Journal of Lipid Research, Vol 21, 993-1003, Copyright © 1980 by Lipid Research, Inc.
Interaction of unilamellar liposomes with serum lipoproteins and apolipoproteins
LS Guo, RL Hamilton, J Goerke, JN Weinstein and RJ Havel
The effect of rat whole blood plasma, serum, serum lipoproteins, and
apolipoproteins on the stability of unilamellar liposomes prepared with
French pressure cell was evaluated by measuring the release of entrapped
carboxyfluorescein and by electron microscopy. In the absence of serum
components, dye escaped very slowly (hours) from egg phosphatidylcholine
and phosphatidylcholine-cholesterol (43 mol % cholesterol) vesicles without
apparent change in liposomal structure. This slow release was both
temperature- and size-dependent. serum and some of its constituents induced
a far more rapid (seconds) loss of entrapped dye from phosphatidylcholine
liposomes, associated with structural changes. For equal masses of protein
the order of potency of this induced activity was: free apolipoproteins
(apo A-I, apo E) > isolated lipoproteins (HDL and VLDL) > whole serum
or whole plasma. Substantial activity was found in three preparations of
bovine serum albumin. This activity could be attributed to small and
variable amounts of contaminating lipoprotein-like particles and
apolipoprotein A-I. Induced release of dye from liposomes by
apolipoproteins was usually associated with rapid formation of discs
although other structures were sometimes formed. Purified rat
apolipoproteins A-I and E appeared to interact identically with liposomes
to induce dye release. This effect was progressively impaired for both
apoproteins by increasing amounts of cholesterol and was completely
inhibited when liposomes contained 37 mol % cholesterol.
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