Association and interaction of serum albumin with lung surfactant extract

Vidyasankar, Sangeetha (2004) Association and interaction of serum albumin with lung surfactant extract. Masters thesis, Memorial University of Newfoundland.

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Abstract

Lung surfactant (LS) stabilizes the alveoli during normal respiration by reducing surface tension of the alveolar air-water interface. Among other diseases, dysfunction of the material occurs in acute respiratory distress syndromes (ARDS). During ARDS, plasma proteins leaked from capillaries inhibit LS surface activity. As models for ARDS, bovine lipid extract surfactant (BLES) and dipalmitoylphosphatidylcholine (DPPC) in monolayer and bilayer dispersions, with and without bovine serum albumin (BSA), were studied. The studies were conducted using Langmuir and adsorption surface balances (monolayer), atomic force microscopy (AFM), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Surface balance studies suggested that BSA inhibited surfactant adsorption to the air-water interface to form monolayer films, and such films did not reach low surface tension upon compression. AFM showed the appearance of well-defined gel-like or condensed domains in films of BLES alone, but with BSA added, these domains appeared less defined, more numerous, and other fluid-like new domains were also detected. With DSC, BLES (2 mgs/ml) bilayer dispersions showed a broad gel to liquid crystalline phase transition between 20-40°C, and addition of BSA (12.5-250 wt% of BLES lipids) to BLES (or DPPC) made the transition more diffuse suggesting protein interactions with the bilayer. TEM studies showed elongation of BLES multilamellar vesicles and only minor alterations of such structures with the addition of BSA. FTIR of similar BLES/BSA dispersions suggested that BSA associated with the head group regions of the phospholipid and also affected the hydrophobic tail regions, as monitored from CH₂, C=O and PO₄⁻ vibrational stretching modes. This study suggests that albumin inhibits surfactant by perturbing surfactant lipid packing in monolayers and bilayers. Such alterations may lead to poor surface activity of LS as found in ARDS and other diseases.

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