Adsorption and interactions of lung surfactant lipids and proteins at air /aqueous interfaces and in aqueous solution
New protocols for preparing DPPC lipid dispersion which allow low dynamic surface tension, lower than 1 mN/m, have been developed and the microstructure, stability, and adsorption behavior of DPPC prepared with the new protocols have been studied. When DPPC dispersions are prepared with new protocols, including extensive sonication, they contain mostly vesicles with average size of 100 nm and are quite stable. Dynamic surface tensions lower than 1 mN/m were observed. The lipid adsorbs faster and more extensively for DPPC dispersions containing vesicles than with liposomes. The effect of freezing-thawing and sonication on the aggregate size and dynamic surface tension of aqueous DPPC dispersions was also studied. The freeze-thaw cycle causes substantial aggregation and precipitation of the vesicles. Resonication restores not only the vesicle sizes but also the DST behavior of the vesicular dispersion. These results have implications in designing efficient protocols of lipid dispersion preparation and lung surfactant replacement formulations for treating respiratory disease or for effective administration. ^ The competitive adsorption of DPPC with serum proteins such as bovine serum albumin (BSA) or fibrinogen (FB) was studied. For DPPC/protein mixtures, protein interferes with adsorptiton of DPPC and inhibits its surface tension lowering ability. When a DPPC monolayer is spread onto air/aqueous interface, the DPPC monolayer excludes protein from the surface and controls the tension behavior. When a DPPC dispersion is introduced with the Trurnit’s method, or sprayed dropwise, onto an aqueous DPPC/protein surfaces, the DPPC layer prevents the adsorption of protein and dominates the surface tension behavior. These results have implications in controlling the inhibition of lung surfactant tension behavior by serum proteins, when they leak at the alveolar lining layer, and in developing surfactant replacement therapies for alveolar respiratory diseases. ^ The stability and state of aggregation of aqueous FB and DPPC vesicles in aqueous solution were studied. In water, DPPC dispersions were stable, but FB was quite unstable and formed large aggregates. The addition of DPPC vesicles into FB dispersions reversed FB aggregation and precipitation, and produced stable dispersions. In buffer, both DPPC dispersions and FB solutions were quite stable. Mixing a FB solution and a DPPC dispersion produced highly unstable mixtures, in which large aggregates precipitated. These results have implications in understanding the interactions of lipids and proteins in biological and food processing applications. ^
Elias I. Franses, Purdue University.