Micellar solubilization of cholesterol and of mixtures of cholesterol with cholesteryl esters of C18 fatty acids by a nonionic surfactant

Solubilization of polycyclic aromatic hydrocarbon mixtures in micellar nonionic surfactant solutions

This study sought to examine the solubilization of mixtures of the polycyclic aromatic hydrocarbons (PAHs) in solutions of the nonionic surfactants: Tween 20, Tween 80, Triton X 100, Brij 35, and Brij 58. When pyrene (PYR), fluoranthene (FLA), and phenanthrene (PHE) were solubilized from two-PAH mixtures, the PAH concentrations and molar solubilization ratios deviated very little from those as found in the single-PAH systems. When these PAHs were solubilized from the three-PAH mixtures, however, not all three PAHs reached their single-PAH solubilities. When the PAHs were added sequentially to surfactant solution, the PAH added last reached its single-PAH solubility, while the concentration of other two PAHs were lowered by 14-45%. When the PAHs were added simultaneously to the surfactant solution, the composition of the solid phase influenced which PAH reached its single-PAH solubility. For solids containing equal mole fractions of all three PAHs, FLA and PHE dissolved in surfactant solution to a lesser extent than the single-PAH systems. In similar systems containing no surfactant, only FLA solubility decreased. As the mole fraction of a PAH in the solid phase increased, its solubility in the micelle phase (and in the aqueous phase) increased up to the solubility limit. Based on these studies, both PAH-PAH interactions and micelle-PAH interactions should be taken into account when predicting the concentrations of PAH mixtures in micellar surfactant solutions. This should be done because PAH-PAH interactions can influence aqueous solubility, while micelle-PAH interactions can affect the distribution of PAHs in the micellar phase, which may change as the mixture composition changes.

Effects of substrate composition on the esterification and hydrolysis activity of lysosomal acid sterol ester hydrolase

Lipid microemulsions with various core and surface lipid compositions were prepared by co-sonication of cholesteryl esters, triolein (TO), egg phosphatidylcholine (egg PC), and cholesterol. The heterogeneous emulsion particle mixture was purified by gel filtration and particles with the size and general organization of low density lipoproteins were obtained. These lipid microemulsion particles were used for studies of the cellular metabolism of lipoprotein-derived cholesterol and cholesteryl esters as catalyzed by the enzyme acid sterol ester hydrolase (EC 3.1.1.13). The hydrolysis of cholesteryl oleate (CO) was more than twice and that of cholesteryl linoleate (CL) more than three times faster than the hydrolysis of cholesteryl stearate (CS) over the temperature range 25-39.6 degrees C. Both the synthesis and hydrolysis of cholesteryl esters were insensitive to the physical state of the microemulsion cores. The synthesis of cholesteryl esters by this enzyme was also insensitive to the ratios of cholesterol and egg PC in the microemulsion surface layers. Incorporation of triolein into the microemulsion cholesteryl ester core slightly increased the rate of cholesteryl ester synthesis. A decreasing fatty acyl chain length (C18:0 to C14:0) and an increasing degree of unsaturation (C18:0 to C18:2) enhanced the synthesis rate. It is suggested that the hydrolysis and synthesis of cholesteryl esters in microemulsions (and lipoproteins) take place only in the particle surface layer and that the rate of catalysis is directly dependent on the amount of substrate in this surface layer.