Competitive Adsorption of Lung Surfactant and Serum Proteins at the Air-Liquid Interface: A Grazing Incidence X-Ray Diff
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1027-D05-09
Competitive Adsorption of Lung Surfactant and Serum Proteins at the Air-Liquid Interface: A Grazing Incidence X-Ray Diffraction Study Patrick C Stenger1, Guohui H Wu1, Eva Y Chi2, Shelli L Frey2, Ka Yee C Lee2, Jaroslaw Majewski3, Kristian Kjaer4, and Joseph A Zasadzinski1 1 Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106-5080 2 the University of Chicago, Chicago, IL, 60637 3 Los Alamos National Laboratory, Los Alamos, NM, 87545 4 Risø National Laboratory, Roskilde, Denmark ABSTRACT The competitive adsorption of lung surfactant (LS) and albumin at the air-liquid interface and the ability of polyethylene glycol (PEG) to mediate LS adsorption are analyzed using pressure-area isotherms and grazing incidence x-ray diffraction (GIXD). The addition of albumin drastically reduces the amount of LS on the interface and slightly increases the LS lattice spacing. The addition of PEG restores the characteristic LS peaks, yielding a slightly more compact lattice. The scattering results are consistent with recent work which proposed that albumin creates a physical barrier which eliminates LS adsorption and that PEG enhances LS adsorption but does not significantly change LS surface ordering. INTRODUCTION Lung surfactant (LS) is a unique mixture of lipids and proteins that lines the alveolar air-liquid interface and lowers the surface tension in the lungs, thereby insuring negligible work of breathing and uniform lung inflation [1]. The surface tension control imposed by LS is compromised during Acute Respiratory Distress Syndrome (ARDS) which afflicts 140,000 annually with a 40% mortality rate in the US [2]. The complex pathogenesis of ARDS includes increased permeability of the alveolar-capillary barrier yielding an influx of blood serum proteins into the bronchial and alveolar fluid [3]. In vitro, LS mixed with serum proteins shows an ARDS-like decrease in performance; surfactant inactivation caused by serum protein leakage into the alveoli is one reason why treatment of ARDS with replacement LS is unsuccessful [4]. One possible cause of surfactant inactivation is the competitive adsorption of surface-active serum proteins (such as albumin) that reduces or even eliminates the normal adsorption of LS to the interface [4]. Albumin is surface-active and has a surface pressure, Π, (Π = γw-γ; γw is the surface tension of a clean air-water interface, 72 mN/m, and γ the measured surface tension) that is a logarithmic function of protein concentration up to a saturation concentration, which is ~1 mg/mL for albumin [4]. The saturation surface pressure for albumin is Π ∼18 mN/m, much lower than the Π ∼70 (γ near zero) required for proper respiration [4]. This competitive adsorption of albumin to the alveolar air-liquid interface leads to a steric and electrostatic energy barrier to LS adsorption which can lower the rate of LS transport to the interface [5]. Several hydrophilic polymers, such as PEG have recently been shown to enhance the ability of replacement LS to resist serum inactiv
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