Long- and medium-chain triacylglycerols in neutral lipid-exchange processes with human plasma low-density lipoproteins.

To explore the effects of various molecular species of triacylglycerols on neutral lipid exchange processes, we compared the in vitro transfer of triacylglycerols and cholesteryl esters between phospholipid-stabilized emulsions of medium-chain triacylglycerols (MCT) or long-chain triacylglycerols (LCT) and human plasma low-density lipoproteins (LDL). Incubations were performed with MCT, LCT, or mixed MCT/LCT (1:1, w/w ratio) emulsions with LDL over varying ratios and/or time periods, in the presence or absence of human cholesteryl ester transfer protein (CETP). Relative triacylglycerol mass content increased up to 5-6-fold in LDL with all emulsions, but LDL cholesteryl ester loss was about 33-50% lower with MCT as compared to LCT emulsion. In the absence of CETP, there was a significant transfer of MCT but not of LCT to LDL, and cholesteryl ester exchange never occurred. Spontaneous transfer of MCT in the absence of CETP accounted for half of the total MCT transfer. In fact, CETP-mediated transfer of MCT was less than that of LCT when normalized to the molar concentrations of MCT and LCT in the incubations. Net triacylglycerol accumulation in LDL was accompanied by LDL cholesteryl ester depletion (i.e., exchange), while the greater MCT accumulation could be related to increased solubility at the LDL phospholipid surface (Deckelbaum et al., 1990). This property may also have contributed to some back transfer of MCT from LDL and decreased LDL cholesteryl ester removal, in the presence of MCT emulsions.(ABSTRACT TRUNCATED AT 250 WORDS)