Enhanced Surfactant Adsorption via Polymer Depletion Forces: A Simple Model for Reversing Surfactant Inhibition in Acute Respiratory Distress Syndrome

Abstract

Lung surfactant adsorption to an air-water interface is strongly inhibited by an energy barrier imposed by the competitive adsorption of albumin and other surface-active serum proteins that are present in the lung during acute respiratory distress syndrome. This reduction in surfactant adsorption results in an increased surface tension in the lung and an increase in the work of breathing. The reduction in surfactant adsorption is quantitatively described using a variation of the classical Smolukowski analysis of colloid stability. Albumin adsorbed to the interface induces an energy barrier to surfactant diffusion of order 5 k(B)T, leading to a reduction in adsorption equivalent to reducing the surfactant concentration by a factor of 100. Adding hydrophilic, nonadsorbing polymers such as polyethylene glycol to the subphase provides a depletion attraction between the surfactant aggregates and the interface that eliminates the energy barrier. Surfactant adsorption increases exponentially with polymer concentration as predicted by the simple Asakura and Oosawa model of depletion attraction. Depletion forces can likely be used to overcome barriers to adsorption at a variety of liquid-vapor and solid-liquid interfaces.

Environmental tobacco smoke effects on lung surfactant film organization

“…It requires about a 4:1 compression ratio to reach low surface tensions after Curosurf has been exposed to ETS, compared to the 2:1 compression ratio for the pristine Curosurf for identical amounts of deposited Curosurf. This suggests that ETS exposure decreases the ability of Curosurf to adsorb to the air-water interface from the subphase [60]. …”

“…2 shows fluorescence images of Curosurf and ETS (TSP = 77 mg/m 3 ) exposed Curosurf at 25°C on the second cycle. Discrete black domains coexist in a continuous medium gray background, similar to model lung surfactant lipid-protein mixtures and other commercial lung surfactants [13, 60, 61]. The dark domains are condensed phases (typically semi-crystalline areas enriched in saturated lipids [20, 25, 26, 35]) that exclude the bulky fluorophore-labeled Texas Red-DHPE, which cannot pack into a crystalline lattice [62].…”

“…The stated concentrations of Survanta and Curosurf dispersions were deposited dropwise onto the saline buffer subphase (150 mM NaCl, 2 mM CaCl 2 , and 0.2 mM NaHCO 3 , pH = 7) of the Langmuir trough at the stated total surfactant concentrations and allowed to equilibrate 20 minutes before beginning cycling. Surfactant deposited in this fashion adsorbs from the subphase to the interface as multilayer aggregates that convert to a monolayer on contact with the air-water interface [33, 60, 61]. …”

Surface active properties of chitosan and its derivatives

“…The surface tension control imposed by lung surfactant (LS), a unique mixture of lipids and proteins that lowers the interfacial tension in the lungs and facilitates normal breathing [96], is compromised during acute respiratory distress syndrome (ARDS). Lung surfactant is a mixture of lipids (primarily dipalmitoylphosphatidylcholine) and four lung surfactant-specific proteins (SP-A, B, C, and D) that lines the interior of the lung alveoli and acts to lower the interfacial tension in the lungs, thereby insuring a negligible work of breathing and uniform lung inflation [97].…”

Restoration of the interfacial properties of lung surfactant with a newly designed hydrocarbon/fluorocarbon lipid

“…Under these conditions, the surface-active serum proteins leak into the alveolar subphase. Previous studies have shown that the serum protein levels are highly elevated in case of ARDS [16][17][18][19][20]. In vitro research studies performed using LS and surface-active serum proteins together have shown that the presence of the serum proteins also damages the functionality of LS [21].…”