34 research outputs found
Characterization of human high-density lipoprotein subclasses LP A-I and LP A-I/A-II and binding to HepG2 cells
Abstract
Plasma HDL can be classified according to their apolipoprotein content into at least two types of lipoprotein particles: lipoproteins containing both apo A-I and apo A-II (LP A-I/A-II) and lipoproteins with apo A-I but without apo A-II (LP A-I). LP A-I and LP A-I/A-II were isolated by immuno-affinity chromatography. LP A-I has a higher cholesterol content and less protein compared to LP A-I/A-II. The average particle mass of LP A-I is higher (379 kDa) than the average particle weight of LP A-I/A-II (269 kDa). The binding of 125I-LP A-I to HepG2 cells at 4°C, as well as the uptake of [3H]cholesteryl ether-labelled LP A-I by HepG2 cells at 37° C, was significantly higher than the binding and uptake of LP A-I/A-II. It is likely that both binding and uptake are mediated by apo A-I. Our results do not provide evidence in favor of a specific role for apo A-II in the binding and uptake of HDL by HepG2 cells
Dietary trans fatty acids increase serum cholesterylester transfer protein activity in man
The average diet may provide some 8–10 g/day of unsaturated fatty acids with a trans double bond. Previous studies showed that dietary trans fatty acids may simultaneously raise low-density lipoprotein (LDL) cholesterol and reduce high-density lipoprotein (HDL) cholesterol. Human plasma contains a protein (CETP) which transfers cholesterylesters from HDL to lipoproteins of lower density. We hypothesized that CETP could play a role in the effect of trans fatty acids on lipoproteins and measured the activity levels of CETP in serum samples from a 9-week study in which 55 volunteers were fed three controlled diets with different fatty acid profiles. Mean activity was 114 (% of reference serum) after consumption of a high trans fatty acid diet, as opposed to 96 after linoleic acid and 97 after stearic acid (P < 0.02). We conclude that the increased activity of CETP may contribute to the rise in LDL cholesterol and the fall in HDL cholesterol seen on diets with high contents of trans fatty acids
Turnover and uptake by organs of radioactive serum high-density lipoprotein cholesteryl esters and phospholipids in the rat in vivo
Induction of adrenal scavenger receptor BI and increased high density lipoprotein-cholesteryl ether uptake by in vivo inhibition of hepatic lipase
Hepatic lipase (HL) and scavenger receptor type B class I (SR-BI) have
both been implicated in high density lipoprotein (HDL)-cholesteryl ester
uptake in cholesterol-utilizing tissues. Inactivation of HL by
gene-directed targeting in mice results in up-regulation of SR-BI
expression in adrenal gland (Wang, N., Weng, W., Breslow, J. L., and Tall,
A. R. (1996) J. Biol. Chem. 271, 21001-21004). The net effect on
HDL-cholesteryl ester uptake is not known. We determined the impact of
acute in vivo inhibition of rat adrenal HL activity by antibodies on SR-BI
expression and on human and rat HDL-[3H]cholesteryl ether (CEth) uptake in
the adrenal gland. Rat HDL was isolated from rats in which HL activity had
been inhibited for 1 h. The rats were studied under basal conditions (not
ACTH-treated) and after previous treatment with ACTH for 6 days
(ACTH-treated). Intravenous injection of anti-HL resulted in 70% lowering
of adrenal HL activity in both conditions which were maintained for at
least 8 h. In not ACTH-treated rats, inhibition of adrenal HL increased
adrenal SR-BI mRNA (5.2-fold) and mass (1. 6-fold) within 4 h. HL
inhibition resulted in 41% and 14% more adrenal accumulation of human
HDL-[3H]CEth during 4 and 24 h, respectively. The adrenal uptake of rat
HDL-[3H]CEth increased by 68%, 4 h after the antibody injection. ACTH
treatment increased total adrenal HL activity from 3.7 +/- 0.5 milliunits
to 34.0 +/- 17. 2 milliunits, as well as adrenal SR-BI mRNA from 2.9 +/-
0.7 arbitrary units (A.U.) to 86.8 +/- 41.1 A.U. and SR-BI mass from 7.7
+/- 1.8 A.U. to 63.16 +/- 46.7 A.U. The human HDL-[3H]CEth uptake by
adrenals was also significantly increased from 0.58 +/- 0.11% of injected
dose to 7.24 +/- 1.58% of injected dose. Inhibition of adrenal HL activity
did not result in further induction of SR-BI expression and did not affect
human HDL-[3H]CEth uptake. These findings indicate that SR-BI expression
may be influenced by changes in HL activity. HL activity is not needed for
the SR-BI-mediated HDL-cholester
Elevation of plasma phospholipid transfer protein in transgenic mice increases VLDL secretion
Two lipid transfer proteins are active in human plasma, cholesteryl ester
transfer protein (CETP), and phospholipid transfer protein (PLTP). Mice by
nature do not express CETP. Additional inactivation of the PLTP gene
resulted in reduced secretion of VLDL and subsequently in decreased
susceptibility to diet-induced atherosclerosis. The aim of this study is
to assess possible effects of differences in PLTP expression on VLDL
secretion in mice that are proficient in CETP and PLTP. We compared human
CETP transgenic (huCETPtg) mice with mice expressing both human lipid
transfer proteins (huCETPtg/huPLTPtg). Plasma cholesterol in huCETPtg mice
was 1.5-fold higher compared with huCETPtg/huPLTPtg mice (P < 0.001). This
difference was mostly due to a lower HDL level in the huCETPtg/huPLTPtg
mice, which subsequently could lead to the somewhat decreased CETP
activity and concentration that was found in huCETPtg/huPLTPtg mice (P <
0.05). PLTP activity was 2.8-fold increased in these animals (P < 0.001).
The human PLTP concentration was 5 microg/ml. Moderate overexpression of
PLTP resulted in a 1.5-fold higher VLDL secretion compared with huCETPtg
mice (P < 0.05). The composition of nascent VLDL was similar in both
strains. These results indicate that elevated PLTP activity in huCETPtg
mice results in an increase in VLDL secretion. In addition, PLTP
overexpression decreases plasma HDL cholesterol as well as CETP
Evaluation of phospholipid transfer protein and cholesteryl ester transfer protein as contributors to the generation of pre beta-high-density lipoproteins
High-density lipoproteins (HDLs) are considered anti-atherogenic because
they mediate peripheral cell cholesterol transport to the liver for
excretion and degradation. An important step in this reverse
cholesterol-transport pathway is the uptake of cellular cholesterol by a
specific subclass of small, lipid-poor apolipoprotein A-I particles
designated pre beta-HDL. The two lipid-transfer proteins present in human
plasma, cholesteryl ester transfer protein (CETP) and phospholipid
transfer protein (PLTP), have both been implicated in the formation of pre
beta-HDL. In order to investigate the relative contribution of each of
these proteins, we used transgenic mouse models. Comparisons were made
between human CETP transgenic mice (huCETPtg), human PLTP transgenic mice
(huPLTPtg) and mice transgenic for both lipid-transfer proteins
(huCETPtg/huPLTPtg). These animals showed elevated plasma levels of CETP
activity, PLTP activity or both activities, respectively. We evaluated the
generation of pre beta-HDL in mouse plasma by immunoblotting and crossed
immuno-electrophoresis. Generation of pre beta-HDL was equal in huCETPtg
and wild-type mice. In contrast, in huPLTPtg and huCETPtg/huPLTPtg mice,
pre beta-HDL generation was 3-fold higher than in plasma from either
wild-type or huCETPtg mice. Our findings demonstrate that, of the two
plasma lipid-transfer proteins, PLTP rather than CETP is responsible for
the generation of pre beta-HDL. These data support the hypothesis of a
role for PLTP in the initial stage of reverse cholesterol transport
Human plasma phospholipid transfer protein increases the antiatherogenic potential of high density lipoproteins in transgenic mice
Plasma phospholipid transfer protein (PLTP) transfers phospholipids
between lipoprotein particles and alters high density lipoprotein (HDL)
subfraction patterns in vitro, but its physiological function is poorly
understood. Transgenic mice that overexpress human PLTP were generated.
Compared with wild-type mice, these mice show a 2.5- to 4.5-fold increase
in PLTP activity in plasma. This results in a 30% to 40% decrease of
plasma levels of HDL cholesterol. Incubation of plasma from transgenic
animals at 37 degrees C reveals a 2- to 3-fold increase in the formation
of pre-beta-HDL compared with plasma from wild-type mice. Although
pre-beta-HDL is normally a minor subfraction of HDL, it is known to be a
very efficient acceptor of peripheral cell cholesterol and a key mediator
in reverse cholesterol transport. Further experiments show that plasma
from transgenic animals is much more efficient in preventing the
accumulation of intracellular cholesterol in macrophages than plasma from
wild-type mice, despite lower total HDL concentrations. It is concluded
that PLTP can act as an antiatherogenic factor preventing cellular
cholesterol overload by generation of pre-beta-HDL
Elevation of plasma phospholipid transfer protein increases the risk of atherosclerosis despite lower apolipoprotein B-containing lipoproteins.
Plasma phospholipid transfer protein (PLTP) transfers phospholipids
between lipoproteins and mediates HDL conversion. PLTP-overexpressing mice
have increased atherosclerosis. However, mice do not express cholesteryl
ester transfer protein (CETP), which is involved in the same metabolic
pathways as PLTP. Therefore, we studied atherosclerosis in heterozygous
LDL receptor-deficient (LDLR(+/-)) mice expressing both human CETP and
human PLTP. We used two transgenic lines with moderately and highly
elevated plasma PLTP activity. In LDLR(+/-)/huCETPtg mice, cholesterol is
present in both LDL and HDL. Both are decreased in
LDLR(+/-)/huCETPtg/huPLTPtg mice (>50%). An atherogenic diet resulted in
high levels of VLDL+LDL cholesterol. PLTP expression caused a strong PLTP
dose-dependent decrease in VLDL and LDL cholesterol (-26% and -69%) and a
decrease in HDL cholesterol (-70%). Surprisingly, atherosclerosis was
increased in the two transgenic lines with moderately and highly elevated
plasma PLTP activity (1.9-fold and 4.4-fold, respectively), indicating
that the adverse effect of the reduction in plasma HDL outweighs the
beneficial effect of the reduction in apolipoprotein B (apoB)-containing
lipoproteins. The activities of the antiatherogenic enzymes paraoxonase
and platelet-activating factor acetyl hydrolase were both PLTP
dose-dependently reduced ( approximately -33% and -65%, respectively). We
conclude that expression of PLTP in this animal model results in increased
atherosclerosis in spite of reduced apoB-containing lipoproteins, by
reduction of HDL and of HDL-associated antioxidant enzyme activities
Increased risk of atherosclerosis by elevated plasma levels of phospholipid transfer protein.
Plasma phospholipid transfer protein (PLTP) is thought to be involved in
the remodeling of high density lipoproteins (HDL), which are
atheroprotective. It is also involved in the metabolism of very low
density lipoproteins (VLDL). Hence, PLTP is thought to be an important
factor in lipoprotein metabolism and the development of atherosclerosis.
We have overexpressed PLTP in mice heterozygous for the low density
lipoprotein (LDL) receptor, a model for atherosclerosis. We show that
increased PLTP activity results in a dose-dependent decrease in HDL, and a
moderate stimulation of VLDL secretion (</=1.5-fold). The mice were given
a high fat, high cholesterol diet, which resulted in hypercholesterolemia
in all animals. HDL concentrations were dramatically reduced in
PLTP-overexpressing animals when compared with LDL receptor controls,
whereas VLDL + LDL cholesterol levels were identical. Susceptibility to
atherosclerosis was increased in a PLTP dose-responsive manner. We
conclude that PLTP increases susceptibility to atherosclerosis by lowering
HDL concentrations, and therefore we suggest that an increase in PLTP is a
novel, long term risk factor for atherosclerosis in humans
Elevated Expression of Phospholipid Transfer Protein in Bone Marrow Derived Cells Causes Atherosclerosis
Background: Phospholipid transfer protein (PLTP) is expressed by various cell types. In plasma, it is associated with high density lipoproteins (HDL). Elevated levels of PLTP in transgenic mice result in decreased HDL and increased atherosclerosis. PLTP is present in human atherosclerosis lesions, where it seems to be macrophage derived. The aim of the present study is to evaluate the atherogenic potential of macrophage derived PLTP. Methods and Findings: Here we show that macrophages from human PLTP transgenic mice secrete active PLTP. Subsequently, we performed bone marrow transplantations using either wild type mice (PLTPwt/wt), hemizygous PLTP transgenic mice (huPLTPtg/wt) or homozygous PLTP transgenic mice (huPLTPtg/tg) as donors and low density lipoprotein receptor deficient mice (LDLR-/-) as acceptors, in order to establish the role of PLTP expressed by bone marrow derived cells in diet-induced atherogenesis. Atherosclerosis was increased in the huPLTPtg/wt → LDLR-/ - mice (2.3-fold) and even further in the huPLTPtg/tg→LDLR-/ - mice (4.5-fold) compared with the control PLTPwt/wt→LDLR-/- mice (both P<0.001). Plasma PLTP activity levels and non-HDL cholesterol were increased and HDL cholesterol decreased compared with controls (all P<0.01). PLTP was present in atherosclerotic plaques in the mice as demonstrated by immunohistochemistry and appears to co-localize with macrophages. Isolated macrophages from PLTP transgenic mice do not show differences in cholesterol efflux or in cytokine production. Lipopolysaccharide activation of macrophages results in increased production of PLTP. This effect was strongly amplified in PLTP transgenic macrophages. Conclusions: We conclude that PLTP expression by bone marrow derived cells results in atherogenic effects on plasma lipids, increased PLTP activity, high local PLTP protein levels in the atherosclerotic lesions and increased atherosclerotic lesion size