Differential Effects of Lysophosphatidylcholine on the Adsorption of Phospholipids to an Air/Water Interface

Abstract

To determine how the hydrophobic surfactant proteins promote insertion of the surfactant lipids into an air/water interface, we measured the effect of lysophosphatidylcholine (LPC) on adsorption. Existing models contend that the proteins function either by disordering the lipids or by stabilizing a negatively curved structure located between the adsorbing vesicle and the interface. Because LPC produces greater disorder but positive curvature, the models predict opposite effects. With vesicles containing either dioleoyl phosphatidylcholine (DOPC) or the neutral and phospholipids isolated from calf surfactant, LPC increased the initial rate at which surface tension fell. The final surface tension, however, remained well above the value of approximately 25 mN/m expected for a saturated surface. With two preparations, dioleoyl phosphatidylethanolamine and gramicidin A-DOPC, which form the negatively curved hexagonal-II (H(II)) phase and adsorb rapidly, LPC instead had little effect on initial adsorption but delayed the fall of surface tension below approximately 30 mN/m. LPC produced a similar inhibition of the late adsorption for extracted calf surfactant. Unlike dioleoyl phosphatidylethanolamine and gramicidin A-DOPC, small-angle x-ray scattering and (31)P-nuclear magnetic resonance for extracted calf surfactant detected no evidence for the H(II) phase. Our results indicate that although LPC can promote the initial adsorption of vesicles containing only lamellar lipids, it inhibits the facilitation by the hydrophobic proteins of late adsorption. Our findings support a model in which the surfactant proteins accelerate adsorption by producing a focal tendency to stabilize a negatively curved kinetic intermediate without a general shift to the H(II) phase.

High-throughput evaluation of pulmonary surfactant adsorption and surface film formation

“…We have shown that a direct time-course monitoring of the amount of a fluorescently labeled surfactant reaching the interface, under conditions eliminating the background signal coming from nonadsorbed material, successfully reproduces the outcome of classical methods that follow surfactant adsorption by measuring changes in surface tension (8,(33)(34)(35). The fluorimetric determination, however, can be taken to a multi-well plate reader, permitting carrying out dozens or even hundreds of simultaneous assays, meaning a change in scale with respect to the possibilities of evaluating surfactant performance with desired repetitivity and a proper analysis of statistical significance.…”

“…Deactivation of surfactant by serum components and by inflammatory mediators leaked into the alveolar spaces is thought to be a major determinant of the respiratory failure in acute respiratory distress associated with lung injury (16,47). The surface-inhibitory activity of proteins such as albumin (8,48), fibrinogen (49), C-reactive protein (9,50), or lipases (51) toward surfactant has been well documented, as well as the deactivating effect of metabolites such as neutral lipids (46,52), FFAs (53), bile salts (54), heme derivatives (55), or lysophospholipids (33,53). Lung injury with different sources and to different extents is probably associated with particular complex and possibly multifactorial profiles of surfactant deactivation that have been only preliminarly characterized.…”

The biophysical function of pulmonary surfactant

“…In lipid mixtures without the surfactant proteins, factors that promote formation of the H II phase, including both lipids (Yu et al, 1984; Perkins et al, 1996; Biswas et al, 2007) and peptides (Biswas et al, 2005), accelerate adsorption. Although this observation suggests that adsorption of phospholipids, like the fusion of vesicles, proceeds via a structure with negative curvature, adsorption of these model systems and of pulmonary surfactant could proceed along different pathways.…”

Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature

“…The components of surfactant vesicles insert into the interface collectively (16)(17)(18). As with fusion, several compounds affect adsorption according to how they alter curvature (19)(20)(21)(22)(23). These results suggest that surfactant proteins might accelerate adsorption by facilitating the formation of a negatively curved, rate-limiting intermediate ( Fig.…”