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Visualizing the analogy between competitive adsorption and colloid stability to restore lung surfactant function.

ABSTRACT: We investigated a model of acute respiratory distress syndrome in which the serum protein albumin adsorbs to an air-liquid interface and prevents the thermodynamically preferable adsorption of the clinical lung surfactant Survanta by inducing steric and electrostatic energy barriers analogous to those that prevent colloidal aggregation. Chitosan and polyethylene glycol (PEG), two polymers that traditionally have been used to aggregate colloids, both allow Survanta to quantitatively displace albumin from the interface, but through two distinct mechanisms. Direct visualization with confocal microscopy shows that the polycation chitosan coadsorbs to interfacial layers of both Survanta and albumin, and also colocalizes with the anionic domains of Survanta at the air-liquid interface, consistent with it eliminating the electrostatic repulsion by neutralizing the surface charges on albumin and Survanta. In contrast, the PEG distribution does not change during the displacement of albumin by Survanta, consistent with PEG inducing a depletion attraction sufficient to overcome the repulsive energy barrier toward adsorption.

SUBMITTER: Shieh IC

PROVIDER: S-EPMC3283804 | biostudies-other | 2012 Feb

REPOSITORIES: biostudies-other

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Visualizing the analogy between competitive adsorption and colloid stability to restore lung surfactant function.

Shieh Ian C IC Waring Alan J AJ Zasadzinski Joseph A JA

Biophysical journal 20120221 4

We investigated a model of acute respiratory distress syndrome in which the serum protein albumin adsorbs to an air-liquid interface and prevents the thermodynamically preferable adsorption of the clinical lung surfactant Survanta by inducing steric and electrostatic energy barriers analogous to those that prevent colloidal aggregation. Chitosan and polyethylene glycol (PEG), two polymers that traditionally have been used to aggregate colloids, both allow Survanta to quantitatively displace albu ...[more]

PMID: 22385848

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Project description:Lung surfactant (LS) is a mixture of lipids and proteins that line the alveolar air-liquid interface, lowering the interfacial tension to levels that make breathing possible. In acute respiratory distress syndrome (ARDS), inactivation of LS is believed to play an important role in the development and severity of the disease. This review examines the competitive adsorption of LS and surface-active contaminants, such as serum proteins, present in the alveolar fluids of ARDS patients, and how this competitive adsorption can cause normal amounts of otherwise normal LS to be ineffective in lowering the interfacial tension. LS and serum proteins compete for the air-water interface when both are present in solution either in the alveolar fluids or in a Langmuir trough. Equilibrium favors LS as it has the lower equilibrium surface pressure, but the smaller proteins are kinetically favored over multi-micron LS bilayer aggregates by faster diffusion. If albumin reaches the interface, it creates an energy barrier to subsequent LS adsorption that slows or prevents the adsorption of the necessary amounts of LS required to lower surface tension. This process can be understood in terms of classic colloid stability theory in which an energy barrier to diffusion stabilizes colloidal suspensions against aggregation. This analogy provides qualitative and quantitative predictions regarding the origin of surfactant inactivation. An important corollary is that any additive that promotes colloid coagulation, such as increased electrolyte concentration, multivalent ions, hydrophilic non-adsorbing polymers such as PEG, dextran, etc. added to LS, or polyelectrolytes such as chitosan, also promotes LS adsorption in the presence of serum proteins and helps reverse surfactant inactivation. The theory provides quantitative tools to determine the optimal concentration of these additives and suggests that multiple additives may have a synergistic effect. A variety of physical and chemical techniques including isotherms, fluorescence microscopy, electron microscopy and X-ray diffraction show that LS adsorption is enhanced by this mechanism without substantially altering the structure or properties of the LS monolayer.

Project description:ObjectivesThis study was aimed at the investigation of the supramolecular systems based on cationic surfactants bearing cyclic head groups (imidazolium and pyrrolidinium) and polyanions (polyacrylic acid (PAA) and human serum albumin (HSA)), and factors governing their structural behavior to create functional nanosystems with controlled properties. Research hypothesis. Mixed PE-surfactant complexes based on oppositely charged species are characterized by multifactor behavior strongly affected by the nature of both components. It was expected that the transition from a single surfactant solution to an admixture with PE might provide synergetic effects on structural characteristics and functional activity. To test this assumption, the concentration thresholds of aggregation, dimensional and charge characteristics, and solubilization capacity of amphiphiles in the presence of PEs have been determined by tensiometry, fluorescence and UV-visible spectroscopy, and dynamic and electrophoretic light scattering.ResultsThe formation of mixed surfactant-PAA aggregates with a hydrodynamic diameter of 100-180 nm has been shown. Polyanion additives led to a decrease in the critical micelle concentration of surfactants by two orders of magnitude (from 1 mM to 0.01 mM). A gradual increase in the zeta potential of HAS-surfactant systems from negative to positive value indicates that the electrostatic mechanism contributes to the binding of components. Additionally, 3D and conventional fluorescence spectroscopy showed that imidazolium surfactant had little effect on HSA conformation, and component binding occurs due to hydrogen bonding and Van der Waals interactions through the tryptophan amino acid residue of the protein. Surfactant-polyanion nanostructures improve the solubility of lipophilic medicines such as Warfarin, Amphotericin B, and Meloxicam.PerspectivesSurfactant-PE composition demonstrated beneficial solubilization activity and can be recommended for the construction of nanocontainers for hydrophobic drugs, with their efficacy tuned by the variation in surfactant head group and the nature of polyanions.

Dataset Information

Visualizing the analogy between competitive adsorption and colloid stability to restore lung surfactant function.

Publications

Visualizing the analogy between competitive adsorption and colloid stability to restore lung surfactant function.

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