Cholesterol-ester prevents lipoprotein core from solidifying: Molecular dynamics simulation

As an important part of lipid metabolism the liver produces large particles called very low density lipoproteins, filled mostly with triglyceride and cholesterol esters mixture. A large percentage of the mixture composition components has a melting point above physiological temperature. Thus solid cluster formation or phase transition could be expected. Though various single-component triglyceride systems are well researched both experimentally and by various simulation techniques, to our best knowledge, tripalmitin/cholesteryl-palmitate binary mixture was not yet studied. We study tripalmitin single component system, as well as 20%-80% and 50%-50% binary mixtures of cholesteryl-palmitate and tripalmitin using molecular dynamics approach. All systems are studied at the pressure of 1 atm and the physiological temperature of 310 K, which is below the melting points of both tripalmitin and cholesteryl-palmitate. Our results show that at the time of 1000 ns, there is still no phase transition, but there is a noticeable tendency to intermolecular organizing and early signs of clustering. We check fatty acid arrangements of tripalmitin molecules in both single component system and binary mixtures with two different percentages of cholesteryl-palmitate mixed in. Our results show that the more cholesteryl-palmitate molecules are in the mixture the smaller number of tripalmitin molecules transitions to 'a fork/chair' configuration during the same calculation time. Calculated angle distributions between fatty acid chains of tripalmitin molecules confirm that. Thus, our simulation results suggest slowing down or interfering effect of cholesteryl-palmitate on the crystallizing process of the binary mixture.