Restoring the charge and surface activity of bovine lung extract surfactants with cationic and anionic polysaccharides.

Chitosan, a cationic polysaccharide, has been found to improve the surface activity of lung surfactant extracts in the presence of various inhibitors. It has been proposed that chitosan binds to anionic lipids (e.g. phosphatidyl glycerols) in lung surfactants, producing stable lipid films at the air-water interface. This binding also reverses the net charge of the surfactant aggregates, from negative to positive. Unfortunately, positively charged aggregates may adsorb or interact with the negatively charged epithelial tissue, leading to poor surfactant performance. To address this issue an anionic polysaccharide, dextran sulfate (dexS), was used as a secondary coating to reverse the charge of chitosan-lung surfactant extracts without affecting the surface activity of the preparation. The dynamic surface tension and zeta potential of bovine lipid extract surfactant (BLES) containing chitosan chloride (chiCl) and dexS were evaluated as a function of dexS concentration. These studies were conducted in the absence and presence of sodium bicarbonate buffer, and in the absence and presence of bovine serum used as model inhibitor. It was determined that using an appropriate concentration of dexS, especially at physiological pH, it is possible to restore the negative charge of the surfactant aggregates, and retain their surface activity, even in the presence of bovine serum. High concentrations of dexS affect the binding of chiCl to BLES, and the surface activity of the preparation.