Lysozyme Influence on Monolayers of Individual and Mixed Lipids

Abstract

Fatty acids, cholesterol, and phospholipids are amphiphilic compounds of biological interest, which form ordered monolayers mimicking biomembranes, and can be studied with the Langmuir technique using surface pressure-area isotherms and compressibility plots. Proteins are also components of biomembranes or are present in body fluids. In this study, the influence of lysozyme on different films of a fatty acid (stearic acid or oleic acid), cholesterol, a phospholipid (dipalmitoylphosphatidylcholine, DPPC, or palmitoyloleoylphosphatidylcholine, POPC), and mixtures of them is presented using a 0.9% saline solution as subphase. Results show that the presence of lysozyme alters the lipid monolayer formation in an important way at the beginning (low surface pressures) and the middle (intermediate surface pressures) parts of the isotherm. At high surface pressures, the phospholipids DPPC and POPC and the saturated fatty acid, stearic acid, expel lysozyme from the surface, while oleic acid and cholesterol permit the presence of lysozyme on it. The mixtures of oleic acid-DPPC also expel lysozyme from the surface at high surface pressures, while mixtures of oleic acid-POPC and cholesterol-POPC permit the presence of lysozyme on it. The compressibility of the monolayer is affected in all cases, with an important reduction in the elastic modulus values and an increase in the fluidity, especially at low and intermediate surface pressures.

Cholesterol Alters the Phase Separation in Model Membranes Containing hBest1

“…Cs −1 (max) was 56 mN/m for the monolayer in a NaCl subphase versus 60 mN/m for the monolayer in a NaCl subphase supplemented with CaCl2, which is slightly above the upper limit of 50 mN/m suggested by Davies and Rideal [27] for the LE phase. These values are higher than the Cs −1 (max) of the hBest1 monolayers (10.7 mN/m according to [17]) and considerably lower than the Cs −1 (max) of the POPC (∼110 mN/m according to [34]) and the Chol (839 mN/m according to [35]) monolayers, which is an indication of mixing the three components of this ternary monolayer. The LE state of the hBest1/POPC/Chol monolayer and the reduced value of πcol also indicate very good mixing of the monolayer components.…”

Drug Release from Lipid Microparticles—Insights into Drug Incorporation and the Influence of Physiological Factors

“…Lysozyme is abundant in the tear fluid and has antimicrobial activity. Although lysozyme is not a typical lipolytic enzyme digesting the lipid matrix of microparticles, the interaction of lysozyme present in the aqueous layer of the tear film with lipids (fatty acids, cholesterol, phospholipids, and their mixtures) present in the lipid layer and other lipid films is a subject of current research [ 42 ]. Therefore, it was considered justified to clarify whether lysozyme used in vitro mimics the in vivo conditions.…”