Journal of Lipid Research, Vol 29, 1405-1415, Copyright © 1988 by Lipid Research, Inc.
Behavior of human apolipoprotein A-I: phospholipid and apoHDL:phospholipid complexes in vitro and after injection into rabbits
J Koizumi, M Kano, K Okabayashi, A Jadhav and GR Thompson
MRC Lipoprotein Team, Hammersmith Hospital, London, U.K.
Apolipoprotein A-I was purified from human high density lipoprotein and
complexed with polyunsaturated phosphatidylcholine (PC) in deoxycholate
(Lipostabil); the bile salt was removed subsequently by dialysis. The
behavior of the resultant apoA-I/PC complexes was compared with that of
Lipostabil in vitro and after injection into rabbits. In vivo apoA-I/PC
complexes had the density of HDL throughout but had both alpha and pre beta
electrophoretic mobility, the latter probably reflecting dissociation of
apoA-I from PC. Lipostabil initially behaved like LDL but gradually
acquired the density of HDL after incubation with plasma and in vivo. Both
preparations increased plasma total phospholipids in normolipidemic rabbits
to a similar extent, but, increments in HDL phospholipid were greater after
apoA-I/PC complexes were injected. ApoHDL/PC complexes, prepared in a
similar manner, appeared to promote efflux of cholesterol from perfused
rabbit aortas in the presence of lecithin:cholesterol acyltransferase
(LCAT) activity, consistent with a stimulatory effect on cholesterol
mobilization. Injection of apoHDL/PC complexes into hyperlipidemic rabbits
decreased plasma cholesterol but increased HDL cholesterol, whereas
Lipostabil decreased both. These findings suggest that human apoA-I/PC
complexes resemble HDL in their behavior more closely than does Lipostabil,
and show that both types of liposome undergo modification upon interaction
with plasma. It remains to be shown whether they possess any therapeutic
potential.