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Transfer and exchange of phospholipid between small unilamellar liposomes and rat plasma high density lipoproteins Dependence on cholesterol content and phospholipid composition

1981; Elsevier BV; Volume: 665; Issue: 3 Linguagem: Inglês

10.1016/0005-2760(81)90268-x

1879-145X

Jan Damen, Joke Regts, Gerrit L. Scherphof,

Lipid metabolism and biosynthesis

We investigated the ability of small unilamellar liposomes of various lipid compositions to maintain their integrity in the presence of rat plasma or plasma fractions. Liposomal damage was determined in terms of release of an entrapped water-soluble marker, carboxyfluorescein, and, simultaneously, loss of liposomal 14C-labeled phospholipid. Complete retentions of carboxyfluorescein during a 30-min incubation with plasma could be attained with liposomes containing at least 40 mol% cholesterol. By substituting sphingomyelin for phosphatidylcholine a considerable prolongation of solute retention was achieved. Sphingomyelin/cholesterol (molar ratio 3 : 2) liposomes retained nearly all of the entrapped dye during a 20-h incubation with plasma, while phosphatidylcholine/cholesterol liposomes lost as much as 40%. Incorporation of cholesterol also reduces the transfer of 14C-labeled phospholipid from liposomes to plasma HDL. While transfer of phosphatidylcholine was partially reduced, transfer of sphingomyelin was completely inhibited under the same conditions. Isolated HDL was unable to bring about the extent of carboxyfluorescein release and phospholipid transfer which was observed with whole plasma, but required the addition of lipoprotein-free plasma. The subfraction of HDL that is rich in apolipoprotein E (HDL1) plays at most a minor role in liposome-plasma interactions. Native HDL phospholipids were biosynthetically labeled with 32P and isolated HDL was incubated with 14C-labeled liposomes in presence of lipoprotein-free plasma. In this way we demonstrated that, whereas phosphatidylcholine transfer from cholesterol-poor liposomes is mainly an unidirectional process leading to excessive liposome degradation, phosphatidylcholine transfer from cholesterol-rich liposomes involves an exchange process and is attended by almost complete retention of entrapped solute.