Influence of pH on sphingomyelin monolayer at air/aqueous solution interface

Effect of phospholipid matrix on emulsion stability, microstructure, proteolysis, and in vitro digestibility in model infant formula emulsion

The effects of adding different phospholipid (PL) matrices [milk sphingomyelin (SM) vs soy phosphatidylcholine (PC)] on emulsion stability, microstructure, and in vitro simulated lipid digestion were examined using a Model Infant Formula Emulsion (MIFE). The emulsion stability of MIFE increased significantly with PL addition (0.1 and 0.2 %). Compared to sole MIFE or MIFE + PC, the incorporation of SM resulted in increased emulsion stability (p < 0.05) and a greater amount of free fatty acid release (p < 0.05) during in vitro simulated digestion. This was mainly due to the reduction of intensive droplet aggregation, thus providing a large surface area and improved digestibility. This is further experimentally supported by the evolution of particle size distribution, zeta-potential, and microstructure analysis using confocal laser scanning microscopy. The incorporation of SM in the emulsion formation significantly delayed digestion of β-lactoglobulin during in vitro digestion. Lipid digestibility in MIFE was altered depending on the type of PL matrix, and SM displayed a superior effect to PC. Thus, the creation of a novel emulsion interface by the appropriate selection of emulsifiers can be used to improve lipid digestion in infants and obtain desirable nutritional consequences.

Binding of trivalent metal ions (Al3+, In3+, La3+) with phosphatidylcholine liposomal membranes investigated by microelectrophoresis

Interactions between trivalent metal ions (Al³⁺, In³⁺, La³⁺) and phosphatidylcholine (PC) liposomes are studied by microelectrophoresis. The dependence of the PC membrane surface charge density and zeta potential on [Formula: see text] ([Formula: see text] range from 2 to 10) of the aqueous metal chloride solutions is determined. The obtained results indicate the adsorption of Al³⁺, In³⁺ and La³⁺ ions on phosphatidylcholine model membranes, leading to changes in the electrical properties of the membranes. The theoretical considerations on equilibria occurring between phosphatidylcholine liposomal membrane and trivalent metal ions are presented. A mathematical model describing the interactions in a quantitative way is proposed.

The effect of divalent ions on L-α-phosphatidylcholine from egg yolk monolayers at the air/water interface

The Langmuir monolayers of L-α-phosphatidylcholine from egg yolk were studied by Wilhelmy method. The surface pressure versus molecular area isotherm of lipid on pure water and different subphase (with a presence of divalent ions: Sr²⁺, Cd²⁺, Ba²⁺, Pb²⁺) was obtained. The limiting area of the isotherms depends on the presence of subphase ions. The addition of divalent ions to the subphase stabilized the monolayers and increased the limiting areas of the monolayer. During the compression in monolayer complexes of 1:1 and 2:1 stoichiometry between L-α-phosphatidylcholine from egg yolk and divalent ions are formed. We used the equilibrium theory to describe the behavior of monolayer components at the air/water interface. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants and area occupied by one molecule of LMe²⁺ or L₂Me²⁺ complexes, and complex formation energy (Gibbs free energy) values. These mathematically derived and experimentally confirmed values are of great importance for the interpretation of phenomena occurring in lipid monolayers and bilayers.

Pathological levels of glucosylceramide change the biophysical properties of artificial and cell membranes

Accumulation of glucosylceramide decreases membrane fluidity in artificial membranes and in cell models of Gaucher disease.

Phosphatidylcholine-fatty Alcohols Equilibria in Monolayers at the Air/Water Interface

Monolayers of phosphatidylcholine (PC), tetradecanol (TD), hexadecanol (HD), octadecanol (OD) and eicosanol (E) and their binary mixtures were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate π–A isotherms. The surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. The interactions between phosphatidylcholine and fatty alcohols (tetradecanol, hexadecanol, octadecanol, eicosanol) result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants, Gibbs free energy values and areas occupied by one molecules of PC–TD, PC–HD, PC–OD and PC–E complexes. We considered the equilibrium between the individual components and the complex and established that phosphatidylcholine and fatty alcohols formed highly stable 1:1 complexes.

Influence of intracellular membrane pH on sphingolipid organization and membrane biophysical properties

Glucosylceramide (GlcCer) is a signaling lipid involved in the regulation of several cellular processes. It is present in different organelles, including the plasma membrane, Golgi apparatus, endoplasmic reticulum, and lysosomes. Accordingly, GlcCer is exposed to different pH environments in each organelle, which may lead to alterations in its properties and lateral organization and subsequent biological outcome. In this study, we addressed the effect of pH on the biophysical behavior of this lipid and other structurally related sphingolipids (SLs). Membranes composed of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and C16-GlcCer, sphingomyelin, and different acyl chain ceramides were characterized by fluorescence spectroscopy, confocal microscopy, and surface pressure-area measurements under neutral and acidic conditions. The results show that changing the pH from 7.4 to 5.5 has a larger impact on C16-GlcCer-containing membranes compared to other SLs. In addition, acidification mainly affects the organization and packing properties of the GlcCer-enriched gel phase, suggesting that the interactions established by the glucose moiety, in the GlcCer molecule, are those most affected by the increase in the acidity. These results further highlight the role of GlcCer as a modulator of membrane biophysical properties and will possibly contribute to the understanding of its biological function in different organelles.