Three different approaches for the clarification of the interactions between lipoproteins and chondroitin-6-sulfate.

Two different experimental approaches were used for obtaining a comprehensive view and understanding of the interactions between apolipoprotein B-100 (ApoB-100) of low-density lipoprotein and apolipoprotein E (ApoE) of high-density lipoprotein and chondroitin-6-sulfate (C6S) of arterial proteoglycan. The techniques employed were partial filling affinity capillary electrophoresis (PF-ACE) and continuous flow quartz crystal microbalance (QCM). In addition, molecular dynamic (MD) simulations were used to provide a supportive visual insight into the interaction mechanism. A new tool for analysis of QCM-data was utilized, i.e., adsorption energy distribution calculations, which allowed a deeper understanding of the interactions, especially at different temperatures. The PF-ACE technique probed mainly the strong adsorption interactions whereas in the MD calculations short- and long-range interactions could be distinguished. Although there are differences in the techniques, a pretty good agreement was achieved between the three approaches for the interaction of 19 amino acid peptide of ApoB with C6S giving log affinity constants of 4.66 by QCM, 5.02 by PF-ACE, and 7.39 by MD, and for 15 amino acid peptide of ApoE with C6S 5.34 by QCM, 5.28 by PT-ACE, and 4.60 by MD at physiological temperature 37.0 °C.

Sugar treatment of human lipoprotein particles and their separation by capillary electrophoresis.

Entrapment of lipoprotein particles in the extracellular matrix of the arterial intima is a characteristic feature of the development of atherosclerosis, the disease behind myocardial infarction and stroke. In this study, sugars were exploited in the separation of lipoproteins by CE. Monosaccharides, disaccharides and one sugar alcohol used during ultracentrifugal isolation of lipoproteins prevented the strong and unfavorable adsorption of lipoprotein particles on the capillary wall, allowing their selective separation in uncoated fused silica capillary. The effect of ionic strength of the phosphate BGE solution on the separation at physiological pH was clarified. Asymmetrical flow field-flow fractionation and dynamic light scattering showed that sugars affected the structure of lipoproteins by decreasing their sizes. Although in molecular dynamics simulations, only a 19 amino acid peptide of apolipoprotein B-100 and a 15 amino acid peptide of apolipoprotein E were employed, the results also indicated a decrease in lipoprotein size, supporting the asymmetrical flow field-flow fractionation and dynamic light scattering results.

Partial filling affinity capillary electrophoresis with cationic poly(vinylpyrrolidone)-based copolymer coatings for studies on human lipoprotein-steroid interactions.

Human plasma lipoproteins have strong hydrophobic interactions with steroids and their fatty acyl derivatives such as estradiol fatty acyl esters. In this work, affinity capillary electrophoresis with the partial filling technique was applied to study the hydrophobic interactions between lipoproteins, which are nanometer-sized particles, and nonconjugated steroids. The capillaries were first rinsed with one of two novel poly(vinylpyrrolidone) (PVP)-based cationic copolymers that were strongly adsorbed onto the fused-silica surface via electrostatic interactions. This surface treatment greatly suppressed the adsorption of lipoproteins. Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles were then employed in the coated capillaries as pseudostationary phase in the partial filling mode. The changes in corrected migration times of steroids increased linearly with the filling time of the lipoproteins. The affinity constants between the steroids and lipoproteins were calculated, and the most hydrophobic steroid studied, progesterone, had stronger affinity than testosterone or androstenedione toward both LDL and HDL. Affinity between steroids and LDL was stronger than that between steroids and HDL. Interactions between the steroids and lipoproteins were mainly nonspecific with particle lipid components, whereas some were site specific with the apolipoproteins. The developed technique has great potential for determination of the affinity of various compounds toward lipoproteins.