Comparative adsorption of natural lung surfactant, extracted phospholipids, and artificial phospholipid mixtures to the air-water interface

Adsorption to the air-water interface of natural lung surfactant obtained by bovine lung lavage is compared and contrasted with the adsorption of mixtures of synthetic phospholipids and of extracted mixed lung lipids containing minimal protein. Surface pressure-time (pi-t) adsorption isotherms are measured at 35 degrees C for the surfactant mixtures as a function of the presence or absence of divalent metal cations (Ca2+ and Mg2+) and of heating to 45 degrees C or 90 degrees C. The effect of aqueous dispersion technique (sonication or mechanical vortexing) on the adsorption process is also studied for the extracted or synthetic phospholipid mixtures. The results imply that the protein component is necessary for the optimal adsorption of natural lung surfactant. However, by taking advantage of different methods available for phospholipid dispersion in an aqueous phase in vitro, it is possible to formulate dispersions of extracted lung phospholipids containing of order 1% protein which adsorb as well as the complete surfactant system. These results suggest that protein concentrations in surfactant mixtures can be minimized for applications such as exogenous lung surfactant replacement for the neonatal Respiratory Distress Syndrome (RDS). However, for situations which may involve alterations in endogenous surfactant function such as in lung injury, effects involving pulmonary surfactant protein and protein-lipid interactions may be of functional significance.     

Biophysical inhibition of synthetic lung surfactants

The biophysical activity and inhibition of a series of synthetic surfactant mixtures was studied and correlated with physiological effectiveness in restoring pressure-volume (P-V) mechanics of excised lungs. Results showed that several simple mixtures of dipalmitoyl phosphatidylcholine (DPPC) with fatty acids or diacylglycerols could be formulated to give good adsorption facility and dynamic surface tension lowering to less than 1 mN/m in pulsating bubble measurements at 37 degrees C. However, although biophysical activity approached that of natural lung surfactant (LS) and a related surfactant extract (CLSE) under normal conditions, surface properties were sharply inhibited by relatively small amounts of the plasma protein albumin (2 mg/ml) with minimum surface tensions greater than 30 nM/m even at high surfactant concentrations (5-20 mg lipids/ml). This sensitivity to biophysical inhibition was markedly increased compared to LS and CLSE, and had direct consequences for physiological efficacy: in spite of initially high activity, synthetic surfactants did not exert beneficial effects on P-V mechanics when instilled into surfactant-deficient excised rat lungs. Endogenous protein material was shown to be present upon surfactant recovery by lavage, and bubble measurements confirmed surface activity well below pre-instillation levels. Moreover, full biophysical activity was restored when lavage fluid was extracted to separate the synthetic surfactants from endogenous inhibitors. These results show that it is important to define relative sensitivity to biophysical inhibition in the development of effective lung surfactant substitutes. In addition, the existence of inhibition effects can generate an apparent lack of correspondence between initial biophysical activity and ultimate physiological actions of exogenous surfactant mixtures.     

Molecular mobility in the monolayers of foam films stabilized by porcine lung surfactant.

Certain physical properties of a range of foam film types that are believed to exist in vivo in the lung have been investigated. The contribution of different lung surfactant components found in porcine lung surfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and thickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using the fluorescence recovery after photobleaching technique. Fluorescent phospholipid probe molecules in foam films stabilized by porcine lung surfactant samples or their hydrophobic extracts consisting of surfactant lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhibited more rapid diffusion than observed in films of its principal lipid component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effect appears to be due to contributions from minor lipid components present in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfactant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant proteins in the sample reduced the diffusion coefficient (D) of the lipid analog in the adsorbed layer of the films. Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying above the heating curve. However, in cases where some surface molecular aggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobilized. The thickness, size, capillary pressure, configuration, and composition of foam films of lung surfactant prepared in vitro support their investigation as realistic structural analogs of the surface films that exist in vivo in the lung. Compared to other models currently in use, foam films provide new opportunities for studying the properties and function of physiologically important alveolar surface films.     

Proteolipid in bovine lung surfactant: its role in surfactant function

The chemical and biophysical properties of the proteins in the lipid extracts of lung surfactant have not clearly been determined. These proteins were isolated from lung surfactant lipids by Sephadex LH-20 chromatography and purified with silicic acid chromatography followed by dialysis against organic solvents. The proteolipid thus obtained had a protein to phospholipid ratio of 3 to 1 (w/w). The proteolipid apoprotein had a nominal molecular weight of ca. 5 kDa. We evaluated the functional role of this proteolipid by combining it with proteolipid-depleted surfactant lipids or synthetic dipalmitoylphosphatidylcholine (DPPC) and then measuring with a pulsating bubble surfactometer. The proteolipid and DPPC recombinant reproduced the surface activity of natural lung surfactant. We conclude that this 5 kDa proteolipid apoprotein is a functionally important constituent of lung surfactant.     

Synthesis and surface activity of diether-linked phosphoglycerols: potential applications for exogenous lung surfactants

The synthesis of three phosphoglycerols is described, one of which contains the previously unknown phosphonoglycerol headgroup. The surface tension-lowering capabilities of synthetic lung surfactant mixtures containing the PG analogs were measured on the pulsating bubble surfactometer and compared to known controls. The PG-containing mixtures exhibited superior surface tension-lowering properties indicating the significant potential of these analogs as components in synthetic exogenous lung surfactants.     

Biophysical activity of synthetic phospholipids combined with purified lung surfactant 6000 dalton apoprotein

This research studies the biophysical surface activity of synthetic phospholipids combined in vitro with purified lung surfactant apoprotein, having an Mr of 6000. Hydrophobic surfactant-associated protein (SAP-6) was delipidated and purified from both bovine and canine lung lavage, and was combined in vitro with a synthetic phospholipid mixture (SM) of similar composition to natural lung surfactant phospholipids. SM phospholipids were also combined and studied biophysically with another purified surfactant-associated protein, SAP-35. The biophysical activity of synthetic phospholipid-apoprotein combinants was assessed by measurements of adsorption facility and dynamic surface tension lowering ability at 37 degrees C. The SM-SAP-6 combinants had adsorption facility equivalent to natural lung surfactant, and to the surfactant extract preparations CLSE and surfactant-TA used in exogenous surfactant replacement therapy for the neonatal Respiratory Distress Syndrome (RDS). The synthetic phospholipid-SAP-6 combinants also lowered surface tension to less than 1 dyne/cm under dynamic compression in an oscillating bubble apparatus at concentrations as low as 0.5 mg phospholipid/ml. A striking finding was that this excellent dynamic surface activity was preserved as SAP-6 composition was reduced to values as low as 5 micrograms/5 mg SM phospholipid (0.1% SAP-6 protein), an order of magnitude less than the 1% protein content of CLSE and surfactant-TA. Mixtures of SM phospholipids plus SAP-35, the major surfactant glycoprotein, had significantly lower biophysical activity, which did not approach that of a functional lung surfactant. These results suggest that synthetic exogenous surfactants of potential utility for replacement therapy in RDS can be formulated by combining synthetic phospholipids in vitro with specifically purified, hydrophobic surfactant-associated protein, SAP-6.     

Molecular dynamics simulations of lung surfactant lipid monolayers

Pulmonary surfactant provides for a lipid rich film at the lung air-water interface, which prevents alveolar collapse at the end of expiration. The films are likely enriched in the major surfactant component dipalmitoylphosphatidylcholine (DPPC), which, due to its saturated fatty acid chains, can withstand high surface pressures up to 70 mN/m, thereby reducing surface tension in that interface to very low values (close to 1 mN/m). Despite many experimental measurements in situ, as well as in vitro for native lung surfactant films, the exact mechanism by which other fluid lipid components of surfactant, in combination with surfactant proteins, allow for such low surface tension values to be reached is not well understood. We have performed molecular dynamics simulation of films composed of DPPC alone and in mixtures with other fluid and acidic lipid components of surfactant at the high densities relevant to the low surface tension regime. 10-50 ns simulations were performed with the software GROMACS, with 40-64 lipids molecules plus water, using 5 different lipid compositions and 7 different areas per lipid. The primary focus was to learn how differences in lipid composition affect the response of the monolayer to compression, such as the development of curvature or the loss of lipids to the exterior of the monolayer. The systems studied exhibit features of two of the major schools of thought of lung surfactant mechanisms, in that although unsaturated lipids did not appear to prevent the monolayers from achieving high surface pressure, POPG did appear to be selectively squeezed out of the DPPC/POPG monolayers at high lipid densities.     

Purification of a hydrophobic surfactant peptide using high-performance liquid chromatography

A 4- to 6-kDa hydrophobic peptide (SP4-6) was purified from human pulmonary surfactant. Sep Pak Florisil cartridges removed most of the lipids and the 18-kDa peptide. Analytical wide-pore reversed-phase HPLC column separated a single peptide that contained no detectable lipids (less than 1 nmol/2.5 micrograms protein). N-terminal analysis indicated that this peptide was pure, but the N-terminal amino acid was blocked. The peptide was capable of restoring the in vitro surface properties of synthetic phospholipids, which is characteristic of native lung surfactant.     

Naturally derived commercial surfactants differ in composition of surfactant lipids and in surface viscosity

Pulmonary surfactant biophysical properties are best described by surface tension and surface viscosity. Besides lecithin, surfactant contains a variety of minor lipids, such as plasmalogens, polyunsaturated fatty acid-containing phospholipids (PUFA-PL), and cholesterol. Plasmalogens and cholesterol improve surface properties of lipid mixtures significantly. High PUFA-PL and plasmalogen content in tracheal aspirate of preterm infants reduces the risk of developing chronic lung disease. Different preparations are available for exogenous surfactant substitution; however, little is known about lipid composition and surface viscosity. Thus lipid composition and surface properties (measured by oscillating drop surfactometer) of three commercial surfactant preparations (Alveofact, Curosurf, Survanta) were compared. Lipid composition exhibited strong differences: Survanta had the highest proportion of disaturated PL and total neutral lipids and the lowest proportion of PUFA-PL. Highest plasmalogen and PUFA-PL concentrations were found in Curosurf (3.8 +/- 0.1 vs. 26 +/- 1 mol%) compared with Alveofact (0.9 +/- 0.3 vs. 11 +/- 1) and Survanta (1.5 +/- 0.2 vs. 6 +/- 1). In Survanta samples, viscosity increased >8 x 10(-6) kg/s at surface tension of 30 mN/m. Curosurf showed only slightly increased surface viscosity below surface tensions of 25 mN/m, and viscosity did not reach 5 x 10(-6) kg/s. By adding defined PL to Survanta, we obtained a Curosurf-like lipid mixture (without plasmalogens) that exhibited biophysical properties like Curosurf. Different lipid compositions could explain some of the differences in surface viscosity. Therefore, PL pattern and minor surfactant lipids are important for biophysical activity and should be considered when designing synthetic surfactant preparations.     

Combined effects of polymers and KL4 peptide on surface activity of pulmonary surfactant lipids

Addition of ionic and nonionic polymers can improve the function of therapeutic surfactants in vitro and in vivo, especially under conditions that tend to inhibit surfactant activity. Since surfactant proteins also act to reduce surfactant inhibition, we studied the relative effects of a synthetic peptide (that mimics some of the properties of a surfactant protein), polymers, and their combination on function of surfactant phospholipid activity in vitro. We evaluated surface activity after adding polymers—polyethylene glycol or hyaluronan—to a lipid mixture with or without the synthetic peptide, sinapultide (KL₄). Using a pulsating bubble surfactometer, we measured peptide/polymer effects separately or combined at two peptide concentrations. Phospholipid mixtures, with or without KL₄ or polymers, all demonstrated good surface activity. With serum present as an inhibiting agent, adding either concentration of KL₄ reduced inhibition. Mixtures containing the higher concentration of KL₄ required higher concentrations of serum for inhibition to occur. Adding either polymer to mixtures with KL₄ further decreased susceptibility to inhibition (required higher serum concentrations). In the presence of serum, high molecular weight hyaluronan with KL₄ at 0.4 mg/ml improved surface activity to a greater degree than 0.8 mg/ml KL₄ without polymer. If the beneficial effects of adding polymer to KL₄-lipid mixtures are also borne out in the treatment of experimental lung injury, these peptide-polymer surfactant combinations may eventually prove useful in the treatment of some forms of acute lung injury in humans.     

Anti-inflammatory and anti-viral actions of anionic pulmonary surfactant phospholipids

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.     

The influence of water on the phase transition of sheep lung surfactant. A possible mechanism for surfactant phase transitions in vivo

The effect of water on the thermal properties of sheep lung surfactant lipids was determined by differential scanning calorimetry. Dry surfactant exhibited a phase transition with an upper limit of about 54 degrees C, whereas that of the fully hydrated surfactant was about 30 degrees C. The effect of water was confined to a range of hydration values from 0 to 25%. The results indicate that pulmonary surfactant lipids are capable of undergoing both thermotropic and lyotropic mesomorphism in vitro. The degree of hydration of the surfactant could influence its in vivo biophysical role in alveolar dynamics. Indeed, small changes in the surfactant to water ratio induced by regional differences in the surfactant concentration at the alveolar surface during alveolar expansion and contraction could be sufficient to trigger isothermal phase transitions in the surfactant lipids. This would allow changes to occur in the equilibrium between solidus and fluidus surfactant during the respiratory cycle.     

Content-dependent activity of lung surfactant protein B in mixtures with lipids

The content-dependent activity of surfactant protein (SP)-B was studied in mixtures with dipalmitoyl phosphatidylcholine (DPPC), synthetic lipids (SL), and purified phospholipids (PPL) from calf lung surfactant extract (CLSE). At fixed SP-B content, adsorption and dynamic surface tension lowering were ordered as PPL/SP-B approximately SL/SP-B > DPPC/SP-B. All mixtures were similar in having increased surface activity as SP-B content was incrementally raised from 0.05 to 0.75% by weight. SP-B had small but measurable effects on interfacial properties even at very low levels < or =0.1% by weight. PPL/SP-B (0.75%) had the highest adsorption and dynamic surface activity, approaching the behavior of CLSE. All mixtures containing 0.75% SP-B reached minimum surface tensions <1 mN/m in pulsating bubble studies at low phospholipid concentration (1 mg/ml). Mixtures of PPL or SL with SP-B (0.5%) also had minimum surface tensions <1 mN/m at 1 mg/ml, whereas DPPC/SP-B (0.5%) reached <1 mN/m at 2.5 mg/ml. Physiological activity also was strongly dependent on SP-B content. The ability of instilled SL/SP-B mixtures to improve surfactant-deficient pressure-volume mechanics in excised lavaged rat lungs increased as SP-B content was raised from 0.1 to 0.75% by weight. This study emphasizes the crucial functional activity of SP-B in lung surfactants. Significant differences in SP-B content between exogenous surfactants used to treat respiratory disease could be associated with substantial activity variations.     

Inhibition of mixtures of surfactant lipids and synthetic sequences of surfactant proteins SP-B and SP-C

The respiratory distress syndrome of premature infants is caused by both surfactant deficiency and surfactant inhibition by capillary-alveolar leakage of serum factors. Dispersions of a standard surfactant lipid mixture, with and without various synthetic peptides, modeled on human surfactant proteins SP-B (residues 1-25, 49-66, 1-78) and SP-C (residues 1-10), were evaluated for inhibition by serum and by plasma constituents using a pulsating bubble surfactometer. Inhibition was derived from the changes in surface properties of these mixtures after addition of human serum or plasma constituents. Modified bovine surfactant (TA) containing native SP-B and SP-C was used as a control. In the absence of serum inhibitors, mixtures with synthetic peptides gave results similar to surfactant TA. However, inhibition was more evident in the dispersions with synthetic peptides when compared with surfactant TA. The peptide/phospholipid mixture with the entire sequence of SP-B and the first 10 residues of SP-C were more resistant to inhibition than mixtures with synthetic peptides containing fewer domains. Addition of calcium reduced the inhibitory effects of serum both in mixtures containing synthetic peptides and in surfactant TA. Therefore, synthetic SP-B and SP-C peptides in surfactant lipids, in cooperation with calcium, permit resistance to inhibition by several plasma constituents that probably inactivate surfactant by a variety of different mechanisms.     

Inhibition of surfactant activity by Pneumocystis carinii organisms and components in vitro

This study examines the direct inhibitory effects of Pneumocystis carinii (Pc) organisms and chemical components on the surface activity and composition of whole calf lung surfactant (WLS) and calf lung surfactant extract (CLSE) in vitro. Incubation of WLS suspensions with intact Pc organisms (10(7) per milligram of surfactant phospholipid) did not significantly alter total phospholipid levels or surfactant protein A content. Incubation with intact Pc organisms also did not impair dynamic surface tension lowering in suspensions of WLS or centrifuged large surfactant aggregates on a bubble surfactometer (37 degrees C, 20 cycles/min, 0.5 and 2.5 mg phospholipid/ml). However, exposure of WLS or CLSE to disrupted (sonicated) Pc organisms led to severe detriments in activity, with minimum surface tensions of 17-19 mN/m vs. <1 mN/m for surfactants alone. Extracted hydrophobic chemical components from Pc (98.8% lipids, 0.1 mM) reduced the surface activity of WLS and CLSE similarly to sonicated Pc organisms, whereas extracted hydrophilic chemical components from Pc (primarily proteins) had only minor effects on surface tension lowering. These results indicate that in addition to surfactant dysfunction induced by inflammatory lung injury and edema-derived inhibitors in Pc pneumonia, disrupted Pc organisms in the alveolar lumen also have the potential to directly inhibit endogenous and exogenous lung surfactants in affected patients.     

Effects of lung surfactant proteins, SP-B and SP-C, and palmitic acid on monolayer stability

Langmuir isotherms and fluorescence and atomic force microscopy images of synthetic model lung surfactants were used to determine the influence of palmitic acid and synthetic peptides based on the surfactant-specific proteins SP-B and SP-C on the morphology and function of surfactant monolayers. Lung surfactant-specific protein SP-C and peptides based on SP-C eliminate the loss to the subphase of unsaturated lipids necessary for good adsorption and respreading by inducing a transition between monolayers and multilayers within the fluid phase domains of the monolayer. The morphology and thickness of the multilayer phase depends on the lipid composition of the monolayer and the concentration of SP-C or SP-C peptide. Lung surfactant protein SP-B and peptides based on SP-B induce a reversible folding transition at monolayer collapse that allows all components of surfactant to be retained at the interface during respreading. Supplementing Survanta, a clinically used replacement lung surfactant, with a peptide based on the first 25 amino acids of SP-B also induces a similar folding transition at monolayer collapse. Palmitic acid makes the monolayer rigid at low surface tension and fluid at high surface tension and modifies SP-C function. Identifying the function of lung surfactant proteins and lipids is essential to the rational design of replacement surfactants for treatment of respiratory distress syndrome.     

Phospholipid binding and biophysical activity of pulmonary surfactant-associated protein (SAP)-35 and its non-collagenous COOH-terminal domains

Surfactant-associated protein of Mr = 35,000, SAP-35, is the major glycoprotein present in mammalian pulmonary surfactants. In this study, canine SAP-35 and several of its COOH-terminal peptides were purified and characterized by amino acid composition and NH2-terminal sequencing analysis. These proteins were then studied in terms of their specific lipid-binding characteristics and surface activity when combined with a synthetic phospholipid mixture, SM, chosen as an approximation of lung surfactant phospholipids. Purified, delipidated SAP-35 bound SM strongly. In contrast, SAP-21 (a non-collagenous fragment generated by collagenase digestion) bound phospholipid weakly; SAP-18 (an acidic COOH-terminal fragment comprising residues Gly-118 to Phe-231) did not bind phospholipid, demonstrating the importance of hydrophobic amino acid residues Gly-81 to Val-117 and the NH2-terminal collagenous domain in interaction of the SAP-35 with phospholipids. In surface activity experiments, purified SAP-35 enhanced the adsorption of SM phospholipids in terms of both rate and overall surface tension lowering. However, the adsorption facility of the SM-SAP-35 mixture did not approach that of either whole surfactant or the surfactant extract preparations, calf lung surfactant extract or surfactant-TA, used in exogenous surfactant replacement therapy for the neonatal respiratory distress syndrome. In addition, the dynamic surface activity of the SM-SAP-35 mixture was well below that of natural surfactant or surfactant extracts. This was also true of mixtures of SM phospholipids combined with the SAP-18 and SAP-21 fragments of SAP-35.     

Interaction between chitosan and bovine lung extract surfactants

The interaction between a cationic polyelectrolyte, chitosan, and an exogenous bovine lung extract surfactant (BLES) was studied using dynamic compression/expansion cycles of dilute BLES preparations in a Constrained Sessile Drop (CSD) device equipped with an environmental chamber conditioned at 37 degrees C and 100% R.H. air. Under these conditions, dilute BLES preparations tend to produce variable and relatively high minimum surface tensions. Upon addition of "low" chitosan to BLES ratios, the minimum surface tension of BLES-chitosan preparations were consistently low (i.e. <5 mJ/m2), and the resulting surfactant monolayers (adsorbed at the air-water interface) were highly elastic and stable. However, the use of "high" chitosan to BLES ratios induced the collapse of the surfactant monolayer at high minimum surface tensions (i.e. >15 mJ/m2). The zeta potential of the lung surfactant aggregates in the subphase suggests that chitosan binds to the anionic lipids (phosphatidyl glycerols) in BLES, and that this binding is ultimately responsible for the changes in the surface activity (elasticity and stability) of these surfactant-polyelectrolyte mixtures. Furthermore the transition from "low" to "high" chitosan to BLES ratios correlates with the flocculation and de-flocculation of surfactant aggregates in the subphase. It is proposed that the aggregation/segregation of "patches" of anionic lipids in the surfactant monolayer produced at different chitosan to BLES ratios explains the enhancing/inhibitory effects of chitosan. These observations highlight the importance of electrostatic interactions in lung surfactant systems.     

Natural and artificial lung surfactant replacement therapy in premature lambs

The effect of tracheal instillation of surface-active mixtures in premature lambs was studied as an animal model of exogenous surfactant replacement therapy for the respiratory distress syndrome (RDS). Specific mixtures studied were 7:3 (molar ratio) dipalmitoyl phosphatidylcholine (DPPC):egg phosphatidylglycerol (PG) and extracted mixed lipids (with 1% protein) from cow lung lavage (CLL). Preventilatory tracheal instillation of greater than 15 mg/kg of CLL in 10 ml 0.15 M NaCl to premature lambs gave improved alveolar-arterial O2 gradient and blood gases and increased lung compliance, compared with control lambs over a 15-h period. Lambs receiving 7:3 DPPC:PG dispersions were not improved over controls with regard to pressure-volume characteristics and were worse than controls in arterial oxygenation. In terms of in vitro surface properties, both extracted natural CLL and 7:3 DPPC:egg PG were able to lower aqueous surface tension to 1 dyn/cm under dynamic compression. However, the dynamic respreading of CLL films on successive surface cycles was superior to that of 7:3 DPPC:PG. Moreover, after dispersal in 0.15 M NaCl by vortexing (5 mg/80 ml), CLL adsorbed to surface pressure (tau values of 45 dyn/cm within 10 min. 7:3 DPPC:PG adsorbed to significantly lower tau values after subphase dispersal by a variety of methods.     

Effect of budesonide and salbutamol on surfactant properties.

The objective of this study was to evaluate the in vitro effect of budesonide and salbutamol on the surfactant biophysical properties. The surface-tension properties of two bovine lipid extracts [bovine lipid extract surfactant (BLES) and Survanta] and a rat lung lavage natural surfactant were evaluated in vitro by the captive bubble surfactometer. Measurements were obtained before and after the addition of a low and high concentration of budesonide and salbutamol. Whereas salbutamol had no significant effect, budesonide markedly reduced the surface-tension-lowering properties of all surfactant preparations. Surfactant adsorption (decrease in surface tension vs. time) was significantly reduced (P < 0.01) at a high budesonide concentration with BLES, both concentrations with Survanta, and a low concentration with natural surfactant. At both concentrations, budesonide reduced (P < 0.01) Survanta film stability (minimal surface vs. time at minimum bubble volume), whereas no changes were seen with BLES. The minimal surface tension obtained for all surfactant preparations was significantly higher (P < 0.01), and the percentage of film area compression required to reach minimum surface tension was significantly lower after the addition of budesonide. In conclusion, budesonide, at concentrations used therapeutically, adversely affects the surface-tension-lowering properties of surfactant. We speculate that it may have the same adverse effect on the human surfactant.