(Circulation. 1998;98:1993-1999.)
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department of Medicine, Helsinki University Central Hospital (M.S., M.S.N., M.H.F., M-R.T.); the Department of Medicine and Biocenter Oulu, Oulu University Hospital and University of Oulu (H.K., Y.A.K.); the Department of Medicine, Tampere University Hospital (S.M., V.V., A.P.); and the Department of Biochemistry, National Public Health Institute, Helsinki (C.E.), Finland.
| Abstract |
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Methods and ResultsMen who had undergone coronary bypass surgery (n=372) completed a randomized, placebo-controlled study with gemfibrozil 1200 mg/d. They were selected primarily for HDL cholesterol levels that corresponded to the lowest third for middle-aged men. Average baseline lipid and lipoprotein levels were serum triglyceride, 1.60; serum cholesterol, 5.17; ultracentrifugally separated LDL cholesterol, 3.43; HDL2 cholesterol, 0.41; and HDL3 cholesterol, 0.61 mmol/L. In the gemfibrozil group, these levels were reduced on average by 40%, 9%, and 6% or increased by 5% and 9%, respectively. On-trial IDL and LDL triglyceride and cholesterol levels significantly predicted global angiographic progression, taking into account changes in native segments and in bypass grafts. HDL3 but not HDL2 cholesterol concentration was associated with protection against progression, especially focal disease in native coronary lesions. VLDL was the lipoprotein most predictive of new lesions in vein grafts; IDL was also significantly related.
ConclusionsThis study expands the previous evidence of the triglyceride-rich lipoproteins, especially IDL, as predictors of angiographic progression of CAD but does not negate the significance of mildly elevated LDL levels. Of the HDL subfractions, only HDL3 was protective in this group of men selected for their low initial HDL levels.
Key Words: coronary disease bypass lipoproteins angiography trials
| Introduction |
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Despite marked benefits from treating dyslipidemia in CAD patients, most studies, including LOCAT, showed that angiographic progression continued during active therapy, albeit at a slower pace than in patients who received placebo. The present study reports which lipoproteins, separated by preparative ultracentrifugation, predict angiographic progression in the LOCAT study population.
| Methods |
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1.1 mmol/L (42.5
mg/dL), LDL cholesterol
4.5 mmol/L (174 mg/dL), and
serum triglyceride
4.0 mmol/L (354 mg/dL) were
randomized to receive 1200 mg/d gemfibrozil or placebo. Three hundred
seventy-two patients (placebo, 187; gemfibrozil, 185) completed the
study with a baseline and follow-up angiogram that were suitable for
quantitative analysis, and these patients constitute the
population of this report.
Angiographic Data
As previously reported,5 we used the
average diameters of coronary segments (ADS) to describe
changes in diffuse CAD and minimum luminal diameters (MLD) of
stenoses to characterize focal CAD. We classified the patients
into those showing progression only, a mixed response of progression
and regression, regression only, and no significant change. Those with
progression only or a mixed response were considered progressors, and
the remaining patients were nonprogressors. Progression or regression
was defined as a change in ADS or MLD
0.40 mm in any native
coronary segment.7 New lesions and new
total occlusions were also defined as progression. Venous
aortocoronary bypass grafts were taken into account by defining
a new graft lesion as progression. The rationale for this post hoc
classification, rather than one based only on changes in the
nonbypassed native vessels and segments distal to graft insertions as
we originally planned,6 was a report by the
Cholesterol Lowering Atherosclerosis Study
(CLAS) investigators showing that a global coronary score that
takes into account all native segments and bypass grafts predicts
future clinical events in postbypass
patients.8
We also calculated per-patient mean changes in ADS and MLD (
ADS and
MLD) in all native coronary segments and stenoses
available for analysis. An additional outcome variable was
the appearance of new lesions in vein grafts.
Lipoprotein and Other Risk-Variable Data
Blood samples were obtained after an overnight fast at the
randomization visit, 1 year after randomization, and
2 years after
randomization. Lipoproteins (VLDL, d<1.006 g/mL; IDL,
d=1.006 to 1.019 g/mL; LDL, d=1.019 to 1.063
g/mL; HDL, d=1.063 to 1.210 g/mL; and the HDL subfractions
HDL2, d=1.063 to 1.120 g/mL; and
HDL3, d=1.120 to 1.210 g/mL) were
separated by preparative ultracentrifugation as
described elsewhere.6 Triglyceride,
cholesterol, free (nonesterified) cholesterol,
and phospholipid were measured in unfractionated serum and in the
lipoprotein fractions, and protein was measured in the
fractions.6 Cholesteryl ester concentrations were
calculated as 1.67x(total minus free cholesterol [in
mg/dL]).9 Lipoprotein compositions were
calculated as the percentages of triglyceride, esterified
cholesterol, free cholesterol, phospholipid,
and protein (all in mg/dL) of the sum of these constituents. Serum
apolipoprotein B (apoB) and lipoprotein(a) [Lp(a)] concentrations
were determined as described.6
Triglyceride and cholesterol in serum and lipoproteins and serum apoB were measured at both 1- and 2-year visits and averaged. On-trial data for other lipoprotein constituents and Lp(a) were available only at the 1-year visit.
An oral glucose tolerance test with glucose, insulin, and C-peptide measurements was performed at baseline as described,6 and fasting insulin was also measured at the final study visit. Height was measured at baseline; weight, waist and hip circumferences, blood pressure, and heart rate were determined at each visit.6
Statistical Analyses
Data are given as mean±SD or median (25th, 75th percentile).
Unpaired t tests were used to compare on-trial lipoprotein
data in the randomized groups after logarithmic transformations for
skewed data. Categorical variables were compared by the
2 test. Simple correlations were assessed by
Pearson's coefficients. Associations between risk factors and the
global progressor status were evaluated by logistic regression
analyses. All analyses were adjusted for the time
interval between the baseline and follow-up angiograms. For the
calculation of odds ratios, lipoprotein data were made comparable by
transformation to standardized z scores (they have the same
distribution as the original data but a mean value of zero and SD=1).
Other logistic models were created to control for the randomization
group and to study the associations in the placebo and gemfibrozil
groups separately. The continuous outcome variables (
ADS and
MLD) were analyzed by linear regression, controlling for the
time between angiograms and the baseline values of the dependent
variables. These analyses were performed for the whole
study population and for the randomized groups separately. Further
analyses were adjusted for the treatment group. For linear
regression analyses, skewed variables were logarithmically
transformed. Finally, we performed multivariate
stepwise linear regression analyses.
| Results |
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The change in serum and VLDL triglyceride values in the
gemfibrozil group was highly correlated with the baseline value (Figure 1A
). In 170 patients (92%), VLDL
triglyceride levels decreased during active therapy. For
HDL cholesterol, there was also a significant, albeit
weaker, correlation between the baseline value and treatment response
(Figure 1B
). Although most patients (n=126, 68%), as expected,
experienced an increase in HDL cholesterol levels, a
substantial minority were nonresponders. For the
HDL2 subfraction, 111 patients (60%) had an
increase during gemfibrozil therapy, and for
HDL3, 129 patients (70%) (Figure 1C
). LDL
cholesterol levels decreased during gemfibrozil therapy in
113 patients (61%), and the change in LDL cholesterol was
also related to the baseline value (r=-0.430,
P<0.001).
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Serum apoB concentration at baseline was 102±19 mg/dL in the placebo group and 102±18 mg/dL in the gemfibrozil group. On-trial values (averages of 1- and 2-year visits) were 108±19 and 88±17 mg/dL in the placebo and gemfibrozil groups, respectively (P<0.001). Lp(a) concentrations [median (25th, 75th percentile)] at baseline were 173 (63, 440) and 161 (76, 412) and after 1 year of randomized therapy 176 (66, 466) and 181 (75, 411) mg/L in the placebo and gemfibrozil groups, respectively (not significant).
Lipoprotein Compositions
All lipoprotein classes were significantly depleted of
triglyceride by gemfibrozil (Table 1
, Figure 2
). In the triglyceride-rich
lipoproteins (VLDL and IDL), all lipid constituents were markedly
reduced (Table 2
). In VLDL, the protein
concentration also fell (from 24.0±8.7 to 18.6±9.2 mg/dL), suggesting
that VLDL particles were both decreased in number and depleted of
lipid. By contrast, there was no suggestion of any reduction in IDL
particle numbers. For LDL, there was also no change in protein
concentrations (Table 2
), but there was a significant increase in the
placebo group (data not shown), resulting in 11% lower levels in the
gemfibrozil group during randomized therapy. On-trial concentrations of
all LDL lipid components were lower in the gemfibrozil than in the
placebo group, and the differences ranged from 7% (free
cholesterol) to 21% (triglyceride).
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HDL2 protein concentrations remained unchanged
during gemfibrozil therapy (Table 2
), indicating no change in particle
numbers, but there was some depletion of triglyceride and
phospholipid and a concomitant increase in esterified and free
cholesterol contents (Figure 2
). HDL3
protein concentrations increased, suggesting an increased number of
these particles. The particles were depleted of
triglyceride and enriched in esterified
cholesterol (Figure 2
).
Global Angiographic Progression
In the placebo group, 95 patients were classified as showing
progression only, 31 had a mixed response, 40 had no significant
change, and 21 had regression only. In the group allocated to
gemfibrozil therapy, 61 subjects had progression only; 40, a mixed
response; 57, no change; and 27, regression only
(
2 P=0.007). Thus, 126 placebo and 101
gemfibrozil patients had any progression and 61 and 84 patients,
respectively, had no progression (odds ratio for progression in the
gemfibrozil versus placebo group, 0.582; 95% CI, 0.382 to 0.887;
P=0.012).
Age, body mass index, waist-to-hip circumference ratio, heart rate, known duration of CAD, and history of hypertension, myocardial infarction, or angina at baseline were not related to global progression. There was also no significant relation between disease progression and blood pressure values or glucose, insulin, or C-peptide concentrations.
Total serum cholesterol and both triglyceride
and cholesterol in the IDL and LDL fractions were
positively and significantly associated with the risk of progression
(Figure 3
, Table 3
). HDL cholesterol
concentration was not associated with protection against progression.
HDL2 cholesterol had, if anything, a
positive relation, and only HDL3 had a
borderline-significant protective effect.
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On-trial apoB concentration was a predictor of progression in the whole study population (P=0.002) and also after adjustment for study group (P=0.018). Lp(a) levels were not related to global progression (data not shown).
Quantitative Changes of Lumen Diameters in Native Coronary
Vessels
On-trial concentrations of the components of apoB-containing
lipoproteins, especially IDL, were related to angiographic progression,
both diffuse (
ADS, Table 4
) and focal
(
MLD, Table 5
). In many instances,
these associations remained significant after adjustment for the
randomized group allocation. Tables 4
and 5
also show that total HDL
concentrations were not associated with protection from progression.
HDL2 levels even tended to be positively related
to the risk of luminal narrowing. Conversely, concentrations of
esterified cholesterol in the HDL3
fraction were strongly and inversely related to progression of focal
disease (Table 5
), and this relationship persisted after adjustment for
group allocation. Essentially similar results were obtained when the
randomized groups were analyzed separately (data not
shown).
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New Lesions in Vein Grafts
Nineteen patients in the placebo group had 1 new lesion and 4
patients had 2 new lesions in their vein grafts in the follow-up
angiogram; in the gemfibrozil group, 4 patients had 1 new vein-graft
lesion (P<0.001). Total serum triglyceride
concentration was a powerful predictor of new vein-graft lesions in the
whole study population (standardized odds ratio, 1.774; 95% CI, 1.303
to 2.414; P<0.001). When study group allocation was taken
into account, both triglyceride level (P=0.042)
and the grouping factor (P=0.013) independently predicted
the appearance of new lesions. Total cholesterol also
predicted new lesions in logistic regression analyses
unadjusted (odds ratio, 1.899; 95% CI, 1.259 to 2.864;
P=0.002) and adjusted (P=0.075) for the grouping
factor (P=0.007). The lipoproteins responsible for these
associations were VLDL (both triglyceride and
cholesterol, P<0.001) and IDL
(triglyceride, P=0.036; cholesterol,
P=0.096). LDL and HDL levels were not associated with new
vein-graft lesions.
Multivariate Models
The strongest univariate predictor of
MLD in each
lipoprotein class (VLDL phospholipid, IDL triglyceride, LDL
triglyceride, HDL2
triglyceride [all log-transformed], and
HDL3 cholesterol; Table 5
) was
entered into a stepwise linear regression model, adjusted for baseline
MLD and the time between angiograms. IDL triglyceride
(P=0.001) and HDL3
cholesterol (inverse, P=0.003) were retained in
the model as significant predictors of the progression of focal
coronary atherosclerosis. When the grouping
factor was included in the model, it was not independently related to
angiographic progression (P=0.405), whereas IDL
triglyceride (P=0.002) and
HDL3 cholesterol (inverse,
P=0.013) were.
| Discussion |
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The on-trial concentrations of the triglyceride-rich lipoproteins VLDL and IDL were strong determinants of CAD progression in the present study. VLDL components were especially strong predictors of new vein-graft lesions, and IDL was the individual lipoprotein class most closely associated with progression in native coronary vessels. In previous studies, IDL10 and a lipoprotein fraction containing IDL and small VLDL particles have been associated with the angiographic severity11 and presence12 of CAD. Despite marked differences in enrollment criteria and interventions used, 3 previous secondary-prevention trials13 14 15 have found IDL to predict the angiographic progression of CAD. Markers of triglyceride-rich lipoproteins have been further associated with CAD progression in CLAS16 and with atherosclerosis progression in coronary17 18 and carotid19 arteries in the Monitored Atherosclerosis Regression Study (MARS). Finally, the Bezafibrate Coronary Atherosclerosis Intervention Trial (BECAIT)4 showed benefits from fibrate therapy associated with marked reductions of triglyceride-rich lipoproteins and no change in LDL levels.
Taken together, the available evidence unequivocally implicates triglyceride-rich lipoproteins, especially IDL, in the progression of CAD. This relationship is particularly strong when LDL levels have been efficiently reduced, as in CLAS and in MARS20 and when baseline LDL values are relatively normal, as in LOCAT. Although in the present study IDL levels were markedly reduced by gemfibrozil therapy, this lipoprotein class remained a significant risk factor after adjustment for the treatment group and within the gemfibrozil group. Therefore, therapeutic measures that reduce IDL levels even more aggressively might provide further benefits in preventing the progression of CAD.
On average, LDL levels changed little in the present study. Although subjects with grossly elevated LDL cholesterol levels (>4.5 mmol/L) were excluded at baseline, LDL cholesterol was significantly related to the angiographic outcome. This is compatible with subgroup data from the Cholesterol and Recurrent Events trial,3 which showed benefits from LDL lowering with pravastatin in patients with baseline LDL cholesterol levels >3.2 mmol/L (125 mg/dL), closely corresponding to the mean on-trial value of our gemfibrozil group. Also, the Post Coronary Artery Bypass Graft trial21 showed that aggressive LDL cholesterol lowering (a goal of 1.6 to 2.2 mmol/L) conferred superior protection against progressing vein-graft disease compared with moderate lowering (to 3.4 to 3.6 mmol/L). It is therefore reasonable to speculate that reaching lower LDL levels than was possible with gemfibrozil therapy might have improved the outcome of the present trial.
A specific goal of LOCAT was to test the hypothesis that increasing low HDL levels prevents the progression of CAD.6 We found no evidence of any protective effect of HDL2. Conversely, the on-trial concentration of HDL3 cholesterol was a strong protective factor against progression, especially that of focal CAD. This raises the possibility that enhanced cholesterol efflux from coronary lesions into HDL precursors and its subsequent esterification22 is reflected in higher HDL3 cholesterol levels. HDL3 was associated with protection against CAD progression also in the St Thomas' Atherosclerosis Regression Study14 and in MARS.15
In conclusion, our results add to growing evidence of the atherogenicity of triglyceride-rich lipoproteins, especially IDL, and antiatherogenic influence of HDL3. Notably, reductions of triglyceride levels that are commonly considered normal seem to provide protection against progressive CAD.
| Acknowledgments |
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| Footnotes |
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1 The investigators participating in the Lopid Coronary Angiography Trial were listed in Circulation. 1997;96:2142. ![]()
Received February 3, 1998; revision received June 22, 1998; accepted June 23, 1998.
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