Spontaneous and plasma factor-mediated transfer of pyrenyl cerebrosides between model and native lipoproteins

A series of pyrenyl glucocerebrosides was synthesized by reacylation of psychosine with pyrene-labeled fatty acids having 3-11 methylene units. When incorporated into model high-density lipoproteins consisting of dimyristoylphosphatidylcholine-apolipoprotein A-II complexes and incubated with unlabeled complexes, these lipids exhibited spontaneous transfer. Half times of transfer varied from 1.5 min to 365 min at 37° C. The logarithm of the rate of transfer was linearly related to the number of fatty acyl methylene units and HPLC retention time. Transfer occurred by passage of lipid monomers through the aqueous phase. Spontaneous transfer of the glycolipids also occurred when they were incorporated into native high-density lipoproteins. Rates of transfer between native high-density lipoprotein particles were higher than those observed between model high-density lipoprotein particles. A partially purified lipid exchange protein from plasma, as well as unfractionated lipoprotein-deficient serum, stimulated the transfer of fluorescent glycolipid between model high-density lipoprotein or native high-density lipoprotein and low-density lipoprotein 2-24 fold. The protein also stimulated the transfer of tritiated ganglioside G_M3 between native low-density lipoprotein and high-density lipoprotein. This protein may play a role in glycolipid exchange in vivo.