Synthetic Surfactant Preparations Research Articles

Treatment of Respiratory Distress Syndrome with Single Recombinant Polypeptides that Combine Features of SP-B and SP-C.

Treatment of respiratory distress syndrome (RDS) with surfactant replacement therapy in prematurely born infants was introduced more than 30 years ago; however, the surfactant preparations currently in clinical use are extracts from animal lungs. A synthetic surfactant that matches the currently used nature-derived surfactant preparations and can be produced in a cost-efficient manner would enable worldwide treatment of neonatal RDS and could also be tested against lung diseases in adults. The major challenge in developing fully functional synthetic surfactant preparations is to recapitulate the properties of the hydrophobic lung surfactant proteins B (SP-B) and SP-C. Here, we have designed single polypeptides that combine properties of SP-B and SP-C and produced them recombinantly using a novel solubility tag based on spider silk production. These Combo peptides mixed with phospholipids are as efficient as nature-derived surfactant preparations against neonatal RDS in premature rabbit fetuses.

Disulphide Bridges in Surfactant Protein B Analogues Affect Their Activity in Synthetic Surfactant Preparations

Background: 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. Objective: 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. Methods: 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. Results: 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. Conclusion: 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.

Efficient Interfacially Driven Vehiculization of Corticosteroids by Pulmonary Surfactant.

Pulmonary surfactant is a crucial system to stabilize the respiratory air-liquid interface. Furthermore, pulmonary surfactant has been proposed as an effective method for targeting drugs to the lungs. However, few studies have examined in detail the mechanisms of incorporation of drugs into surfactant, the impact of the presence of drugs on pulmonary surfactant performance at the interface under physiologically meaningful conditions, or the ability of pulmonary surfactant to use the air-liquid interface to vehiculise drugs to long distances. This study focuses on the ability of pulmonary surfactant to interfacially vehiculize corticosteroids such as beclomethasone dipropionate (BDP) or Budesonide (BUD) as model drugs. The main objectives have been to (a) characterize the incorporation of corticosteroids into natural and synthetic surfactants, (b) evaluate whether the presence of corticosteroids affects surfactant functionality, and (c) determine whether surfactant preparations enable the efficient spreading and distribution of BDP and BUD along the air-liquid interface. We have compared the performance of a purified surfactant from porcine lungs and two clinical surfactants: Poractant alfa, a natural surfactant of animal origin extensively used to treat premature babies, and CHF5633, a new synthetic surfactant preparation currently under clinical trials. Both, natural and clinical surfactants spontaneously incorporated corticosteroids up to at least 10% by mass with respect to phospholipid content. The presence of the drugs did not interfere with their ability to efficiently adsorb into air-liquid interfaces and form surface active films able to reach and sustain very low surface tensions (<2 mN/m) under compression-expansion cycling mimicking breathing dynamics. Furthermore, the combination of clinical surfactant with corticosteroids efficiently promoted the active diffusion of the drug to long distances along the air-liquid interface. This effect could not be mimicked by vehiculisation of corticosteroids in liposomes or in micellar emulsions similar to the formulations currently in use to deliver anti-inflammatory corticosteroids through inhalation.

Thin liquid films from a new synthetic pulmonary surfactant preparation

A new pulmonary surfactant with synthetic analogs of surfactant proteins SP-B and SP-C (CHF5633) was studied by the method of thin liquid films (foam and wetting films). For foam films dependences such as probability W for formation of black foam films vs. surfactant concentration (Cs), disjoining (capillary) pressure isotherms (Π(h)) and film thickness (h) were studied. The minimum CHF5633 concentration for a black foam film formation was established in 75μg/cm3 (after 30min). The results obtained were compared with those of therapeutic pulmonary surfactant preparations and in particular to Curosurf®, the one that showed the best profile among the tested animal-derived surfactants with respect to black film formation, stability and homogeneity. It was shown that with respect to stability surfactant CHF 5633 (from W/C curves) was very close to Curosurf®. The differences involved black foam film thicknesses which for the synthetic surfactant (at 200μg/cm3) were h=14.7nm and for Curosurf® (at 200μg/cm3), h=12.6nm, i.e. film thickness of the synthetic surfactant was larger, probably due to the larger quantities of surfactant protein analogs SP-B and SP-C contained in it and/or to the different phospholipid composition. The same was observed for h(Cs) dependence. For wetting films equilibrium thickness vs. degree of hydrophobicity on a solid surface was measured as well as wetting contact angles. Practically no significant difference in the wetting behaviour of the aqueous suspensions of natural surfactant preparation Curosurf® and CHF 5633 was established, however about 25% less Curosurf® was needed to achieve almost the same wetting behavior.

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

BackgroundNatural 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.AimThe 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.MethodsPurified 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.ResultsNeither 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.ConclusionFor 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.

Animal derived surfactant extract versus protein free synthetic surfactant for the prevention and treatment of respiratory distress syndrome.

A wide variety of surfactant preparations have been developed and tested including synthetic surfactants and surfactants derived from animal sources. Although clinical trials have demonstrated that both synthetic surfactant and animal derived surfactant preparations are effective, comparison in animal models has suggested that there may be greater efficacy of animal derived surfactant products, perhaps due to the protein content of animal derived surfactant. To compare the effect of animal derived surfactant to protein free synthetic surfactant preparations in preterm infants at risk for or having respiratory distress syndrome (RDS). Searches were updated of the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2014), PubMed, CINAHL and EMBASE (1975 through November 2014). All languages were included. Randomized controlled trials comparing administration of protein free synthetic surfactants to administration of animal derived surfactant extracts in preterm infants at risk for or having respiratory distress syndrome were considered for this review. Data collection and analysis were conducted according to the standards of the Cochrane Neonatal Review Group. Fifteen trials met the inclusion criteria. The meta-analysis showed that the use of animal derived surfactant rather than protein free synthetic surfactant resulted in a significant reduction in the risk of pneumothorax [typical relative risk (RR) 0.65, 95% CI 0.55 to 0.77; typical risk difference (RD) -0.04, 95% CI -0.06 to -0.02; number needed to treat to benefit (NNTB) 25; 11 studies, 5356 infants] and a marginal reduction in the risk of mortality (typical RR 0.89, 95% CI 0.79 to 0.99; typical RD -0.02, 95% CI -0.04 to -0.00; NNTB 50; 13 studies, 5413 infants).Animal derived surfactant was associated with an increase in the risk of necrotizing enterocolitis [typical RR 1.38, 95% CI 1.08 to 1.76; typical RD 0.02, 95% CI 0.01 to 0.04; number needed to treat to harm (NNTH) 50; 8 studies, 3462 infants] and a marginal increase in the risk of any intraventricular hemorrhage (typical RR 1.07, 95% CI 0.99 to 1.15; typical RD 0.02, 95% CI 0.00 to 0.05; 10 studies, 5045 infants) but no increase in Grade 3 to 4 intraventricular hemorrhage (typical RR 1.08, 95% CI 0.91 to 1.27; typical RD 0.01, 95% CI -0.01 to 0.03; 9 studies, 4241 infants).The meta-analyses supported a marginal decrease in the risk of bronchopulmonary dysplasia or mortality associated with the use of animal derived surfactant preparations (typical RR 0.95, 95% CI 0.91 to 1.00; typical RD -0.03, 95% CI -0.06 to 0.00; 6 studies, 3811 infants). No other relevant differences in outcomes were noted. Both animal derived surfactant extracts and protein free synthetic surfactant extracts are effective in the treatment and prevention of respiratory distress syndrome. Comparative trials demonstrate greater early improvement in the requirement for ventilator support, fewer pneumothoraces, and fewer deaths associated with animal derived surfactant extract treatment. Animal derived surfactant may be associated with an increase in necrotizing enterocolitis and intraventricular hemorrhage, though the more serious hemorrhages (Grade 3 and 4) are not increased. Despite these concerns, animal derived surfactant extracts would seem to be the more desirable choice when compared to currently available protein free synthetic surfactants.

Synthetic lung surfactant reduces alveolar-capillary protein leakage in surfactant-deficient rabbits

ABSTRACTPurpose of the Study: Alveolar-capillary leakage of proteinaceous fluid impairs alveolar ventilation and surfactant function and decreases lung compliance in acute lung injury. We investigated the correlation between lung function and total protein levels in bronchoalveolar lavage fluid (BALF) of ventilated, lavaged surfactant-deficient rabbits treated with various clinical and synthetic lung surfactant preparations. Materials and Methods: 109 ventilated, young adult New Zealand White rabbits underwent lung lavage to induce surfactant-deficiency (PaO2 <100 torr in 100% O2), were treated with a clinical surfactant or a synthetic surfactant preparation with surfactant protein B (SP-B) and/or surfactant protein C (SP-C) analogs, and mechanically ventilated for 120 min. Total protein levels in postmortem BALF were correlated with arterial PO2 (PaO2) and dynamic lung compliance values at 120 min post-surfactant treatment. Results: Repeated lung lavages decreased mean PaO2 values from 540 to 58 torr and lung compliance from 0.64 to 0.33 mL/kg/cm H2O. Two hours after surfactant therapy and mechanical ventilation, mean PaO2 values had increased to 346 torr and lung compliance to 0.44 mL/kg/cm H2O. Eighty-six rabbits (79%) responded to surfactant therapy with an increase in PaO2 to values >200 torr. Fourteen non-responders received inactive surfactant preparations. BALF protein levels were inversely correlated with PaO2 and lung compliance (P < .001). Surfactant preparations containing both SP-B and SP-C proteins or peptide analogs outperformed single protein/peptide preparations. Conclusions: Clinical and synthetic surfactant therapy reduces alveolar-capillary protein leakage in surfactant-deficient rabbits. Surfactant preparations with both SP-B and SP-C (analogs) were more efficient than preparations with SP-B or SP-C alone.

Aerosol delivery of synthetic lung surfactant.

Background. Nasal continuous positive airway pressure (nCPAP) is a widely accepted technique of non-invasive respiratory support in premature infants with respiratory distress syndrome due to lack of lung surfactant. If this approach fails, the next step is often intubation, mechanical ventilation (MV) and intratracheal instillation of clinical lung surfactant.Objective. To investigate whether aerosol delivery of advanced synthetic lung surfactant, consisting of peptide mimics of surfactant proteins B and C (SP-B and SP-C) and synthetic lipids, during nCPAP improves lung function in surfactant-deficient rabbits.Methods. Experimental synthetic lung surfactants were produced by formulating 3% Super Mini-B peptide (SMB surfactant), a highly surface active SP-B mimic, and a combination of 1.5% SMB and 1.5% of the SP-C mimic SP-Css ion-lock 1 (BC surfactant), with a synthetic lipid mixture. After testing aerosol generation using a vibrating membrane nebulizer and aerosol conditioning (particle size, surfactant composition and surface activity), we investigated the effects of aerosol delivery of synthetic SMB and BC surfactant preparations on oxygenation and lung compliance in saline-lavaged, surfactant-deficient rabbits, supported with either nCPAP or MV.Results. Particle size distribution of the surfactant aerosols was within the 1–3 µm distribution range and surfactant activity was not affected by aerosolization. At a dose equivalent to clinical surfactant therapy in premature infants (100 mg/kg), aerosol delivery of both synthetic surfactant preparations led to a quick and clinically relevant improvement in oxygenation and lung compliance in the rabbits. Lung function recovered to a greater extent in rabbits supported with MV than with nCPAP. BC surfactant outperformed SMB surfactant in improving lung function and was associated with higher phospholipid values in bronchoalveolar lavage fluid; these findings were irrespective of the type of ventilatory support (nCPAP or MV) used.Conclusions. Aerosol delivery of synthetic lung surfactant with a combination of highly active second generation SP-B and SP-C mimics was effective as a therapeutic approach towards relieving surfactant deficiency in spontaneously breathing rabbits supported with nCPAP. To obtain similar results with nCPAP as with intratracheal instillation, higher dosage of synthetic surfactant and reduction of its retention by the delivery circuit will be needed to increase the lung dose.

Biophysical inhibition of synthetic vs. naturally-derived pulmonary surfactant preparations by polymeric nanoparticles

Reasonable suspicion has accumulated that inhaled nano-scale particulate matter influences the biophysical function of the pulmonary surfactant system. Hence, it is evident to provide novel insights into the extent and mechanisms of nanoparticle–surfactant interactions in order to facilitate the fabrication of safe nanomedicines suitable for pulmonary applications.Negatively- and positively-charged poly(styrene) nanoparticles (diameters of ~100nm) served as model carriers. Nanoparticles were incubated with several synthetic and naturally-derived pulmonary surfactants to characterize the sensitivity of each preparation to biophysical inactivation. Changes in surface properties (i.e. adsorption and dynamic surface tension behavior) were monitored in a pulsating bubble surfactometer.Both nanoparticle formulations revealed a dose-dependent influence on the biophysical behavior of all investigated pulmonary surfactants. However, the surfactant sensitivity towards inhibition depended on both the carrier type, where negatively-charged nanoparticles showed increased inactivation potency compared to their positively-charged counterparts, and surfactant composition. Among the surfactants tested, synthetic mixtures (i.e. phospholipids, phospholipids supplemented with surfactant protein B, and Venticute®) were more susceptible to surface-activity inhibition as the more complex naturally-derived preparations (i.e. Alveofact® and large surfactant aggregates isolated from rabbit bronchoalveolar lavage fluid).Overall, nanoparticle characteristics and surfactant constitution both influence the extent of biophysical inhibition of pulmonary surfactants.

Lucinactant for the treatment of respiratory distress syndrome in neonates

Respiratory distress syndrome (RDS) is a leading cause of morbidity and mortality in premature neonates. This syndrome is caused by a lack of endogenous surfactant production in the lungs. Surfactant replacement was established as a safe and effective treatment in the 1990s and has become the standard of care for these infants. Surfactant products are either protein-free synthetic phospholipid compounds or animal-derived lung preparations. Currently, about 90,000 infants a year receive treatment with one of the commercially available animal-derived surfactants. Lucinactant (Surfaxin®) is a new synthetic surfactant with a pulmonary surfactant-associated protein B mimic that recently received FDA approval. The clinical trials that have been performed, although underpowered, may indicate that lucinactant is superior to phospholipid synthetic surfactant preparations and at least as effective as animal-derived surfactants in reducing morbidity and mortality from RDS. This review summarizes the current clinical knowledge about lucinactant.

Lung preservation in experimental ischemia/reperfusion injury and lung transplantation: A comparison of natural and synthetic surfactants

Surfactant inactivation results from ischemia/reperfusion injury and plays a major role in the pathogenesis of primary graft dysfunction after clinical lung transplantation. Thus, prophylactic administration of exogenous surfactant preparations before the onset of ischemia/reperfusion has proven to be effective in preserving pulmonary structure and function. Various natural and synthetic surfactant preparations exhibit differences regarding the biochemical composition and biophysical properties. In this study we compared the efficacy of preservation of pulmonary structure and function of the natural surfactant preparations Curosurf and Survanta to that of a synthetic surfactant containing an analog of surfactant protein C (SPC-33) in a rat model of ischemia/reperfusion injury. The oxygenation capacity and peak inspiratory pressure during the reperfusion period were recorded. By applying design-based stereology at the light- and electron-microscopic level, pathologic alterations, including alveolar edema, injury of the blood-air barrier and the intra-alveolar as well as intracellular surfactant pools, were quantified. The best oxygenation and preservation of lung structure was achieved with Curosurf. Survanta treatment was associated with the most severe injury of the blood-air barrier, and SPC-33 demonstrated signs of microatelectasis. The intra-alveolar surfactant pool after Curosurf and SPC-33 was dominated by active surfactant subtypes, whereas Survanta was associated with the highest fraction of inactive surfactant. The intracellular surfactant pool did not show any differences between the treatment groups. Taken together, Curosurf achieved the best structural and functional lung preservation, whereas Survanta was inferior to both Curosurf and SPC-33.

Cochrane review: Protein containing synthetic surfactant versus animal derived surfactant extract for the prevention and treatment of respiratory distress syndrome

AbstractBackgroundRespiratory distress syndrome (RDS) is a significant cause of morbidity and mortality in preterm infants. RDS is caused by a deficiency, dysfunction, or inactivation of pulmonary surfactant. Numerous surfactants of either animal extract or synthetic design have been shown to improve outcomes. New surfactant preparations that include peptides or whole proteins that mimic endogenous surfactant protein have recently been developed and tested.ObjectivesTo assess the effect of administration of synthetic surfactant containing surfactant protein mimics compared to animal derived surfactant extract on the risk of mortality, chronic lung disease, and other morbidities associated with prematurity in preterm infants at risk for or having RDS.Search strategyStandard search methods of the Cochrane Neonatal Review Group were used. The search included MEDLINE (1966 ‐ May 2007) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library) in all languages. In addition, published abstracts of the Society of Pediatric Research were searched electronically. For abstract books that did not include key words, the search was limited to the relevant sections on pulmonary and neonatology. The bibliography cited in each publication was obtained and searched in order to identify additional relevant articles.Selection criteriaRandomized and quasi‐randomized controlled clinical trials were considered for this review. Studies that enrolled preterm infants or low birth weight infants at risk for or having RDS who were treated with either a synthetic surfactant containing surfactant protein mimics or an animal‐derived surfactant preparation were included for this review. Studies that either attempted to treat or prevent respiratory distress syndrome were included.Data collection and analysisPrimary outcome measures, including mortality, chronic lung disease and multiple secondary outcome measures were abstracted by the reviewers. Statistical analysis was performed using Review Manager software. Categorical data was analyzed using relative risk, risk difference, and number needed to treat. 95% confidence intervals reported. A fixed effects model was used for the meta‐analysis. Heterogeneity was assessed using the I‐squared statistic.Main resultsTwo studies were identified that compared protein containing synthetic surfactants to animal derived surfactant preparations. In a meta‐analysis of these two studies, infants who received protein containing synthetic surfactant compared to animal derived surfactant extract did not demonstrate significantly different risks of prespecified primary outcomes: mortality at 36 weeks [typical RR 0.81 (95% CI 0.64, 1.03)], chronic lung disease at 36 weeks [typical RR 0.99 (95% CI 0.84, 1.18)], or the combined outcome of mortality or chronic lung disease at 36 weeks [typical RR 0.96 (95% CI 0.82, 1.12)]. There were also no differences in any of the secondary outcomes regarding complications of prematurity between the two surfactant groups with the exception of necrotizing enterocolitis. A decrease in the risk of necrotizing enterocolitis was noted in infants who received protein containing synthetic surfactants compared to animal derived surfactant extract [typical RR 0.60 (95% CI 0.42, 0.86)]. However, this was a secondary outcome in both of the primary studies and there was moderate heterogeneity between the studies.Authors' conclusionsIn two trials of protein containing synthetic surfactants compared to animal derived surfactant extract, no statistically different clinical differences in death and chronic lung disease were noted. In general, clinical outcomes between the two groups were similar. Further well designed studies of adequate size and power will help confirm and refine these findings.Plain Language SummaryProtein containing synthetic surfactant versus animal derived surfactant extract for the prevention and treatment of respiratory distress syndromeRespiratory distress syndrome (RDS) is a significant cause of illness in preterm infants. Respiratory distress syndrome is caused by a deficiency or a dysfunction of the chemicals that line the lung, called pulmonary surfactant. Numerous preparations that contain surfactants of either animal origin or synthetic design have been developed and tested to treat or prevent respiratory distress syndrome. In general, these surfactant preparations have decreased lung rupture (pneumothorax), decreased the risk of dying, and increased the number of survivors without lung damage. From previous research, the surfactants that are obtained from animals seem to have a better effect than the synthetic surfactants. This might be due to the surfactant proteins contained in animal surfactant that are absent in the previously available synthetic surfactants.Recently developed synthetic surfactant preparations include whole surfactant proteins or parts of the proteins (called peptides) that act like surfactant protein. These preparations have been recently tested in comparison to the animal derived surfactant preparations.Two recent trials of protein containing synthetic surfactant compared to animal derived surfactant preparations have demonstrated a trend towards decreasing death and decreasing rates of bowel disease (necrotizing enterocolitis), while other clinical outcomes were similar. Further studies will help refine recommendations concerning use of protein containing synthetic surfactants.

PICO Summary: Do protein containing synthetic surfactant preparations improve pulmonary outcomes more than animal derived surfactant preparations in preterm infants with the need for mechanical ventilation for RDS?

PICO Summary: Do protein containing synthetic surfactant preparations improve pulmonary outcomes more than animal derived surfactant preparations in preterm infants with the need for mechanical ventilation for RDS?

Inflammatory cytokine mRNA in monocytes is modified by a recombinant (SP-C)-based surfactant and porcine surfactant

Respiratory distress syndrome (RDS) is mainly caused by a deficiency of surfactant in structurally immature lungs. Therapy for RDS consists of mechanical ventilation and administration of exogenous surfactant. Animal-derived surfactant preparations that are used to treat newborn infants show inhibition of proinflammatory cytokines. There are no data available concerning the effects of the new generation of surfactants. In the present study, the effects of an animal-derived surfactant (Curosurf) and a synthetic surfactant (Venticute) on lipopolysaccharide (LPS)-induced inflammation were tested in human monocyte THP-1 cells. The effects were measured as changes in messenger RNA (mRNA) expression of the chemokine interleukin-8 (IL-8), proinflammatory TNF-alpha and the anti-inflammatory IL-10 cytokine. Both surfactant preparations inhibited the LPS-induced increase in TNF-alpha expression. A comparison of both preparations revealed a similar effect on IL-10 expression. However, IL-10 expression was higher after incubation with Venticute. Curosurf increased IL-8 expression at higher concentrations, but Venticute had no effect. The anti-inflammatory effect of an animal-derived surfactant and a new-generation synthetic surfactant preparation may influence postnatal pulmonary inflammation.

Biomimicry of Surfactant Protein C

Since the widespread use of exogenous lung surfactant to treat neonatal respiratory distress syndrome, premature infant survival and respiratory morbidity have dramatically improved. Despite the effectiveness of the animal-derived surfactant preparations, there still remain some concerns and difficulties associated with their use. This has prompted investigation into the creation of synthetic surfactant preparations. However, to date, no clinically used synthetic formulation is as effective as the natural material. This is largely because the previous synthetic formulations lacked analogues of the hydrophobic proteins of the lung surfactant system, SP-B and SP-C, which are critical functional constituents. As a result, recent investigation has turned toward the development of a new generation of synthetic, biomimetic surfactants that contain synthetic phospholipids along with a mimic of the hydrophobic protein portion of lung surfactant. In this Account, we detail our efforts in creating accurate mimics of SP-C for use in a synthetic surfactant replacement therapy. Despite SP-C's seemingly simple structure, the predominantly helical protein is extraordinarily challenging to work with given its extreme hydrophobicity and structural instability, which greatly complicates the creation of an effective SP-C analogue. Drawing inspiration from Nature, two promising biomimetic approaches have led to the creation of rationally designed biopolymers that recapitulate many of SP-C's molecular features. The first approach utilizes detailed SP-C structure-activity relationships and amino acid folding propensities to create a peptide-based analogue, SP-C33. In SP-C33, the problematic and metastable polyvaline helix is replaced with a structurally stable polyleucine helix and includes a well-placed positive charge to prevent aggregation. SP-C33 is structurally stable and eliminates the association propensity of the native protein. The second approach follows the same design considerations but makes use of a non-natural, poly-N-substituted glycine or "peptoid" scaffold to circumvent the difficulties associated with SP-C. By incorporating unique biomimetic side chains in a non-natural backbone, the peptoid mimic captures both SP-C's hydrophobic patterning and its helical secondary structure. Despite the differences in structure, both SP-C33 and the SP-C peptoid mimic capture many requisite features of SP-C. In a surfactant environment, these analogues also replicate many of the key surface activities necessary for a functional biomimetic surfactant therapy while overcoming the difficulties associated with the natural protein. With improved stability, greater production potential, and elimination of possible pathogenic contamination, these biomimetic surfactant formulations offer not only the potential to improve the treatment of respiratory distress syndrome but also the opportunity to treat other respiratory-related disorders.

Une nouvelle génération de surfactants de synthèse

There are numerous pulmonary conditions in which qualitative or quantitative anomalies of the surfactant system have been demonstrated. In premature newborns with immature lungs, a functional deficit in surfactant is the main physiopathologic mechanism of the neonatal respiratory distress syndrome (RDS). Since the landmark pilot study of Fujiwara, published more than 20 years ago, the efficacy of exogenous surfactant for the treatment of neonatal RDS has been established by numerous controlled studies and meta-analyses. Enlightened by a growing insight into both the structure and function of the different surfactant components, a new generation of synthetic surfactants has been developed. Various complementary approaches have confirmed the fundamental role of the two hydrophobic proteins, SP-B and SP-C, in the surfactant system, thus opening the way to the design of analogues, either by chemical synthesis or expression in a prokaryotic system. An example of these peptide-containing synthetic surfactant preparations, lucinactant (Surfaxin), has been recently tested in comparison to a synthetic surfactant that does not contain protein as well as to animal derived surfactant preparations. Major clinical outcomes between lucinactant and animal-derived surfactant preparations were fund similar in two randomized controlled trials, opening the way to a new generation of synthetic surfactants in the near future.

Synthetic Pulmonary Surfactant Preparations: New Developments and Future Trends

Pulmonary surfactant is a lipid-protein complex that coats the interior of the alveoli and enables the lungs to function properly. Upon its synthesis, lung surfactant adsorbs at the interface between the air and the hypophase, a capillary aqueous layer covering the alveoli. By lowering and modulating surface tension during breathing, lung surfactant reduces respiratory work of expansion, and stabilises alveoli against collapse during expiration. Pulmonary surfactant deficiency, or dysfunction, contributes to several respiratory pathologies, such as infant respiratory distress syndrome (IRDS) in premature neonates, and acute respiratory distress syndrome (ARDS) in children and adults. The main clinical exogenous surfactants currently in use to treat some of these pathologies are essentially organic extracts obtained from animal lungs. Although very efficient, natural surfactants bear serious defects: i) they could vary in composition from batch to batch; ii) their production involves relatively high costs, and sources are limited; and iii) they carry a potential risk of transmission of animal infectious agents and the possibility of immunological reaction. All these caveats justify the necessity for a highly controlled synthetic material. In the present review the efforts aimed at new surfactant development, including the modification of existing exogenous surfactants by adding molecules that can enhance their activity, and the progress achieved in the production of completely new preparations, are discussed.

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 ≧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.

Effect of SP-B Peptides on the Uptake of Liposomes by Alveolar Cells

Background: Exogenous surfactant has been accepted worldwide as a therapy of RDS in premature and term infants. Exogenous surfactant is usually derived from lung extracts containing phospholipids and the surfactant proteins SP-B and SP-C. Synthetic peptides of SP-B and SP-C are being tested with the aim to develop a completely synthetic surfactant preparation. Nevertheless, the effects of these peptides on the endogenous surfactant metabolism remain unknown. Objectives: The effect of synthetic SP-B peptides on uptake of surfactant-like liposomes was investigated in alveolar cells. Native SP-B and seven SP-B peptides were included: monomeric and dimeric SP-B_1–25 (Cys-11 → Ala-11), SP-B_63–78and Ala-SP-B_63–78 (Cys-71 → Ala-71;Cys-77 → Ala-77)and their serine mutants. Methods: In vitro, alveolar macrophages (AM) and alveolar type II cells (ATII) were incubated with liposomes containing SP-B or one of its peptides. In vivo, rats received intratracheally various SP-B peptides (SP-B/lipid ratio 1:33 w/w) incorporated in fluorescent surfactant-like liposomes. One hour after instillation, AM and ATII were isolated and cell-associated fluorescence was determined using flow cytometry. Confocal laser microscopy was performed to ensure internalization of the liposomes. Results: In vitro uptake by AM or ATII was not influenced by the SP-B peptides. In vivo, SP-B_1–25 and Ser-SP-B_1–25 increased the uptake by AM whereas dSP-B_1–25 decreased the uptake. Neither SP-B_1–25 nor dSP-B_1–25affected total uptake by ATII. The overall uptake by SP-B_63–78 variants was not changed. Conclusions: Surface-active synthetic SP-B peptides do not interfere with the normaluptake of surfactant by ATII.

Surfactants in the Management of Respiratory Distress Syndrome in Extremely Premature Infants

Respiratory distress syndrome (RDS) is primarily due to decreased production of pulmonary surfactant, and it is associated with significant neonatal morbidity and mortality. Exogenous pulmonary surfactant therapy is currently the treatment of choice for RDS, as it demonstrates the best clinical and economic outcomes. Studies confirm the benefits of surfactant therapy to include reductions in mortality, pneumothorax, and pulmonary interstitial emphysema, as well as improvements in oxygenation and an increased rate of survival without bronchopulmonary dysplasia. Phospholipids (PL) and surfactant-associated proteins (SP) play key roles in the physiological activity of surfactant. Different types of natural and synthetic surfactant preparations are currently available. To date, natural surfactants demonstrate superior outcomes compared to the synthetic surfactants, at least during the acute phase of RDS. This disparity is often attributed to biochemical differences including the presence of surfactant-associated proteins in natural products that are not found in the currently available synthetic surfactants. Comparative trials of the natural surfactants strive to establish the precise differences in clinical outcomes among the different preparations. As new surfactants become available, it is important to evaluate them relative to the known benefits of the previously existing surfactants. In order to elucidate the role of surfactant therapy in the management of RDS, it is important to review surfactant biochemistry, pharmacology, and outcomes from randomized clinical trials.