Surfactant protein interactions with neutral and acidic phospholipid films

Abstract

The captive bubble tensiometer was employed to study interactions of phospholipid (PL) mixtures of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) at 50 microg/ml with physiological levels of the surfactant protein (SP) A SP-B, and SP-C alone and in combination at 37 degrees C. All surfactant proteins enhanced lipid adsorption to equilibrium surface tension (gamma), with SP-C being most effective. Kinetics were consistent with the presence of two adsorption phases. Under the conditions employed, SP-A did not affect the rate of film formation in the presence of SP-B or SP-C. Little difference in gamma(min) was observed between the acidic POPG and the neutral POPC systems with SP-B or SP-C with and without SP-A. However, gamma(max) was lower with the acidic POPG system during dynamic, but not during quasi-static, cycling. Considerably lower compression ratios were required to generate low gamma(min) values with SP-B than SP-C. DPPC-POPG-SP-B was superior to the neutral POPC-SP-B system. Although SP-A had little effect on film formation with SP-B, surface activity during compression was enhanced with both PL systems. In the presence of SP-C, lower compression ratios were required with the acidic system, and with this mixture, SP-A addition adversely affected surface activity. The results suggest specific interactions between SP-B and phosphatidylglycerol, and between SP-B and SP-A. These observations are consistent with the presence of a surface-associated surfactant reservoir which is involved in generating low gamma during film compression and lipid respreading during film expansion.

Pulmonary Surfactant Protein-A (SP-A) Restores the Surface Properties of Surfactant after Oxidation by a Mechanism That Requires the Cys6 Interchain Disulfide Bond and the Phospholipid Binding Domain

“…Compressibility at ␥ 20 (C 20 ) was 0.078 Ϯ 0.020. As reported previously, control BLES adsorbed at 50 g/ml required ϳ60% surface area reduction to lower ␥ from equilibrium (23 mN/m) to near zero during the first compression (16,35,42).…”

“…Effect of Free Radical Exposure on Surfactant Function-The effects of free radical exposure on surfactant function were studied with the CBT (16,35). With this apparatus, the ability of a surfactant to adsorb to the interface is assessed, after which surface area compression-expansion isotherms are performed, either quasi-statically or dynamically, to evaluate the surface properties of the sample under conditions that mimic…”

Chitosan Enhances the In Vitro Surface Activity of Dilute Lung Surfactant Preparations and Resists Albumin-Induced Inactivation

“…To resist or reverse the inactivation, the phospholipid components of lung surfactant must overcome these barriers by adsorbing more rapidly than albumin and/or effectively replacing the albumin molecules at the interface. Chitosan may outperform the nonionic polymers in mitigating the electrostatic barrier imposed by albumin by providing extra positive charges, similar to the function of lung surfactant proteins (21,36,37).…”

Lipid compositional analysis of pulmonary surfactant monolayers and monolayer-associated reservoirs

“…The resulting DPPC enrichment is considered necessary in order for the monolayer to achieve the low surface tensions required to stabilize the lung. Recently, a number of physicochemical studies have demonstrated that low surface tension can be achieved with smaller surface area reductions than would be predicted by the squeeze-out mechanism (43)(44)(45)(46). It has consequently been proposed that sorting or refining of surfactant lipids occurs during adsorption so as to generate a monolayer already enriched in DPPC (3-7, 37, 38).…”

“…Recent physicochemical measurements have demonstrated that surface area reductions required to attain surface tensions near 0 mN/m during initial film compression of adsorbed surfactant films can be lower than that predicted by the DPPC content of surfactant (37,(43)(44)(45)(46). These observations led to the proposal that the surface monolayer may become enriched in DPPC during adsorption (3-6, 37, 38).…”