Cholesteryl ester transfer from phospholipid vesicles to human density lipoproteins

The exchange of cholesteryl esters between different lipoproteins was reported to bae mediated by a protein present in human plasma. In this study wer have examined the movement of cholesteryl ester from unilamellar phospholipid vesicles to high density lipoprotein (HDL). Experimental conditions were establisehd so that vesicles containing egg yolk lecithin and cholesteryl oleatea (molar ratio of 86:1) could be incubated with human HDL so that neaither disruption of particles nor transfer of lipid occurred. Addition of human lipoprotein-deficient plasma to the system promoted the transfer of cholesteryl oleate, but not phospholipid, from vesicles to HDL. Cholesteryl oleate transfer was dependent upon amount of HDL or lipoproteain-deficient plasma added and occurred when either HDL2 or HDL3 were present. Addition of unesterified cholesterol to the vesicles did not influence lcholesteryl ester transfer to HDL. When phospholipid vesicles containing both cholesteryl oleate and triolein (molar ratio 86:1:1) were incubated with HDL and lipoprotein-deficient plasma, only cholesteryl oleate was transferred from the vesicles to HDL. Lipoprotein-deficient plasma derived from rabbits promoted the selective transfer of cholesteryl oleate from these visicles, but rat plasma did not cause any movement of cholesteryl oleate or triolein from vesicles to HDL. HDL containing labeled cholesteryl esters was prepared and incubated with vesicles containing unlabeled cholesteryl esters or phospholipid alone. Addition of lipoprotein-deficient plasma did not promote transfer of cholesteryl esters from HDL to vesicles, whereas transfer from HDL to low density lipoprotein was readily observed. The results indicated that a protein present in rabbit and human plasma is effective in the selective, unidirectional transport of cholesteryl esters from a phospholipid bilayer to a plasma lipoprotein.