L. Krimbou et al., IN-VITRO FACTORS AFFECTING THE CONCENTRATION OF GAMMA-LPE (GAMMA-LPE)IN HUMAN PLASMA, Journal of lipid research, 39(4), 1998, pp. 861-872
Gamma-LpE (gamma-LpE), a sphingomyelin-rich lipoprotein that contains
apolipoprotein (ape) E as its only protein component, has been propose
d to play a role in cellular cholesterol efflux by acting, like pre-be
ta(1)-LpA-I, as an initial acceptor of cell-derived cholesterol. In or
der to further char acterize the presence of gamma-LpE in human plasma
, we have separated gamma-LpE by two-dimensional non-denaturing polyac
rylamide-gradient gel electrophoresis and detected its presence by imm
unoblotting with I-125-labeled polyclonal anti-apoE antibody. Five spe
cies of gamma-LpE were routinely detected in human plasma, ranging in
mean particle diameter from 9.5 to 16.5 nm. The largest proportion of
gamma-migrating apoE was associated with gamma(2)-LpE having a diamete
r of 13.0 nm. Neither the amount of gamma-LpE apoE (representing less
than 1-2% of total plasma apoE) nor the number of gamma-LpE subfractio
ns was different in serum vs. plasma, or was affected by the presence
of agents able to inhibit protein dimerization. gamma-LpE subfractions
were present in the plasma of patients having different apoE phenotyp
es (i.e., apoE 2/2, 3/3, or 4/4). Incubation of plasma at 37 degrees C
(90 min) caused a significant decrease in plasma gamma-LpE (>80%) tha
t was not dependent on LCAT or CETP activity. Storage (at -70 degrees
C) of hypertriglyceridemic but not normolipidemic plasma resulted in a
n increase in gamma-LpE. Freezing of postprandial plasma samples, cont
aining increased amounts of triglyceride-rich lipoproteins (TRL) enric
hed in apoE, also caused an increase in gamma-LpE. Incubation of VLDL
(d < 1.006 g/ml) with lipase resulted in the production of gamma-migra
ting apoE. These results demonstrate that: 1) different gamma-LpE subf
ractions exist in human plasma; 2) the amount of apoE associated with
gamma-LpE subfractions is dependent on in vitro conditions of plasma s
torage; and 3) TRL can act as a source of gamma-LpE apoE in vitro.