|
|
|
|||||||
|
|||||||||
J Biol Chem, Vol. 275, Issue 14, 10077-10084, April 7, 2000
From the Plasma levels of high density lipoprotein (HDL)
cholesterol and its major protein component apolipoprotein (apo) A-I
are significantly reduced in both acute and chronic inflammatory
conditions, but the basis for this phenomenon is not well understood.
We hypothesized that secretory phospholipase A2
(sPLA2), an acute phase protein that has been found in
association with HDL, promotes HDL catabolism. A series of HDL
metabolic studies were performed in transgenic mice that specifically
overexpress human sPLA2 but have no evidence of local or
systemic inflammation. We found that HDL isolated from these mice have
a significantly lower phospholipid and cholesteryl ester and
significantly greater triglyceride content. The fractional catabolic
rate (FCR) of 125I-HDL was significantly faster in
sPLA2 transgenic mice (4.08 ± 0.01 pools/day)
compared with control wild-type littermates (2.16 ± 0.48 pools/day). 125I-HDL isolated from sPLA2
transgenic mice was catabolized significantly faster than
131I-HDL isolated from wild-type mice after injection in
wild-type mice (p < 0.001). Injection of
125I-tyramine-cellobiose-HDL demonstrated significantly
greater degradation of HDL apolipoproteins in the kidneys of
sPLA2 transgenic mice compared with control mice
(p < 0.05). The fractional catabolic rate of
[3H]cholesteryl ether HDL was significantly faster in
sPLA2-overexpressing mice (6.48 ± 0.24 pools/day)
compared with controls (4.80 ± 0.72 pools/day). Uptake of
[3H] cholesteryl ether into the livers and adrenals of
sPLA2 transgenic mice was significantly enhanced compared
with control mice. In summary, these data demonstrate that
overexpression of sPLA2 alone in the absence of
inflammation causes profound alterations of HDL metabolism in
vivo and are consistent with the hypothesis that
sPLA2 may promote HDL catabolism in acute and chronic
inflammatory conditions.
Plasma concentrations of high density lipoprotein
(HDL)1 cholesterol and its
major apoprotein apoA-I are inversely associated with atherosclerotic
cardiovascular disease (1, 2). The factors responsible for the
substantial variation in HDL cholesterol and apoA-I levels in humans
remain incompletely understood. Metabolic studies of HDL and apoA-I in
humans have established that variation in their levels is due in
substantial part to variation in the rate of apoA-I catabolism (3-7).
Although the determinants of apoA-I catabolism have not been fully
elucidated, the size and lipid composition of HDL have been recognized
to substantially influence the catabolic rate of apoA-I (8, 9).
One clinical setting that is invariably associated with reduced HDL
cholesterol and apoA-I levels is systemic inflammation. Acute
inflammatory states such as sepsis are associated with profoundly reduced HDL cholesterol levels (10). Furthermore, chronic inflammatory states such as rheumatoid arthritis and systemic lupus are also associated with reduced levels of HDL cholesterol (11-18), as well as
with increased risk of cardiovascular disease (19, 20). One of the
major factors thought to be implicated in the reduced levels of HDL
cholesterol during inflammation is the serum amyloid A (SAA) protein,
which increases markedly during acute infection and inflammation and is
also elevated in chronic inflammatory states (10, 21, 22). However,
expression of SAA has never been directly demonstrated to alter HDL
metabolism in vivo in the absence of systemic inflammation.
We recently demonstrated that marked overexpression of human SAA alone
in the absence of a generalized acute phase response had no effect on
HDL cholesterol and apoA-I levels in human apoA-I transgenic mice (23).
This observation raised the question as to whether other factors
associated with systemic inflammation may modulate HDL metabolism.
Group IIA secretory phospholipase A2 (sPLA2) is
an acute phase protein and plasma levels of sPLA2 are
increased in the setting of both acute and chronic inflammation (24,
25). A variety of circumstantial evidence suggests that hydrolysis of
HDL phospholipids by sPLA2 could play a role in modulating
HDL metabolism and function. Snake venom sPLA2 hydrolyzes
HDL phospholipids, alters HDL size and density, and results in
increased HDL uptake by rat hepatocytes in vitro (26). Snake
bites are associated with reduction in HDL cholesterol levels in
proportion to the severity of the snake bite (27). Induction of the
acute phase response in mice was shown to cause a significant decrease
in the phospholipid content of HDL (28). Plasma from patients with
sepsis contains large amounts of sPLA2 that is found almost
entirely in association with HDL (29).
We therefore hypothesized that sPLA2 expression induced
during inflammation has a physiologic effect in modulating HDL
metabolism. In this study we utilized group II sPLA2
transgenic mice to demonstrate that specific overexpression of
sPLA2 in the absence of generalized inflammation markedly
increased the rate of catabolism and altered sites of tissue uptake of
both HDL cholesteryl ester and apoA-I.
Animals--
The generation of human group IIA sPLA2
transgenic mice has been described previously (30, 31). These mice have
elevated plasma levels of sPLA2 comparable to those seen in
the acute phase response, but do not have any evidence of local or
systemic inflammation (30, 31). The sPLA2 transgenic line
has been backcrossed to the C57BL/6 background for 6 backcrosses. For
the studies described, non-transgenic littermates from further breeding
of these sPLA2 transgenic mice with C57BL/6 mice (Jackson
Laboratory, Bar Harbor, ME) were used as controls. The animals were
caged in animal rooms with alternating 12-h periods of light (7 a.m. to
7 p.m.) and dark (7 p.m. to 7 a.m.) with ad
libitum access to water and mouse chow diet. Mice transgenic for
sPLA2 were identified by Western blot analysis. One µl of
mouse plasma was electrophoresed under nonreducing conditions on a 15%
polyacrylamide gel (UltraPure, Life Technologies, Inc.) and
subsequently electroblotted to nitrocellulose (Protran, 0.45 µm,
Schleicher & Schuell). Human group IIA sPLA2 was identified
by blotting with a monoclonal mouse anti-human primary antibody at a
concentration of 2 µg/ml (Roche Molecular Biochemicals) and
visualized with a goat anti-mouse secondary antibody conjugated to
horseradish peroxidase (Jackson ImmunoResearch Laboratories, West
Grove, PA ) using the ECL (enhanced chemiluminescence) detection system
(Amersham Pharmacia Biotech).
Plasma Lipid and Lipoprotein Analysis--
Mice were bled from
the retroorbital plexus after a 4 h fast using heparinized
capillary tubes. Blood was drawn into tubes containing 2 mM
EDTA, 0.2% NaN3, and 1 mM benzamidine.
Aliquots of plasma were stored at
Pooled plasma samples from 4 mice (120 µl total volume) were
subjected to fast protein liquid chromatography (FPLC) gel filtration using two Superose 6 columns (Pharmacia LKB Biotechnology, Uppsala, Sweden) as described (32). Samples were chromatographed at a flow rate
of 0.5 ml/min, and lipoprotein fractions of 500 µl each were
collected. Individual fractions were assayed for cholesterol concentrations using commercially available assay kits (Wako Pure Chemical Industries, Ltd., Osaka, Japan).
For the analysis of HDL composition, HDL was isolated from 100 µl of
mouse plasma by tabletop sequential ultracentrifugation (1.063 < d < 1.21) (33). After dialysis, concentrations of
total and free cholesterol, triglycerides, and phospholipids were
determined with commercially available assays modified for microtiter
plates (Wako Pure Chemical Industries, Ltd.).
HDL Apolipoprotein Metabolic Studies--
HDL3 was
isolated from human donors by sequential ultracentrifugation (density:
1.125 < d <1.21). After dialysis against three changes of PBS with 0.01% EDTA, the isolated HDL3 fraction
was passed two times over a heparin-Sepharose column (Heparin Sepharose CL-6B, Amersham Pharmacia Biotech, Uppsala, Sweden) for removal of
apolipoprotein E containing HDL particles. After extensive dialysis
against four changes of buffer containing sterile PBS with 0.01% EDTA,
HDL was labeled with 125I (NEN Life Science Products) by a
modification of the iodine monochloride method (34). The labeled HDL
contained less than 0.1% non-trichloroacetic acid-precipitable counts.
For the HDL turnover study, 5 µCi of 125I-HDL were
injected into the tail veins of fasted sPLA2 transgenic and
control mice. Blood samples were drawn by retroorbital bleeding at 5 min, 30 min, 1 h, 3 h, 5 h, 8 h, 12 h, 24 h, and 48 h (about 25 µl at each time point). This procedure was
well tolerated by all experimental animals. An aliquot of 10 µl of
plasma from each time point was counted using a Cobra II
To assess radiotracer curves specific for apoA-I and apoA-II, 1 µl of
plasma for each time point was mixed with 14 µl of PBS and 5 µl of
4× non-reducing sample buffer and run on a 15% polyacrylamide gel
(UltraPure, Life Technologies, Inc.) with running buffer containing final concentrations of 25 mM Tris, 192 mM
glycine, and 0.1% (w/v) SDS, pH 8.3 (34). Subsequently, gels were
stained with Coomassie Blue for 1 h, destained with a solution
containing 10% acetic acid and 20% methanol, and dried under vacuum
(model 583, Bio-Rad). ApoA-I- and apoA-II-specific bands were
identified, cut out of the gels, and counted in a
In addition to these studies with human HDL, we performed a series of
double-label kinetic experiments with autologous mouse HDL. 6 ml of
mouse plasma from sPLA2 transgenic mice and wild-type littermates was used for HDL isolation by sequential
ultracentrifugation (density: 1.063 < d < 1.21).
The isolated mouse HDL was processed and labeled as described above.
Wild-type mouse HDL was labeled with 125I, and HDL from
sPLA2 transgenic mice was labeled with 131I.
Both tracers were then injected simultaneously into wild-type and
sPLA2 transgenic mice according to the experimental
protocol described above.
Tyramine-cellobiose Labeling of HDL Protein and Metabolic
Studies--
The synthesis of tyramine-cellobiose using cellobiose,
tyramine, and sodium cyanoborohydride (Sigma) was carried out as
described (36). The purity of the synthesis product was checked by TLC as described (36). For the production of
125I-tyramine-cellobiose (TC)-labeled HDL3,1
mCi of carrier-free 125I (NEN Life Science Products) and 1 IODOBEAD (Pierce) were added to a glass tube and incubated for 5 min.
Then 0.1 mmol of tyramine-cellobiose in 10 ml of 0.4 M
sodium phosphate buffer (pH 7.4) was added and the iodination allowed
to proceed for 30 min at room temperature. To this solution of
125I-tyramine-cellobiose, 0.1 mmol of cyanuric chloride
(Sigma) in 20 µl of acetone was added to activate the
125I-tyramine-cellobiose and the reaction allowed to
proceed for less than 1 min. For the protein binding, 0.3 mmol of
HDL3 at a concentration of 5 mg/ml in a total volume of 1.8 ml of 0.4 M sodium phosphate buffer, pH 7.4, was added to
the activated 125I-tyramine-cellobiose and the reaction
allowed to proceed for 3 h at room temperature. The unbound iodine
was then removed by passing the solution over a Sephadex G25 desalting
column (Amersham Pharmacia Biotech). Finally the HDL was reisolated by
ultracentrifugation at density 1.125 < d <1.21,
dialyzed against three changes of PBS containing 0.01% EDTA,
filter-sterilized, and stored at 4 °C until use. In order to ensure
that the TC labeling did not alter the in vivo metabolism of
the HDL, the metabolism of 125I-tyramine-cellobiose-HDL was
directly compared with 131I-HDL by co-injection in the same
mice. No differences were observed between 131I-HDL and
125I-TC-HDL in plasma decay curves.
To measure the organ uptake of HDL apolipoproteins, 4 µCi of
125I-TC-HDL were injected into sPLA2 transgenic
and control mice, and plasma decay curves were assessed as described
above. At 24 h after injection, the mice were anesthesized with an
intraperitoneal injected ketamine/xylazine mixture and perfused with
cold PBS by cardiac puncture; and liver, spleen, kidney and adrenals
were harvested. Radioactivity uptake into the organs was determined by
HDL Cholesteryl Ester Metabolic Studies--
HDL3
particles for these studies were isolated as described above. The
labeling with cholesteryl hexadecyl ether
(cholesteryl-1,2-3H) was carried out as described
previously (37). Briefly, 1.0 mCi of cholesteryl hexadecyl ether (NEN
Life Science Products) in toluene were dried down under a stream of
nitrogen. 0.075 ml of ethanol were then added, and the solution was
taken up in a microliter pipette (Hamilton Co., Reno, NV). This was
added dropwise to the HDL solution (300 µl of dialyzed HDL containing
6 mg of protein was added to 700 µl of sterile PBS) over a period of
5 min while gently shaking with short interruptions for a brief vortex.
Finally, the HDL from this solution was reisolated by ultracentrifugation at the original density and the
[3H]HDL was dialyzed overnight against four changes of
PBS containing 0.01% EDTA. Finally, the [3H]HDL was
filter-sterilized using 0.45- and 0.2-µm disposable sterile filters
(Corning Glass Works, Corning, NY) and stored at 4 °C until injection.
For the metabolic study, 1 million dpm of HDL labeled with
[3H]cholesteryl hexadecyl ether were injected into the
tail veins of fasted sPLA2 transgenic and control mice as
described (38). Blood samples were drawn by retroorbital bleeding at 2 min, 30 min, 1 h, 2 h, 4 h, 6 h, 9 h, 24 h, and 48 h after injection. Aliquots of 6 µl of plasma were
counted in duplicate for each time point by adding the plasma to 5 ml
of scintillation fluid (Scintiverse BD, Fisher Scientific, Fair Lawn,
NJ) and counting for 10 min on a scintillation counter (Beckman LS6500,
Beckman Instruments, Palo Alto, CA). After correction with blank
values, plasma disappearance curves were generated by dividing the
plasma counts at each time point by the plasma counts determined at the initial 2 min time point after tracer injection. The fractional catabolic rates (FCR) were determined using the SAAM II program.
After the 48-h blood sample was collected, liver, spleen, kidney, and
adrenals were harvested as described above. The organs were weighed,
and then weighed sections were minced and incubated with Solvable
(Packard, Meriden, CT) according to the manufacturer's instructions
for 3 h at 50 °C. 100 µl of 30% hydrogen peroxide was added
to each vial and the samples were incubated for another 1-h time period
at 50 °C. The samples were cooled at room temperature, mixed with
Scintiverse BD (Fisher Scientific), incubated overnight in the dark at
room temperature, and counted the next day.
To assess HDL-CE tissue uptake, the counts recovered in each of the
organs were related to the injected dose. Initial plasma counts were
multiplied by the estimated plasma volume (3.5% of total body weight)
and counts recovered in organs expressed as a percentage of this value.
To determine absolute rates of HDL-CE delivery to different tissues,
first tissue-specific FCR values were calculated by multiplying plasma
FCR and percentage of injected dose found in the respective organs. The
delivery rate of HDL-CE to each tissue per hour was then calculated as
the product of relative tissue FCR and HDL-CE pool.
Statistical Analysis--
Values are presented as mean ± S.D. unless otherwise indicated. Comparisons between different
experimental groups were carried out using Student's t test
for independent samples (two-tailed). p values less than
0.05 were considered statistically significant.
Expression of sPLA2 Results in Lower Plasma HDL
Cholesterol Levels and Altered HDL Composition--
Plasma lipid
levels in sPLA2 transgenic mice and their nontransgenic
littermates are summarized in Table I.
Total plasma cholesterol levels were significantly lower in sPLA2
transgenic mice as compared with controls (67 ± 11 mg/dl
versus 86 ± 20 mg/dl, respectively, p < 0.01). This was mainly due to a 28% decrease in the HDL cholesterol
fraction in these mice (39 ± 6 mg/dl versus 54 ± 6 mg/dl in controls, p < 0.01). Plasma triglyceride
levels were not different. Plasma phospholipids were significantly
decreased in the sPLA2 transgenic mice compared with
controls (143 ± 19 mg/dl versus 178 ± 32 mg/dl,
respectively, p < 0.01). FPLC gel filtration of pooled
plasma from sPLA2 transgenic mice and nontransgenic littermates was
performed in order to separate lipoproteins based on size (Fig.
1). For the non-HDL fractions there was
no difference in cholesterol distribution detectable in the two groups
of mice studied. In contrast, the HDL cholesterol peak in
sPLA2 transgenic mice was smaller and shifted toward
smaller HDL particles. Analysis of the lipid composition of HDL
particles isolated by ultracentrifugation from plasma after a 4-h fast
(Table II) revealed a significant decrease in cholesteryl ester (27 ± 1% versus 44 ± 2%, respectively, p < 0.001) and phospholipids
(33 ± 4% versus 44 ± 3%, respectively, p < 0.001) in sPLA2 transgenic mice as
compared with controls. On the other hand, the percentage of
triglycerides in HDL particles of sPLA2 transgenic mice was
markedly increased (33 ± 2% versus 6 ± 0.5%,
respectively, p < 0.001), while the relative
proportion of free cholesterol was not different between both groups.
These differences in HDL lipid composition between both groups of mice were also obtained when the concentration values (mg/dl) for each HDL
component were taken.
Expression of sPLA2 Causes Rapid Catabolism of HDL
ApoA-I but Not ApoA-II--
To further investigate the metabolic
mechanism leading to decreased HDL cholesterol and apoA-I levels in
sPLA2 transgenic mice, kinetic studies with human
125I-HDL were performed. The labeled HDL was catabolized
much faster in the sPLA2 transgenic mice than in their
nontransgenic littermates (Fig.
2A). Fractional catabolic
rates were 2.16 ± 0.48 pools/day in the controls and 4.08 ± 0.01 pools/day in the sPLA2 transgenic mice
(p < 0.001, Table III).
To determine the effect of sPLA2 expression on specific
apolipoproteins, apoA-I and apoA-II were analyzed separately (Fig. 2,
B and C). The fractional catabolic rate of apoA-I
was significantly faster in the sPLA2 mice (3.60 ± 0.02 pools/day) compared with control mice (1.92 ± 0.02 pools/day, p < 0.001, Table III). In contrast, the FCR
of apoA-II in the sPLA2 transgenic mice was not
significantly different from that in non-transgenic littermates (4.32 ± 0.22 pools/day versus 4.08 ± 0.24 pools/day, respectively, Table III). These results demonstrate that
sPLA2 expression leads to faster catabolism of apoA-I but
not apoA-II.
In addition, kinetic experiments using autologous mouse HDL as a tracer
were performed (Fig. 3A).
131I-HDL isolated from sPLA2 transgenic mice
was catabolized significantly faster in sPLA2 transgenic
mice than was wild-type 125I-HDL in wild-type mice
(5.18 ± 0.07 pools/day versus 2.18 ± 0.05 pools/day, respectively, p < 0.001, Table
IV). The FCR values obtained were
remarkably similar to those obtained using a human HDL tracer described
above. Since this study was performed using a double-label design, we
also directly compared the catabolism of the two mouse HDL tracers in
both groups of mice (Fig. 3, B and C).
Interestingly, HDL isolated from sPLA2 transgenic mice was
catabolized significantly faster in wild-type mice than the autologous
wild-type HDL (2.98 ± 0.15 pools/day versus 2.18 ± 0.05 pools/day, respectively, p < 0.001, Fig.
3B, Table IV), indicating that sPLA2-modified
HDL is metabolically abnormal even in a normal environment. On the
other hand, there was no statistically significant difference between
the catabolism of wild-type HDL and sPLA2-modified HDL in
the sPLA2 transgenic mice (4.58 ± 0.88 pools/day
versus 5.18 ± 0.07 pools/day, respectively, not
significant, Fig. 3C, Table IV). Importantly, the catabolism
of wild-type mouse HDL was much faster in sPLA2 transgenic
mice than in wild-type mice (Table IV), suggesting that either
modification of normal HDL by sPLA2 occurred rapidly after
injection or apoA-I tracer exchanged rapidly onto the sPLA2
HDL.
sPLA2 Expression Promotes Catabolism of HDL
Apolipoproteins by the Kidneys--
To investigate the sites of HDL
apolipoprotein catabolism, HDL was labeled with the trapped ligand
125I-TC. To assure that this chemical modification had no
influence on the in vivo catabolism of the HDL particle, we
compared 125I-tyramine-cellobiose-HDL and
131I-HDL using a dual-label approach in the same animals
and found that the FCRs were not significantly different (data not
shown). 125I-TC was injected into sPLA2
transgenic and control mice. There was no difference between
sPLA2 and wild-type mice in the fraction of injected dose
found in the liver, but there was a significantly greater fraction of
the injected dose found in the kidneys of the sPLA2
transgenic mice (p < 0.05). Therefore, the ratio of HDL protein catabolized in the kidney relative to the liver was significantly higher in the sPLA2-expressing mice
(p < 0.05) (Fig. 4). In
contrast, this ratio for spleen and adrenals was not different between
the experimental groups (Fig. 4).
Expression of sPLA2 Promotes Catabolism of HDL
Cholesteryl Ester by Liver and Adrenals--
To investigate the effect
of sPLA2 on the kinetics and metabolic fate of HDL
cholesteryl esters, HDL was labeled with [3H]cholesteryl
hexadecyl ether, an analogue of cholesteryl ester. This lipid behaves
in plasma as cholesteryl ester but has the advantage that it cannot be
hydrolyzed in mammalian tissues, allowing the assessment of tissue
uptake and organ distribution of the label (39). Cholesteryl
ether-labeled HDL was catabolized 35% faster in sPLA2
transgenic mice (Fig. 5), with FCRs of
6.48 ± 0.24 pools/day in the sPLA2 mice compared with
4.80 ± 0.72 pools/day in the controls (p < 0.001, Table III).
To evaluate which organs contributed to enhanced clearance of HDL
cholesteryl ether in sPLA2 transgenic mice, tracer uptake was measured in liver, spleen, kidney, and adrenals at 48 h after tracer administration. The weights of the organs were not significantly different between the experimental groups. From the data obtained, the
contribution of each of these organs to the uptake of the injected
tracer was calculated as a percentage of initial counts (Fig.
6A). Tracer uptake by liver
exceeded by far the uptake by other organs as described previously
(39). The uptake rates of CE from HDL into both liver and adrenals were
significantly increased in sPLA2 transgenic mice as
compared with controls (each p < 0.01). There was no
difference between the groups of mice for HDL-CE uptake into spleen and
kidneys. The flux of CE from HDL into each organ was determined.
sPLA2 transgenic mice had significantly increased flux of
HDL-CE into liver and adrenals compared with control mice (Fig.
6B, p < 0.05 and p < 0.01, respectively). In contrast, HDL-CE flux into spleen and kidneys was not
different between the experimental groups.
The results of this study demonstrate that overexpression of
sPLA2, an acute phase protein with phospholipase
A2 enzymatic activity, results in alterations of HDL
metabolism in vivo in the absence of generalized
inflammation. It is well established that humans with acute and chronic
inflammatory states have low levels of HDL cholesterol and that
induction of the acute phase response in animals leads to a marked
decrease in plasma HDL cholesterol levels (22). These changes in HDL
have traditionally been ascribed to the expression of SAA, an acute
phase protein that has the structural and interfacial properties of an
apolipoprotein and is found in association with HDL (21). However, we
recently demonstrated that overexpression of SAA in the absence of
generalized inflammation did not result in changes of HDL cholesterol
or apoA-I levels in vivo (23). Therefore, SAA induction
alone does not fully explain the changes in HDL cholesterol and apoA-I
levels seen in inflammation.
Another acute phase protein that could plausibly influence HDL
metabolism is sPLA2. Increased plasma levels of
sPLA2 have been described in acute inflammatory conditions
such as sepsis as well as in chronic inflammatory diseases (24, 25,
40). Plasma sPLA2 is physically associated with HDL in
humans (29). Acute phase human HDL is an excellent substrate for
sPLA2 ex vivo (41). Reduction of HDL
phospholipids by incubation with phospholipase A2 alters
the physical characteristics of HDL (42) and apoA-I epitope expression
(43) and results in destabilization of the helical segments of apoA-I
(44). Therefore, induction of sPLA2 by inflammatory stimuli
could result in hydrolysis of HDL phospholipids and subsequent
alteration of HDL structure and metabolism in vivo.
To test this hypothesis, we utilized a transgenic mouse model
overexpressing sPLA2 (30, 31) that was previously shown to
have reduced levels of HDL cholesterol (45). Importantly, despite high
levels of sPLA2 expression comparable to those in inflammatory states, these mice do not have evidence of local or
systemic inflammation (30, 31). We found that sPLA2
transgenic mice had significantly lower plasma levels of HDL
cholesterol and phospholipids compared with nontransgenic wild-type
littermates. FPLC gel filtration analysis revealed that the major HDL
cholesterol peak was shifted toward smaller sized HDL particles. HDL
from the sPLA2 transgenic mice was significantly depleted
in phospholipids and cholesteryl esters and enriched in triglycerides.
Interestingly, triglyceride enrichment of HDL is a prominent feature of
the acute phase response (46). Because the cholesterol and triglyceride composition of HDL particles is a known determinant of HDL apoA-I catabolic rate (9), this finding was consistent with our hypothesis that sPLA2 expression may modulate HDL metabolism in
vivo.
Given the fact that the catabolic rates and pathways of HDL
apolipoproteins and HDL cholesteryl ester are divergent, we
specifically investigated the effect of sPLA2 expression on
both HDL apolipoprotein and HDL cholesteryl ester turnover and sites of
catabolism. Radioiodinated HDL apolipoproteins were catabolized nearly
twice as fast in sPLA2 transgenic as in the control mice
using either human HDL or autologous mouse HDL as tracers. Furthermore,
HDL isolated from sPLA2 mice was catabolized significantly
faster than normal wild-type HDL in wild-type mice, indicating that
modification of HDL by sPLA2 leads to structural and
compositional changes that result in alteration of its metabolic
properties even in a normal environment lacking sPLA2.
Interestingly, normal HDL isolated from wild-type mice was catabolized
just as fast as autologous sPLA2 HDL in sPLA2 mice, suggesting that either modification of normal HDL by
sPLA2 occurred rapidly after injection or apoA-I tracer
exchanged rapidly onto the sPLA2 HDL. The effect of
sPLA2 expression was primarily on the catabolism of apoA-I,
whereas the apoA-II catabolic rate remained unchanged. This suggests
that phospholipid hydrolysis of HDL by sPLA2 influences
apoA-I but not apoA-II catabolism. In humans, the FCR of apoA-I varies
more than that of apoA-II (8, 9) and the rate of catabolism of apoA-I
associated with lipoprotein A-I is faster than that associated with
lipoprotein A-I:A-II (47). ApoA-I binds less tightly to lipid than
apoA-II (48), and therefore hydrolysis of HDL phospholipids may be more likely to destabilize apoA-I than apoA-II. Further experiments will be
required to determine the specific mechanism of the selective effect of
sPLA2 on apoA-I compared with apoA-II catabolism.
We specifically determined whether sPLA2 expression altered
the sites of tissue uptake of HDL apolipoprotein. Experiments performed
in rats using tyramine cellobiose-labeled HDL as a trapped ligand have
demonstrated that HDL apolipoproteins are catabolized primarily in the
liver and the kidneys (39). It has been suggested that poorly lipidated
apoA-I is more likely to be catabolized by the kidneys, possibly via
glomerular filtration and catabolism by the proximal tubular epithelium
(49). We found that the sPLA2 transgenic mice had a
significantly greater proportion of HDL apolipoprotein catabolized in
the kidney relative to the liver. This suggests that expression of
sPLA2 may generate more lipid-poor apoA-I in
vivo, possibly through destabilization and subsequent dissociation
of apoA-I from HDL particles, followed by more rapid catabolism in the
kidneys. Further studies will be required to prove this mechanism.
Previous in vitro studies showed that snake venom
PLA2 treatment of HDL resulted in increased uptake of
cholesteryl ester by rat hepatocytes (26). In our in vivo
studies, HDL cholesteryl ether was catabolized significantly faster in
the sPLA2 transgenic mice compared with wild-type mice.
Interestingly, we found significantly higher uptake of HDL cholesteryl
ether by the liver and the adrenals in the sPLA2 mice
compared with wild-type mice. Liver and adrenals express high levels of
SR-BI, a cell surface HDL receptor that mediates selective uptake of
HDL cholesteryl ester into cells (50, 51). SR-BI expression in liver
was not different between sPLA2 transgenic mice and control
wild-type mice as assessed by Western blot analysis (data not shown).
Our findings are consistent with a model in which
sPLA2-mediated hydrolysis of HDL phospholipids in
vivo enhanced the SR-BI-mediated selective uptake of HDL
cholesteryl ester into organs with high expression of the SR-BI
receptor. Although this process contributes to reduced HDL cholesterol
levels, it could potentially be protective against atherosclerosis if it promotes reverse cholesterol transport.
Why does a secreted phospholipase that is up-regulated by inflammatory
stimuli have these effects on HDL metabolism? One potential reason is
that acute inflammatory conditions require increased synthesis of
steroid hormones; HDL cholesteryl ester is a known source of
cholesterol for steroid hormone synthesis (52) and sPLA2
may make HDL cholesteryl ester more accessible to steroidogenic tissues
for use in hormone biosynthesis. Another possibility is that apoA-I has
been shown to have a protective effect against endotoxinemia in
vitro (53) and in vivo (54, 55). Poorly lipidated
apoA-I has been demonstrated to be more effective in inactivating
bacterial endotoxins than large HDL particles (56). Therefore, the
generation of poorly lipidated A-I by the action of sPLA2
on HDL during the acute phase reaction might represent a protective
mechanism in the host response against Gram-negative infections. More
studies are needed to test these hypotheses.
Our findings are consistent with the concept that up-regulation of
sPLA2 in inflammation is an important factor responsible for reduced HDL cholesterol and apoA-I levels. This might have clinical
implications for patients with chronic inflammatory diseases, such as
rheumatoid arthritis and SLE, which are associated with increased
cardiovascular risk (19, 20). Treatment strategies aimed at specific
inhibition of sPLA2 in chronic inflammatory states might be
a novel strategy for raising HDL cholesterol levels and possibly
reducing atherosclerotic cardiovascular disease in these conditions.
Interestingly, atherosclerosis itself is increasingly recognized as a
chronic inflammatory condition. Epidemiologic studies have indicated
that systemic markers of inflammation are associated with coronary
events (57-59). Pathologic studies have indicated substantial evidence
for inflammation within the atherosclerotic plaque (60). Group IIA
sPLA2 is synthesized constitutively within the vessel wall
by vascular smooth muscle cells (61, 62) and is associated with heparan
sulfate proteoglycans of the extracellular matrix (63, 64).
Administration of heparin to humans results in a marked increase in
plasma PLA2 activity and immunoreactive group IIA
sPLA2 (65), suggesting that it is present in the vessel wall under physiologic conditions. Cytokines up-regulate VSMC expression of group IIA sPLA2 in vitro (61) and
in vivo (62), and sPLA2 is present in markedly
increased amounts within the atherosclerotic plaque (63, 64, 66).
Transgenic overexpression of sPLA2 in mice results in
increased atherosclerosis (67). HDL is likely to encounter
sPLA2 within the extracellular matrix of the normal
arterial wall and increasingly within the developing atherosclerotic
plaque. Therefore, the concept that atherosclerosis, by up-regulating
local and systemic inflammatory mediators such as sPLA2,
may itself influence HDL metabolism is plausible and could play a role
in the strong inverse association between atherosclerosis and HDL
cholesterol levels.
In summary, hydrolysis of HDL phospholipids by sPLA2 alters
the structure and composition of HDL particles with the metabolic consequences of increased catabolism of apoA-I by the kidneys and
increased selective uptake of HDL cholesteryl ester by tissues expressing SR-BI. Although these mechanisms might be beneficial for
host defense in the setting of acute infection, they result in reduced
plasma levels of HDL cholesterol and apoA-I and may contribute to
increased incidence of atherosclerotic cardiovascular disease
associated with chronic inflammatory conditions.
We are indebted to Pearle Smith, Anna
Lillethun, and Robert Hughes for excellent technical assistance.
*
This work was supported by National Institutes of Health
Grant HL55323 (to D. J. R.), a grant from the Deutsche
Forschungsgemeinschaft (to U. J. F. T.), and a grant
from ARCOLL, France (to C. M.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
The abbreviations used are:
HDL, high density
lipoprotein;
FPLC, fast protein liquid chromatography;
sPLA2, secretory phospholipase A2;
apo, apolipoprotein;
PBS, phosphate-buffered saline;
FCR, fractional
catabolic rate;
SAA, serum amyloid A;
TC, tyramine-cellobiose.
Overexpression of Secretory Phospholipase A2 Causes
Rapid Catabolism and Altered Tissue Uptake of High Density Lipoprotein
Cholesteryl Ester and Apolipoprotein A-I*
,,
,
Department of Medicine and Department
of Molecular and Cellular Engineering, University of Pennsylvania
Health System, Philadelphia, Pennsylvania 19104, the
§ Department of Biology, University of Delaware, Newark,
Delaware 19716, ¶ Chrysalis DNX Transgenic Sciences, Princeton,
New Jersey 08540, and the ** Department of Internal Medicine, University
of Kentucky and Veterans Affairs Medical Center,
Lexington, Kentucky 40536
ABSTRACT
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
EXPERIMENTAL PROCEDURES
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
20 °C until analysis. All
analyses were performed within 10 days of obtaining blood. Plasma total
cholesterol, triglycerides, phospholipids, and HDL cholesterol levels
were measured enzymatically on a Cobas Fara (Roche Diagnostics Systems Inc., Nutley, NJ) using Sigma Diagnostics reagents (Sigma Diagnostics).
counter
(Packard Instruments, Downers Grove, IL). Plasma decay curves were
generated by dividing the plasma radioactivity at each time point by
the plasma radioactivity determined at the initial 5-min time point
after tracer injection. The fractional catabolic rates (FCR) were
determined from the area under the plasma disappearance curves fitted
to a bicompartmental model using the SAAM II program (35).
counter. More
than 90% of the total radioactivity applied to the gel migrated in the
apoA-I and apoA-II positions. Relative proportions of apoA-I- and
apoA-II-specific radioactivity were assessed for each of the time
points. These proportions were applied to the total plasma counts for
the respective time point and apoA-I- and apoA-II-specific values were
generated. These apoA-I- and apoA-II-specific plasma disappearance
curves were modeled using the SAAM II program. Apolipoprotein-specific fractional catabolic rates for each mouse were determined.
counting and uptake of the 125I-tracer into the
respective organs expressed in relation to hepatic tracer uptake.
RESULTS
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
Plasma lipid and apolipoprotein concentrations (mg/dl) in sPLA2
transgenic mice and nontransgenic littermates
View larger version (15K):
[in a new window]
Fig. 1.
FPLC cholesterol profiles in
sPLA2 transgenic mice (diamonds) and
nontransgenic littermates (squares). Pooled
plasma samples were subjected to gel filtration using Superose 6 columns, and cholesterol levels in each fraction were measured using an
enzymatic assay kit. Relative elution positions of different
lipoprotein subclasses are indicated.
HDL composition in sPLA2 transgenic mice and nontransgenic
littermates
View larger version (12K):
[in a new window]
Fig. 2.
A, plasma kinetics of
125I-labeled human HDL in sPLA2 transgenic mice
(diamonds) and nontransgenic littermates
(squares). The tracer was administered by tail vein
injection, and blood samples were taken at the indicated time points
and analyzed for radioactivity by counting. Values are the fraction
of the injected dose remaining at each time point. The curves were
analyzed using a bicompartmental model on the SAAM II program, and FCR
values were calculated. By independent sample t test, the
FCR values of the sPLA2 transgenic mice were found
significantly higher (p < 0.001) than in the control
group. Data are given as mean ± S.D.; n = 5 mice/group. B and C, specific plasma kinetics of 125I-labeled HDL-ApoA-I
(B) and 125I-labeled HDL-ApoA-II (C)
in sPLA2 transgenic mice (diamonds) and
nontransgenic littermates (squares). Plasma samples from
each of the mice at each of the timepoints of the experiment shown in
panel A were subjected to non-denaturing gel
electrophoresis. ApoA-I- and apoA-II-specific bands were cut out of the
gel, and radioactivity was determined using a counter. From these
data tracer disappearance curves specific for apoA-I and apoA-II were
generated. These curves were analyzed using a bicompartmental model on
the SAAM II program, and FCR values were calculated. By independent
sample t test, the apoA-I-specific FCR values of the
sPLA2 transgenic mice were found significantly higher
(p < 0.001) compared with the control group, while
there was no difference for apoA-II-specific values between both
experimental groups. Data are given as mean ± S.D.;
n = 5 mice/group.
HDL fractional catabolic rates (pool/day) in sPLA2 transgenic
mice and nontransgenic littermates using human HDL as tracer
View larger version (12K):
[in a new window]
Fig. 3.
Comparison of the kinetic properties of HDL
isolated from sPLA2 transgenic mice
(diamonds) and nontransgenic littermates
(squares). Both tracers were injected
simultaneously into wild-type mice and sPLA2 transgenic
mice. A, plasma kinetics of 125I-labeled HDL
from wild-type mice (squares) and 131I-labeled
HDL from sPLA2 transgenic mice (diamonds) in the
respective groups of mice. B, plasma kinetics of
125I-labeled HDL from wild-type mice
(squares) and 131I-labeled HDL from
hsPLA2 transgenic mice (diamonds) in wild-type
mice. C, plasma kinetics of 125I-labeled HDL
from wild-type mice (squares) and
131I-labeled HDL from sPLA2 transgenic mice (diamonds) in sPLA2 transgenic mice. The
tracers were administered by tail vein injection, and blood samples
were taken at the indicated time points and analyzed for radioactivity
by counting. Values are the fraction of the injected dose remaining
at each time point. The curves were analyzed using a bicompartmental
model on the SAAM II program, and FCR values were calculated.
sPLA2 transgenic mice had a significantly faster HDL
catabolic rate than wild-type mice using autologous tracers
(p < 0.001, panel A). The
nontransgenic controls catabolized the HDL from the sPLA2
transgenic mice significantly faster compared with HDL isolated from
wild-type mice (p < 0.001, panel
B). On the other hand, there was no difference in the rate
these tracers were catabolized in the sPLA2 transgenic mice
(panel C).
HDL fractional catabolic rates (pool/day) in sPLA2 transgenic
mice and nontransgenic littermates using mouse HDL as tracer
View larger version (29K):
[in a new window]
Fig. 4.
Tissue sites of catabolism of
125I-TC HDL in sPLA2 transgenic mice and
nontransgenic littermates. Labeled HDL was prepared as described
under "Experimental Procedures" and injected via tail vein. After
24 h the mice were sacrificed and thoroughly perfused with PBS to
remove any residual blood, and the respective tissues harvested. Uptake
of radiotracer into each of the organs was determined by counting.
The data shown compare the ratio of tissue uptake into each organ to
liver. Hepatic uptake of tracer did not differ between the experimental
groups. As assessed by independent sample t test, uptake of
125I-HDL into kidneys was significantly higher in
sPLA2 transgenic mice (p < 0.05).
View larger version (13K):
[in a new window]
Fig. 5.
Plasma kinetics of HDL labeled with
[3H]cholesteryl hexadecyl ether in sPLA2
transgenic mice (diamonds) and nontransgenic
littermates (squares). The tracer was
administered by tail vein injection, and blood samples were taken at
the indicated time points and analyzed for radioactivity on a
scintillation counter. Values are the fraction of the injected dose
remaining at each time point. The curves were analyzed using a
bicompartmental model on the SAAM II program, and FCR values were
calculated. By independent sample t test, the FCR values of
the sPLA2 transgenic mice were found significantly higher
(p < 0.001) than in the control group. Data are given
as mean ± S.D.; n = 5 mice/group.
View larger version (43K):
[in a new window]
Fig. 6.
Relative tissue uptake and rate of delivery
of HDL CE in hsPLA2 transgenic mice and nontransgenic
littermates. Mice used in the [3H]cholesteryl
ether-labeled HDL kinetic study presented in Fig. 5 were sacrificed at
48 h, and the tissues indicated were harvested. Incorporated
counts in each of the tissues were measured by scintillation counting
as described under "Experimental Procedures." A, counts
recovered in each organ as a percentage of plasma counts found at 2 min
after tracer injection. B, rate of HDL CE uptake into each
organ indicated per hour. This uptake rate was calculated as the
product of the relative tissue FCR and the HDL CE plasma pool. The
relative tissue FCR was calculated as the product of plasma FCR and the
percentage of initial plasma counts recovered in each organ as
presented in A. The HDL CE plasma pool was determined by
multiplying plasma volume of each mouse and the respective HDL CE
concentration. Data are mean ± S.D.; n = 5 mice/group. Note the different scale of the y axis for liver
in each panel.
DISCUSSION
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
ACKNOWLEDGEMENTS
FOOTNOTES
To whom correspondence should be addressed: University of
Pennsylvania Medical Center, 614 BRB II/III, 421 Curie Blvd.,
Philadelphia, PA 19104-6100. Tel.: 215-898-4011; Fax: 215-573-6725;
E-mail: rader@mail.med.upenn.edu.
ABBREVIATIONS
REFERENCES
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
1.
Gordon, D. J.,
and Rifkind, B. M.
(1989)
N. Engl. J. Med.
321,
1311-1316[Medline]
[Order article via Infotrieve]
2.
Goldbourt, U.,
Yaari, S.,
and Medalie, J. H.
(1997)
Arterioscler. Thromb. Vasc. Biol.
17,
107-113 3.
Schaefer, E. J.,
Zech, L. A.,
Jenkins, L. J.,
Bronzert, T. J.,
Rubalcaba, E. A.,
Lindgren, F. T.,
Aamodt, R. L.,
and Brewer, H. B.
(1982)
J. Lipid Res.
23,
850-862[Abstract]
4.
Gylling, H.,
Vega, G. L.,
and Grundy, S. M.
(1992)
J. Lipid Res.
33,
1527-1539[Abstract]
5.
Brinton, E. A.,
Eisenberg, S.,
and Breslow, J. L.
(1989)
J. Clin. Invest.
84,
262-269
6.
Brinton, E. A.,
Eisenberg, S.,
and Breslow, J. L.
(1991)
J. Clin. Invest.
87,
536-544
7.
Rader, D. J.,
Ikewaki, K.,
Duverger, N.,
Feuerstein, I.,
Zech, L.,
and Connor, W., Jr.
(1993)
Lancet
342,
1455-1458[CrossRef][Medline]
[Order article via Infotrieve]
8.
Breslow, J. L.,
Eisenberg, S.,
and Brinton, E. A.
(1993)
Ann. N. Y. Acad. Sci.
676,
157-162[Medline]
[Order article via Infotrieve]
9.
Rader, D. J.,
and Ikewaki, K.
(1996)
Curr. Opin. Lipidol.
7,
117-123[Medline]
[Order article via Infotrieve]
10.
Bausserman, L.,
Vernier, D.,
McAdam, K.,
and Herbert, P.
(1988)
Eur. J. Clin. Invest.
18,
619-626[Medline]
[Order article via Infotrieve]
11.
Rossner, S.
(1978)
Atherosclerosis
31,
93-99[CrossRef][Medline]
[Order article via Infotrieve]
12.
Lakatos, J.,
and Harsagyi, A.
(1988)
Clin. Biochem.
21,
93-96[CrossRef][Medline]
[Order article via Infotrieve]
13.
Situnayake, R. D.,
and Kitas, G.
(1997)
Ann. Rheum. Dis.
56,
341-342 14.
Lazarevic, M. B.,
Vitic, J.,
Mladenovic, V.,
Myones, B. L.,
Skosey, J. L.,
and Swedler, W. I.
(1992)
Semin. Arthr. Rheum.
22,
172-178
15.
Ilowite, N.,
Samuel, P.,
and Beseler, L.
(1989)
J. Pediatr.
114,
823-826[CrossRef][Medline]
[Order article via Infotrieve]
16.
Svenson, K. L.,
Lithell, H.,
and Hallgren, R.
(1987)
Arch. Intern. Med.
147,
1912-1916 17.
Petri, M.,
Perez-Guttham, S.,
Spence, D.,
and Hochberg, M. C.
(1992)
Am. J. Med.
93,
513-519[CrossRef][Medline]
[Order article via Infotrieve]
18.
Ettinger, W. H.,
Goldberg, A. P.,
Applebaum-Bowden, D.,
and Hazzard, W. R.
(1987)
Am. J. Med.
83,
503-508[CrossRef][Medline]
[Order article via Infotrieve]
19.
Reilly, P. A.,
Cosh, J. A.,
and Maddison, P. J.
(1990)
Ann. Rheum. Dis.
49,
363-369 20.
Homcy, C. J.,
Liberthson, R. P.,
and Fallon, J. T.
(1982)
Am. J. Cardiol.
49,
478-484[CrossRef][Medline]
[Order article via Infotrieve]
21.
Malle, E.,
Steinmetz, A.,
and Raynes, J. G.
(1993)
Atherosclerosis
102,
131-146[CrossRef][Medline]
[Order article via Infotrieve]
22.
Lindhorst, E.,
Young, D.,
Bagshaw, W.,
Hyland, M.,
and Kisilevsky, R.
(1997)
Biochim. Biophys. Acta
1339,
143-154[CrossRef][Medline]
[Order article via Infotrieve]
23.
Hosoai, H.,
Webb, N. R.,
Glick, J. M.,
Tietge, U. J. F.,
Purdom, M. S.,
deBeer, F. C.,
and Rader, D. J.
(1999)
J. Lipid Res.
40,
648-653 24.
Nevalainen, T.
(1993)
Clin. Chem.
39,
228-238
25.
Lin, M. K.,
Farewell, V.,
Vadas, P.,
Bookman, A. A.,
Keystone, E. C.,
and Pruzanski, W.
(1996)
J. Rheumatol.
23,
1162-1166[Medline]
[Order article via Infotrieve]
26.
Collet, X.,
Perret, B. P.,
Simard, G.,
Vieu, C.,
and Douste-Blazy, L.
(1990)
Biochim. Biophys. Acta
1043,
301-310[Medline]
[Order article via Infotrieve]
27.
Winkler, E.,
Chovers, M.,
and Almog, S.
(1993)
J. Lab. Clin. Med.
121,
774-778[Medline]
[Order article via Infotrieve]
28.
Hoffman, J.,
and Benditt, E.
(1982)
J. Biol. Chem.
257,
10510-10517 29.
Gijon, M. A.,
Perez, C.,
Mendez, E.,
and Crespo, M. S.
(1995)
Biochem. J.
306,
167-175
30.
Grass, D. S.,
Felkner, R. H.,
Chiang, M. Y.,
Wallace, R. E.,
Nevalainen, T. J.,
Bennett, C. F.,
and Swanson, M. E.
(1996)
J. Clin. Invest.
97,
2233-2241[Medline]
[Order article via Infotrieve]
31.
Nevalainen, T. J.,
Laine, V. J. O.,
and Grass, D. S.
(1997)
J. Histochem. Cytochem.
45,
1109-1119 32.
Tsukamoto, K.,
Smith, P.,
Glick, J. M.,
and Rader, D. J.
(1997)
J. Clin. Invest.
100,
107-114[Medline]
[Order article via Infotrieve]
33.
Brousseau, T.,
Clavey, V.,
Bard, J. M.,
and Fruchart, J. C.
(1993)
Clin. Chem.
39,
960-964 34.
Ikewaki, K.,
Rader, D. J.,
Schaefer, J. R.,
Fairwell, T.,
Zech, L. A.,
and Brewer, H. B., Jr.
(1993)
J. Lipid Res.
34,
2207-2215[Abstract]
35.
Barrett, P. H. R.,
Bradley, M. B.,
Cobelli, C.,
Golde, H.,
Schumitzky, A.,
Vicini, P.,
and Foster, D. M.
(1998)
Metabolism
47,
484-492[CrossRef][Medline]
[Order article via Infotrieve]
36.
Pittman, R. C.,
and Taylor, C. A. J.
(1986)
Methods Enzymol.
129,
612-628[Medline]
[Order article via Infotrieve]
37.
Foger, B.,
Santamarina-Fojo, S.,
Shamburek, R. D.,
Parrot, C. L.,
Talley, G. D.,
and Brewer, H. B.
(1997)
J. Biol. Chem.
272,
27393-27400 38.
Plump, A. S.,
Axrolan, N.,
Odaka, H.,
Wu, L.,
Jiang, X.,
Tall, A.,
Eisenberg, S.,
and Breslow, J. L.
(1997)
J. Lipid Res.
38,
1033-1047[Abstract]
39.
Glass, C.,
Pittman, R. C.,
Weinstein, D. B.,
and Steinberg, D.
(1983)
Proc. Natl. Acad. Sci. U. S. A.
80,
5435-5439 40.
Pruzanski, W.,
Keystone, E. C.,
Sternby, B.,
Bombardier, C.,
Snow, K. M.,
and Vadas, P.
(1988)
J. Rheumatol.
15,
1351-1355[Medline]
[Order article via Infotrieve]
41.
Pruzanski, W.,
Stefanski, E.,
de Beer, F. C.,
de Beer, M. C.,
Vadas, P.,
Ravandi, A.,
and Kuksis, A.
(1998)
J. Lipid Res.
39,
2150-2160 42.
Gorshkova, I. N.,
Menschikowski, M.,
and Jaross, W.
(1996)
Biochim. Biophys. Acta
1300,
103-113[Medline]
[Order article via Infotrieve]
43.
Menschikowski, M.,
Hempel, U.,
Dinnebier, G.,
Lattke, P.,
Wenzel, K. W.,
and Jaross, W.
(1995)
Atherosclerosis
117,
159-167[CrossRef][Medline]
[Order article via Infotrieve]
44.
Sparks, D.,
Lund-Katz, S.,
and Phillips, M.
(1992)
J. Biol. Chem.
267,
25839-25847 45.
de Beer, F. C.,
de Beer, M. C.,
van der Westhuyzen, D. R.,
Castellani, L. W.,
Lusis, A. J.,
Swanson, M. E.,
and Grass, D. S.
(1997)
J. Lipid Res.
38,
2232-2239[Abstract]
46.
Cabana, V. G.,
Lukens, J. R.,
Rice, K. S.,
Hawkins, T. J.,
and Getz, G. S.
(1996)
J. Lipid Res.
37,
2662-2674[Abstract]
47.
Rader, D. J.,
Castro, G.,
Zech, L. A.,
Fruchart, J. C.,
and Brewer, H. B., Jr.
(1991)
J. Lipid Res.
32,
1849-1859[Abstract]
48.
Lagocki, P.,
and Scanu, A. M.
(1980)
J. Biol. Chem.
255,
3701-3706 49.
Horowitz, B. S.,
Goldberg, I. J.,
Merab, J.,
Vanni, T. M.,
Ramakrishnan, R.,
and Ginsberg, H. N.
(1993)
J. Clin. Invest.
91,
1743-1752
50.
Krieger, M.
(1998)
Proc. Natl. Acad. Sci. U. S. A.
95,
4077-4080 51.
Acton, S.,
Rigotti, A.,
Landschultz, K. T.,
Xu, S.,
Hobbs, H. H.,
and Krieger, M.
(1996)
Science
271,
460-461[CrossRef][Medline]
[Order article via Infotrieve]
52.
Rigotti, A.,
Edelman, E. R.,
Seifert, P.,
Iqbal, S. N.,
DeMattos, R. B.,
Temel, R. E.,
Krieger, M.,
and Williams, D. L.
(1996)
J. Biol. Chem.
271,
33545-33549 53.
Flegel, W. A.,
Baumstark, M. W.,
Weinstock, C.,
Berg, A.,
and Northoff, H.
(1993)
Infect. Immun.
61,
5140-5146 54.
Levine, D. M.,
Parker, T. S.,
Donnelly, T. M.,
Walsh, A.,
and Rubin, A. L.
(1993)
Proc. Natl. Acad. Sci. U. S. A.
90,
12040-12044 55.
Pajkrt, D.,
Doran, J. E.,
Koster, F.,
Lerch, P. G.,
Arnet, B.,
van der Poll, T.,
ten Cate, J. W.,
and van Deventer, S. J.
(1996)
J. Exp. Med.
184,
1601-1608 56.
Emancipator, K.,
Csako, G.,
and Elin, R. J.
(1992)
Infect. Immun.
60,
596-601 57.
Ridker, P. M.,
Cushman, M.,
Stampfer, M. J.,
Tracy, R. P.,
and Hennekens, C. H.
(1997)
N. Engl. J. Med.
336,
973-979 58.
Ridker, P. M.,
Buring, J. E.,
Shih, J.,
Matias, M.,
and Hennekens, C. H.
(1998)
Circulation
98,
731-733 59.
Ridker, P. M.,
Hennekens, C. H.,
Roitman-Johnson, B.,
Stampfer, M. J.,
and Allen, J.
(1998)
Lancet
351,
88-92[CrossRef][Medline]
[Order article via Infotrieve]
60.
Lee, R. T.,
and Libby, P.
(1997)
Arterioscler. Thromb. Vasc. Biol.
17,
1859-1867 61.
Nakano, T.,
Ohara, O.,
Teraoka, H.,
and Arita, H.
(1990)
FEBS Lett.
261,
171-174[CrossRef][Medline]
[Order article via Infotrieve]
62.
Nakano, T.,
and Arita, H.
(1990)
FEBS Lett.
273,
23-26[CrossRef][Medline]
[Order article via Infotrieve]
63.
Hurt-Camejo, E.,
Anderson, S.,
Standal, R.,
Rosengren, B.,
Sartipy, P.,
Stadberg, E.,
and Johanses, B.
(1997)
Arterioscler. Thromb. Vasc. Biol.
17,
300-309 64.
Romano, M.,
Romano, E.,
Bjorkerud, S.,
and Hurt-Camejo, E.
(1998)
Arterioscler. Thromb. Vasc. Biol.
18,
519-525 65.
Nakamura, H.,
Kim, D. K.,
Philbin, D. M.,
Peterson, M. B.,
Debros, F.,
Koski, G.,
and Bonventre, J. V.
(1995)
J. Clin. Invest.
95,
1062-1070
66.
Menschikowski, M.,
Kasper, M.,
Lattke, P.,
Schiering, A.,
Schiefer, S.,
Stockinger, H.,
and Jaross, W.
(1995)
Atherosclerosis
118,
173-181[CrossRef][Medline]
[Order article via Infotrieve]
67.
Ivandic, B.,
Castellani, L. W.,
Wang, X. P.,
Qiao, J.-H.,
Mehrabian, M.,
Navab, M.,
Fogelman, A. M.,
Grass, D. S.,
Swanson, M. E.,
de Beer, M. C.,
De Beer, F.,
and Lusis, A. J.
(1999)
Arterioscler. Thromb. Vasc. Biol.
19,
1284-1290
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  H. Wiersma, A. Gatti, N. Nijstad, F. Kuipers, and U. J. F. Tietge Hepatic SR-BI, not endothelial lipase, expression determines biliary cholesterol secretion in mice J. Lipid Res., August 1, 2009; 50(8): 1571 - 1580. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Shaposhnik, X. Wang, J. Trias, H. Fraser, and A. J. Lusis The synergistic inhibition of atherogenesis in apoE-/- mice between pravastatin and the sPLA2 inhibitor varespladib (A-002) J. Lipid Res., April 1, 2009; 50(4): 623 - 629. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Boyanovsky, M. Zack, K. Forrest, and N. R. Webb The Capacity of Group V sPLA2 to Increase Atherogenicity of ApoE-/- and LDLR-/- Mouse LDL In Vitro Predicts its Atherogenic Role In Vivo Arterioscler. Thromb. Vasc. Biol., April 1, 2009; 29(4): 532 - 538. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Nijstad, H. Wiersma, T. Gautier, M. van der Giet, C. Maugeais, and U. J. F. Tietge Scavenger Receptor BI-mediated Selective Uptake Is Required for the Remodeling of High Density Lipoprotein by Endothelial Lipase J. Biol. Chem., March 6, 2009; 284(10): 6093 - 6100. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Jahangiri, M. C. de Beer, V. Noffsinger, L. R. Tannock, C. Ramaiah, N. R. Webb, D. R. van der Westhuyzen, and F. C. de Beer HDL Remodeling During the Acute Phase Response Arterioscler. Thromb. Vasc. Biol., February 1, 2009; 29(2): 261 - 267. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. R. Lagor, R. J. Brown, S.-A. Toh, J. S. Millar, I. V. Fuki, M. de la Llera-Moya, T. Yuen, G. Rothblat, J. T. Billheimer, and D. J. Rader Overexpression of Apolipoprotein F Reduces HDL Cholesterol Levels In Vivo Arterioscler. Thromb. Vasc. Biol., January 1, 2009; 29(1): 40 - 46. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
U. J. F. Tietge, N. Nijstad, R. Havinga, J. F. W. Baller, F. H. van der Sluijs, V. W. Bloks, T. Gautier, and F. Kuipers Secretory phospholipase A2 increases SR-BI-mediated selective uptake from HDL but not biliary cholesterol secretion J. Lipid Res., March 1, 2008; 49(3): 563 - 571. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Luchtefeld, H. Schunkert, M. Stoll, T. Selle, R. Lorier, K. Grote, C. Sagebiel, K. Jagavelu, U. J.F. Tietge, U. Assmus, et al. Signal transducer of inflammation gp130 modulates atherosclerosis in mice and man J. Exp. Med., August 6, 2007; 204(8): 1935 - 1944. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. S. Millar, S. J. Stone, U. J. F. Tietge, B. Tow, J. T. Billheimer, J. S. Wong, R. L. Hamilton, R. V. Farese Jr., and D. J. Rader Short-term overexpression of DGAT1 or DGAT2 increases hepatic triglyceride but not VLDL triglyceride or apoB production J. Lipid Res., October 1, 2006; 47(10): 2297 - 2305. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. C. de Beer and N. R. Webb Inflammation and atherosclerosis: Group IIa and Group V sPLA2 are not redundant. Arterioscler. Thromb. Vasc. Biol., July 1, 2006; 26(7): 1421 - 1422. [Full Text] [PDF]
|
|
|
|
|
|
U. J. F. Tietge, D. Pratico, T. Ding, C. D. Funk, R. B. Hildebrand, T. Van Berkel, and M. Van Eck Macrophage-specific expression of group IIA sPLA2 results in accelerated atherogenesis by increasing oxidative stress J. Lipid Res., August 1, 2005; 46(8): 1604 - 1614. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M. Boekholdt, T. T. Keller, N. J. Wareham, R. Luben, S. A. Bingham, N. E. Day, M. S. Sandhu, J. W. Jukema, J. J.P. Kastelein, C. E. Hack, et al. Serum Levels of Type II Secretory Phospholipase A2 and the Risk of Future Coronary Artery Disease in Apparently Healthy Men and Women: The EPIC-Norfolk Prospective Population Study Arterioscler. Thromb. Vasc. Biol., April 1, 2005; 25(4): 839 - 846. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Schieffer, T. Selle, A. Hilfiker, D. Hilfiker-Kleiner, K. Grote, U. J.F. Tietge, C. Trautwein, M. Luchtefeld, C. Schmittkamp, S. Heeneman, et al. Impact of Interleukin-6 on Plaque Development and Morphology in Experimental Atherosclerosis Circulation, November 30, 2004; 110(22): 3493 - 3500. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Khovidhunkit, M.-S. Kim, R. A. Memon, J. K. Shigenaga, A. H. Moser, K. R. Feingold, and C. Grunfeld Thematic review series: The Pathogenesis of Atherosclerosis. Effects of infection and inflammation on lipid and lipoprotein metabolism mechanisms and consequences to the host J. Lipid Res., July 1, 2004; 45(7): 1169 - 1196. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. C. Broedl, C. Maugeais, J. S. Millar, W. Jin, R. E. Moore, I. V. Fuki, D. Marchadier, J. M. Glick, and D. J. Rader Endothelial Lipase Promotes the Catabolism of ApoB-Containing Lipoproteins Circ. Res., June 25, 2004; 94(12): 1554 - 1561. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Maugeais, U. J.F. Tietge, U. C. Broedl, D. Marchadier, W. Cain, M. G. McCoy, S. Lund-Katz, J. M. Glick, and D. J. Rader Dose-Dependent Acceleration of High-Density Lipoprotein Catabolism by Endothelial Lipase Circulation, October 28, 2003; 108(17): 2121 - 2126. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. C. Hudgins, T. S. Parker, D. M. Levine, B. R. Gordon, S. D. Saal, X.-c. Jiang, C. E. Seidman, J. D. Tremaroli, J. Lai, and A. L. Rubin A single intravenous dose of endotoxin rapidly alters serum lipoproteins and lipid transfer proteins in normal volunteers J. Lipid Res., August 1, 2003; 44(8): 1489 - 1498. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. J. F. Tietge, C. Maugeais, W. Cain, and D. J. Rader Acute inflammation increases selective uptake of HDL cholesteryl esters into adrenals of mice overexpressing human sPLA2 Am J Physiol Endocrinol Metab, August 1, 2003; 285(2): E403 - E411. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Murakami, S. Masuda, S. Shimbara, S. Bezzine, M. Lazdunski, G. Lambeau, M. H. Gelb, S. Matsukura, F. Kokubu, M. Adachi, et al. Cellular Arachidonate-releasing Function of Novel Classes of Secretory Phospholipase A2s (Groups III and XII) J. Biol. Chem., March 14, 2003; 278(12): 10657 - 10667. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. R. Webb, M. A. Bostrom, S. J. Szilvassy, D. R. van der Westhuyzen, A. Daugherty, and F. C. de Beer Macrophage-Expressed Group IIA Secretory Phospholipase A2 Increases Atherosclerotic Lesion Formation in LDL Receptor-Deficient Mice Arterioscler. Thromb. Vasc. Biol., February 1, 2003; 23(2): 263 - 268. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Hanasaki, K. Yamada, S. Yamamoto, Y. Ishimoto, A. Saiga, T. Ono, M. Ikeda, M. Notoya, S. Kamitani, and H. Arita Potent Modification of Low Density Lipoprotein by Group X Secretory Phospholipase A2 Is Linked to Macrophage Foam Cell Formation J. Biol. Chem., August 2, 2002; 277(32): 29116 - 29124. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
U. J.F. Tietge, C. Maugeais, S. Lund-Katz, D. Grass, F. C. deBeer, and D. J. Rader Human Secretory Phospholipase A2 Mediates Decreased Plasma Levels of HDL Cholesterol and ApoA-I in Response to Inflammation in Human ApoA-I Transgenic Mice Arterioscler. Thromb. Vasc. Biol., July 1, 2002; 22(7): 1213 - 1218. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Murakami, K. Yoshihara, S. Shimbara, G. Lambeau, M. H. Gelb, A. G. Singer, M. Sawada, N. Inagaki, H. Nagai, M. Ishihara, et al. Cellular Arachidonate-releasing Function and Inflammation-associated Expression of Group IIF Secretory Phospholipase A2 J. Biol. Chem., May 17, 2002; 277(21): 19145 - 19155. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Petrovic, C. Grove, P. E. Langton, N. L. A. Misso, and P. J. Thompson A simple assay for a human serum phospholipase A2 that is associated with high-density lipoproteins J. Lipid Res., October 1, 2001; 42(10): 1706 - 1714. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| All ASBMB Journals | Molecular and Cellular Proteomics |
| Journal of Lipid Research | ASBMB Today |