© 1997 American Heart Association, Inc.
Articles |
Normolipidemic Subjects With Low HDL Cholesterol Levels Have Altered HDL Subpopulations
From the Division of Lipoprotein Metabolism and Pathophysiology, Department of Physiology, Louisiana State University Medical Center, New Orleans (B.F.A., T.A.F., L.W., P.S.R.), and the Division of Diet and Heart Disease, Pennington Biomedical Research Center, Baton Rouge (M.L., R.T., M.W.), La.
Correspondence to Paul S. Roheim, MD, Louisiana State University Medical Center, Department of Physiology, 1542 Tulane Ave, New Orleans, LA 70112. E-mail dbarra{at}nomvs.lsumc.edu
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Abstract |
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Abstract Epidemiological studies have established that plasma concentration of HDL is inversely correlated with the risk of coronary heart disease, even in the absence of increased LDL cholesterol levels. We postulate that specific HDL subpopulations may be responsible for antiatherogenic properties of HDL. HDL subpopulations were quantitated by two-dimensional gel electrophoresis in 79 normolipidemic healthy male subjects. To eliminate the influence of diet, volunteers consumed an average American diet for 6 weeks. After the diet period, subjects were stratified according to their HDL cholesterol (HDL-C) levels to low HDL-C <0.91 mmol/L (<35 mg/dL), medium >0.91<1.30 mmol/L (>35 <50 mg/dL), and high
1.30 mmol/L
(50 mg/dL) groups. Plasma triglycerides and insulin
levels were in the normal range, but subjects with low HDL-C levels had
higher concentrations of plasma triglycerides and insulin
than subjects with medium or high HDL-C concentrations. The absolute
concentration (mg/dL) of apoA-I in the largest 
-migrating HDL
subpopulation (1) was (P<.01) lower in the
low HDL-C subjects compared with the medium and high HDL-C groups. The
relative concentration (percent distribution) of apoA-I was decreased
(P<.01) in 1 and increased
(P<.01) in 3 subpopulations. A positive
correlation between HDL-C and 1 (P<.001) and
a negative correlation between HDL-C and 3 were
observed. The inverse correlation of apoA-I distribution (relative
concentration) between 1 and 3 suggests
an interconversion of 1 and 3
subpopulations, possibly by cholesteryl ester transfer protein. Pre-ß
subpopulations showed an inverse trend with HDL-C, while the pre-
subpopulation behaved similarly to the -migrating subpopulation.
Colocalization of apoA-I and apoA-II particles in the different HDL
subpopulations demonstrated that 1,
pre-ß1, and pre-ß2 subpopulations are
apoA-I–only particles rather than apoA-I:A-II particles.
Key Words: apoA-I–containing HDL subpopulations • LpA-I • LpA-I:A-II particles • cholesterol • diet
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Introduction |
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The inverse relationship between HDL and risk of coronary heart disease (CHD) has been established for several decades.1 Low plasma levels of HDL are associated with increased risk of CHD, even in the absence of elevated LDL concentrations.2 3 4 5 Plasma concentration of HDL is influenced by several factors, including gender, race, diet, and lifestyle.6 7 8
HDLs are heterogeneous, containing several subpopulations differing in size,9 hydrated density, lipid and apoprotein composition, and functional properties.10 11 Subclasses of HDL can be separated by ultracentrifugation,10 11 gel filtration chromatography,12 polyanion precipitation,13 one-9 and two-dimensional14 15 16 polyacrylamide gel electrophoresis, or by immunoaffinity chromatography.17 18
Although most data have been obtained through subfractionation of
HDL subpopulations by ultracentrifugation, this
procedure produces artifacts resulting in loss of pre-ß1
and pre-ß2 particles and an overall change in the
distribution of and pre- particles.15 Additional
artifacts can be produced by in vitro remodeling of HDL subpopulations
by factors present in plasma,11 requiring appropriate
methods for sample collection and preservation. Association of HDL
subpopulations with CHD has been widely investigated, but conclusions
are equivocal.18 19 20 21 22 Separation of HDL subpopulations based
on apoprotein composition17 18 22 suggests that a decrease
of apoA-I–only particles is associated with an increase in the risk of
CHD. Using a 2DE system, it is possible to separate and quantify HDL
subpopulations reproducibly and precisely.15 These
well-defined apoA-I–containing subpopulations differ in charge
(pre-ß, , and pre-) and size.
It has been postulated that HDL subpopulations may directly influence the atherogenic process.23 Using immunoaffinity chromatography and nondenaturing polyacrylamide gel electrophoresis, Cheung et al24 reported significant differences in the size of HDL in patients with CHD compared with healthy subjects. They found that the presence of CHD was more strongly associated with HDL particle size distribution than with low HDL-C levels.
Considerable variation is reported in HDL-C levels among
normolipidemic subjects,25 but no information is available
on the distribution of HDL subpopulations at different HDL-C levels in
normolipidemic subjects. The scarcity of information is more evident in
groups whose dietary intake is controlled. In this study using 2DE, we
compared the distribution of apoA-I–containing HDL subpopulations in
normolipidemic male subjects consuming an average American diet for 6
weeks with low (<0.91 mmol/L, <35 mg/dL), medium
(>0.91<1.30 mmol/L, >35 <50 mg/dL), and high (1.30
mmol/L, 50 mg/dL) HDL-C concentrations.
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Methods |
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Subjects
Seventy-nine male subjects (ages 22 to 65 years) were recruited to participate in a study examining the relationship between diet and risk factors for CHD. Participants were selected to have total plasma cholesterol and LDL cholesterol between the 10th and 90th percentile. HDL-C above 0.65 mmol/L (25 mg/dL) or below the 95th percentile and triglycerides below the 95th percentile were adjusted for age and race as determined by the NHANES II data.26 The lipid cutoff points were selected to eliminate subjects with lipid disorders.
Exclusion criteria included the presence of (1) renal, hepatic, cardiovascular, endocrine, gastrointestinal, or other systemic disease; (2) body mass index greater than 32; (3) hypertension; (4) history of drug or alcohol abuse; and (5) data obtained from medical questionnaires, psychological evaluations, blood chemistry and lipid profiles, and urinalyses and physical examination during screening visits.
Diet
Subjects consumed an AAD designed to provide 38% calories as
fat (Table 1
).
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Study Design
A 6-week dietary period was chosen to enable stabilization
of the lipoprotein end points.27 Participants were
provided with all foods during this time. On weekdays, the study
protocol required subjects to consume breakfast and dinner at the
Pennington Biomedical Research Center dining facility. Weekday packaged
lunches were distributed at breakfast, and evening snacks were
distributed at dinner. Weekend meals were packaged and distributed at
the Friday dinner. Subjects were allowed the option of a "free
choice meal" for Saturday dinner; approximately 25% of Saturday
dinners were "free choice." Since the Pennington Biomedical
Research Center provided 95% of caloric intake, we assumed that this
free meal would not substantially influence variables measured in
this study. Furthermore, performing measurements at the end of the
sixth week, when dietary influences were stabilized, minimized the
potential short-term effects of this "free choice meal."
Participants were allowed a limited choice of items such as alcoholic
drinks and sugar-free beverages. Subjects recorded symptoms of
illness, medication use, selected food items, and any deviations in
food diaries. Dietary energy adjustments were made as needed to
maintain weight. Meals were prepared at four energy levels (2200, 2600,
3000, and 3400 kcal/d). One hundred kcal unit foods that matched
the composition of the diet were used for energy adjustments. Subjects
started on the energy level most closely matching their estimated
energy requirement. Body weight (without shoes, jackets, or heavy
sweaters) was measured twice weekly. If a subject's weight differed
from the initial level by more than 1 kg, the subject was switched to
another energy level or the number of unit foods was changed until the
weight returned to within 1 kg of the initial value.
Processing of Blood
At the end of the 6-week dietary period, fasting blood samples
for lipid and apolipoprotein analysis were collected in tubes
containing 1.2 g/L EDTA and placed on ice immediately after
collection. Plasma was isolated by centrifugation at
30 000g min. Multiples (0.5 to 1.0 mL) of each sample were
stored in cryovials at -80°C until samples were analyzed for
lipids and apoproteins.
For 2DE, blood samples were collected and placed on ice with the following additives in final concentrations: 1.2 g/L EDTA, 0.1 g/L sodium azide, 80 mg/L gentamicin sulfate, and 10 KU/L kallikrein inactivator (aprotinin). Plasma was separated immediately by centrifugation at 5°C. Additional preservatives were added to the plasma in 1 mmol/L final concentration: PMSF in DMSO, benzamidine in DMSO, and N'-ethylmaleimide (dissolved just before use because it is stable in water only for about 1 hour) in water.
After separation, plasma was frozen and stored in liquid nitrogen until
samples were processed by 2DE. Four microliters of plasma was applied
and run on agarose in the first dimension followed by electrophoresis
into a 3% to 35% nondenaturing concave gradient
polyacrylamide gel at 280 V for 24 hours at 10°C. In this 2DE
system, the agarose electrophoresis differs from the one generally used
in that the agarose contains no albumin. This modification
provides a clearer separation of and pre- particles.
Electrophoretic transfer, fixing, blocking, and immunolocalization were
performed as described previously.15 Bound radioactivity
was quantified by PhoshorImager analysis (Molecular
Dynamics).28 Monospecific polyclonal anti–apoA-I and
–apoA-II antibodies used for these studies were produced in goats in
our laboratory as previously described.29 For secondary
antibody, F(ab')2 fragments of anti-goat gamma globulins were used
(Zymed). Subpopulations were characterized by: (1) charge (pre-ß,
, and pre-) based on their relative mobility with respect to
albumin and (2) size determined from molecular weight standards
run simultaneously in the same gel. With this system, we
were able to separate and quantify apoA-I–containing subpopulations.
Interassay and intra-assay coefficients of variation for different
subpopulations varied between 3% ( subpopulations) and 15%
(pre-ß subpopulations). Criteria for designation of HDL subfractions
of 1, 2, and
315 are based on integration of
-migrating HDL in the two-dimensional system. Three distinct peaks
are observed, providing a basis for the designation of
1, 2, 3 (Fig 1). Quantification was calculated based
on valley-to-valley area under the scanned curves.
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Chemical Methods
Serum total cholesterol, HDL-C, and
triglycerides were determined using enzymatic assays on a
Beckman Synchron CX5 automated chemistry analyzer. HDL-C was
determined after precipitation of the non-HDL fractions by dextran
sulfate (50 000 molecular weight; DMA) following the protocol of
Warnick et al.30 Assayed controls provided by DMA were
used to verify accuracy. VLDL was calculated using the Friedewald
equation. The interassay coefficient of variation was less than
2.0%.
ApoA-I and apoB were measured on a Beckman Array analyzer employing reagents supplied by the manufacturer. The interassay coefficients of variation for assays were less than 7%.
Statistical Analysis
Initially, descriptive statistics, scatterplots, and Pearson
correlation coefficients summarized data. For analysis,
nonnormally distributed data were transformed using the natural
logarithm to approach a Gaussian distribution. ANOVA tested the
hypothesis of no difference in mean levels of given variables among
three HDL-C categories. Post hoc (a posteriori) comparisons,
appropriate only when ANOVA is statistically
significant,31 32 33 evaluated all pairwise differences among
three HDL-C subgroups by Duncan's multiple range test.
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Results |
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The objective of this study was to compare the distribution of HDL subpopulations in low, medium, and high HDL-C subjects consuming the AAD for 6 weeks. Subjects with <0.91 mmol/L (<35 mg/dL) HDL-C were designated as low HDL-C, while subjects between >0.91<1.30 mmol/L (>35 <50 mg/dL) and
1.30 mmol/L (50 mg/dL) HDL-C were defined as
medium and high HDL-C individuals, respectively.34
Table 2 presents screening values for
lipids, insulin, and selected anthropometric variables by the three
HDL-C categories and all categories combined. Plasma total and LDL
cholesterol concentrations were similar in all three
groups, whereas triglycerides and insulin levels were the
highest in the low HDL-C group. Table 3
presents lipid values obtained after consuming the AAD for 6 weeks.
In general, the overall values were very similar to the values obtained
at screening.
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After 6 weeks on the AAD, lipid values were
stabilized27 so that the distribution of HDL
subpopulations would be more representative for each
HDL-C group. On the AAD, the average HDL-C values were 0.82, 1.09, and
1.46 mmol/L (31.6, 42.3, and 56.5 mg/dL) in the low,
medium, and high HDL-C groups, respectively (Table 3
). No significant
differences in total cholesterol or LDL
cholesterol were noted among the three groups, but
triglyceride and VLDL cholesterol
concentrations were higher (33% and 72%) in the low HDL-C group than
the medium and high HDL-C groups, respectively. It should be noted that
in this sample of normolipidemic subjects, triglyceride
concentration was inversely proportional to HDL-C concentration. ApoA-I
concentrations paralleled those of HDL-C. Low, medium, and high
HDL-C groups had mean apoA-I concentrations of 108.4, 124.7, and 138.4
mg/dL, respectively, and were significantly different from one
another. ApoB concentration was the lowest in the high HDL-C, high
apoA-I individuals. The low HDL-C group had a significantly lower
HDL-C/apoA-I ratio compared with the medium and high HDL-C groups,
suggesting a decrease in cholesterol-rich HDL
particles.
Using 2DE, the apoA-I–containing HDL subpopulations were
compared in these three HDL-C groups. Fig 1 shows a typical
distribution of HDL subpopulations for subjects with low (A), medium
(B), and high (C) HDL-C. It is apparent that low HDL-C subjects had a
considerable decrease in the largest HDL subpopulation
(1).
In this study, we distinguished between absolute concentrations of apoA-I (mg/dL apoA-I in the subpopulations) and relative concentrations (percent distribution of apoA-I among the subpopulations). The absolute apoA-I concentration in a subpopulation is a function of plasma apoA-I concentration and its percent distribution among the subpopulations.
ApoA-I concentrations in the different HDL subpopulations were compared
in the three HDL-C groups (Fig 2A).
Absolute concentrations of apoA-I in the 1 subpopulation
was the lowest in the low HDL-C group and highest in the high HDL-C
group. The concentration of apoA-I in 2 behaved
similarly to 1, but the differences were smaller between
the low and the high HDL-C groups. Absolute concentrations of apoA-I in
3 was the lowest in the high HDL-C group. Absolute
concentrations of pre- subpopulations followed the patterns of
subpopulations.
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When relative concentrations of apoA-I in HDL subpopulations were
compared (Fig 2B), 1 had the lowest apoA-I
concentrations in the low HDL-C group and the highest in the high HDL-C
group. In contrast to our observations indicating a difference in
absolute concentration of 2 among HDL-C groups
(P<.05), relative concentrations of apoA-I (percent
distribution) did not differ among HDL-C categories. Relative
concentration of apoA-I in 3 was the highest in the low
HDL-C group and the lowest in the high HDL-C group (P<.01)
in contrast to absolute apoA-I concentrations where no difference was
found among HDL-C groups (P>.05). Pre- subpopulations in
general followed the patterns of the subpopulations. Percent
distribution of pre-ß2a and pre-ß2c in the
low HDL-C group exceeded that in the high HDL-C group. The
pre-ß2b was the highest in the low HDL-C group compared
with medium and high HDL-C categories. Although no significant
differences were noted among HDL-C groups in the percent distribution
of pre-ß1 (P=.0792, F=2.62, ANOVA), a lower
mean level was observed in the high HDL-C category.
To better evaluate the interrelationship among the three major
-migrating HDL subpopulations, HDL-C concentrations were correlated
with both the absolute and relative concentrations of apoA-I in
1, 2, and 3 subpopulations
(Fig 3). It is apparent that HDL-C is
highly correlated with apoA-I concentrations in the 1
subpopulation in both absolute (Fig 3a) and relative concentrations
(Fig 3b). In the 2 subpopulation, HDL-C correlated well
with the absolute concentrations (Fig 3c) but was not statistically
different from zero with respect to relative concentrations (Fig 3d) of
apoA-I. In the 3 subpopulation, HDL-C did not correlate
(P>.05) with absolute apoA-I concentration (Fig 3e) but
showed a significant negative correlation with the relative
concentration of apoA-I (Fig 3f).
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Since it appears that changes in relative distributions of apoA-I
can be explained by the interconversion of 1 and
3, we determined the correlation among the relative
concentrations of apoA-I in 1, 2, and
3 (Fig 4). A negative
correlation was observed in the relative concentrations (Fig 4a) of
1 and 3, which suggests that in vivo
redistribution of apoA-I may be responsible for decreased apoA-I levels
in 1 and increased levels in 3
subpopulations. While the correlation between 1 and
3 is very strong, those between 1 and
2 and between 2 and 3 are
not different from zero (P>.05; Fig 4b and 4c).
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Correlations were also calculated between pre-ß1,
pre-ß2, and 1. In both cases, the
r value was less than 0.26 and there was no statistical
significance. It should be noted that the absolute as well as relative
concentrations of 1 apoA-I were lower in the low HDL-C
group than in the medium and high HDL-C groups (Fig 2a and 2b).
Low HDL-C subjects have increased risk of CHD and a decrease in
LpA-I–only concentrations.18 35 A major difference in the
1 subpopulations was found among the low HDL-C and the
medium and high HDL-C subjects; therefore, it was important to
establish the nature of this particle and determine whether the
1 is an LpA-I–only or an LpA-I:A-II particle. The
distribution of apoA-I and apoA-II in the HDL subpopulations were
examined in two different ways. After 2DE, apoA-I and apoA-II were
immunolocalized separately on individual membranes and superimposed to
evaluate colocalization. It was found that the 1
particle did not contain apoA-II; thus, it is an apoA-I–only particle.
Similar results were obtained when the membranes were immunolocalized
first for apoA-II followed by immunolocalization of apoA-I on the same
membrane (Fig 5). It was also shown that
both pre-ß1 and pre-ß2 subpopulations are
apoA-I–only particles and do not contain apoA-II. ApoA-I and apoA-II
colocalized in the 2 and 3
subpopulations. These results should not be considered to imply that
2 and 3 subpopulations are only
apoA-I:apoA-II particles. It is likely that apoA-I–only particles may
also be present in the same area.
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Discussion |
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We compared the lipid values obtained at screening with values 6 weeks after the consumption of the AAD. The values at screening and after 6 weeks on the AAD showed no difference. These data suggest that the diet of subjects before the study was similar to the AAD consumed during the study. However, it should be noted that 23% of the subjects shifted within HDL-C categories; considering the categories at screening, six subjects moved from low to medium and seven subjects from medium to low HDL-C groups. From the high HDL-C categories, three subjects shifted to medium, while one subject moved to the high HDL-C group. Despite these changes of subjects among HDL-C categories, the lipid compositions were similar at screening and after AAD, suggesting characteristic lipid composition for each category.
We also compared the screening insulin and triglyceride
levels in subjects with low, medium, and high HDL-C (Table 2). Insulin
and TG levels segregated on the basis of HDL-C concentration (ie, low
HDL-C subjects had higher insulin and plasma triglyceride
concentrations). However, according to the screening criteria for this
study, subjects were normolipidemic with triglyceride
concentrations within normal limits.25 These data suggest
possible insulin resistance among low HDL-C individuals.
Considerable variation is found in HDL-C levels in normolipidemic
subjects.25 Our experimental design assumed that
controlled consumption of the AAD for 6 weeks stabilized plasma lipid
values and decreased or eliminated variations of diet-induced
changes.27 36 There is no information available on the
distribution of HDL subpopulation of healthy normolipidemic subjects
consuming a standard well-controlled diet for a defined period of time.
The objective of this study was to compare HDL subpopulations in
normolipidemic individuals with different HDL-C levels. Table 3 shows
the comparison of lipid values in the different HDL-C groups at the end
of 6 weeks on an AAD. An increase (33% and 72%) in plasma
triglycerides was found in the low HDL-C subjects compared
with the medium and high HDL-C groups, respectively.
Two-dimensional electrophoresis was used for the quantification of apoA-I–containing HDL subpopulations. This method established that HDL subpopulations can be separated accurately and reproducibly.15 In this study, special attention was paid to prevent in vitro remodeling of HDL subpopulations by using the appropriate preservation at the time of blood sampling.
When apoA-I levels in HDL subpopulations were compared among different
HDL-C groups, we observed that the 1 subpopulation was
the lowest in the low HDL-C group, in both absolute and relative
concentrations of apoA-I. These findings are also supported by the
decreased HDL-C/apoA-I ratios (Table 3) in low HDL-C groups, suggesting
a decrease in cholesterol-rich HDL particles. The
2 subpopulation was significantly different in HDL-C
groups in absolute concentrations but not in the relative
concentrations (percent distributions of apoA-I). In contrast to
2 subpopulations, there was no significant difference in
the absolute concentrations of apoA-I in 3, but the
relative concentrations (percent distributions) of apoA-I were
significantly lower in the medium and high HDL-C groups.
Mechanisms for these differences may be partially explained by
differences in CETP activities. Increased CETP activity has been
demonstrated in subjects with low HDL-C concentration.37
We did not measure CETP mass or CETP activity; however, we should
consider that low HDL-C subjects had increased TG concentrations, which
favors enhanced cholesterol ester transfer despite similar
CETP mass.38 Increased CETP activity may be responsible
for the decreased relative concentration of apoA-I in 1
subpopulations and the increase in relative concentrations of
3. When CETP in conjunction with hepatic lipase activity
transfers cholesterol ester to LDL and VLDL from large HDL
particles, a decrease in the large (1) and an increase
in the small (3) HDL particles takes
place.39 40 If increased CETP activity results in a
redistribution of apoA-I from 1 to 3,
then we should be able to demonstrate a correlation between the
relative concentration of 1 and 3 (Fig 4a) but no correlation with 2 and 3 (Fig 4b and 4c). Indeed, we observed a strong negative correlation between
the relative concentrations (percent distributions) of 1
and 3 (Fig 4a) but no correlation (P>.05) in
relative concentrations between either 1 and
2 or 2 and 3
subpopulations (Fig 4b and 4c). Increased CETP activity is
consistent with the observation of an increased fractional
catabolic rate of apoA-I41 42 and may explain decreased
HDL-C concentrations. It is possible that in addition to increased CETP
activity, a decrease in phospholipid transfer protein activity may also
be responsible for the changes in HDL subpopulations. It has been shown
that phospholipid transfer protein activity favors the formation of
larger-sized HDL particles.43 The differences in
subpopulation mass may not necessarily be the result of
interconversion, but rather there may be differences in the
metabolism of subpopulations in the three HDL-C
populations.
Low levels of HDL-C concentrations have been attributed to changes in
lipoprotein lipase and hepatic triglyceride lipase
activities; decreased lipoprotein lipase/ hepatic
triglyceride lipase ratio was observed in low HDL-C
subjects.37 41 This decreased ratio will result in an
increased fractional catabolic rate of an apoA-I–only
particle.41 This is consistent with our finding
that the 1, an apoA-I–only particle, is decreased in
low HDL-C subjects.44
HDL can be separated into LpA-I–only and LpA-I:A-II
particles.18 22 35 Low HDL-C subjects have low levels of
LpA-I–only lipoproteins. It has been shown that the incidence of CHD
is associated with a decrease of LpA-I–only
lipoproteins.22 Therefore, it was important to determine
whether the 1 subpopulation is an LpA-I–only particle.
We colocalized apoA-I and apoA-II (Fig 5) and found that apoA-II did
not colocalize with 1; thus, 1 HDL
subpopulation is an LpA-I–only particle. These data are similar to
data reported previously.14 We have also shown that both
pre-ß1 and pre-ß2 subpopulations are
LpA-I–only particles, in agreement with Hennessy et al.45
Colocalization of apoA-I and apoA-II was observed in 2
and 3 subpopulations. Lack of colocalization can be
proof of the existence of a separate apoA-I–only or an apoA-II–only
particle, but colocalization does not necessarily mean that apoA-I and
apoA-II are on the same particle.
These studies were conducted on normolipidemic male subjects. Since HDL-C levels in females are considerably higher,46 it would be important to establish what HDL-C level would result in an alteration of HDL-C subpopulations in females that is characteristic of low HDL-C subjects in males. Postmenopausal women have an increased incidence of CHD47 48 ; therefore, it also would be important to follow changes in HDL subpopulations in this segment of the population.
It has been shown that cholesterol efflux correlates
well with HDL-C concentrations.49 It is possible that
altered HDL subpopulations observed in low HDL-C subjects influence
susceptibility to CHD by decreased reverse cholesterol
transport. We hypothesize that a decreased 1
subpopulation may be partially responsible or is a marker for
susceptibility to development of CHD. The finding that 1
is an apoA-I–only particle and that it is decreased in the low HDL-C
group is consistent with the observation that decreased LpA-I
is associated with CHD.22
The Framingham studies have demonstrated that CHD preferentially occurs in subjects with low HDL-C.3 We do not know whether changes in HDL subpopulations in the low HDL-C group are causally related to increased susceptibility to atherosclerosis or whether it is an epiphenomenon. It is also possible that the change in HDL subpopulations is an indicator that the subjects are prone to CHD. In the future, it will be important to establish the association of HDL-C and changes in HDL subpopulations in the development of CHD.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This work was supported by a grant from the Dairy Management, Inc. and the National Institutes of Health/National Heart, Lung, and Blood Institute (HL-56160 and HL-25596). The authors wish to thank Dr Howard Eder for his suggestions, Katalin Horvath and Colleen Tierney for their excellent technical help, and Debbie Plaisance and Marci Crosby for their editorial assistance and manuscript preparation.
Received May 5, 1997; accepted August 4, 1997.
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References |
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