The effects of exercise on the lipoprotein subclass profile: A meta-analysis of 10 interventions.

OBJECTIVE: The goal was to examine lipoprotein subclass responses to regular exercise as measured in 10 exercise interventions derived from six cohorts. METHODS: Nuclear magnetic resonance spectroscopy was used to quantify average particle size, total and subclass concentrations of very low-density lipoprotein, low-density lipoprotein, and high-density lipoprotein particles (VLDL-P, LDL-P, and HDL-P, respectively) before and after an exercise intervention in 1555 adults from six studies, encompassing 10 distinct exercise programs: APOE (N = 106), DREW (N = 385), GERS (N = 79), HERITAGE (N = 715), STRRIDE I (N = 168) and II (N = 102). Random-effects meta-analyses were performed to evaluate the overall estimate of mean change across the unadjusted and adjusted mean change values from each exercise group. RESULTS: Meta-analysis of unadjusted data showed that regular exercise induced significant decreases in the concentration of large VLDL-P, small LDL-P, and medium HDL-P and mean VLDL-P size, with significant increases in the concentration of large LDL-P and large HDL-P and mean LDL-P size. These changes remained significant in meta-analysis with adjustment for age, sex, race, baseline body mass index, and baseline trait value. CONCLUSIONS: Despite differences in exercise programs and study populations, regular exercise produced putatively beneficial changes in the lipoprotein subclass profile across 10 exercise interventions. Further research is needed to examine how exercise-induced changes in lipoprotein subclasses may be associated with (concomitant changes in) cardiovascular disease risk.

A systematic approach to obtain validated partial least square models for predicting lipoprotein subclasses from serum NMR spectra.

A systematic approach is described for building validated PLS models that predict cholesterol and triglyceride concentrations in lipoprotein subclasses in fasting serum from a normolipidemic, healthy population. The PLS models were built on diffusion-edited (1)H NMR spectra and calibrated on HPLC-derived lipoprotein subclasses. The PLS models were validated using an independent test set. In addition to total VLDL, LDL, and HDL lipoproteins, statistically significant PLS models were obtained for 13 subclasses, including 5 VLDLs (particle size 64-31.3 nm), 4 LDLs (particle size 28.6-20.7 nm) and 4 HDLs (particle size 13.5-9.8 nm). The best models were obtained for triglycerides in VLDL (0.82 < Q(2) <0.92) and HDL (0.69 < Q(2) <0.79) subclasses and for cholesterol in HDL subclasses (0.68 < Q(2) <0.96). Larger variations in the model performance were observed for triglycerides in LDL subclasses and cholesterol in VLDL and LDL subclasses. The potential of the NMR-PLS model was assessed by comparing the LPD of 52 subjects before and after a 4-week treatment with dietary supplements that were hypothesized to change blood lipids. The supplements induced significant (p < 0.001) changes on multiple subclasses, all of which clearly exceeded the prediction errors.

Diabetic retinopathy and serum lipoprotein subclasses in the DCCT/EDIC cohort.

PURPOSE: To determine associations between retinopathy status and detailed serum lipoprotein subclass profiles in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study (DCCT/EDIC) cohort. METHODS: Persons with type 1 diabetes (440 women, 548 men) from the DCCT/EDIC cohort were studied. Retinopathy was characterized by Early Treatment Diabetic Retinopathy Study (ETDRS) scores, hard exudate scores, and ETDRS scores minus the hard exudate component. Lipoproteins were characterized by conventional lipid profile, nuclear magnetic resonance lipoprotein subclass profile (NMR-LSP), apoA1, apoB, lipoprotein(a), and susceptibility of LDL to oxidation. Data were analyzed with and without the following covariates: age, gender, duration of diabetes, HbA(1c), albumin excretion rate (AER), creatinine clearance, hypertension, body mass index, waist-hip ratio, DCCT treatment group, smoking status. RESULTS: The severity of retinopathy was positively associated with triglycerides (combined cohort) and negatively associated with HDL cholesterol (men, combined cohort). NMR-LSP identified retinopathy as being positively associated with small and medium VLDL and negatively with VLDL size. In men only, retinopathy was positively associated with small LDL, LDL particle concentration, apoB concentration, and small HDL and was negatively associated with large LDL, LDL size, large HDL, and HDL size. No associations were found with apoA1, Lp(a), or susceptibility of LDL to oxidation. All three measures of retinopathy revealed the same associations. CONCLUSIONS: NMR-LSP reveals new associations between serum lipoproteins and severity of retinopathy in type 1 diabetes. The data are consistent with a role for dyslipoproteinemia involving lipoprotein subclasses in the pathogenesis of diabetic retinopathy.

Subclasses of low-density lipoprotein and very low-density lipoprotein in familial combined hyperlipidemia: relationship to multiple lipoprotein phenotype.

OBJECTIVE: The present study addresses the presence of distinct metabolic phenotypes in familial combined hyperlipidemia (FCHL) in relation to small dense low-density lipoprotein (sd LDL) and very low-density lipoprotein (VLDL) subclasses. METHODS AND RESULTS: Hyperlipidemic FCHL relatives (n=72) were analyzed for LDL size by gradient gel electrophoresis. Pattern B LDL (sd LDL, particle size <258 A) and pattern A LDL (buoyant LDL, particle size > or =258 A) were defined. Analyses showed bimodal distribution of LDL size associated with distinct phenotypes. Subjects with predominantly large, buoyant LDL showed a hypercholesterolemic phenotype and the highest apo B levels. Subjects with predominantly sd LDL showed a hypertriglyceridemic, low high-density lipoprotein (HDL) cholesterol phenotype, with moderately elevated apoB, total cholesterol level, and LDL cholesterol level. Subjects with both buoyant LDL and sd LDL (pattern AB, n=7) showed an intermediate phenotype, with high normal plasma triglycerides. VLDL subfraction analysis showed that the sd LDL phenotype was associated with a 10-times higher number of VLDL1 particles of relatively lower apo AI and apo E content, as well as smaller VLDL2 particles, in combination with increased plasma insulin concentration in comparison to pattern A. CONCLUSIONS: The present observations underscore the importance of the VLDL triglyceride metabolic pathway in FCHL as an important determinant of the phenotypic heterogeneity of the disorder.

Lipoprotein subclass measurements by nuclear magnetic resonance spectroscopy improve the prediction of coronary artery disease in Type 1 diabetes. A prospective report from the Pittsburgh Epidemiology of Diabetes Complications Study.

AIM/HYPOTHESIS: To examine whether nuclear magnetic resonance lipoprotein spectroscopy improves the prediction of coronary artery disease in patients with Type 1 diabetes, independently of conventional lipid and other risk factors. METHODS: A prospective nested case-control design of subjects with childhood onset Type 1 diabetes from the Pittsburgh Epidemiology of Diabetes Complications Study was used. 59 controls were age-, sex- and duration-matched to 59 incident cases of coronary artery disease (fatal or non-fatal myocardial infarction, angina, coronary stenosis >50%) occurring during 10 years of follow-up. Lipid mass and particle concentrations of VLDL, LDL, and HDL subclasses, grouped into three size categories (large, medium, and small), were assessed prior to event with nuclear magnetic resonance spectroscopy. RESULTS: Univariate analyses showed that both lipid mass and particle concentrations of all three VLDL subclasses, small LDL, medium LDL, and medium HDL were increased in CAD cases compared to controls, while large HDL was decreased. Mean LDL and HDL particle sizes were lower in cases. In multivariate models using conventional lipid and non-lipid risk factors, triglycerides and overt nephropathy were the strongest predictors of CAD. Nuclear magnetic resonance measures further improved the prediction, i.e. large HDL particle concentration (OR=0.43, p=0.030), medium HDL mass (OR=3.79, p=0.026) and total VLDL particle concentration (OR=2.33, p=0.033). CONCLUSION/INTERPRETATION: While these results underscore the importance of triglycerides and overt nephropathy in CAD risk in Type 1 diabetic patients, they also suggest that nuclear magnetic resonance lipoprotein spectroscopy could further refine its prediction and show novel findings concerning HDL subclasses.

Differences in the relation of obesity to serum triacylglycerol and VLDL subclass concentrations between black and white children: the Bogalusa Heart Study.

BACKGROUND: Obese children and adults, particularly those with abdominal obesity, have an elevated serum triacylglycerol concentration. Furthermore, triacylglycerol concentrations are generally higher in whites than in blacks, and the relation of obesity to triacylglycerol concentrations may be stronger in whites. However, there is little information on the relation of obesity to the metabolically distinct subclasses of VLDL in children. OBJECTIVE: The objective was to examine possible differences between blacks (n = 367) and whites (n = 549) in mean concentrations of triacylglycerols, in mean concentrations of small and large VLDL, and in the relation of waist circumference to concentrations of triacylglycerol and VLDL subclasses. DESIGN: We measured VLDL subclass concentrations and assessed the relation of various obesity indexes to triacylglycerols in a cross-sectional study of 10- to 17-y-olds. RESULTS: The mean triacylglycerol concentration was 0.3 mmol/L (25 mg/dL) higher in white than in black children, primarily because of a 0.2-mmol/L (140%) difference in mean concentrations of large VLDL. In contrast, the mean concentrations of small VLDL differed by only 0.05 mmol/L (29%). In addition, the relations of waist girth to concentrations of triacylglycerol and large VLDL were 2- to 6-fold stronger among white children than among black children. Although white children had higher concentrations of large VLDL than did black children, this difference increased from 0.1 to 0.4 mmol/L across quintiles of waist circumference. Waist circumference was not significantly related to concentrations of small VLDL. CONCLUSION: These contrasting associations with obesity, which differ between white and black children, suggest that information on VLDL subclasses could provide additional information on the risk of obesity-related ischemic heart disease.

Lipoprotein-complexed C-reactive protein and the biphasic transmittance waveform in critically ill patients.

The 'biphasic transmittance waveform' (BTW) refers to a decrease in light transmittance that often occurs prior to clotting in coagulation assays of critically ill patient plasmas. It correlates with disseminated intravascular coagulation and mortality. The present work shows that the BTW is due to the rapid formation of a precipitate and a coincident change in turbidity in re-calcified plasma. The precipitate was isolated from patient plasma and contained lipids typical of very low density lipoprotein (VLDL), plus the proteins apolipoprotein B-100 and C-reactive protein (CRP). Precipitation also occurred in normal plasma supplemented with CRP. In addition, CRP precipitated with VLDL and intermediate density lipoprotein, but not low density lipoprotein or high density lipoprotein. The Kd value for the CRP/VLDL interaction is 340 nM. The IC50 value of Ca2+ for complex formation is 5.0 mM, and epsilon-aminocaproic acid inhibits the process. In 15 plasmas with the BTW from critically ill patients, CRP was highly elevated (77-398 microg/mL) and VLDL cholesterol ranged from 0.082 to 1.32 mM. The magnitude of the turbidity change on re-calcification correlated well with the calculated level of the CRP/VLDL complex. Thus, the Ca2+-dependent formation of a complex between CRP and VLDL accounts for the BTW.

Mechanisms of postprandial hyperlipidaemia--remnants and coronary artery disease.

High plasma concentrations of triglyceride-rich lipoprotein are associated with an increased risk of coronary artery disease (CAD). In the postprandial state, there is a large increase in chylomicron and very low-density lipoprotein (VLDL) concentrations. The accumulation of potentially atherogenic particles is controlled by the balance of their synthesis and clearance. Chylomicrons are rich in triglyceride and secreted by the intestine postprandially. Chylomicrons compete with VLDL for hydrolysis by lipoprotein lipase (LPL). This competition may cause the increase in large plasma concentration of VLDL seen in the postprandial state. Postprandial increases in atherogenic plasma lipoprotein concentrations are accentuated in insulin-resistant states. Insulin resistance is associated with greater flux of free fatty acids, which may in turn lead to enhanced synthesis of VLDL. Alimentary lipidaemia has been shown to effect changes in the coagulation cascade which may provide additional connections between postprandial lipaemia and CAD. Thus, specific postprandial changes in plasma lipids may be indicative of atherogenic risk. Measurement of postprandial plasma triglyceride concentration and the apo B-48 and apo B-100 contents in triglyceride-rich lipoprotein fractions are probably useful indicators of postprandial dyslipidaemia, but prospective studies of how these lipid variables relate to CAD progression are needed.

Isolation and characterization of two distinct species of human very low density lipoproteins lacking apolipoprotein E.

We have isolated two fractions of very low density lipoprotein particles in human plasma that lack apolipoprotein (apo) E by combined anti-apoE and heparin affinity chromatography of whole plasma followed by ultracentrifugation. The two fractions are distinguished by their ability to bind to heparin. Each of these fractions, designated "B" particles to distinguish them from very low density lipoproteins that contain apoE ("B,E" particles), comprises an appreciable fraction of total particles in very low density lipoproteins of normolipidemic and hypertriglyceridemic subjects. The heparin-unbound B particles, which have been reported previously by others, are larger and have negligible affinity for low density lipoprotein receptors. The heparin-bound B particles are smaller and do bind to low density lipoprotein receptors, albeit with much lower affinity than B,E particles. No differences in accessibility to limited protease digestion were found between apoB-100 in the two types of B particles. Our data indicate that a substantial fraction of human very low density lipoproteins lacks apoE, the principal ligand for lipoprotein receptors that mediate the terminal catabolism of these lipoproteins. Whereas the B particles that fail to bind to heparin are likely to represent a form of nascent lipoprotein, the origin of those B particles that bind to heparin remains to be determined.

Accumulation of large very low density lipoprotein in plasma during intravenous infusion of a chylomicron-like triglyceride emulsion reflects competition for a common lipolytic pathway.

Very low density lipoproteins (VLDL) are produced in the liver and contain apolipoprotein (apo) B-100 and endogenous lipids. By contrast, ingestion of fat leads to formation of chylomicrons containing apoB-48 secreted from the intestine. In this study, a 60-min intravenous infusion of a chylomicron-like triglyceride emulsion was given to healthy young men to examine whether competition between chylomicrons and VLDL for the same lipolytic pathway explains the increase in VLDL seen after meals. The responses of two major VLDL subfractions were determined by measuring the concentrations of apoB-100 in fractions of triglyceride-rich lipoproteins with Svedberg flotation rates of 60-400 (large VLDL) and 20-60 (small VLDL) that were separated from plasma by density gradient ultracentrifugation. A threefold elevation in plasma triglycerides was observed during the infusion together with a consistent linear increase of large VLDL. The rate at which large VLDL accumulated in plasma differed markedly among individuals and was not enhanced by doubling of the infusion rate. The response of small VLDL was more heterogeneous; however, a decrease was seen in most subjects. The combined pattern for the two VLDL species is what would be expected if large VLDL particles are the precursors of smaller VLDL species and if lipolysis of large VLDL is inhibited through competition from the triglyceride emulsion. The extent to which the triglyceride emulsion inhibited the lipolysis of VLDL and/or influenced the synthesis rate of large VLDL was estimated from simultaneous stable isotope studies. The emulsion caused a 75-90% block of the conversion of large VLDL apoB to small VLDL apoB and there was no sign of enhanced synthesis of large VLDL after infusion of the triglyceride emulsion. The corollary of these findings is that chylomicrons and their remnants impede the normal lipolytic degradation of VLDL and could thereby be indirectly implicated in the generation of atherogenic remnant lipoproteins.

Separation of VLDL subfractions by density gradient ultracentrifugation.

To assess the presence and composition of very-low-density lipoprotein (VLDL) in various types of hyperlipoproteinemia, a method of density gradient ultracentrifugation has been developed. After 2 hours of density gradient ultracentrifugation, human serum VLDL is separated into two distinct VLDL cholesterol peaks (VLDL1 and VLDL2). The two VLDL subfractions were detected in the serum samples from all subjects in the study, including subjects with normolipidemia (n = 10), familial dysbetalipoproteinemia (n = 12), and type IIa (n = 8), type IIb (n = 12), and type IV/V (n = 10) hyperlipoproteinemia. The cholesterol profiles obtained by the density gradient ultracentrifugation technique resembled the band patterns after electrophoresis of identical serum samples on 2% to 16% nondenaturing polyacrylamide gradient gel: VLDL1 represents relatively large VLDL particles (diameter of about 67 nm) and VLDL2 represents relatively small VLDL particles (diameter of about 38 nm). Recentrifugation of isolated VLDL1 and isolated VLDL2 did not result in any change in their density distribution. In all groups studied, the fluidity of VLDL1 was significantly higher than that of VLDL2, in accordance with the finding that VLDL1 particles were relatively rich in triglycerides and VLDL2 particles were relatively rich in cholesteryl esters. These results indicate that the two VLDL subfractions isolated represent distinct VLDL subclasses. The density gradient ultracentrifugation technique presented in this study allows the rapid isolation and characterization of VLDL subfractions from the serum samples of normolipidemic individuals and patients with hyperlipoproteinemia.

Characterization of constitutive human serum amyloid A protein (SAA4) as an apolipoprotein.

Serum amyloid A proteins (SAAs), a family of homologous molecules, are apolipoproteins of high density lipoprotein (HDL). They can be divided into two groups. The first group comprises the well-characterized acute phase SAAs that associate with HDL during inflammation, thereby remodeling the HDL particle by displacing apolipoprotein (apo)A-I. The second group consists of the recently discovered constitutive SAAs, mouse SAA5 and human SAA4. They exist as minor apolipoproteins on HDL but constitute more than 90% of the total SAA during homeostasis. We have characterized human SAA4 as an apolipoprotein. During homeostasis, SAA4 is synthesized only in the liver. Purification of SAA4 has been described and its plasma concentration has been established at 55 +/- 13 micrograms/ml in 26 healthy individuals. It was present on all HDL density classes and very low density lipoprotein (VLDL) but was absent from low density lipoprotein (LDL). Using two-dimensional electrophoresis and phosphorimaging, SAA4 was found to be associated with a specific subpopulation of only three HDL particles, not involved in the initial cholesterol transfer from cells.

Metabolism of VLDL and LDL subclasses.

The recognition of lipoprotein heterogeneity has given new depth to our understanding of lipoprotein metabolism and the role of plasma triglyceride as a determinant of lipoprotein subclass distribution and potential atherogenicity. It has also provided insight into the relationship between exogenous and endogenous lipid transport pathways, the roles of endothelial lipases and lipid transfer proteins in the remodelling of lipoproteins, and the link between insulin resistance, lipids and coronary disease.

Presence of multiple subpopulations of lipoproteins of intermediate density in normal subjects.

Analysis of human plasma by gradient gel electrophoresis (GGE) revealed multiple distinct bands in the size range between very low density (VLDL) and low density lipoproteins (LDL). GGE of intermediate density lipoproteins (IDL) from normal subjects consistently showed two major bands with particle diameters in the range of 275 to 300 A. The larger, usually predominant subspecies was designated IDL-1, and the smaller, IDL-2. GGE also demonstrated two sizes of subpopulations in the VLDL density range in all subjects. A discontinuous nonequilibrium density gradient ultracentrifugation technique was devised to isolate a series of fractions containing progressively smaller lipoproteins. Successive fractions showed progressive enrichment in cholesteryl-esters, depletion of triglyceride, slower migration on agarose, and depletion of apo E and the C apolipoproteins relative to apo B. The IDL-1 and IDL-2 subspecies appeared to represent two distributions of lipoproteins overlapping in size (particle diameter 280-300 A and 268-284 A, respectively) and buoyant density (d = 1.008-1.022 g/ml and d = 1.013-1.028 g/ml, respectively). Plasma from two patients with dysbetalipoproteinemia showed predominant increases in fractions normally containing small VLDL and IDL-1, while patients with severe hypertriglyceridemia had increases primarily in levels of larger VLDL. Heterogeneity of lipoprotein precursors could account for the discrete subspecies of LDL observed in human plasma.

Concentration and chemical composition of plasma lipoprotein subfractions in patients with peripheral vascular disease. Evidence for normal apolipoprotein B but low cholesteryl ester content in small VLDL.

Subfractionation of the 3 major plasma lipoprotein classes was performed in 20 male patients with symptomatic peripheral vascular disease (PVD) and 18 male healthy controls of similar age and serum lipid levels as the patients in order to investigate if, at comparable levels of total serum lipids, any difference in the distribution or the chemical composition of the lipoprotein subfractions existed between patients and controls. Concentrations of free and esterified cholesterol, triglycerides, phospholipids, apolipoprotein B (apo B) and soluble apolipoproteins did not differ significantly in any lipoprotein subfraction of PVD patients compared to controls. Calculated molecular weights and numbers of lipoprotein particles/ml plasma were also similar in the 2 groups except that there were more heavy LDL particles in the patient group. Plotting concentrations of apo B against cholesteryl ester in the VLDL-D subfraction (Sf 20-100) yielded a linear regression in both groups. The PVD regression line was significantly steeper than that of controls. Calculation of the molecular mass of the various constituents of the VLDL-D fraction in the subjects with the highest content of esterified cholesterol in VLDL-D, where this difference was most pronounced, suggests that this difference was due entirely to a decreased number of cholesteryl ester molecules per lipoprotein particle in PVD. The findings suggest that a disordered metabolism of plasma cholesteryl esters may be present in certain PVD patients.