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Journal of Lipid Research, Vol 38, 1242-1253, Copyright © 1997 by Lipid Research, Inc.
A natural apolipoprotein A-I variant, apoA-I (L141R)Pisa, interferes with the formation of alpha-high density lipoproteins (HDL) but not with the formation of pre beta 1-HDL and influences efflux of cholesterol into plasma
R Miccoli, Y Zhu, U Daum, J Wessling, Y Huang, R Navalesi, G Assmann and A von Eckardstein
Institut fur Arterioskleroseforschung, Universitat Munster, Germany.
ApoA-I(L141R)Pisa is a naturally occurring apolipoprotein A-I variant that
causes virtual absence of HDL in hemizygotes and hypoalphalipoproteinemia
with half-normal levels of HDL-cholesterol in heterozygotes. In this study
we analyzed the distribution of HDL subclasses in plasmas of four
hemizygotes for this mutation. We also investigated the abilities of these
plasmas to esterify cholesterol and to promote cholesterol efflux. Residual
apoA-I-containing lipoproteins in plasmas of hemizygotes for
apoA-I(L141R)Pisa correspond to pre beta 1-LpA-I and small alpha-LpA-I.
Unlike normal pre beta 1-LpA-I, pre beta 1-LpA-I of apoA-I(L141R)Pisa
hemizygotes was not converted into a larger alpha-migrating particle.
Plasmas of apoA-I(L141R)Pisa hemizygotes were significantly reduced in
their activity to esterify cholesterol in either endogenous or exogenous
lipoproteins. Cholesterol efflux capacity was significantly lower than that
of normal plasma. Efflux of [3H] cholesterol from radiolabeled fibroblasts
into apoB- depleted plasma of normal probands was biphasic with fast
cholesterol efflux occurring in the first minute. Thereafter, cholesterol
efflux was slow and unsaturable. After incubation with radiolabeled
fibroblasts, efflux values of [3H]cholesterol into apoB-depleted plasma
from normal controls and from apoA-I(L141R)Pisa hemizygotes were
indistinguishable at 1 min. Longer incubations with apoB-free plasma from
apoA-I(L141R)Pisa hemizygotes did not, however, lead to the unsaturable
increase in cholesterol efflux that was observed during incubations with
apoB-free plasma of normolipidemic probands. Pre beta 1-LpA-I of
apoA-I(L141R)Pisa hemizygotes took up significantly less cell-derived
[3H]cholesterol than pre beta 1-LpA-I of normal donors. We conclude that
apoA-I(L141R)Pisa interferes with the formation of lipid- rich alpha-HDL
but not with that of lipid-poor pre beta 1-LpA-I. Very low concentrations
of alpha-HDL in plasmas of apoA-I(L141R)Pisa hemizygotes combined with
reduced LCAT activity cause a decrease of the slow, unspecific, and
LCAT-dependent components of cholesterol efflux into plasma.

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Copyright © 1997 by the American Society for Biochemistry and Molecular Biology.
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