anti-inflammatory cytokine response in balance.

Effects of the New Generation Synthetic Reconstituted Surfactant CHF5633 on Pro- and Anti-Inflammatory Cytokine Expression in Native and LPS-Stimulated Adult CD14+ Monocytes

Background

Surfactant replacement therapy is the standard of care for the prevention and treatment of neonatal respiratory distress syndrome. New generation synthetic surfactants represent a promising alternative to animal-derived surfactants. CHF5633, a new generation reconstituted synthetic surfactant containing SP-B and SP-C analogs and two synthetic phospholipids has demonstrated biophysical effectiveness in vitro and in vivo. While several surfactant preparations have previously been ascribed immunomodulatory capacities, in vitro data on immunomodulation by CHF5633 are limited, so far. Our study aimed to investigate pro- and anti-inflammatory effects of CHF5633 on native and LPS-stimulated human adult monocytes.

Methods

Highly purified adult CD14⁺ cells, either native or simultaneously stimulated with LPS, were exposed to CHF5633, its components, or poractant alfa (Curosurf^®). Subsequent expression of TNF-α, IL-1β, IL-8 and IL-10 mRNA was quantified by real-time quantitative PCR, corresponding intracellular cytokine synthesis was analyzed by flow cytometry. Potential effects on TLR2 and TLR4 mRNA and protein expression were monitored by qPCR and flow cytometry.

Results

Neither CHF5633 nor any of its components induced inflammation or apoptosis in native adult CD14⁺ monocytes. Moreover, LPS-induced pro-inflammatory responses were not aggravated by simultaneous exposure of monocytes to CHF5633 or its components. In LPS-stimulated monocytes, exposure to CHF5633 led to a significant decrease in TNF-α mRNA (0.57 ± 0.23-fold, p = 0.043 at 4h; 0.56 ± 0.27-fold, p = 0.042 at 14h). Reduction of LPS-induced IL-1β mRNA expression was not significant (0.73 ± 0.16, p = 0.17 at 4h). LPS-induced IL-8 and IL-10 mRNA and protein expression were unaffected by CHF5633. For all cytokines, the observed CHF5633 effects paralleled a Curosurf®-induced modulation of cytokine response. TLR2 and TLR4 mRNA and protein expression were not affected by CHF5633 and Curosurf®, neither in native nor in LPS-stimulated adult monocytes.

Conclusion

The new generation reconstituted synthetic surfactant CHF5633 was tested for potential immunomodulation on native and LPS-activated adult human monocytes. Our data confirm that CHF5633 does not exert unintended pro-inflammatory effects in both settings. On the contrary, CHF5633 significantly suppressed TNF-α mRNA expression in LPS-stimulated adult monocytes, indicating potential anti-inflammatory effects.

Development of a Synthetic Surfactant Using a Surfactant Protein-C Peptide Analog: In Vitro Studies of Surface Physical Properties

PURPOSE

Pulmonary surfactant (PS) replacement has been the gold standard therapy for neonatal respiratory distress syndrome; however, almost all commercial PSs contain animal proteins. We prepared a synthetic PS by using a human surfactant protein (SP) analog and evaluated its in vitro properties.

MATERIALS AND METHODS

A peptide sequence (CPVHLKRLLLLLLLLLLLLLLLL) of human SP-C was chosen to develop the peptide analog (SPa-C). The new synthetic SP-C PS (sSP-C PS) was synthesized from SPa-C, dipalmitoyl phosphatidylcholine, phosphatidyl glycerol, and palmitic acid. Physical properties of the sSP-C PS were evaluated by measuring the maximum and minimum surface tensions (STs), surfactant spreading, and adsorption rate. In addition, we recorded an ST-area diagram. The data obtained on sSP-C PS were subsequently compared with those of purified natural bovine surfactant (PNBS), and the commercial product, Surfacten®.

RESULTS

The sSP-C PS and Surfacten® were found to have maximum ST values of 32-33 mN/m, whereas that of PNBS was much lower at 19 mN/m. The minimum ST values of all three products were less than 10 mN/m. The values that were measured for the equilibrium ST of rapidly spreading sSP-C PS, Surfacten®, and PNBS were 27, 27, and 24 mN/m, respectively. The surface adsorptions were found to be the same for all three PSs (20 mN/m). ST-area diagrams of sSP-C PS and Surfacten® revealed similar properties.

CONCLUSION

In an in vitro experiment, the physical properties exhibited by sSP-C PS were similar to those of Surfacten®. Further study is required to evaluate the in vivo efficacy.

New surfactant with SP-B and C analogs gives survival benefit after inactivation in preterm lambs

BACKGROUND

Respiratory distress syndrome in preterm babies is caused by a pulmonary surfactant deficiency, but also by its inactivation due to various conditions, including plasma protein leakage. Surfactant replacement therapy is well established, but clinical observations and in vitro experiments suggested that its efficacy may be impaired by inactivation. A new synthetic surfactant (CHF 5633), containing synthetic surfactant protein B and C analogs, has shown comparable effects on oxygenation in ventilated preterm rabbits versus Poractant alfa, but superior resistance against inactivation in vitro. We hypothesized that CHF 5633 is also resistant to inactivation by serum albumin in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

Nineteen preterm lambs of 127 days gestational age (term = 150 days) received CHF 5633 or Poractant alfa and were ventilated for 48 hours. Ninety minutes after birth, the animals received albumin with CHF 5633 or Poractant alfa. Animals received additional surfactant if P(a)O(2) dropped below 100 mmHg. A pressure volume curve was done post mortem and markers of pulmonary inflammation, surfactant content and biophysiology, and lung histology were assessed. CHF 5633 treatment resulted in improved arterial pH, oxygenation and ventilation efficiency index. The survival rate was significantly higher after CHF 5633 treatment (5/7) than after Poractant alfa (1/8) after 48 hours of ventilation. Biophysical examination of the surfactant recovered from bronchoalveolar lavages revealed that films formed by CHF 5633-treated animals reached low surface tensions in a wider range of compression rates than films from Poractant alfa-treated animals.

CONCLUSIONS

For the first time a synthetic surfactant containing both surfactant protein B and C analogs showed significant benefit over animal derived surfactant in an in vivo model of surfactant inactivation in premature lambs.

Development of lentiviral vectors with regulated respiratory epithelial expression in vivo

Development of gene transfer vectors with regulated, lung-specific expression will be a useful tool for studying lung biology and developing gene therapies. In this study we constructed a series of lentiviral vectors with regulatory elements predicted to produce lung-specific transgene expression: the surfactant protein C promoter (SPC) for alveolar epithelial type II cell (AECII) expression, the Clara cell 10-kD protein (CC10) for Clara cell expression in the airway, and the Jaagskiete sheep retrovirus (JSRV) promoter for expression in both cell types. Transgene expression from the SPC and CC10 vectors was restricted to AECII and Clara cell lines, respectively, while expression from the JSRV vector was observed in multiple respiratory and nonrespiratory cell types. After intratracheal delivery of lentivector supernatant to mice, transgene expression was observed in AECII from the SPC lentivector, and in Clara cells from the CC10-promoted lentivector. Transgene expression was not detected in nonrespiratory tissues after intravenous delivery of CC10 and SPC lentiviral vectors to murine recipients. In summary, incorporation of genomic regulatory elements from the SPC and CC10 genes resulted in respiratory specific transgene expression in vitro and in vivo. These vectors will provide a useful tool for the study of lung biology and the development of gene therapies for lung disorders.

Concentration dependence of a poly-leucine surfactant protein C analogue on in vitro and in vivo surfactant activity

BACKGROUND

Modified natural surfactants currently used for treatment of respiratory distress syndrome contain about 0.5-1% (w/w phospholipids) of each of the surfactant proteins SP-B and SP-C. The supply of these preparations is limited and synthetic surfactant preparations containing lipids and peptides are under development.

OBJECTIVES

To investigate the potential of different concentrations of the SP-C analogue SP-C33 in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (68:31, w/w).

METHODS

Surface activity was evaluated in pulsating and captive bubble surfactometers and in immature newborn rabbits.

RESULTS

Preparations containing >or=1% SP-C33 achieve minimum surface tension <5 mN/m indicating good biophysical activity, and increase tidal volumes in premature rabbit fetuses to the same level as a modified natural surfactant preparation does. Alveolar patency at end expiration, as evaluated by measurement of lung gas volumes, histological assessment of alveolar expansion and determination of alveolar volume density, was lower in the animals treated with synthetic surfactant than in those receiving modified natural surfactant.

CONCLUSIONS

These data suggest that SP-C33 is similarly efficient as the native peptide in improving surface properties of phospholipids mixtures and in increasing lung compliance in surfactant-deficient states, but that other components are needed to maintain alveolar stability at low airway pressures.

Protein- and lipid modification of natural bovine surfactant. Effects in experimental lung failure with special consideration of the response in neonates

Surfactant therapy does not lead to a uniform, optimal and sustained effect on gas exchange in neonatal respiratory distress syndrome (RDS) and acute respiratory distress syndrome (ARDS). The aim of the present study therefore was to compare the effects of a lipid-enriched and protein-modified natural surfactant preparations with a licensed, clinically used bovine surfactant preparation - SF-Ril (Alveofact).

METHODS

SF-Ril was enriched with phosphatidylglycerol, sphingomyeline, phosphatidylethanolamine plasmalogen, phosphatidylethanolamine. Furthermore, SF-Ril was modified with increased surfactant protein B (SP-B)/surfactant protein C (SP-C) content and finally a mercaptoethanol (ME) treated preparation for breaking the sulfhydril bondage of SP-B/SP-C by chemical reduction in methylene chloride using ME was developed. Finally ME was removed by vacuum extraction. These modified surfactants were tested at a dosage of 100 mg/ kg each in a model of respiratory failure induced by lung lavage in male adult rats and compared with SF-Ril at an identical dosage. Mechanical ventilation was standardised with fraction of inspiratory oxygen (FiO2) 1.0 and time-cycled pressure limited ventilation 16/0.8 cmH2O before and 26/6 cmH2O (peak inspiratory pressure/positive endexpiratory pressure) after lung lavage (target arterial oxygen pressure [pa02] < 100 mmHg), respiratory rate 36/min, inspiration/expiration time ratio 1:2.

RESULTS

During the observation period of 120 min, the sphingomyeline substituted and protein-modified (ME reduced) surfactant preparations exerted improved and sustained oxygenation compared with SF-Ril. Similar effects were observed for tidal volumes. All other preparations were equal or inferior to SF-Ril in our model.

CONCLUSION

For the development of surfactant preparations less prone for inactivation the above mentioned data may provide useful information, provided they can be confirmed in further investigations employing other alternative models.

Effects of a recombinant surfactant protein-C-based surfactant on lung function and the pulmonary surfactant system in a model of meconium aspiration syndrome

OBJECTIVE

Meconium aspiration syndrome (MAS) remains a relevant cause of neonatal respiratory failure and is characterized by severe impairment of pulmonary gas exchange, surfactant inactivation, and pronounced inflammatory changes. Surfactant administration has been shown as an effective treatment strategy in MAS. The present study aimed at investigating the impact of a recombinant surfactant protein (SP)-C-based surfactant on pulmonary gas exchange and lung function in this model of neonatal lung injury. Furthermore, SP-B and -C were determined on the transcriptional and protein level.

DESIGN

Laboratory experiment.

SETTING

University laboratory.

SUBJECTS

Twenty three newborn piglets (median age 6 days, weight 1900-2500 g).

INTERVENTIONS

Piglets were intubated and mechanically ventilated and then received 20% sterile meconium (5 mL/kg) for induction of lung injury. After 30 mins, animals were randomized for control (n = 7, MAS controls), recombinant SP-C surfactant (n = 8), or natural surfactant (n = 8). Surfactant preparations were administered as an intratracheal bolus (75 mg/kg), and animals were ventilated for another 330 mins. Nonventilated newborn piglets at term (n = 28; median weight 1484 g, range 720-1990 g) served as a healthy reference group (healthy controls).

MEASUREMENTS AND MAIN RESULTS

Lung function variables, arterial blood gas samples, and lung tissues were obtained. Expression of SP-B and -C messenger RNA was quantified in left lung lobe tissue using real-time polymerase chain reaction. Protein concentrations were determined by enzyme-linked immunosorbent assay. Scanning electron microscopy and transmission electron microscopy were performed in tissue samples of the right lung lobe. Compared with healthy controls, SP-B messenger RNA expression was significantly increased in MAS (p < .02), whereas SP-C messenger RNA expression was found to be significantly reduced (p < .001). SP concentrations, however, were not significantly different. Although a significant improvement of gas exchange and lung function was observed after surfactant administration in both groups, surfactant messenger RNA expression and protein concentrations were not significantly altered. Scanning and transmission electron microscopy showed severe pulmonary ultrastructural changes after meconium aspiration improving after surfactant treatment.

CONCLUSIONS

Impairment of lung function in MAS, associated with marked changes in SP messenger RNA expression, can be sufficiently treated using recombinant SP-C-based or natural surfactant. Despite improved lung function and gas exchange as well as pulmonary ultrastructure after treatment, pulmonary SP messenger RNA expression and concentrations remained significantly affected, giving important insight into the time course following surfactant treatment in MAS.

New Synthetic Surfactants – Basic Science

The hydrophobic surfactant proteins, SP-B and SP-C, promote adsorption of surface-active lipids to the air-liquid interface of the alveoli and are essential for alveolar stability and gas exchange. Synthetic surfactant preparations must contain at least one of these hydrophobic proteins, or analogs thereof, to have optimal effects when administered into the airways of patients with lung diseases. However, development of clinically active artificial surfactants has turned out to be more complicated than initially anticipated since the native hydrophobic proteins are structurally complex or unstable in pure form. The proteins have been replaced by different analogs which have the right conformation without forming oligomers. Increased understanding of the surfactant proteins will hopefully lead to development of effective synthetic surfactants which can be produced in large quantities for treatment of a wide range of respiratory disorders. Furthermore, the lipid composition seems to be important, as well as a high lipid concentration in the suspension. For successful treatment of many respiratory diseases, it is also desirable that the synthetic surfactant resists inactivation by plasma components leaking into the alveoli.

Surfactant protein C: basics to bedside

Development of clinically active synthetic surfactants has turned out to be more complicated than initially anticipated. Surfactant protein analogues must have the right conformation without forming oligomers. Furthermore, the lipid composition, as well as a high lipid concentration in the suspension seem to be important. For successful treatment of many respiratory diseases, it is desirable that the synthetic surfactant may stabilize the alveoli at end-expiration and may resist inactivation by components leaking into the alveoli.

Distinct effects of SP-B and SP-C on the uptake of surfactant-like liposomes by alveolar cells in vivo and in vitro

The effects of surfactant protein B (SP-B) and SP-C on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages were studied both in vivo and in vitro. In vivo, mechanically ventilated rats were intratracheally instilled with fluorescently labeled liposomes that had SP-B and/or SP-C incorporated in different concentrations. Consequently, the alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that the incorporation of SP-B does not influence the uptake, and it also does not in the presence of essential cofactors. The inclusion of SP-C in the liposomes enhanced the alveolar type II cells at a SP-C to lipid ratio of 2:100. If divalent cations (calcium and magnesium) were present at physiological concentrations in the liposome suspension, uptake of liposomes by alveolar macrophages was also enhanced. In vitro, the incorporation of SP-B affected uptake only at a protein-to-lipid ratio of 8:100, whereas the inclusion of SP-C in the liposomes leads to an increased uptake at a protein-to-lipid ratio of 1:100. From these results, it can be concluded that SP-B is unlikely to affect uptake of surfactant, whereas SP-C in combination with divalent cations and other solutes are capable of increasing the uptake.

Nitric oxide synthase‐2 down‐regulates surfactant protein‐B expression and enhances endotoxin‐induced lung injury in mice

Acute respiratory distress syndrome (ARDS) is a life-threatening ailment characterized by severe lung injury involving inflammatory cell recruitment to the lung, cytokine production, surfactant dysfunction, and up-regulation of nitric oxide synthase 2 (NOS2) resulting in nitric oxide (NO) production. We hypothesized that NO production from NOS2 expressed in lung parenchymal cells in a murine model of ARDS would correlate with abnormal surfactant function and reduced surfactant protein-B (SP-B) expression. Pulmonary responses to nebulized endotoxin (lipopolysaccharide, LPS) were evaluated in wild-type (WT) mice, NOS2 null (-/-) mice, and NOS2-chimeric animals derived from bone marrow transplantation. NOS2-/- animals exhibited significantly less physiologic lung dysfunction and loss of SP-B expression than did WT animals. However, lung neutrophil recruitment and bronchoalveolar lavage cytokine levels did not significantly differ between NOS2-/- and WT animals. Chimeric animals for NOS2 exhibited the phenotype of the recipient and therefore demonstrated that parenchymal production of NOS2 is critical for the development of LPS-induced lung injury. Furthermore, administration of NO donors, independent of cytokine stimulation, decreased SP-B promoter activity and mRNA expression in mouse lung epithelial cells. This study demonstrates that expression of NOS2 in lung epithelial cells is critical for the development of lung injury and mediates surfactant dysfunction independent of NOS2 inflammatory cell expression and cytokine production.

Cellular antiendotoxin activities of lung surfactant protein C in lipid vesicles

The respiratory system is continuously exposed to airborne particles containing lipopolysaccharide. Our laboratory established previously that the hydrophobic surfactant protein C (SP-C) binds to lipopolysaccharide and to one of its cellular receptors, CD14. Here we examined the influence of SP-C, and of a synthetic analog, on some cellular in vitro effects of lipopolysaccharide. When associated with vesicles of dipalmitoylphosphatidylcholine, SP-C inhibits the binding of a tritium-labeled lipopolysaccharide to the macrophage cell line RAW 264.7. Under similar conditions of presentation, SP-C inhibits the mitogenic effect of lipopolysaccharide on mouse splenocytes, and inhibits the lipopolysaccharide-induced production of tumor necrosis factor-alpha by peritoneal and alveolar macrophages, and of nitric oxide by RAW 264.7 cells. In contrast, tumor necrosis factor-alpha production induced by a lipopeptide, and nitric oxide production induced by picolinic acid, were not affected by SP-C. The lipopolysaccharide-binding capacity of SP-C is resistant to peroxynitrite, a known mediator of acute lung injury formed by reaction of nitric oxide with superoxide anions. These results indicate that SP-C may play a role in lung defense; SP-C resists degradation under inflammatory conditions and traps lipopolysaccharide, preventing it from inducing production of noxious mediators in alveolar cells.

Monocyte function in preterm, term, and adult sheep

The preterm infant has functionally immature monocytes. The effects of common clinical interventions and exposures that might modulate inflammation were evaluated using monocytes isolated from blood of preterm lambs [130 d gestational age (GA)], near-term lambs (141 d GA), and adult sheep. Endotoxin stimulated hydrogen peroxide production by adult monocytes, but monocytes from 130-d and 141-d GA lambs had a reduced and delayed hydrogen peroxide production. Endotoxin did not decrease apoptosis of monocytes from 130-d and 141-d GA lambs but decreased apoptosis of adult monocytes. Dexamethasone increased the phagocytosis of bacteria and apoptotic cells by adult monocytes by 35% but not by monocytes from 130-d and 141-d GA lambs. Synthetic and natural surfactants and dipalmitoylphosphatidylcholine increased phagocytosis of apoptotic cells by monocytes from preterm, term, and adult sheep. Monocytes from preterm and term lambs differ from adult monocytes in tests of both the initiation and the resolution of inflammation. The reduced phagocytosis of apoptotic cells by monocytes from the preterm may contribute to prolonged inflammation in diseases such as bronchopulmonary dysplasia.

Effects of various forms of surfactant protein C on tidal volume in ventilated immature newborn rabbits

Surfactant protein (SP)-C is characterized by alpha-helix structure and palmitoyl groups attached to two cysteine residues. We examined the function of palmitoylation and dimerization in promotion of tidal volume in immature newborn rabbits. Reconstituted surfactants were made from a mixture of synthetic phospholipids and porcine SP-B (basic mixture) by adding various forms of SP-Cs: normal SP-C isolated from porcine lungs and monomeric or dimeric forms of SP-C. These latter two were isolated from patients with pulmonary alveolar proteinosis and were less palmitoylated. Animals were ventilated at an inspiratory pressure of 25 cmH2O. Median tidal volumes were <2 ml/kg in nontreated controls, 7.7 ml/kg in animals receiving the basic mixture without SP-C, and >18 ml/kg in animals treated with reconstituted surfactants containing 3% normal or 2% dimeric SP-C (P < 0.05 vs. basic mixture). The physiological effect of basic mixture was not improved by monomeric SP-C. We conclude that palmitoyl groups are important for the physiological effects of SP-C and that the dimeric form also improves physiological effects.

Fibrinolysis-inhibitory capacity of clot-embedded surfactant is enhanced by SP-B and SP-C

Incorporation of pulmonary surfactant into fibrin inhibits its plasmic degradation. In the present study we investigated the influence of surfactant proteins (SP)-A, SP-B, and SP-C on the fibrinolysis-inhibitory capacity of surfactant phospholipids. Plasmin-induced fibrinolysis was quantified by means of a (125)I-fibrin plate assay, and surfactant incorporation into polymerizing fibrin was analyzed by measuring the incorporation of (3)H-labeled L-alpha-dipalmitoylphosphatidylcholine into the insoluble clot material. Incorporation of a calf lung surfactant extract (Alveofact) and an organic extract of natural rabbit large surfactant aggregates (LSA) into a fibrin clot revealed a stronger inhibitory effect on plasmic cleavage of this clot than a synthetic phospholipid mixture (PLX) and unprocessed LSA. Reconstitution of PLX with SP-B and SP-C increased, whereas reconstitution with SP-A decreased, the fibrinolysis-inhibitory capacity of the phospholipids. The SP-B effect was paralleled by an increased incorporation of phospholipids into fibrin. We conclude that the inhibitory effect of surfactant incorporation into polymerizing fibrin on its susceptibility to plasmic cleavage is enhanced by SP-B and SP-C but reduced by SP-A. In the case of SP-B, increased phospholipid incorporation may underlie this finding.

Effects of the human pulmonary surfactant protein-C (SP-C), SP-CL16(6-28) on surface activities of surfactants with various phospholipids

We previously reported that a human analogue of pulmonary surfactant protein-C (SP-C), SP-CL16(6-28), with 23 residues was the most active analogue in a reconstituted lipid mixture and had the shortest chain among the poly-leucine-analogues examined. There has been little research on the chemical components of synthetic lung surfactants (SLSs). In the present study, we attempted to compare SLS with various phospholipids in surface activity. That is, SP-CL16(6-28) plus various phosphatidylglycerols (PG) were tested for surface activity in a Langmuir-Wilhelmy surface balance (WSB) apparatus and pulsating bubble surfactmeter (PBS). Further, SLSs were examined for biological properties using an animal model of surfactant deficiency, infant respiratory distress syndrome (IRDS), in vivo. Palmitoyl-oleoyl-phosphatidylglycerol (POPG)-SLS exhibited minimum and maximum surface tensions of 1.7 mN/m and 28.6 mN/m in WSB and 8.5 mN/m and 36.2 mN/m in PBS, respectively. Moreover, in the IRDS model, POPG-SLS remarkably improved the lung volume (LV) of a premature lagomorph fetus at LV30 cmH2O and LV5 cmH2O. That is, a significant improvement equal to the LV of a full-term fetus was observed. The level of LV exhibited respiratory improvement equivalent to surfactant-TA. SLS seemed comparable in surface activity with Surfacten (Surfactant-TA), a modified surfactant preparation which has been used for the treatment of RDS.