Small dense low density lipoprotein has increased affinity for LDL receptor-independent cell surface binding sites: a potential mechanism for increased atherogenicity

New automated assay of small dense low-density lipoprotein cholesterol identifies risk of coronary heart disease: the Multi-ethnic Study of Atherosclerosis

OBJECTIVE

Coronary heart disease (CHD) is the leading cause of death in the United States, yet assessing risk of its development remains challenging. The present study evaluates a new automated assay of small dense low-density lipoprotein cholesterol content (sdLDL-C) and whether sdLDL-C is a risk factor for CHD compared with LDL-C or small LDL particle concentrations derived from nuclear magnetic resonance spectroscopy.

APPROACH AND RESULTS

sdLDL-C was measured using a new automated enzymatic method, and small LDL concentrations were obtained by nuclear magnetic resonance in 4387 Multi-Ethnic Study of Atherosclerosis participants. Cox regression analysis estimated hazard ratios for developing CHD for 8.5 years after adjustments for age, race, sex, systolic blood pressure, hypertension medication use, high-density lipoprotein cholesterol, and triglycerides. Elevated sdLDL-C was a risk factor for CHD in normoglycemic individuals. Those in the top sdLDL-C quartile showed higher risk of incident CHD (hazard ratio, 2.41; P=0.0037) compared with those in the bottom quartile and indicated greater CHD risk than the corresponding quartile of LDL-C (hazard ratio, 1.75; P=0.019). The association of sdLDL-C with CHD risk remained significant when LDL-C (<2.57 mmol/L) was included in a multivariate model (hazard ratio, 2.37; P=0.012). Nuclear magnetic resonance-derived small LDL concentrations did not convey a significant risk of CHD. Those with impaired fasting glucose or diabetes mellitus showed higher sdLDL-C and small LDL concentrations but neither was associated with higher CHD risk in these individuals.

CONCLUSIONS

This new automated method for sdLDL-C identifies risk for CHD that would remain undetected using standard lipid measures, but only in normoglycemic, nondiabetic individuals.

The elevation of apoB in hypercholesterolemic patients is primarily attributed to the relative increase of apoB/Lp-PLA₂

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is a risk factor of cardiovascular disease. Plasma Lp-PLA₂ is mainly associated with apolipoprotein (apo)B-containing lipoproteins, primarily with low density lipoproteins (LDLs). Importantly, only a proportion of circulating lipoproteins contain Lp-PLA₂. We determined the plasma levels of Lp-PLA₂-bound apoB (apoB/Lp-PLA₂) in patients with primary hypercholesterolemia. The effect of simvastatin therapy was also addressed. The plasma apoB/Lp-PLA₂ concentration in 50 normolipidemic controls and 53 patients with primary hypercholesterolemia at baseline and at 3 months posttreatment with simvastatin (40 mg/day) was determined by an enzyme-linked immunosorbent assay. The concentration of the apoB-containing lipoproteins that do not bind Lp-PLA₂ [apoB/Lp-PLA₂⁻] was calculated by subtracting the apoB/Lp-PLA₂ from total apoB. The apoB/Lp-PLA₂ levels were 3.6-fold higher, while apoB/Lp-PLA₂⁻ were 1.3-fold higher in patients compared with controls. After 3 months of simvastatin treatment apoB/Lp-PLA₂ and apoB/Lp-PLA₂⁻ levels were reduced by 52% and 33%, respectively. The elevation in apoB-containing lipoproteins in hypercholesterolemic patients is mainly attributed to the relative increase in the proatherogenic apoB/Lp-PLA₂, while simvastatin reduces these particles to a higher extent compared with apoB/Lp-PLA₂⁻. Considering that Lp-PLA₂ is proatherogenic, the predominance of apoB/Lp-PLA₂ particles in hypercholesterolemic patients may contribute to their higher atherogenicity and incidence of cardiovascular disease.

Nutritional lipidomics: molecular metabolism, analytics, and diagnostics

The field of lipidomics is providing nutritional science a more comprehensive view of lipid intermediates. Lipidomics research takes advantage of the increase in accuracy and sensitivity of mass detection of MS with new bioinformatics toolsets to characterize the structures and abundances of complex lipids. Yet, translating lipidomics to practice via nutritional interventions is still in its infancy. No single instrumentation platform is able to solve the varying analytical challenges of the different molecular lipid species. Biochemical pathways of lipid metabolism remain incomplete and the tools to map lipid compositional data to pathways are still being assembled. Biology itself is dauntingly complex and simply separating biological structures remains a key challenge to lipidomics. Nonetheless, the strategy of combining tandem analytical methods to perform the sensitive, high-throughput, quantitative, and comprehensive analysis of lipid metabolites of very large numbers of molecules is poised to drive the field forward rapidly. Among the next steps for nutrition to understand the changes in structures, compositions, and function of lipid biomolecules in response to diet is to describe their distribution within discrete functional compartments lipoproteins. Additionally, lipidomics must tackle the task of assigning the functions of lipids as signaling molecules, nutrient sensors, and intermediates of metabolic pathways.

Effect of fish oil supplementation on serum triglycerides, LDL cholesterol and LDL subfractions in hypertriglyceridemic adults

BACKGROUND AND AIMS

The well-established triglyceride (TG) lowering effect of fish oil is accompanied by an increase in LDL-cholesterol (LDL-C) concentration. Less is known about the differential impact on LDL particle distribution - the smaller particles being associated with a greater risk for atherosclerosis. We aimed to examine the changes in serum concentrations of four subclasses of LDL particles as well as shifts in LDL phenotype patterns (A, B, AB) among hypertriglyceridemic adults.

METHODS AND RESULTS

This was a secondary analysis from a double-blind, parallel design, placebo controlled trial with 42 adults that experienced significant TG lowering and modest increases in total LDL-C concentrations after 12 weeks of 4 g/d EPA + DHA. Reduction in serum TG concentrations (mean ± SEM) was -26 ± 4% (-0.81 ± 10.12 mmol/L), p < 0.0001. Total LDL-C concentration increased by 13 ± 3% (+0.31 ± 0.08 mmol/L), p < 0.0001. The 12-week changes in concentrations of LDL1, LDL2, LDL3 and LDL4 were +0.06 ± 0.02 mmol/L [+2.2 ± 0.7 mg/dL], +0.07 ± 0.03 mmol/L [+2.6 ± 1.0 mg/dL], +0.16 ± 0.05 mmol/L [+6.3 ± 1.8 mg/dL], and +0.04 ± 0.04 mmol/L [+1.4 ± 1.7 mg/dL], respectively (+20 ± 5%, +64 ± 13%, +26 ± 6%, and +17 ± 9%), p < 0.05 for all but LDL4. Changes in LDL phenotype patterns A, B and A/B were negligible and not statistically significant.

CONCLUSION

In this population of hypertriglyceridemic adults, dietary supplementation with fish oil resulted in an increase in total LDL-C concentration which was distributed relatively evenly across the range of smaller and more atherogenic as well as larger and less atherogenic LDL particles.

Serum uric acid: marker for atherosclerosis as it is positively associated with "atherogenic index of plasma"

CONTEXT

Serum uric acid (SUA) has been known to be associated with cardiovascular diseases. "Atherogenic index of plasma" (AIP) is considered a very sensitive predictor of future cardiovascular events.

OBJECTIVES

This study was conducted to analyse the association of AIP with SUA and various other lipid parameters.

METHODS

Parameters were measured on a fully automated analyser using standard reagent kits in a retrospective study involving 248 male Indian subjects between 40 to 59 years of age.

RESULTS

AIP correlates: moderately with TC/HDL-C (r = 0.47, p < 0.0001); to a lesser extent but comparably (r = 0.2, p < 0.01) with SUA, LDL-C/HDL-C and TC; negligibly with LDL-C and age.

DISCUSSION AND CONCLUSION

As SUA is positively associated with AIP it can be used as a supplementary marker for atherosclerosis/CVD in upper-middle-aged men.

Hypertriglyceridemia secondary to obesity and diabetes

Hypertriglyceridemia is a common lipid abnormality in persons with visceral obesity, metabolic syndrome and type 2 diabetes. Hypertriglyceridemia typically occurs in conjunction with low HDL levels and atherogenic small dense LDL particles and is associated with increased cardiovascular risk. Insulin resistance is often an underlying feature and results in increased free fatty acid (FFA) delivery to the liver due to increased peripheral lipolysis. Increased hepatic VLDL production occurs due to increased substrate availability via FFAs, decreased apolipoprotein B100 degradation and increased lipogenesis. Postprandial hypertriglyceridemia also is a common feature of insulin resistance. Small dense LDL that coexist with decreased HDL particles in hypertriglyceridemic states are highly pro-atherogenic due to their enhanced endothelial permeability, proteoglycan binding abilities and susceptibility to oxidation. Hypertriglyceridemia also occurs in undertreated individuals with type 1 diabetes but intensive glucose control normalizes lipid abnormalities. However, development of visceral obesity in these patients unravels a similar metabolic profile as in patients with insulin resistance. Modest hypertriglyceridemia increases cardiovascular risk, while marked hypertriglyceridemia should be considered a risk for pancreatitis. Lifestyle modification is an important therapeutic strategy. Drug therapy is primarily focused on lowering LDL levels with statins, since efforts at triglyceride lowering and HDL raising with fibrates and/or niacin have not yet been shown to be beneficial in improving cardiovascular risk. Fibrates, however, are first-line agents when marked hypertriglyceridemia is present. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Smaller Mean LDL Particle Size and Higher Proportion of Small Dense LDL in Korean Type 2 Diabetic Patients

BACKGROUND

Small dense low density lipoprotein (sdLDL) has recently emerged as an important risk factor of coronary heart disease.

METHODS

The mean LDL particle size was measured in 203 patients with type 2 diabetes mellitus (T2DM) and 212 matched subjects without diabetes using polyacrylamide tube gel electrophoresis. Major vascular complications were defined as stroke, angiographically-documented coronary artery disease or a myocardial infarction. Peripheral vascular stenosis, carotid artery stenosis (≥50% in diameter) or carotid artery plaque were considered minor vascular complications. Overall vascular complications included both major and minor vascular complications.

RESULTS

Diabetic patients had significantly smaller mean-LDL particle size (26.32 nm vs. 26.49 nm) and a higher percentage of sdLDL to total LDL compared to those of subjects without diabetes (21.39% vs. 6.34%). The independent predictors of sdLDL in this study were serum triglyceride level and body mass index (odds ratio [OR], 1.020 with P<0.001 and OR 1.152 with P<0.027, respectively). However, no significant correlations were found between sdLDL and major vascular complications (P=0.342), minor vascular complications (P=0.573) or overall vascular complications (P=0.262) in diabetic subjects.

CONCLUSION

Diabetic patients had a smaller mean-LDL particle size and higher proportion of sdLDL compared to those of subjects without diabetes. Obese diabetic patients with hypertriglyceridemia have an increased risk for atherogenic small dense LDL. However, we could not verify an association between LDL particle size and vascular complications in this study.

Glycation of LDL by methylglyoxal increases arterial atherogenicity: a possible contributor to increased risk of cardiovascular disease in diabetes

OBJECTIVE

To study whether modification of LDL by methylglyoxal (MG), a potent arginine-directed glycating agent that is increased in diabetes, is associated with increased atherogenicity.

RESEARCH DESIGN AND METHODS

Human LDL was isolated and modified by MG in vitro to minimal extent (MG(min)-LDL) as occurs in vivo. Atherogenic characteristics of MG(min)-LDL were characterized: particle size, proteoglycan-binding, susceptibility to aggregation, LDL and non-LDL receptor-binding, and aortal deposition. The major site of modification of apolipoprotein B100 (apoB100) modification was investigated by mass spectrometric peptide mapping.

RESULTS

MG(min)-LDL contained 1.6 molar equivalents of MG modification-mostly hydroimidazolone-as found in vivo. MG(min)-LDL had decreased particle size, increased binding to proteoglycans, and increased aggregation in vitro. Cell culture studies showed that MG(min)-LDL was bound by the LDL receptor but not by the scavenger receptor and had increased binding affinity for cell surface heparan sulfate-containing proteoglycan. Radiotracer studies in rats showed that MG(min)-LDL had a similar fractional clearance rate in plasma to unmodified LDL but increased partitioning onto the aortal wall. Mass spectrometry peptide mapping identified arginine-18 as the hotspot site of apoB100 modification in MG(min)-LDL. A computed structural model predicted that MG modification of apoB100 induces distortion, increasing exposure of the N-terminal proteoglycan-binding domain on the surface of LDL. This likely mediates particle remodeling and increases proteoglycan binding.

CONCLUSIONS

MG modification of LDL forms small, dense LDL with increased atherogenicity that provides a new route to atherogenic LDL and may explain the escalation of cardiovascular risk in diabetes and the cardioprotective effect of metformin.

Small dense LDL enhances THP-1 macrophage foam cell formation

AIM

Increased levels of small dense low-density lipoproteins (sd-LDL) have been reported more atherogenic compared to total low-density lipoprotein (LDL); however, no definitive experiments using macrophages have examined this concept in vitro.

METHOD AND RESULT

In this study, we isolated fractions of total LDL (density 1.019-1.063 g/ml) and sd-LDL (density 1.044-1.063 g/ml) from the plasma of subjects with modest hypertriglycidemia. Oxidizabilty as assessed by copper-induced generation (1.6 µmol/L CuSO(4),12 h) of thiobarbituric acid reactive substances (TBARS) was significantly greater (7-fold higher, p < 0.01) for sd-LDL (4.3 ± 1.1 nmol/mg) than for total LDL (0.6 ± 0.2 nmol/mg) at the same cholesterol concentrations. Moreover, oxidized sd-LDL induced more lipid staining in macrophages than oxidized total LDL. When non-oxidized sd-LDL were incubated with THP1 macrophages, there was much greater lipid accumulation as assessed by oil red O staining, and more than a 2-fold increase (p < 0.05) in intracellular triglyceride content as compared to non-oxidized total LDL. Furthermore, non-oxidized sd-LDL in contrast to non-oxidized total LDL enhanced macrophage lectin-like oxidized LDL receptor-1 (LOX-1) protein expression and significantly LOX-1 mRNA levels (+158%, p < 0.05), with no effect on scavenger receptor A or CD36 gene expression. These effects of non-oxidized sd-LDL on LOX-1 gene expression were suppressed when Toll-like receptor 4 was inactivated either by RNAi or antibody.

CONCLUSION

Our data indicate for the first time that sd-LDL is much more effective in promoting macrophage triglyceride accumulation and LOX-1 gene expression than total LDL.

Should we measure routinely oxidised and atherogenic dense low-density lipoproteins in subjects with type 2 diabetes?

Beyond low-density lipoprotein (LDL)-cholesterol concentrations, in recent years, several clinical studies have shown that both oxidised and small, dense LDL have a strong predictive role for the presence of vascular atherosclerosis. These two lipid parameters seem to have a synergistic impact on cardiovascular risk, with a greater importance in patients at higher-risk, such as those with type-2 diabetes. Increased levels of oxidised and small, dense LDL levels are a feature of diabetic dyslipidaemia, and small, dense LDL have been shown to be a good predictor of future cardiovascular events, at both univariate and multivariate analyses. On the other hand, although the association of oxidised LDL with surrogate markers of atherosclerosis is consistent, the correlation with hard clinical end points seems to be smaller. Yet, measurement of these two lipid parameters has not been widely used in daily practice because of the limited availability of clinical data and methodological problems: lack of availability of easy, cheap and reproducible essays for measurement of oxidised and, particularly, small, dense LDL has reduced their assessment in large clinical end-points trials. However, on the basis of available data, the therapeutic modulation of small, dense LDL is significantly associated with reduced cardiovascular risk, even after adjustment for confounding factors. In conclusion, the routine measurement of oxidised and small, dense LDL in patients with type-2 diabetes cannot be recommended in daily clinical practice so far; yet, their measurement is strongly encouraged to better understand their role on the cardiovascular risk of patients with type-2 diabetes.

n-3, but not n-6 lipid particle uptake requires cell surface anchoring

Omega-3 (n-3) fatty acids are emerging as bioactive agents protective against cardiovascular disease. However, their cellular delivery pathways are poorly defined. Here we questioned whether the uptake of n-3 triglyceride-rich particles (TGRP) is mediated by cell surface proteoglycans (PG) using LDL receptor (LDLR)+/+ and LDLR-/- cell models. LDLR+/+ but not LDLR-/- cells showed higher n-6 over n-3 TGRP uptake. Removal of cell surface proteins and receptors by pronase markedly enhanced the uptake of n-3 but not n-6 TGRP. Lactoferrin blockage of apoE-mediated pathways decreased the uptake of n-6 TGRP by up to 85% (p<0.05) but had insignificant effect on n-3 TGRP uptake. PG removal by sodium chlorate in LDLR+/+ cells substantially reduced n-3 TGRP uptake but had little effect on n-6 TGRP uptake. Thus, while n-6 TGRP uptake is preferentially mediated by LDLR-dependent pathways, the uptake of n-3 TGRP depends more on PG and non-LDLR cell surface anchoring.

Effect of L-carnitine on the size of low-density lipoprotein particles in type 2 diabetes mellitus patients treated with simvastatin

Therapeutic modulation of low-density lipoprotein (LDL) size could be of benefit in reducing the risk of cardiovascular events in diabetic patients. This study evaluated the efficacy of L-carnitine on the size of LDL particles in type 2 diabetes mellitus patients treated with simvastatin. Eighty diabetic patients were randomly assigned to 1 of 2 treatment groups for 3 months. The 2 groups received either simvastatin monotherapy 20 mg (n = 40) or L-carnitine 2 g/d and simvastatin 20 mg (n = 40). The following variables were assessed at baseline; after washout; and at 1, 2, and 3 months of treatment: body mass index, fasting plasma glucose, glycosylated hemoglobin, total cholesterol, LDL cholesterol, LDL subclasses, LDL size, high-density lipoprotein cholesterol, triglycerides, apolipoprotein A-1, and apolipoprotein B-100. After 12 weeks, comparing the 2 groups, we observed a decrease in fasting plasma glucose (1.45 vs 0.61 mmol/L, P < .001) and an increase in glycosylated hemoglobin (0.2% vs 0.4%, P < .05). Moreover, there was a decrease in total cholesterol (2.07 vs 1.45 mmol/L, P < .001), LDL (1.65 vs 1.29 mmol/L, P < .001), triglycerides (1.36 vs 0.41 mmol/L, P < .001), apo B-100 (49 vs 9 g/L, P < .001), and small-sized LDL proportion (10.8% vs 4.9%, P < .001), whereas LDL particle size increased (6 vs 3 A, P < .001) and HDL increased (0.2 vs 0.11 mmol/L, P < .001). We observed that patients treated with carnitine and simvastatin showed a reduction in small-sized LDL proportion and an increase in LDL particle size.

The role of pioglitazone in modifying the atherogenic lipoprotein profile

Pioglitazone, a thiazolidinedione, has established efficacy in improving glycaemic control in patients with type 2 diabetes. Pioglitazone also improves components of the mixed dyslipidaemia profile common in these patients, as typified by raised levels of plasma triglycerides, low levels of HDL cholesterol (HDL-C) and a raised proportion of LDL cholesterol (LDL-C) occurring as the small dense subfraction. In head-to-head trials, pioglitazone has consistently shown superior benefits on LDL-C and HDL-C as well as triglycerides compared with rosiglitazone and sulphonylureas. Pioglitazone used as monotherapy or combination therapy reduces levels of small dense LDL3 particles while raising levels of larger and less atherogenic LDL fractions. In addition, pioglitazone reduces cholesterol load and particle numbers of LDL3. Importantly, the differential effects of pioglitazone on LDL subfractions are complimentary and additive to those of simvastatin. Pioglitazone increases total HDL-C levels by 10-20%, mainly because of an increase in the larger HDL2 subfraction. Pioglitazone also significantly reduces plasma triglyceride levels by 10-25%. In recent studies, pioglitazone significantly reduced carotid and coronary atherosclerosis compared with the sulphonylurea glimepiride. The antidyslipidaemic effects of pioglitazone--in particular, improvements in HDL-C and reduction of small dense LDL3--may have contributed to these effects.

Atherogenic dyslipidemia and oxidative stress: a new look

Although results from in vitro studies and clinical trials demonstrate strong associations between oxidative stress and cardiovascular risk, to date still no convincing data are available to suggest that treatment with antioxidants might reduce vascular events. Oxidative modifications of low-density lipoproteins (LDL) represent an early stage of atherosclerosis, and small, dense LDL are more susceptible to oxidation than larger, more buoyant particles. Oxidized LDL are independent predictors of subclinical and clinical atherosclerosis. Recent studies suggested that novel therapeutic strategies may take into account the removal of such particles from circulation. Future research is required to explore the potential synergistic impact of markers of oxidative stress and atherogenic dyslipidemia, particularly small dense LDL, on cardiovascular risk.

Quantitative and qualitative effects of rosuvastatin on LDL-cholesterol: what is the clinical significance?

BACKGROUND

Statins have emerged as the global leader in pharmacologic therapy for dyslipidaemia, and rosuvastatin has demonstrated clinical efficacy as well as safety in several clinical trials and postmarketing analyses.

AIM

The present article reviewed the effects of rosuvastatin on the quantity and the quality of low-density lipoproteins (LDL).

METHODS

We searched for and reviewed all the available evidence in a systematic way. A literature search (by Medline and Scopus) was performed using the following headings: 'LDL-cholesterol', 'LDL size', 'LDL subclasses', 'small dense LDL', 'apolipoprotein B, apo B' and 'rosuvastatin' up to 11 November 2008. The authors also manually reviewed the references of selected articles for any pertinent material.

RESULTS

Rosuvastatin reduces LDL-cholesterol levels to a greater extent than other statins and is able to modulate significantly LDL size and subclasses towards less atherogenic particles as well as the LDL particle number, as indirectly measured by the levels of apo B.

DISCUSSION AND CONCLUSIONS

The recent Justification for the Use of statins in Primary prevention: an Intervention Trial Evaluating Rosuvastatin study provides more evidence about the effectiveness of rosuvastatin therapy in reducing cardiovascular risk, even among persons who would not currently be considered for pharmacotherapy. Further insights on cardiovascular outcomes will be available by the on-going trials included in the GALAXY program that includes subjects with type-2 diabetes, haemodialysis recipients, patients with congestive heart failure and specific ethnic groups, such as African American, Hispanic and South Asian populations.

The therapeutic modulation of atherogenic dyslipidemia and inflammatory markers in the metabolic syndrome: what is the clinical relevance?

The metabolic syndrome consists of a constellation of clinical and biochemical risk factors that cluster together and heighten the risk for atherogenesis, cardiovascular diseases, and diabetes. Established risk cardiovascular factors like hypertension, atherogenic dyslipidaemia, and glucose intolerance occur in the setting of insulin resistance and central adiposity, with genetic and environmental influences modulating the ultimate risk. Chronic insults to the endothelium take its toll in the form of silent as well as clinically evident cardiovascular events. The cellular and vascular accompaniments have shed some light into the underlying pathophysiology. Heightened, low-grade inflammatory processes as well as a continuum of vascular insults ranging from early endothelial derangements to advanced atherosclerosis have been examined. In recent years there has been an explosion of basic and clinical knowledge related to the metabolic syndrome. Although dyslipidaemia is considered a traditional risk component for the syndrome, its qualitative aspects, genetically determined subfractions, and variation in proatherogenic tendency have generated renewed interest and debate. New targets within the dyslipidaemic spectrum that have differing clinical relevance are being evaluated. The effect of heredity, lifestyle changes, pharmacotherapeutic agents, and supplements is being investigated. Further research into the impact of dyslipidemia and inflammation as both pathophysiologic risk factors and objects for targeted therapy in the metabolic syndrome should deepen our understanding and unravel answers to the underlying dynamics in this global epidemic.

Improved cardio-respiratory fitness correlates with changes in the number and size of small dense LDL: randomized controlled trial with exercise training and dietary instruction

OBJECTIVE

To investigate the correlation between lifestyle improvements, in particular increased cardio-respiratory fitness and changes in the blood lipid profile.

METHODS

The participants were 217 residents of Fuji and Yamato Towns, Saga City, with mildly abnormal blood pressure, serum lipids or blood glucose detected at health check-ups in 2003. Participants were randomly allocated to an Intervention (108 subjects) or Control group (109 subjects), matched for age and various conditions. The Intervention group was given exercise advice and prescription and dietary instructions. Cardio-respiratory fitness was evaluated using the work rate at double product breaking point. Changes of lipid parameters were compared before and after intervention, and examined the relationship with cardio-respiratory fitness.

RESULTS

Seventy nine subjects in each group could be followed up for 17 months without requiring pharmacotherapy. Body mass index, waist circumference, systolic blood pressure, homeostasis model assessment insulin resistance, and triglycerides were decreased in the Intervention group. Furthermore, apolipoprotein B levels were lower (p<0.05), and the ratio of LDL cholesterol to apolipoprotein B (LDL/ApoB) was higher (p<0.001). When all subjects were divided into 3 subgroups according to the degree of improvement in cardio-respiratory fitness, LDL/ApoB increased and apolipoprotein B decreased as the degree of improvement increased (p<0.05).

CONCLUSION

Improvement was seen in atherosclerotic risk factors through lifestyle modification. In particular, improved cardiorespiratory fitness was associated with qualitative and quantitative changes in LDLs.

Low density lipoproteins as circulating fast temperature sensors

Background

The potential physiological significance of the nanophase transition of neutral lipids in the core of low density lipoprotein (LDL) particles is dependent on whether the rate is fast enough to integrate small (±2°C) temperature changes in the blood circulation.

Methodology/Principal Findings

Using sub-second, time-resolved small-angle X-ray scattering technology with synchrotron radiation, we have monitored the dynamics of structural changes within LDL, which were triggered by temperature-jumps and -drops, respectively. Our findings reveal that the melting transition is complete within less than 10 milliseconds. The freezing transition proceeds slowly with a half-time of approximately two seconds. Thus, the time period over which LDL particles reside in cooler regions of the body readily facilitates structural reorientation of the apolar core lipids.

Conclusions/Significance

Low density lipoproteins, the biological nanoparticles responsible for the transport of cholesterol in blood, are shown to act as intrinsic nano-thermometers, which can follow the periodic temperature changes during blood circulation. Our results demonstrate that the lipid core in LDL changes from a liquid crystalline to an oily state within fractions of seconds. This may, through the coupling to the protein structure of LDL, have important repercussions on current theories of the role of LDL in the pathogenesis of atherosclerosis.

Mathematical model for low density lipoprotein (LDL) endocytosis by hepatocytes

Individuals with elevated levels of plasma low density lipoprotein (LDL) cholesterol (LDL-C) are considered to be at risk of developing coronary heart disease. LDL particles are removed from the blood by a process known as receptor-mediated endocytosis, which occurs mainly in the liver. A series of classical experiments delineated the major steps in the endocytotic process; apolipoprotein B-100 present on LDL particles binds to a specific receptor (LDL receptor, LDL-R) in specialized areas of the cell surface called clathrin-coated pits. The pit comprising the LDL-LDL-R complex is internalized forming a cytoplasmic endosome. Fusion of the endosome with a lysosome leads to degradation of the LDL into its constituent parts (that is, cholesterol, fatty acids, and amino acids), which are released for reuse by the cell, or are excreted. In this paper, we formulate a mathematical model of LDL endocytosis, consisting of a system of ordinary differential equations. We validate our model against existing in vitro experimental data, and we use it to explore differences in system behavior when a single bolus of extracellular LDL is supplied to cells, compared to when a continuous supply of LDL particles is available. Whereas the former situation is common to in vitro experimental systems, the latter better reflects the in vivo situation. We use asymptotic analysis and numerical simulations to study the longtime behavior of model solutions. The implications of model-derived insights for experimental design are discussed.

Hyperlipidemia in the elderly

People are now living longer, largely because of a combination of falling rates of fertility and mortality, thus producing a greater proportion of older people in society. Thirty times more centenarians were alive in 2000 than in 1900, and the population growth in the elderly segment of society is expected to continue at an exponential rate. Vascular disease is responsible for more than a quarter of all deaths worldwide. More than 80% of individuals who die of coronary heart disease are older than 65 years. Although a myocardial infarction may be perceived as fatal, heart attacks do not always lead to death but to conditions such as congestive heart failure, ischemic cardiomyopathy, and angina, which greatly impact quality of life. These issues are only a few that must be contemplated when considering the clinical and economic effects of preventive therapies in the elderly population.

Association of low-density lipoprotein particle size and ratio of different lipoproteins and apolipoproteins with coronary heart disease

BACKGROUND

Worldwide coronary heart disease (CHD) is estimated to be the leading cause of death. Current knowledge about prevention of CHD is mainly derived from developed countries. Therefore, this study aimed to find out the association of CHD with ratios of different lipoproteins and apolipoproteins, LDL particle size, as well as different traditional risk factors in Asian Indian population in Eastern part of India.

METHODS

Case-control study of 100 patients with CHD and 98 healthy controls were age and sex matched. After clinical evaluation, blood samples were collected for biochemical assays.

RESULTS

Multivariate logistic regression analysis found apoB (OR 2.96; 95% CI 1.02-8.54), apoB/HDL-c (OR 4.14; 95% CI 1.33-12.83), nonHDL-c (OR 5.41; 95% CI 2.08-14.10), apoB/apoAI (OR 6.64; 95% CI 2.37-18.57), and LDL particle size (9.59; 95% CI 2.92-31.54) were independently associated with CHD. Area under the ROC curves derived from the model (AUROC 0.947; 95% CI 0.916-0.977) are significantly higher than any other variables.

CONCLUSIONS

Findings from the multivariate analysis, apoB, apoB/HDL-c, nonHDL-c, apoB/apoAI, and LDL particle size are potent indicators and useful for diagnosis of predisposed CHD.

Does simultaneous determination of LDL and HDL particle size improve prediction of coronary artery disease risk?

BACKGROUND

Alterations in plasma lipoprotein subclass distribution affect the risk for coronary artery disease (CAD). However, it is unclear whether the determination of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) phenotypes may or may not improve the ability to predict CAD development.

METHODS

Polyacrylamide gradient (3-31%) gel electrophoresis was used to simultaneously determine size and distribution of lipoprotein subclasses in 181 CAD patients and 178 controls.

RESULTS

Mean LDL and HDL subclass sizes were significantly smaller in patients than in controls (p < 0.001). Multivariate logistic regression analysis showed that small dense LDL particles were independent CAD risk predictors (OR = 2.867, p < 0.01), even when adjusted for other traditional risk factors, while small HDL particles lost their significance after adjustment (OR = 2.071, p = 0.054). The area under the ROC curve for LDL (0.671) and HDL (0.643) particle size measurement demonstrated low clinical accuracy when compared to the combination of traditional lipid risk factor measurements.

CONCLUSIONS

CAD is associated with the predominance of smaller LDL and HDL particles. However, simultaneous determination of these two lipoprotein phenotypes provides no additional power in discriminating CAD and non-CAD subjects, beyond that obtained by the traditional risk factors.

Who needs to care about small, dense low-density lipoproteins?

BACKGROUND

Increasing evidence suggest that the 'quality' rather than only the 'quantity' of low-density lipoprotein (LDL) exerts a great influence on the cardiovascular risk. Small, dense LDL seem to be an important predictor of cardiovascular events and progression of coronary artery disease (CAD) and their predominance has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III.

DISCUSSION

Some studies showed in past years that small, dense LDL are usually elevated in patients at very high cardiovascular risk, such as those with CAD and type 2 diabetes. More recently elevated levels of these particles have been found in other categories of patients at high cardiovascular risk, such as those with non-coronary forms of atherosclerosis (e.g. with carotid artery disease, aortic abdominal aneurysm and peripheral arterial disease) and metabolic diseases (with polycystic ovary syndrome and growth hormone deficiency); notably, in most of them, the predominance of small, dense LDL characterised their type of dyslipidaemia, alone or in combination with elevated triglycerides and reduced high-density lipoproteins cholesterol concentrations.

CONCLUSIONS

The therapeutical modulation of small, dense LDL have been shown to significantly reduce cardiovascular risk and weight reduction and increased physical activity may constitute first-line therapy. In addition, lipid-lowering drugs are able to favourably alter these particles and fibrates and nicotinic acid seem to be the most effective agents. Promising data are also available with the use of rosuvastatin, the latest statin introduced in the market, and ezetimibe, a cholesterol absorption inhibitor.

Lipid-induced oxidative stress causes steatohepatitis in mice fed an atherogenic diet

Recently, nonalcoholic steatohepatitis (NASH) was found to be correlated with cardiovascular disease events independently of the metabolic syndrome. The aim of this study was to investigate whether an atherogenic (Ath) diet induces the pathology of steatohepatitis necessary for the diagnosis of human NASH and how cholesterol and triglyceride alter the hepatic gene expression profiles responsible for oxidative stress. We investigated the liver pathology and plasma and hepatic lipids of mice fed the Ath diet. The hepatic gene expression profile was examined with microarrays and real-time polymerase chain reactions. The Ath diet induced dyslipidemia, lipid peroxidation, and stellate cell activation in the liver and finally caused precirrhotic steatohepatitis after 24 weeks. Cellular ballooning, a necessary histological feature defining human NASH, was observed in contrast to existing animal models. The addition of a high-fat component to the Ath diet caused hepatic insulin resistance and further accelerated the pathology of steatohepatitis. A global gene expression analysis revealed that the Ath diet up-regulated the hepatic expression levels of genes for fatty acid synthesis, oxidative stress, inflammation, and fibrogenesis, which were further accelerated by the addition of a high-fat component. Conversely, the high-fat component down-regulated the hepatic gene expression of antioxidant enzymes and might have increased oxidative stress.

CONCLUSION

The Ath diet induces oxidative stress and steatohepatitis with cellular ballooning. The high-fat component induces insulin resistance, down-regulates genes for antioxidant enzymes, and further aggravates the steatohepatitis. This model suggests the critical role of lipids in causing oxidative stress and insulin resistance leading to steatohepatitis.

Tagging SNP haplotype analysis of the secretory PLA2-V gene, PLA2G5 , shows strong association with LDL and oxLDL levels, suggesting functional distinction from sPLA2-IIA: results from the UDACS study

Animal and human studies suggest that both secretory PLA2 (sPLA2)-V and sPLA2-IIA (encoded, respectively, by the neighbouring PLA2G5 and PLA2G2A genes) contribute to atherogenesis. Elevated plasma sPLA2-IIA predicts coronary heart disease (CHD) risk, but no mass assay for sPLA2-V is available. We previously reported that tagging single nucleotide polymorphism (tSNP) haplotypes of PLA2G2A are strongly associated with sPLA2-IIA mass, but not lipid levels. Here, we use tSNPs of the sPLA2-V gene to investigate the association of PLA2G5 with CHD risk markers. Seven PLA2G5 tSNPs genotypes, explaining >92% of the locus genetic variability, were determined in 519 patients with Type II diabetes (in whom PLA2G2A tSNP data was available), and defined seven common haplotypes (frequencies >5%). PLA2G5 and PLA2G2A tSNPs showed linkage disequilibrium (LD). Compared to the common PLA2G5 haplotype, H1 (frequency 34.9%), haplotypes H2-7 were associated with overall higher plasma LDL (P < 0.00004) and total cholesterol (P < 0.00003) levels yet lower oxLDL/LDL (P = 0.006) and sPLA2-IIA mass (P = 0.04), probably reflecting LD with PLA2G2A. Intronic tSNP (rs11573248), unlikely itself to be functional, distinguished H1 from LDL-raising haplotypes and may mark a functional site. In conclusion, PLA2G5 tSNP haplotypes demonstrate an association with total and LDL cholesterol and oxLDL/LDL, not seen with PLA2G2A, thus confirming distinct functional roles for these two sPLA2s.

The clinical significance of the size of low-density-lipoproteins and the modulation of subclasses by fibrates

BACKGROUND

Beyond total low-density-lipoproteins (LDL) levels, increasing evidence suggests that the 'quality' of LDL exerts a great influence on the cardiovascular risk. Several studies have also shown that the therapeutic modulation of LDL size is of benefit in reducing the risk of cardiovascular events. Hypolipidaemic treatment is able to alter LDL subclass distribution but strong variations have been noticed among different agents. Fibrates have a major impact on triglyceride metabolism and in modulating LDL size and subclasses, but variations exist among the different molecules.

METHODOLOGY

A literature search (by Medline and Scopus) was performed using the following headings: 'small dense LDL', 'LDL size', 'LDL subfractions', 'LDL subclasses', 'LDL distribution' and 'fenofibrate', 'bezafibrate', 'ciprofibrate' and 'gemfibrozil' up to 20 January 2007. The authors also manually reviewed the references of selected articles for any pertinent material.

RESULTS

Analysis of all published studies revealed that treatment with fenofibrate, ciprofibrate, bezafibrate and gemfibrozil is usually beneficial, and fenofibrate may be more efficacious than the other molecules. This is supported by using all the available techniques in subjects with a very wide range of lipid alterations.

CONCLUSION

Among the different agents, fenofibrate has been found to be particularly effective in modulating LDL size and subclasses in patients at higher cardiovascular risk, such as those with type 2 diabetes or the metabolic syndrome.

Obesity induced during sexual maturation is linked to LDL-triacylglycerols in Yucatan miniature swine

The incidence of childhood obesity is rising dramatically throughout industrialised countries. To evaluate and study the impact of childhood obesity on lipoprotein metabolism, we developed a new animal model of premature obesity. Yucatan mini-pigs aged 4 months were studied over a 12-month period from childhood to adulthood. Animals were divided into two groups: the first group were overfed a Western misbalanced diet; the second group were normally fed a recommended human-type diet. Cholesterol and triacylglycerol concentrations in VLDL-, LDL- and HDL-lipoproteins were followed from baseline to adulthood by fast protein liquid chromatography. At 10 (the end of sexual maturation) and 16 months old (adulthood), liver, visceral and subcutaneous adipose tissues were sampled. Real-time RT-PCR was performed in order to compare apo AI, apo B, apo C-III, PPAR-α, insulin receptor and lipoprotein lipase gene expression between groups and ages. Differences between groups were observed only after sexual maturity. Adult overfed mini-pigs had a higher LDL-cholesterol:HDL-cholesterol ratio (P<0·05; 0·55 (SE 0·06) for overfedv. 0·42 (SE 0·04) for normally fed pigs at the tenth month of the study). In both groups, VLDL-triacylglycerol decreased (P<0·05). VLDL-triacylglycerol evolution in the overfed group was associated with an increase in LDL-triacylglycerol plasma concentrations (P<0·05) after sexual maturation. LDL-triacylglycerol concentration in overfed mini-pigs went from an average of 0·28 mmol/l before sexual maturation to reach an average concentration of 0·56 mmol/l afterwards. This phenomenon has never been observed in similar studies when obesity is induced in adult mini-pigs and may represent a specific hallmark of an obesity induced during sexual maturity.

Polyacrylamide gradient gel electrophoresis of lipoprotein subclasses

High-density (HDL), low-density (LDL), and very-low-density (VLDL) lipoproteins are heterogeneous cholesterol-containing particles that differ in their metabolism, environmental interactions, and association with disease. Several protocols use polyacrylamide gradient gel electrophoresis (GGE) to separate these major lipoproteins into known subclasses. This article provides a brief history of the discovery of lipoprotein heterogeneity and an overview of relevant lipoprotein metabolism, highlighting the importance of the subclasses in the context of their metabolic origins, fates, and clinical implications. Various techniques using polyacrylamide GGE to assess HDL and LDL heterogeneity are described, and how the genetic and environmental determinations of HDL and LDL affect lipoprotein size heterogeneity and the implications for cardiovascular disease are outlined.

Small, dense low-density-lipoproteins and the metabolic syndrome

Small, dense low-density-lipoproteins (LDL) are associated with increased risk for cardiovascular diseases and diabetes mellitus and a reduction in LDL size has been reported in patients with coronary and non-coronary forms of atherosclerosis. LDL size has been accepted as an important predictor of cardiovascular events and progression of coronary artery disease as well as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III. Small, dense LDL, with elevated triglyceride levels and low HDL-cholesterol concentrations, constitute the 'atherogenic lipoprotein phenotype (ALP)', a form of atherogenic dyslipidemia that is a feature of type 2 diabetes and the metabolic syndrome. LDL size and subclasses show specific alterations in patients with the metabolic syndrome that probably significantly increase their cardiovascular risk; however, so far it has not been recommended to incorporate LDL size measurements in treatment plans, when hypolipidemic therapies are installed. Patients with type 2 diabetes are at high cardiovascular risk and it is still on debate if the treatment goals may be identical or whether there are distinct groups with different cardiovascular risks and hence with different treatment goals. Measurements beyond traditional lipids, such as measurements on the presence of small, dense LDL in patients with the metabolic syndrome, may help to identify cardiovascular risk subgroups. In addition, it might be possible in the future to individualize hypolipidemic treatments if more than the traditional lipids are taken into account. LDL size measurement may potentially help to assess cardiovascular risk within the metabolic syndrome and adapt the treatment goals thereafter.

Clinical importance and therapeutic modulation of small dense low-density lipoprotein particles

The National Cholesterol Education Programme Adult Treatment Panel III accepted the predominance of small dense low-density lipoprotein (sdLDL) as an emerging cardiovascular disease (CVD) risk factor. Most studies suggest that measuring low-density lipoprotein (LDL) particle size, sdLDL cholesterol content and LDL particle number provides additional assessment of CVD risk. Therapeutic modulation of small LDL size, number and distribution may decrease CVD risk; however, no definitive causal relationship is established, probably due to the close association between sdLDL and triglycerides and other risk factors (e.g., high-density lipoprotein, insulin resistance and diabetes). This review addresses the formation and measurement of sdLDL, as well as the relationship between sdLDL particles and CVD. The effect of hypolipidaemic (statins, fibrates and ezetimibe) and hypoglycaemic (glitazones) agents on LDL size and distribution is also discussed.

Should we measure routinely the LDL peak particle size?

Low density lipoproteins (LDL) do not show in humans a normal distribution and comprise two different main fractions: large, buoyant (phenotype pattern A) and small, dense (phenotype pattern B) particles, that differ not only in size and density but also in physicochemical composition, metabolic behaviour and atherogenicity. The prevalence of small, dense LDL changes with age (30-35% in adult men, 5-10% in men <20 years and in pre-menopausal women, 15-25% in postmenopausal women) and is genetically influenced, with a heritability ranging from 35% to 45%. Small, dense LDL correlate negatively with plasma HDL levels and positively with plasma triglyceride levels and are associated with the metabolic syndrome and with increased risk for cardiovascular disease and diabetes mellitus. LDL size seems also to be an important predictor of cardiovascular events and progression of coronary artery disease and the predominance of small dense LDL has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III. In addition, patients with acute myocardial infarction show an early reduction of LDL size, which persists during hospitalization and seems to precede all other plasma lipoprotein modifications. However, it is still on debate whether to measure the LDL size routinely and in which categories of patients. Since the therapeutic modulation of small, dense LDL particles is of great benefit in reducing the atherosclerotic risk, the LDL size measurement should be extended to patients at high risk of coronary artery disease as much as possible.

Significance of small dense low-density lipoprotein as a risk factor for coronary artery disease and acute coronary syndrome

Small dense LDL (sd-LDL) has recently emerged as an important coronary artery disease (CAD) risk factor. This study was performed to investigate how LDL particle size is related to CAD and acute coronary syndrome (ACS). Blood samples were collected from 504 patients that underwent coronary angiography to evaluate chest pain. The LDL particle size of these samples was measured. The mean LDL particle size was smaller in patients with angiographically proven CAD than in the controls (26.41 +/- 0.95 vs 26.73 +/- 0.64 nm, p < 0.001), and was negatively correlated with the Framingham risk score (r=-0.121, p=0.007). Patients with more extensive CAD had smaller LDL particles. LDL particle size was also smaller in patients with acute coronary syndrome as compared to non-ACS patients (26.09 +/- 1.42 vs 26.54 +/- 0.63 nm, p=0.011). These results suggest that sd-LDL is independently associated with the incidence and extent of CAD, and can be a risk factor for the development of ACS in the Korean population.

Fasting triglyceride is a significant risk factor for coronary artery disease in middle-aged Japanese men

BACKGROUND

It has been well established that dyslipidemia is a significant risk factor for coronary artery disease (CAD), however, the association between fasting triglyceride (TG) and the occurrence of CAD is controversial. The objective of this study was to elucidate the relationship between fasting TG and CAD in middle-aged Japanese men.

METHODS AND RESULTS

A cohort study of 6,966 middle-aged Japanese men (mean +/- SD: 46.6+/-5.2 years) with a 10-year follow-up period was conducted to identify risk factors for the occurrence of CAD. One hundred and eleven cases of CAD were identified during the follow up. The Cox proportional hazard model was used to identify the independent risk factors for CAD. Adjustment was made for variables including age, body mass index, smoking habit, alcohol intake, duration of sleeping, systolic blood pressure, uric acid, total cholesterol, high-density lipoprotein cholesterol, fasting plasma glucose, and TG. Fasting TG was identified as an independent risk factor for CAD. The adjusted hazard ratio of TG for CAD was 3.07 (95% confidence interval: 1.01-9.35, p<0.05). Additionally, a serum TG concentration level greater than 78 mg/dl was a significant risk for CAD.

CONCLUSIONS

By using the long term follow-up data of the study of middle-aged Japanese men, fasting TG was identified to be a significant risk factor for CAD.

Visceral adipose tissue accumulation, secretory phospholipase A2-IIA and atherogenecity of LDL

OBJECTIVE

The aim of the present study was to investigate the combined impact of visceral adipose tissue (VAT) and secretory group IIA phospholipase A(2) (sPLA(2)-IIA) concentrations on the atherogenicity of low-density lipoprotein (LDL) particles among men.

SUBJECTS

Analyses were conducted in 74 mid-obese healthy men (age: (mean+/-s.d.) 37.9+/-11.7 years).

METHODS

Plasma levels of sPLA(2)-IIA were measured with a commercial ELISA and VAT levels were assessed by computed tomography. Distinct subpopulations of LDL particles were characterized from whole plasma using nondenaturating 2-16% gradient gel electrophoresis.

RESULTS

Data indicated that plasma sPLA(2)-IIA levels were approximately 29% (P=0.007) higher among men characterized by a higher accumulation of VAT (>142 vs < or =142 cm(2)). Men having high plasma sPLA(2)-IIA levels (> or =127.2 ng/dl, the median value), were characterized by higher levels of plasma cholesterol (C) and apolipoprotein (apo) B, LDL-C, LDL-apoB, oxidized LDL (OxLDL) and by smaller LDL particles compared to men with sPLA(2)-IIA<127.2 ng/dl. Multiple regression analyses showed that plasma triglycerides and sPLA(2)-IIA levels explained 22.7 and 11.8% of the variance in LDL peak particle size, respectively. Levels of VAT and of sPLA(2)-IIA were the strongest correlates of OxLDL levels explaining, respectively, 15.0 and 5.5% of their variability.

CONCLUSION

Both VAT and sPLA(2)-IIA levels modulate the atherogenecity of LDL by accounting for the reduction in their size and their susceptibility to oxidation.