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Plasma apoE is Elevated in Metabolic Syndrome: Importance of Large Very Low Density and Low Density Lipoprotein Particles | OMICS International
ISSN-2155-9929
Journal of Molecular Biomarkers & Diagnosis

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Plasma apoE is Elevated in Metabolic Syndrome: Importance of Large Very Low Density and Low Density Lipoprotein Particles

Eke G Gruppen1,2, Geesje M Dallinga-Thie3, Stephan JL Bakker1 and Robin PF Dullaart2*

1Department of Nephrology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands

2Department of Endocrinology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands

3Department of Experimental Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands

*Corresponding Author:
Dullaart R.P.F
Department of Endocrinology
University Medical Center Groningen
University of Groningen, P.O. Box 30.001
Groningen, 9700 RB, The Netherlands
Tel: +31 503613731
Fax: +31 503619392
E-mail: [email protected]

Received Date: November 24, 2014; Accepted Date: December 27, 2014; Published Date: January 03, 2014

Citation: Gruppen EG, Thie GMD, Bakker SJ, Dullaart RPF (2015) Plasma apoE is Elevated in Metabolic Syndrome: Importance of Large Very Low Density and Low Density Lipoprotein Particles. J Mol Biomark Diagn 6:210. doi:10.4172/2155-9929.1000210

Copyright: © 2015 Gruppen EG, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Background: Apolipoprotein E (apoE) is carried by all major lipoprotein classes in plasma and is likely to contribute to the development of atherosclerosis. We set out to determine the extent to which plasma apoE is related to various VLDL, LDL and HDL subfractions in subjects with and without metabolic syndrome (MetS).

Methods: Plasma lipids, lipoprotein subfractions (nuclear magnetic resonance spectroscopy) and plasma apoE were determined in 60 subjects with and 62 subjects without MetS (APOE ε2/ε2 carriers excluded).

Results: Plasma apoE was higher in MetS, coinciding with increased total and large VLDL particles, as well as total LDL particles (p<0.01 for each after age, sex and diabetes status adjustment). Age- and sex-adjusted multivariable linear regression analysis revealed that plasma apoE was related positively to the VLDL particle concentration (p=0.003), in particular large VLDL (p<0.001) and to the LDL particle concentration (p=0.013), independent of MetS and diabetes status (p>0.30). Plasma apoE was unrelated to HDL particle concentration (p=0.88).

Conclusions: Plasma apoE is elevated in MetS in conjunction with increased concentrations of (large) VLDL and LDL particles. These novel findings provide a rationale to explore whether preferential association of apoE with (large) VLDL and LDL could modify its influence on atherosclerosis development.

Keywords

Apolipoprotein E; Diabetes mellitus; Metabolic syndrome; Lipoprotein subfractions

Abbreviations

apoE: apolipoprotein E; apoA-I: apolipoprotein A-I; apoB: apolipoprotein B; CVD: Cardiovascular Disease; LDL: Low Density Lipoprotein; VLDL: Very Low Density Lipoprotein; HDL: High Density Lipoprotein; MetS: Metabolic Syndrome; NMR: Nuclear Magnetic Resonance; T2DM: Type 2 diabetes mellitus; BMI: Body Mass Index; HbA1c: Glycated Haemoglobin

Introduction

Apolipoprotein E (apoE) is a multifunctional apolipoprotein that is synthesized by a number of tissues and cell types, including liver, adipose tissue and macrophages [1-3]. ApoE is a constituent of all major lipoprotein classes in plasma [4,5]. ApoE is critically involved in lipid homeostasis by facilitating receptor-mediated uptake of apolipoprotein B (apoB)-containing lipoproteins [1-3,6]. It is widely appreciated that apoE has anti-atherogenic properties, as evidenced by accelerated atherosclerosis development in apoE knock-out mice [1-3]. Besides multiple effects on lipoprotein metabolism, apoE also exerts anti-oxidative and anti-inflammatory properties [2,7-9].

Despite the pivotal role of apoE in lipoprotein metabolism, and the importance of genetic variations in APOE on the development of cardiovascular disease (CVD) [1-3,10], remarkably little is known about the association of plasma apoE levels with incident cardiovascular disease. The apoE content in subfractions of low density lipoproteins (LDL) and very low density lipoproteins (VLDL) was reported to be inversely associated with incident coronary heart disease [11]. On the other hand, in elderly subjects, as well as in a subset of women with increased plasma high density lipoprotein (HDL) cholesterol with concurrently high C-reactive protein levels, plasma apoE was found to be associated positively with incident CVD [12-15]. A high apoE content in HDL may also be associated with an increased risk of recurrent CVD [16].

The plasma apoE concentration is known to be elevated in subjects with the metabolic syndrome (MetS) and obesity [9,17,18]. In line, plasma apoE is strongly correlated with plasma triglycerides and triglyceride-rich lipoproteins levels [2,4,5,9,17]. Accordingly, it has been reported that in hypertriglyceridemia the distribution of apoE among lipoproteins is shifted from HDL towards triglyceride-rich remnant lipoproteins [4,5], although apoE enrichment of HDL was recently suggested in obesity [18]. Both VLDL, LDL and HDL particles are highly heterogeneous in size and composition [19,20]. In view of the potential importance of changes in lipoprotein subfraction distribution for cardiometabolic risk [21-24], and the possibility that the association of apoE with CVD could be dependent on its presence on specific lipoprotein subfractions, it is relevant to discern the relationship of plasma apoE with various lipoprotein subfraction characteristics.

In the absence of data with respect to the relationship of plasma apoE with lipoprotein subfraction distribution, as determined by nuclear magnetic resonance (NMR) spectroscopy, we initiated the present study 1) to determine the extent to which plasma apoE is related to various lipoprotein subfractions, and 2) to assess whether such relationships are altered in subjects with MetS.

Patients and Methods

Participants

This study was performed in a university hospital setting. Participants (aged > 18 years) were Caucasian, and were recruited by advertisement in local newspapers. Subjects without and MetS, defined according to the revised NCEP-ATP III criteria [25], participated. Three or more of the following criteria were required for categorization of subjects with MetS: waist circumference > 102 cm for men and > 88 cm for women; hypertension (blood pressure ≥ 130⁄85 mmHg or use of anti-hypertensive drugs); fasting plasma triglycerides ≥ 1.70 mmol/L; HDL cholesterol<1.0 mmol/L for men and<1.30 mmol/L for women; fasting glucose ≥ 5.6 mmol/L. Subjects with type 2 diabetes mellitus (T2DM), previously diagnosed by primary care physicians using guidelines from the Dutch College of General Practitioners (fasting plasma glucose ≥ 7.0 mmol/L and/or non-fasting plasma glucose ≥11.1 mmol/L) were allowed to participate. Diabetic subjects who were treated with metformin and/or sulfonylurea were allowed to participate, but subjects using insulin were not eligible. The use of anti-hypertensive medication was allowed. Further exclusion criteria were clinically manifest CVD, renal insufficiency (elevated serum creatinine and⁄or proteinuria), thyroid disorders, liver disease, current smoking, pregnancy and use of lipid lowering drugs. Subjects who were homozygous for the APOE ε2 allele were also excluded. Physical examination did not reveal pulmonary or cardiac abnormalities. All subjects were studied after an overnight fast. Body mass index (BMI) was calculated as weight divided by height squared (in kg/m2). Waist circumference was measured between the 10th rib and the iliac crest.

The medical ethics committee of the University Medical Center Groningen, The Netherlands approved the study. All participants provided written informed consent.

Laboratory analyses

Venous blood samples were collected into EDTA-containing tubes (1.5 mg⁄mL) for the measurement of plasma lipids and apolipoproteins. Plasma was prepared by centrifugation at 1400 g for 15 min at 4°C. Blood glucose and glycated haemoglobin (HbA1c) levels were measured directly after blood collection. Samples for other assays were stored at -80°C until analysis.

Plasma total cholesterol and triglycerides were assayed by routine enzymatic methods (Roche/Hitachi cat nos 11875540 and 11876023, respectively; Roche Diagnostics GmbH, Mannheim, Germany). HDL cholesterol was measured with a homogeneous enzymatic colorimetric test (Roche/Hitachi, cat no 04713214; Roche Diagnostics GmbH, Mannheim, Germany). Non-HDL cholesterol was calculated as the difference between total cholesterol and HDL cholesterol. LDL cholesterol was calculated by the Friedewald formula in case of a plasma triglyceride concentration ≤ 4.5 mmol/L. ApoA-I and apoB were assayed by immunoturbidimetry (Roche/Cobas Integra Tina-quant catalog no. 03032566 and 033032574, respectively, Roche Diagnostics). ApoE was measured using an immunoturbidimetric assay (cat. no. 417-35906; Wako Inc., Osaka, Japan).

VLDL, LDL and HDL particle profiles were measured by NMR spectroscopy with the LipoProfile-3 algorithm, as described (LipoScience Inc., Raleigh, North Carolina, USA) [19]. Lipoprotein particle subclasses (expressed in concentration units, i.e. µmol/L or nmol/L) were quantified from the amplitudes of their spectroscopically distinct lipid methyl group NMR signals. Diameter range estimates were for VLDL: large VLDL (including chylomicrons if present >60 nm), medium VLDL (35 to 60 nm) and small VLDL (27 to 35 nm), for LDL: IDL (23 to 27 nm), large LDL (21.2 to 23 nm) and small LDL (18 to 21.2 nm), and for HDL: large HDL (9.4 to 14 nm), medium HDL (8.2 to 9.4 nm), small HDL (7.3-8.2 nm). The total VLDL, LDL and HDL particle concentrations were calculated as the sum of the concentrations of the VLDL, LDL and HDL subclasses, respectively. The lipoprotein particle concentrations are regarded to represent an estimate of the particle numbers [24].

Glucose was measured with an APEC glucose analyzer (APEC Inc., Danvers, MA). HbA1c was measured by high-performance liquid chromatography (Bio-Rad, Veenendaal, the Netherlands; normal range: 4.6–6.1%).

APOE genotyping was performed as follows. DNA was extracted from whole blood using the Qiampmini kit (Qiagen). APOE genotypes (rs429358 and rs7412) were determined by allelic discrimination on a CFX system (Bio Rad), using predesigned primers C-3084793-20 and C-904973-10 and Taqman Universal PCR mastermix (Applied Biosystems, Nieuwerkerka/dIJssel, the Netherlands). The method has been validated against a previously described restriction isotyping procedure [26,27].

Statistical analysis

SPSS (version 20.0, SPSS Inc. Chicago, IL, USA) was used for data analysis. Results are expressed as mean ± SD or as median (interquartile range). Differences between subjects with and without MetS were determined by unpaired T tests and Chi-square tests where appropriate. Differences in variables between subjects with and without MetS were also determined after adjustment for age, sex and diabetes status. Because of skewed distribution, logarithmically transformed values of triglycerides and lipoprotein subfractions were used for regression analysis. Univariate relationships were determined using Pearson correlation coefficients. Multiple linear regression analyses were carried out to disclose variables which independently contributed to plasma apoE levels. Additionally, multiple linear regression analyses were performed to determine interactions between the presence of MetS or alternatively diabetes status and lipoprotein subfractions impacting on apoE. Interaction terms were calculated as the product terms between the variables of interest. To this end the distributions of the various lipoprotein subfractions were centered to their mean value by subtracting the individual value from their group mean to account for possible outliers. Interaction terms were considered to be statistically significant at two-sided p-values<0.10, as recommended by Selvin [28] and by the Food and Drug Administration authorities [29]. Otherwise, the level of significance was set at two-sided p-values<0.05.

Results

Sixty subjects with and 62 subjects without MetS were included in the study. Their clinical characteristics are shown in Table 1. Twenty four subjects with MetS and 5 subjects without MetS used anti-hypertensive medication (mostly angiotensin-converting enzyme inhibitors, angiotensin II receptor antagonists and diuretics, either alone or in combination; p<0.001). T2DM was more frequent in subjects with MetS. Oral glucose lowering drugs, i.e. sulfonylurea and metformin, either alone or in combination, were used by 37 diabetic subjects with MetS and by 10 diabetic subjects without MetS (p<0.001). These medications were not used in non-diabetic subjects. Two postmenopausal women with MetS and 1 premenopausal woman used oral contraceptives. Age and sex distribution were not significantly different between subjects with and without MetS. Blood pressure, waist circumference, BMI, glucose and HbA1c levels were higher in MetS subjects; the difference in HbA1c disappeared after adjustment for age, sex and diabetes status (Table 1). The APOE genotype distribution was not significantly different between the groups (Table 1).

  MetS
(n=60)
No MetS (n=62) p-value p-valuea
Age (years) 58 ± 9 55 ± 10 0.07  
Gender (men/women) 32/28 32/30 0.99  
Diabetes (yes/no) 48/12 18/44 <0.001  
Systolic blood pressure (mm Hg) 146 ± 19 131 ± 22 <0.001 <0.001
Diastolic blood pressure (mm Hg) 89 ± 9 81 ± 11 <0.001 <0.001
BMI (kg/m2) 30.1 ± 4.6 25.1 ± 3.5 <0.001 <0.001
Waist circumference (cm) 104 ± 13 86 ± 11 <0.001 <0.001
Glucose (mmol/L) 8.7 ±2.5 6.3 ± 1.5 <0.001 0.011
HbA1c (mmol/mol) 48 ±9 39 ± 5 <0.001 0.61
APOE genotype
ε2/ε3
ε3/ε3
ε3/ε4
ε4/ε4
  4
38
14
4
  2
49
11
0
0.091  
Total cholesterol (mmol/L) 5.54 ± 0.95 5.56 ± 0.0.96 0.92 0.26
LDL cholesterol (mmol/L) 3.37 ± 0.86 3.36 ± 0.83 0.97 0.33
Non-HDL cholesterol (mmol/L) 4.33 ± 0.95 3.98 ± 1.04 0.057 0.006
HDL cholesterol mmol/L) 1.21 ± 0.36 1.58 ± 0.39 <0.001 <0.001
Triglycerides (mmol/L) 1.95 (1.70-2.52) 1.15 (0.85-1.59) <0.001 <0.001
ApoA-I (g/L) 1.32 ± 0.25 1.46 ± 0.20 0.001 <0.001
ApoB (g/L) 0.98 ± 0.22 0.90 ± 0.23 0.037 0.007
ApoE (g/L) 0.042 ± 0.012 0.037 ± 0.009 0.008 0.006

Table 1: Clinical characteristics, plasma glucose, glycated hemoglobin (HbA1c), apolipoproten E (apoE) genotype, plasma lipids, apolipoproteins (apos) and lipoprotein subfractions in 60 subjects with and in 62 subjects without metabolic syndrome (MetS).

Plasma total cholesterol and LDL cholesterol were not different between the groups (Table 1). Taking account of age, sex and diabetes status, non-HDL cholesterol, triglycerides and apoB levels were higher, whereas HDL cholesterol and apoA-I were lower in MetS subjects (Table 1). Plasma apoE was higher in MetS (Table 1), but was not significantly different between subjects with and without T2DM (0.042 ± 0.012 g/L vs. 0.039 ± 0.009 g/L, p=0.68).

The VLDL particle concentration was higher in MetS, which was due to higher concentrations of large and medium VLDL particles (Table 2); the difference in small VLDL particles was significant after adjustment for age, sex and T2DM). The LDL particle concentration was also higher in MetS, which was due to higher concentration of small LDL particles. The HDL particle concentration was not different between subjects with and without MetS, but the HDL subfraction distribution was shifted towards less large HDL particles and more small HDL particles in MetS (Table 2).

  MetS
(n=60)
No MetS (n=62) p-value p-valuea
VLDL particle concentration (nmol/L) 74.7 (58.7-96.9) 58.5 (39.8-86.4) <0.001 0.001
Large VLDL
(nmol/L)
9.7 (5.3-14.3) 2.7 (1.0-5.3) <0.001 <0.001
Medium VLDL
(nmol/L)
37.8 (22.4-44.3) 20.9 (11.0-40.0) 0.001 <0.001
Small VLDL
(nmol/L)
27.7 (16.8-43.4) 34.0 (21.0-44.7) 0.32 <0.001
LDL particle concentration (nmol/L) 1342 (1095-1530) 1077 (922-1333) <0.001 <0.001
IDL
(nmol/L)
210 (135-258) 191 (141-241) 0.66 0.73
Large LDL
(nmol/L)
404 (288-597) 503 (435-639) 0.047 0.11
Small LDL
(nmol/L)
715 (481-923) 358 (246-532) <0.001 <0.001
HDL particle concentration (μmol/L) 32.5 (28.7-37.1) 34.3 (31.7-36.4) 0.12 0.071
Large HDL
(μmol/L)
3.1 (1.93-5.4) 6.1 (3.4-8.5) <0.001 <0.001
Medium HDL
(μmol/L)
10.6 (6.6-14.0) 12.4 (9.5-15.6) 0.006 0.030
Small HDL
(μmol/L)
18.3 (15.6-21.4) 15.3 (12.5-18.5) 0.001 0.016

Table 2: Very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) subfraction characteristics in 60 subjects with and in 62 subjects without metabolic syndrome (MetS).

In univariate regression analysis including all subjects, plasma apoE levels were correlated positively with plasma total cholesterol, non-HDL cholesterol, LDL cholesterol, triglycerides and apoB (Table 3). Comparable relationships were observed in subjects with and without MetS separately, although apoE was not significantly correlated with LDL cholesterol and apoB in MetS subjects. In all subjects combined, plasma apoE was inversely correlated with HDL cholesterol, but not in the subjects with and without MetS separately. Plasma apoE was unrelated to apoA-I. In addition, apoE was correlated positively with the VLDL particle concentration in the combined subjects (Table 3). The strongest univariate relationship of apoE with individual VLDL subfractions was observed for large VLDL particles. There was also a positive relationship of apoE with the LDL particle concentration. In the combined subjects, plasma apoE was correlated positively with IDL and small LDL. Plasma apoE was not related to the HDL particle concentration, although apoE was correlated inversely with large HDL particles in the combined subjects, and positively with medium HDL particles in subjects without MetS. Figure 1 shows the univariate correlations of plasma apoE with the VLDL particle concentration, large VLDL and the LDL particle concentration.

molecular-biomarkers-diagnosis-plasma-apolipoprotein

Figure 1: Relationship of plasma apolipoprotein E (apoE) with the very low density lipoprotein (VLDL) particle concentration (A), with large VLDL (B) and with the low density lipoprotein (LDL) particle concentration (C) in 60 subjects with metabolic syndrome (Mets) and 62 subjects without MetS. Pearson correlation coefficients are shown in Table 3.

  Total population
(n=122 )
MetS
(n=60)
No MetS
(n=62)
Total cholesterol 0.429c 0.336b 0.577c
Non-HDL cholesterol 0.507c 0.414c 0.578c
LDL cholesterol 0.298c 0.220 0.401b
HDL cholesterol -0.246b -0.207 -0.114
Triglycerides 0.648c 0.599c 0.661c
ApoA-I -0.144 -0.137 0.01
ApoB 0.404c 0.249 0.524c
VLDL particle concentration 0.397c 0.277 a 0.454c
Large VLDL 0.509c 0.462c 0.490c
Medium VLDL 0.322c 0.118 0.434c
Small VLDL -0.006 -0.133 0.197
LDL particleconcentration 0.369c 0.209 0.430c
IDL 0.219a 0.075 0.482c
Large LDL -0.134 -0.052 -0.189
Small LDL 0.340c 0.252 0.301a
HDL particle concentration -0.001 -0.061 0.192
Large HDL -0.180a -0.018 -0.209
Medium HDL 0.042 0.023 0.265a
Small HDL 0.113 -0.006 0.083

Table 3: Relationships of plasma apolipoprotein E with apoA-I, apoB, lipoproteins and lipoprotein subfraction characteristics in 60 subjects with and 62 without metabolic syndrome (MetS)

Multivariable linear regression analyses were first performed to disclose the extent to which plasma apoE was independently related with various lipoprotein subfractions (Table 4). In a model, which included age, sex, diabetes status, the presence of MetS and the VLDL, LDL and HDL particle concentrations, plasma apoE was related positively to the VLDL and the LDL particle concentration, but not to the HDL particle concentration (Table 4, model A). Subsequent analysis, now including the individual VLDL subfractions, showed that apoE was independently related to large VLDL (Table 4, model B). After additional adjustment for the use of glucose lowering drugs and antihypertensive medication, the relationship of apoE with the VLDL and the LDL particle concentrations remained statistically significant (cf. Table 4, model A: VLDL particle concentration: β=0.272, p=0.006; LDL particle concentration: β=0.246, p=0.013; data not shown). Likewise, the relationship of apoE with large VLDL remained present after additional adjustment for the use of these medications (cf. Table 4, model B: large VLDL: β=0.478, p<0.001; data not shown).

  Model A   Model B   Model C   Model D  
  β p-value β p-value β p-value β p-value
Age -0.045 0.61 -0.028 0.74 -0.032 0.73 -0.050 0.58
Sex
(men/women)
-0.122 0.20 -0.152 0.095 -0.218 0.033 -0.029 0.79
Diabetes (yes/no) -0.016 0.87 -0.044 0.66 0.034 0.76 0.00 0.99
MetS (yes/no) 0.107 0.310 -0.052 0.63 0.126 0.260 0.142 0.19
VLDL particle concentration 0.280 0.003     0.257 0.014 0.324 0.001
LDL particle concentration 0.239 0.013 0.205 0.029     0.293 0.006
HDL particle concentration 0.013 0.88 0.000 1.00 -0.014 0.89    
Large VLDL     0.503 <0.001        
Medium VLDL     -0.051 0.67        
Small VLDL     -0.010 0.91        
IDL         0.125 0.169    
Large LDL         -0.040 0.68    
Small LDL         0.084 0.47    
Large HDL             0.096 0.45
Medium HDL             0.072 0.50
Small HDL             -0.080 0.48

Table 4: Multivariable linear regression analysis demonstrating relationships of plasma apolipoprotein E with lipoprotein subfractioncharacteristics in all subjects combined (60 subjects with metabolic syndrome (MetS) and 62 subjects without MetS)

Although plasma apoE was related positively to the LDL particle concentration, there was no significant independent contribution of the individual LDL subfractions to apoE (Table 4, model C). In addition, there was also no independent relationship of apoE with the individual HDL subfractions (Table 4, model D). Of note, all these analyses showed that the association of plasma apoE levels with MetS was no longer significant when taking lipoprotein subfractions into account.

We next examined the extent to which the relationship of apoE with the VLDL particle concentration, large VLDL particles and the LDL particle concentration, i.e. those lipoprotein subfraction characteristics to which apoE was independently related, were modified in the context of MetS or T2DM. Except for a marginally significant positive interaction of the presence of MetS with the large VLDL on apoE (cf. Table 4, model B: β=0.200, p=0.086), there were no interactions of the presence of MetS or T2DM with either the VLDL particle concentration, large VLDL particles or the LDL particle concentration on apoE (β=-0.095 to 0.127, p=0.29 to p=0.80; data not shown).

Finally, multivariable linear regression analyses were repeated now only including APOE ε3/ε3 and ε3/ε4 carriers, comprising 52 subjects with and 60 subjects without MetS. In this analysis, apoE was still independently related to the VLDL and the LDL particle concentration (Table 5, model A), and – in a subsequent analysis – to large VLDL (Table 5, model B). Again, no independent relationship of apoE with individual LDL and HDL subfractions was observed (Table 5, model C and D).

  Model A   Model B   Model C   Model D  
  β p-value β p-value β p-value β p-value
Age -0.016 0.86 0.002 0.98 0.007 0.95 -0.027 0.78
Sex
(men/women)
-0.164 0.10 -0.196 0.042 -0.280 0.010 -0.056 0.63
Diabetes (yes/no) 0.231 0.76 -0.070 0.50 0.026 0.83 -0.009 0.94
MetS (yes/no) 0.108 0.32 -0.057 0.61 0.131 0.26 0.147 0.19
VLDL particle concentration 0.243 0.013     0.213 0.049 0.304 0.004
LDL particle concentration 0.402 0.006 0.249 0.011     0.360 0.002
HDL particle concentration -0.057 0.96 -0.018 0.85 -0.063 0.56    
Large VLDL     0.493 <0.001        
Medium VLDL     -0.059 0.63        
Small VLDL     -0.045 0.63        
IDL         0.161 0.091    
Large LDL         -0.033 0.75    
Small LDL         0.084 0.49    
Large HDL             0.130 0.33
Medium HDL             0.049 0.67
Small HDL             -0.115 0.34

Table 5: Multivariable linear regression analysis demonstrating relationships of plasma apolipoprotein E with lipoprotein subfraction characteristics in APOE ε3/ε3 and ε3/ε4 carriers (52 subjects with metabolic syndrome (MetS) and 60 subjects without MetS).

Discussion

While the present report has confirmed that plasma apoE is elevated in MetS, a novel finding is that plasma E elevations in MetS coincide with increases in the concentration of both VLDL and LDL particles, as determined by NMR spectroscopy. In univariate regression analysis, apoE was related positively to the concentrations of (large) VLDL and LDL particles. Multivariable linear regression analyses demonstrated that the relationships of apoE with these lipoprotein fractions remained present taking account of the presence of MetS and T2DM. Of note, these analyses also demonstrated that the relationship of plasma apoE with MetS was no longer present when the higher VLDL and LDL particle concentrations in MetS were taken into account. These findings substantiate the notion that both VLDL and LDL particles are major carriers of apoE in plasma. Moreover, there was no important modification of the presence of MetS or T2DM on the relationship of plasma apoE with VLDL and LDL subfraction characteristics. This suggests that these relationships were not substantially altered in the context of MetS and chronic hyperglycemia.

Our observation that the VLDL particle concentration is elevated in MetS, along with increased large (approximately three-fold) and medium (approximately two-fold)VLDL particles, and that the LDL concentration is increased as well, along with increased small LDL particles, extends previous findings showing comparable changes in lipoprotein subfractions, determined by NMR in (non-diabetic) subjects with rather severe insulin resistance [23], as well by non-denaturing polyacrylamide gel gradient electrophoresis in subjects with MetS [30]. Another report emphasized predominance of large VLDL in MetS, determined by size exclusion high performance liquid chromatography, even independent of insulin resistance and enlarged waist circumference [31]. The elevated plasma apoE in MetS agrees with previous reports [9,17,18]. We found no difference in plasma apoE between subjects with and without T2DM. This remarkable observation suggests that there is no strong relationship of plasma apoE with chronic hyperglycemia. This finding should be interpreted with caution, since T2DM patients participating in the present study were in general adequately controlled.

It is well appreciated that triglyceride-rich lipoproteins are major carriers of apoE in human plasma [2,4,5]. Accordingly, plasma apoE was strongly related to triglycerides in the present report. In addition, apoE was independently related to the VLDL concentration. Of the individual VLDL subfractions the closest relationship with apoE was observed for large VLDL. Importantly, increased hepatic production of large VLDL particles is considered to be a primary liporegulatory abnormality in MetS. In view of the precursor-product relationship between (large) VLDL and (small) LDL [32,33], the currently documented relationships of apoE with (large) VLDL and LDL appear to be consistent with the possibility that the apoE content in (large) VLDL may represent a determinant of LDL metabolism [34]. On the other hand, overexpression of human apoE in mice results in hypertriglyceridemia which is due to both hepatic VLDL overproduction and impaired VLDL catabolism [35].

In the light of higher levels of plasma apoE in MetS, the close relationship of apoE with large VLDL particles, and the increased VLDL apoE production rate observed in hypertriglyceridemia [36], it seems paradoxical that apoE most probably exerts anti-atherogenic effects [1-3,7-9]. Our novel finding regarding the independent relationships of plasma apoE with the concentrations of both VLDL and LDL particles complements recent findings showing that specific VLDL and LDL subfractions that carry apoE may confer protection against CVD development [11]. Although these relationships suggest that VLDL and LDL particle characteristics should be taken into account when evaluating the association of apoE with incident CVD, it is obvious that the extent to which apoE could modify CVD risk that is attributable the VLDL and LDL subfraction concentrations remains to be more precisely established. In this regard it is important to emphasize that the NMR spectroscopy analysis that we used does not allow to determine the apoE content in various lipoprotein subfractions. Finally, it should be noted that there were no positive relationships of apoE with HDL cholesterol and apoA-I in univariate analysis. There was also no independent relationship of apoE with HDL subfraction characteristics in multivariable linear regression analyses.

Several other methodological aspects and limitations of our study need to be discussed. First, in view of the cross-sectional design of our study, cause-effect relationships of apoE with lipoprotein subfraction characteristics cannot be assessed with certainty. Second, we excluded subjects using lipid lowering drugs in order to avoid treatment-induced effects on lipoproteins and lipoprotein subfractions. Nonetheless, close relationships of plasma apoE with (large) VLDL and LDL were already demonstrated under modestly dyslipidemic circumstances. Third, we excluded subjects with APOE ε2/ε2 genotype in order to circumvent effects of dysbetalipoproteinemia on the relationships of apoE with lipoprotein subfractions. Furthermore, additional analyses that were restricted to APOE ε3/ε3 and ε3/ε4 carriers yielded similar results, underscoring that the relationships of apoE with lipoprotein subfraction characteristics were not to a considerable extent confounded by pathophysiologically important structural variations in apoE. Fourth, we employed a high-throughput NMR spectroscopy analysis to determine lipoprotein subfraction characteristics. There is considerable agreement between this method and more conventional lipoprotein subfraction analyses, but some discrepancies between assay methods cannot be excluded [37].

In conclusion, this study suggests to our knowledge for the first time that elevated plasma apoE is closely related to increased concentrations of (large) VLDL and LDL particles in MetS. These findings provide a rationale to explore whether the preferential association of apoE with (large) VLDL and LDL could modify its influence on atherosclerosis development.

Acknowledgement

R.P.F. Dullaart, MD, PhD is supported by a grant from the Dutch Diabetes Research Foundation (grant 2001.00.012). Plasma lipids were determined in the laboratory of Dr. L.D. Dikkeschei, PhD, Laboratory of Clinical Chemistry, Isala Clinics, Zwolle. The NMR lipoprotein measurements are funded by LipoScience Inc. (Raleigh, North Carolina, USA).

References

  1. Davignon J, Cohn JS, Mabile L, Bernier L (1999) Apolipoprotein E and atherosclerosis: insight from animal and human studies. ClinChimActa 286:115-143
  2. Greenow K, Pearce NJ, Ramji DP (2005) The key role of apolipoprotein E in atherosclerosis. J Mol Med (Berl) 83:329-342.
  3. Pendse AA, Arbones-Mainar JM, Johnson LA, Altenburg MK, Maeda N (2009) Apolipoprotein E knock-out and knock-in mice: atherosclerosis, metabolic syndrome, and beyond. J Lipid Res 50 Suppl:S178-182.
  4. Cohn JS, Tremblay M, Amiot M, Bouthillier D, Roy M, et al. (1996) Plasma concentration of apolipoprotein E in intermediate-sized remnant-like lipoproteins in normolipidemic and hyperlipidemic subjects. ArteriosclerThrombVascBiol 16:149-159.
  5. Marcoux C, Tremblay M, Fredenrich A, Jacques H, Krimbou L, et al. (1998) Plasma remnant-like particle lipid and apolipoprotein levels in normolipidemic and hyperlipidemic subjects. Atherosclerosis 139:161-171.
  6. Schaefer EJ, Gregg RE, Ghiselli G, Forte TM, Ordovas JM, et al. (1986) Familial apolipoprotein E deficiency. J Clin Invest 78:1206-1219.
  7. Jofre-Monseny L, Minihane AM, Rimbach G (2008) Impact of apoE genotype on oxidative stress, inflammation and disease risk. MolNutr Food Res 52:131-145.
  8. Nayyar G, Garber DW, Palgunachari MN, Monroe CE, Keenum TD, et al. (2012) Apolipoprotein E mimetic is more effective than apolipoprotein A-I mimetic in reducing lesion formation in older female apo E null mice. Atherosclerosis 224:326-331.
  9. Dullaart RPF, Kwakernaak AJ, Dallinga-Thie GM (2013) The positive relationship of serum paraoxonase-1 activity with apolipoprotein E is abrogated in metabolic syndrome. Atherosclerosis 230:6-11.
  10. Bennet AM, Di Angelantonio E, Ye Z, Wensley F, Dahlin A, et al. (2007) Association of apolipoprotein E genotypes with lipid levels and coronary risk. JAMA 298:1300-1311.
  11. Mendivil CO, Rimm EB, Furtado J, Sacks FM (2013) Apolipoprotein E in VLDL and LDL with apolipoprotein C-III is associated with a lower risk of coronary heart disease. J Am Heart Assoc 2:e000130.
  12. Mooijaart SP, Berbée JF, van Heemst D, Havekes LM, de Craen AJ, et al. (2006) ApoE plasma levels and risk of cardiovascular mortality in old age. PLoS Med. 3:e176.
  13. van Vliet P, Mooijaart SP, de Craen AJ, Rensen PC, van Heemst D, et al. (2007) Plasma levels of apolipoprotein E and risk of stroke in old age. Ann N Y AcadSci 1100:140-147.
  14. Corsetti JP, Gansevoort RT, Bakker SJ, Navis G, Sparks CE, et al. (2012) Apolipoprotein E predicts incident cardiovascular disease risk in women but not in men with concurrently high levels of high-density lipoprotein cholesterol and C-reactive protein. Metabolism 61:996-1002.
  15. Corsetti JP, Bakker SJ, Sparks CE, Dullaart RPF (2012) Apolipoprotein A-II influences apolipoprotein E-linked cardiovascular disease risk in women with high levels of HDL cholesterol and C-reactive protein. PLoS One 7:e39110.
  16. Sacks FM, Alaupovic P, Moye LA, Cole TG, Sussex B, et al. (2000) VLDL, apolipoproteins B, CIII, and E, and risk of recurrent coronary events in the Cholesterol and Recurrent Events (CARE) trial. Circulation 102:1886-1892.
  17. Söderlund S, Watanabe H, Ehnholm C, Jauhiainen M, Taskinen MR (2010) Increased apolipoprotein E level and reduced high-density lipoprotein mean particle size associate with low high-density lipoprotein cholesterol and features of metabolic syndrome. Metabolism 59:1502-1509.
  18. Talayero B, Wang L, Furtado JD, Carey VJ, Bray GA, et al. (2014) Obesity favors apolipoprotein E and CIII-containing high-density lipoprotein subfractions associated with risk of heart disease. J Lipid Res 55. Epub ahead of print 25 June 2014. DOI 10.1194/jlr.M042333.
  19. Jeyarajah EJ, Cromwell WC, Otvos JD (2006) Lipoprotein particle analysis by nuclear magnetic resonance spectroscopy. Clin Lab Med 26:847-870.
  20. Rosenson RS, Brewer HB Jr, Chapman MJ, Fazio S, Hussain MM, et al. (2011) HDL measures, particle heterogeneity, proposed nomenclature, and relation to atherosclerotic cardiovascular events. ClinChem 57:392-410.
  21. Freedman DS, Otvos JD, Jeyarajah EJ, Barboriak JJ, Anderson AJ, et al. (1998) Relation of lipoprotein subclasses as measured by proton nuclear magnetic resonance spectroscopy to coronary artery disease. ArteriosclerThrombVascBiol 18:1046-1053.
  22. Otvos JD, Collins D, Freedman DS, Shalaurova I, Schaefer EJ, et al. (2006) Low-density lipoprotein and high-density lipoprotein particle subclasses predict coronary events and are favorably changed by gemfibrozil therapy in the Veterans Affairs High-Density Lipoprotein Intervention Trial. Circulation 113:1556-1563.
  23. Garvey WT, Kwon S, Zheng D, Shaughnessy S, Wallace P, et al. (2003) Effects of insulin resistance and type 2 diabetes on lipoprotein subclass particle size and concentration determined by nuclear magnetic resonance. Diabetes 52:453-462.
  24. Mora S, Otvos JD, Rosenson RS, Pradhan A, Buring JE, et al. (2010) Lipoprotein particle size and concentration by nuclear magnetic resonance and incident type 2 diabetes in women. Diabetes 59:1153–1160.
  25. Grundy SM, Cleeman JI, Daniels SR, Donato KA, Eckel RH, et al. (2005) Diagnosis and management of the metabolic syndrome: an American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement. Circulation 112:2735-2752.
  26. Blaauwwiekel EE, Beusekamp BJ, Sluiter WJ, Hoogenberg K, Dullaart RPF (1998) Apolipoprotein E genotype is a determinant of low-density lipoprotein cholesterol and of its response to a low-cholesterol diet in type 1 diabetic patients with elevated urinary albumin excretion. Diabet Med 15:1031–1035.
  27. Reymer PW, Groenemeyer BE, van de Burg R, Kastelein JJ (1995) Apolipoprotein E genotyping on agarose gels. ClinChem 41:1046–1047.
  28. Selvin S (1996) Statistical analysis of epidemiological data. Oxford University Press.
  29. Lu M, Lyden PD, Brott TG, Hamilton S, Broderick JP, et al. (2005) Beyond subgroup analysis: Improving the clinical interpretation of treatment effects in stroke research. J Neurosci Methods 143:209-216.
  30. Dutheil F, Walther G, Chapier R, Mnatzaganian G, Lesourd B, et al. (2014) Atherogenicsubfractions of lipoproteins in the treatment of metabolic syndrome by physical activity and diet - the RESOLVE trial. Lipids Health Dis 13:112.
  31. Lucero D, Zago V, López GH, Cacciagiú L, López GI, et al. (2012) Predominance of large VLDL particles in metabolic syndrome, detected by size exclusion liquid chromatography. ClinBiochem 45:293-297.
  32. Packard CJ, Shepherd J (1997) Lipoprotein heterogeneity and apolipoprotein B metabolism. ArteriosclerThrombVascBiol 17:3542-3556.
  33. Adiels M, Olofsson SO, Taskinen MR, Borén J (2008) Overproduction of very low-density lipoproteins is the hallmark of the dyslipidemia in the metabolic syndrome. ArteriosclerThrombVascBiol 28:1225-1236.
  34. Millar JS, Lichtenstein AH, Ordovas JM, Dolnikowski GG, Schaefer EJ. (2001) Human triglyceride-rich lipoprotein apo E kinetics and its relationship to LDL apo B-100 metabolism. Atherosclerosis 155:477-485.
  35. Huang Y, Liu XQ, Rall SC, Taylor JM, von Eckardstein A, et al. (1998) Overexpression and accumulation of apolipoprotein E as a cause of hypertriglyceridemia. J BiolChem 273; 26388-26393.
  36. Batal R, Tremblay M, Barrett PH, Jacques H, Fredenrich A, et al. (2000) Plasma kinetics of apoC-III and apoE in normolipidemic and hypertriglyceridemic subjects. J Lipid Res 41:706-718.
  37. Arsenault BJ, Lemieux I, Després JP, Wareham NJ, Stroes ES, et al. (2010) Comparison between gradient gel electrophoresis and nuclear magnetic resonance spectroscopy in estimating coronary heart disease risk associated with LDL and HDL particle size. ClinChem 56:789-798.
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