Effect of HDL composition and particle size on the resistance of HDL to the oxidation

High-Density Lipoprotein Subfractions Remodeling: A Critical Process for the Treatment of Atherosclerotic Cardiovascular Diseases

Numerous studies have shown that a low level of high-density lipoprotein cholesterol (HDL-C) is an independent biomarker of cardiovascular disease. High-density lipoprotein (HDL) is considered to be a protective factor for atherosclerosis (AS). Therefore, raising HDL-C has been widely recognized as a promising strategy to treat atherosclerotic cardiovascular diseases (ASCVD). However, several studies have found that increasing HDL-C levels does not necessarily reduce the risk of ASCVD. HDL particles are highly heterogeneous in structure, composition, and biological function. Moreover, HDL particles from atherosclerotic patients exhibit impaired anti-atherogenic functions and these dysfunctional HDL particles might even promote ASCVD. This makes it uncertain that HDL-raising therapy will prevent and treat ASCVD. It is necessary to comprehensively analyze the structure and function of HDL subfractions. We review current advances related to HDL subfractions remodeling and highlight how current lipid-modifying drugs such as niacin, statins, fibrates, and cholesteryl ester transfer protein inhibitors regulate cholesterol concentration of HDL and specific HDL subfractions.

Association of oxidized ApoB and oxidized ApoA-I with high-risk coronary plaque features in cardiovascular disease

BACKGROUND

Oxidized apolipoprotein B (oxLDL) and oxidized ApoA-I (oxHDL) are proatherogenic. Their prognostic value for assessing high-risk plaques by coronary computed tomography angiography (CCTA) is missing.

METHODS

In a prospective, observational study, 306 participants with cardiovascular disease (CVD) had extensive lipoprotein profiling. Proteomics analysis was performed on isolated oxHDL, and atherosclerotic plaque assessment was accomplished by quantitative CCTA.

RESULTS

Patients were predominantly White, overweight men (58.5%) on statin therapy (43.5%). Increase in LDL-C, ApoB, small dense LDL-C (P < 0.001 for all), triglycerides (P = 0.03), and lower HDL function were observed in the high oxLDL group. High oxLDL associated with necrotic burden (NB; β = 0.20; P < 0.0001) and fibrofatty burden (FFB; β = 0.15; P = 0.001) after multivariate adjustment. Low oxHDL had a significant reverse association with these plaque characteristics. Plasma oxHDL levels better predicted NB and FFB after adjustment (OR, 2.22; 95% CI, 1.27-3.88, and OR, 2.80; 95% CI, 1.71-4.58) compared with oxLDL and HDL-C. Interestingly, oxHDL associated with fibrous burden (FB) change over 3.3 years (β = 0.535; P = 0.033) when compared with oxLDL. Combined Met136 mono-oxidation and Trp132 dioxidation of HDL showed evident association with coronary artery calcium score (r = 0.786; P < 0.001) and FB (r = 0.539; P = 0.012) in high oxHDL, whereas Met136 mono-oxidation significantly associated with vulnerable plaque in low oxHDL.

CONCLUSION

Our findings suggest that the investigated oxidized lipids are associated with high-risk coronary plaque features and progression over time in patients with CVD.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT01621594.

FUNDING

National Heart, Lung, and Blood Institute at the NIH Intramural Research Program.

Association Between Triglycerides, High-Density Lipoprotein Cholesterol, and Their Ratio With the Pulse Wave Velocity in Adults From the ELSA-Brasil Study

Atherogenic dyslipidemia is a risk factor for cardiovascular diseases. The present study aimed to evaluate the association between triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and the triglycerides to high-density lipoprotein (TG/HDL-C) ratio with carotid-femoral pulse wave velocity (cf-PWV), a marker of vascular stiffness. Anthropometric, biochemical, and clinical data from 13,732 adults were used to assess this association. Individuals within the third TG/HDL-C tertile presented worse anthropometric, biochemical, and clinical profiles as compared with the participants in the lower TG/HDL-C tertile. There was a linear association between TG, HDL-C, and TG/HDL-C ratio and cf-PWV in both men and women (stronger in women). After adjustment for confounders, lower levels of HDL-C were associated with increased cf-PWV in men (9.63 ± .02 m/s) and women (8.90 ± .03 m/s). However, TG was not significantly associated with cf-PWV after adjustment, regardless of sex. An increased TG/HDL-C ratio is associated with higher cf-PWV only in women (9.01 ± .03 m/s), but after adjustment for HDL-C levels, the association was non-significant (8.99 ± .03 m/s). These results highlight the stronger association of HDL-C with arterial stiffness, and that the association of TG/HDL-C with cf-PWV is dependent on HDL-C.

Air Pollution: Another Threat to HDL Function

Epidemiological studies have consistently demonstrated a positive association between exposure to air pollutants and the incidence of cardiovascular disease, with the strongest evidence for particles with a diameter < 2.5 μm (PM2.5). Therefore, air pollution has been included among the modifiable risk factor for cardiovascular outcomes as cardiovascular mortality, acute coronary syndrome, stroke, heart failure, and arrhythmias. Interestingly, the adverse effects of air pollution are more pronounced at higher levels of exposure but were also shown in countries with low levels of air pollution, indicating no apparent safe threshold. It is generally believed that exposure to air pollution in the long-term can accelerate atherosclerosis progression by promoting dyslipidemia, hypertension, and other metabolic disorders due to systemic inflammation and oxidative stress. Regarding high density lipoproteins (HDL), the impact of air pollution on plasma HDL-cholesterol levels is still debated, but there is accumulating evidence that HDL function can be impaired. In particular, the exposure to air pollution has been variably associated with a reduction in their cholesterol efflux capacity, antioxidant and anti-inflammatory potential, and ability to promote the release of nitric oxide. Further studies are needed to fully address the impact of various air pollutants on HDL functions and to elucidate the mechanisms responsible for HDL dysfunction.

HDL AND ITS SUBPOPULATION (HDL2 AND HDL3) PROMOTE CHOLESTEROL TRANSPORTERS EXPRESSION AND ATTENUATES INFLAMMATION IN 3T3-L1 MATURE ADIPOCYTES INDUCED BY TUMOR NECROSIS FACTOR ALPHA

Obesity activates inflammation causing dysfunction of adipocytes. Increasing high-density lipoprotein (HDL) levels in obesity may be beneficial in overcoming this effect. However, not much data is available on the effects of HDL and its subpopulations in inflamed adipocytes. The objective of this study was to investigate the effects of total HDL (tHDL) and the comparison between its subpopulations (HDL2 & HDL3) on protein and gene expression of cholesterol transporters, inflammation, and adipokines in TNF-α stimulated 3T3-L1 mature adipocytes. TNFα alone had lower adiponectin and higher protein and gene expression of IL-6 and NF-ĸβ (p65) compared to unstimulated adipocytes and these effects were attenuated by HDLs especially HDL3 (in most of the biomarkers). HDL and its subpopulation had higher cholesterol transporters expression in 3T3-L1 mature adipocytes induced by TNF-α compared to unstimulated cells. Increment of cholesterol transporters expression by HDL leads to reduce secretion of inflammatory markers [IL-6 & NF-kB (p65)] and visfatin and increases adiponectin secretion in the inflamed mature adipocytes. HDL exhibits beyond its reverse cholesterol transporter property by exhibiting anti-inflammatory effects thru the deactivation of NF-ĸβ (p65). This may contribute to reducing the progression of obesity-related complications.

Obstructive Sleep Apnoea and Lipid Metabolism: The Summary of Evidence and Future Perspectives in the Pathophysiology of OSA-Associated Dyslipidaemia

Obstructive sleep apnoea (OSA) is associated with cardiovascular and metabolic comorbidities, including hypertension, dyslipidaemia, insulin resistance and atherosclerosis. Strong evidence suggests that OSA is associated with an altered lipid profile including elevated levels of triglyceride-rich lipoproteins and decreased levels of high-density lipoprotein (HDL). Intermittent hypoxia; sleep fragmentation; and consequential surges in the sympathetic activity, enhanced oxidative stress and systemic inflammation are the postulated mechanisms leading to metabolic alterations in OSA. Although the exact mechanisms of OSA-associated dyslipidaemia have not been fully elucidated, three main points have been found to be impaired: activated lipolysis in the adipose tissue, decreased lipid clearance from the circulation and accelerated de novo lipid synthesis. This is further complicated by the oxidisation of atherogenic lipoproteins, adipose tissue dysfunction, hormonal changes, and the reduced function of HDL particles in OSA. In this comprehensive review, we summarise and critically evaluate the current evidence about the possible mechanisms involved in OSA-associated dyslipidaemia.

Characterization of Particle Size Distribution of Plasma Lipoproteins in Dairy Cattle Using High-Resolution Polyacrylamide Electrophoresis

Plasma lipoproteins play critical roles in energy metabolism and inflammation. Concentrations of high-density lipoproteins (HDL) are linked to reproductive outcomes and milk yields in dairy cattle. Low-density lipoproteins (LDL), which are enzymatically formed in the blood from very low-density lipoproteins (VLDL) following secretion by the liver, have been used as a surrogate marker of liver function due to the rapid influx of circulating VLDL into the lactating mammary gland. In humans, the composition of plasma lipoproteins is reflected in lipoprotein particle size distribution, and both of these parameters are highly predictive of disease development and related health outcomes. Bovine HDL are overall larger, less dense particles compared to human HDL. Lipoprotein particle size distribution in both health and disease is understudied in the bovine. We hypothesize that a more detailed analysis of lipoproteins could hold diagnostic and/or prognostic value in the study of dairy cattle health and production. In this study, we took the first steps in this characterization and used a high-resolution polyacrylamide gel electrophoretic assay to better define LDL and HDL at the subfraction level in Holstein cows at different stages of lactation. We extensively characterized the lipoprotein particle size distribution in healthy lactating dairy cattle. We identified subfractions of LDL that were prominent only in the dry period and subfractions of HDL that were highest in cows during mid-lactation. Use of this method could be informative in the study of multiple herds and management strategies, including longitudinal evaluation of animals and production parameters.

Associations between maternal serum HDL-c concentrations during pregnancy and neonatal birth weight: a population-based cohort study

Background

To evaluate the associations between maternal serum concentrations of high-density lipoprotein cholesterol (HDL-c) throughout pregnancy and neonatal birth weight (BW) and small for gestational age (SGA) births.

Methods

A prospective cohort of 2241 pregnant women was followed from recruitment to delivery in three hospitals in Beijing, China between January 2014 and December 2017. Maternal fasting serum lipids concentrations were measured at gestational week 6–12, 16, 24 and 36. Major outcome was neonatal BW. The associations between maternal HDL-c and BW were estimated by linear regression and linear mixed-effects models. Odds ratios (ORs) and 95% confidence intervals of SGA births in relation to HDL-c were evaluated via logistic regression analysis.

Results

There was a tendency that mothers with higher HDL-c concentrations throughout gestation gave birth to infants with lower BW. A negative association was found between maternal HDL-c concentrations and BW at 24th and 36th gestational weeks (B = − 34.044, P = 0.034; B = − 53.528, P = 0.000). The HDL-c trend of change was inversely associated with BW (B = − 442.736, P = 0.000). Mothers with SGA neonates had higher serum HDL-c concentration at the 36th gestational week (P < 0.01). The incidences of SGA in the three groups (HDL-c: 1.84–2.23 mmol/L, 2.24–2.59 mmol/L and ≥ 2.60 mmol/L) were higher than the group with the lowest concentration of HDL-c (< 1.83 mmol/L) (P < 0.01, P < 0.01, P < 0.001) at 36th week. Higher maternal HDL-c concentrations at 36th week (HDL-c: 1.84–2.23 mmol/L, 2.24–2.59 mmol/L and ≥ 2.60 mmol/L) were positively associated with the incidence of SGA (OR = 1.900, P = 0.008; OR = 1.893, P = 0.008; OR = 1.975, P = 0.004). The HDL-c trend of change was positively associated with SGA births (OR = 9.772, P = 0.000).

Conclusions

Maternal serum HDL-c concentrations were inversely associated with BW at 24th and 36th gestational weeks. The high concentrations of HDL-c at the 36th gestational week increased the risk of SGA. The maternal HDL-c trend of change across pregnancy was associated with smaller neonatal size.

High-Density Lipoprotein Subclasses and Mild Cognitive Impairment: Study of Outcome and aPolipoproteins in Dementia (STOP-Dementia)1

BACKGROUND

High-density lipoprotein (HDL) containing apolipoprotein A-I is associated with the pathogenesis of Alzheimer's disease (AD). HDL particle size is modified in the presence of pathological conditions, while the significance of the HDL particle size remains controversial.

OBJECTIVE

The aim of this study was to investigate the HDL lipoprotein subclasses in mild cognitive impairment (MCI) and AD.

METHODS

This cross-sectional study included 20 AD patients, 17 MCI patients, and 17 age-matched controls without cognitive impairment, selected from the database of the Study of Outcome and aPolipoproteins in Dementia (STOP-Dementia) registry. The diagnoses of AD and MCI were performed by expert neurologists according to the Diagnostic and Statistical Manual of Mental Disorders-Fifth Edition criteria. Serum HDL subclasses were measured by electrophoretic separation of lipoproteins using the Lipoprint System. The neutrophil-lymphocyte ratio (NLR), a marker of inflammation, was calculated by dividing the neutrophil count by the lymphocyte count.

RESULTS

Small-sized HDL particle levels in the MCI group were significantly higher than in the control group, although there was no difference in serum HDL-cholesterol levels between MCI and control groups. NLR in the MCI group was higher than in the control group, but this difference was non-significant (p = 0.09). There was no difference in HDL subclasses or NLR between the AD and control groups.

CONCLUSION

These findings suggest that HDL subclasses might be associated with the development of MCI.

Apolipoprotein E particle size is increased in Alzheimer's disease

Introduction

Apolipoprotein E4 (apoE4) is the predominant risk factor for late-onset Alzheimer's disease (AD), but the question of which structural differences might explain its effect remains unclear.

Methods

We compared high-density lipoprotein–like apoE particles from 12 AD and 10 control patients using size-exclusion chromatography.

Results

ApoE particles from patients genotyped as ε4/ε4 were 2.2 ± 0.3 times as massive as particles from ε3/ε3 control subjects and 1.4 ± 0.1 times as massive as particles from ε3/ε3 AD patients. The increased particle size was not because of incorporation of amyloid β or apoE proteolysis products. Particles from AD patients genotyped as ε3/ε3 were 1.59 ± 0.27 times as massive as ε3/ε3 control subjects.

Discussion

Increased particle size in AD is affected by APOE genotype and by disease-related differences in assembly or stability. These differences suggest that lipoprotein assembly or stability in AD brain plays an important role in determining apoE4 pathogenicity.

Pharmacological Intervention to Modulate HDL: What Do We Target?

The cholesterol concentrations of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) have traditionally served as risk factors for cardiovascular disease. As such, novel therapeutic interventions aiming to raise HDL cholesterol have been tested in the clinical setting. However, most trials led to a significant increase in HDL cholesterol with no improvement in cardiovascular events. The complexity of the HDL particle, which exerts multiple physiological functions and is comprised of a number of subclasses, has raised the question as to whether there should be more focus on HDL subclass and function rather than cholesterol quantity. We review current data regarding HDL subclasses and subclass-specific functionality and highlight how current lipid modifying drugs such as statins, cholesteryl ester transfer protein inhibitors, fibrates and niacin often increase cholesterol concentrations of specific HDL subclasses. In addition this review sets out arguments suggesting that the HDL3 subclass may provide better protective effects than HDL2.

Update on the laboratory investigation of dyslipidemias

The role of the clinical laboratory is evolving to provide more information to clinicians to assess cardiovascular disease (CVD) risk and target therapy more effectively. Current routine methods to measure LDL-cholesterol (LDL-C), the Friedewald calculation, ultracentrifugation, electrophoresis and homogeneous direct methods have established limitations. Studies suggest that LDL and HDL size or particle concentration are alternative methods to predict future CVD risk. At this time there is no consensus role for lipoprotein particle or subclasses in CVD risk assessment. LDL and HDL particle concentration are measured by several methods, namely gradient gel electrophoresis, ultracentrifugation-vertical auto profile, nuclear magnetic resonance and ion mobility. It has been suggested that HDL functional assays may be better predictors of CVD risk. To assess the issue of lipoprotein subclasses/particles and HDL function as potential CVD risk markers robust, simple, validated analytical methods are required. In patients with small dense LDL particles, even a perfect measure of LDL-C will not reflect LDL particle concentration. Non-HDL-C is an alternative measurement and includes VLDL and CM remnant cholesterol and LDL-C. However, apolipoprotein B measurement may more accurately reflect LDL particle numbers. Non-fasting lipid measurements have many practical advantages. Defining thresholds for treatment with new measurements of CVD risk remain a challenge. In families with genetic variants, ApoCIII and lipoprotein (a) may be additional risk factors. Recognition of familial causes of dyslipidemias and diagnosis in childhood will result in early treatment. This review discusses the limitations in current laboratory technologies to predict CVD risk and reviews the evidence for emergent approaches using newer biomarkers in clinical practice.

A Shift in ApoM/S1P Between HDL-Particles in Women With Type 1 Diabetes Mellitus Is Associated With Impaired Anti-Inflammatory Effects of the ApoM/S1P Complex

Objective—

Type 1 diabetes mellitus (T1D) patients have an increased risk of cardiovascular disease despite high levels of high-density lipoproteins (HDL). Apolipoprotein M (apoM) and its ligand sphingosine 1-phospate (S1P) exert many of the anti-inflammatory effects of HDL. We investigated whether apoM and S1P are altered in T1D and whether apoM and S1P are important for HDL functionality in T1D.

Approach and Results—

ApoM and S1P were quantified in plasma from 42 healthy controls and 89 T1D patients. HDL was isolated from plasma and separated into dense, medium-dense, and light HDL by ultracentrifugation. Primary human aortic endothelial cells were challenged with tumor necrosis factor-α in the presence or absence of isolated HDL. Proinflammatory adhesion molecules E-selectin and vascular cellular adhesion molecule-1 were quantified by flow cytometry. Activation of the S1P 1 - receptor was evaluated by analyzing downstream signaling targets and receptor internalization. There were no differences in plasma levels of apoM and S1P between controls and T1D patients, but the apoM/S1P complexes were shifted from dense to light HDL particles in T1D. ApoM/S1P in light HDL particles from women were less efficient in inhibiting expression of vascular cellular adhesion molecule-1 than apoM/S1P in denser particles. The light HDL particles were unable to activate Akt, whereas all HDL subfractions were equally efficient in activating Erk and receptor internalization.

Conclusions—

ApoM/S1P in light HDL particles were inefficient in inhibiting tumor necrosis factor-α–induced vascular cellular adhesion molecule-1 expression in contrast to apoM/S1P in denser HDL particles. T1D patients have a higher proportion of light particles and hence more dysfunctional HDL, which could contribute to the increased cardiovascular disease risk associated with T1D.

Impaired HDL2-mediated cholesterol efflux is associated with metabolic syndrome in families with early onset coronary heart disease and low HDL-cholesterol level

Objective

The potential of high-density lipoproteins (HDL) to facilitate cholesterol removal from arterial foam cells is a key function of HDL. We studied whether cholesterol efflux to serum and HDL subfractions is impaired in subjects with early coronary heart disease (CHD) or metabolic syndrome (MetS) in families where a low HDL-cholesterol level (HDL-C) predisposes to early CHD.

Methods

HDL subfractions were isolated from plasma by sequential ultracentrifugation. THP-1 macrophages loaded with acetyl-LDL were used in the assay of cholesterol efflux to total HDL, HDL2, HDL3 or serum.

Results

While cholesterol efflux to serum, total HDL and HDL3 was unchanged, the efflux to HDL2 was 14% lower in subjects with MetS than in subjects without MetS (p<0.001). The efflux to HDL2 was associated with components of MetS such as plasma HDL-C (r = 0.76 in men and r = 0.56 in women, p<0.001 for both). The efflux to HDL2 was reduced in men with early CHD (p<0.01) only in conjunction with their low HDL-C. The phospholipid content of HDL2 particles was a major correlate with the efflux to HDL2 (r = 0.70, p<0.001). A low ratio of HDL2 to total HDL was associated with MetS (p<0.001).

Conclusion

Our results indicate that impaired efflux to HDL2 is a functional feature of the low HDL-C state and MetS in families where these risk factors predispose to early CHD. The efflux to HDL2 related to the phospholipid content of HDL2 particles but the phospholipid content did not account for the impaired efflux in cardiometabolic disease, where a combination of low level and poor quality of HDL2 was observed.

Impaired High-Density Lipoprotein Anti-Oxidative Function Is Associated With Outcome in Patients With Chronic Heart Failure

Background

Oxidative stress is mechanistically linked to the pathogenesis of chronic heart failure (CHF). Antioxidative functions of high‐density lipoprotein (HDL) particles have been found impaired in patients with ischemic cardiomyopathy; however, the impact of antioxidative HDL capacities on clinical outcome in CHF patients is unknown. We therefore investigated the predictive value of antioxidative HDL function on mortality in a representative cohort of patients with CHF.

Methods and Results

We prospectively enrolled 320 consecutive patients admitted to our outpatient department for heart failure and determined antioxidative HDL function using the HDL oxidative index (HOI). During a median follow‐up time of 2.8 (IQR: 1.8‐4.9) years, 88 (27.5%) patients reached the combined cardiovascular endpoint defined as the combination of death due to cardiovascular events and heart transplantation. An HOI ≥1 was significantly associated with survival free of cardiovascular events in Cox regression analysis with a hazard ratio (HR) of 2.28 (95% CI 1.48‐3.51, P<0.001). This association remained significant after comprehensive multivariable adjustment for potential confounders with an adjusted HR of 1.83 (95% CI 1.1‐2.92, P=0.012). Determination of HOI significantly enhanced risk prediction beyond that achievable with N‐terminal pro‐B‐type natriuretic peptide indicated by improvements in net reclassification index (32.4%, P=0.009) and integrated discrimination improvement (1.4%, P=0.04).

Conclusions

Impaired antioxidative HDL function represents a strong and independent predictor of mortality in patients with CHF. Implementation of HOI leads to a substantial improvement of risk prediction in patients with CHF.

The biological activity of high-density lipoprotein fractions and their role in the development of cardiovascular diseases

Increasing the human plasma concentration of high-density lipoproteins (HDL) may be part of strategy for control of cardiovascular diseases (CVD). HDL particles vary in their structure, metabolism, and biological activity. The review describes major HDL fractions (subpopulations) and discusses new findings on the antiatherogenic properties of HDL particles. The whole spectrum of HDL fractions, small, dense, protein-rich lipoproteins, has atheroprotective properties that are determined by the presence of specialized groups of proteins and lipids; however, this activity may be decreased in atherogenic lesion. Comprehensive structural and compositional analysis of HDL may provide key information to identify the fractions that have characteristic biological properties and lose their functionality in CVD. These fractions may be also biomarkers for the risk of CVD and hence represent pharmacological targets.

Development of novel HDL-mimicking α-tocopherol-coated nanoparticles to encapsulate nerve growth factor and evaluation of biodistribution

Nerve Growth Factor (NGF) is one of the members of the neurotrophin family with multifaceted functions. However, clinical application of NGF is hurdled by the challenge on formulation development. The objective of this study was to develop novel high-density lipoproteins (HDL)-mimicking nanoparticles (NPs) coated with α-tocopherol to incorporate NGF by a self-assembly approach. The NPs were prepared by an optimized self-assembly method that is simple and scalable. The composition of HDL-mimicking NPs was optimized. The prototype of the HDL-mimicking α-tocopherol-coated NPs contained phosphatidylserine (a negative charged phospholipid) and d-α-Tocopheryl polyethylene glycol succinate (a source of vitamin E) to enhance the entrapment efficiency of apolipoprotein A-I in the NPs. The entrapment efficiency of apolipoprotein A-I was about 30%. The NPs had particle size about 200nm with a relatively narrow size distribution. Finally, cationic ion-pair agents were optimized to form ion-pairs with NGF to facilitate the incorporation of NGF into the NPs. Protamine sodium salt USP formed an optimal ion-pair complex with NGF. The results showed that the novel HDL-mimicking α-tocopherol-coated NPs successfully encapsulated NGF with over 65% entrapment efficiency by using this ion-pair strategy. In vitro release studies demonstrated a slow release of NGF from NGF NPs in PBS containing 5% BSA at 37°C for 72 h. Further biodistribution studies showed that intravenously injected NGF NPs significantly increased NGF concentration in plasma and decreased the uptake in liver, spleen and kidney, compared to free NGF in mice.

HDL as a prognostic biomarker for coronary atherosclerosis: the role of inflammation

INTRODUCTION

Emerging evidence suggests that the role of high density lipoprotein (HDL) in the atherosclerotic process is not as clear as previously thought, since atheroprotective HDL becomes atherogenic in states of increased inflammatory processes.

AREAS COVERED

In this review we aim to elucidate the role of HDL as a prognostic biomarker and we discuss therapeutic approaches that aim to increase HDL and their possible clinical benefit.

EXPERT OPINION

Given the structural variability and biological complexity of the HDL particle, its role in the atherosclerotic process is far from clear. According to current evidence, the atheroprotective role of HDL turns atherogenic in states of increased inflammatory processes, while even minor alterations in systemic inflammation are likely to hinder the endothelial protective effects of HDL. In accordance, significant data have revealed that HDL-related drugs may be effective in reducing cardiovascular mortality; however they are not as encouraging or unanimous as expected. Possible future goals could be to quantify either HDL subclasses or functions in an attempt to reach safer conclusions as to the prognostic importance of HDL in coronary atherosclerosis. Having achieved that, a more targeted therapy that would aim to raise either HDL functionality or to remodel HDL structure would be more easily designed.

Mass Spectrometry-Based Proteomic Study Makes High-Density Lipoprotein a Biomarker for Atherosclerotic Vascular Disease

High-density lipoprotein (HDL) is a lipid and protein complex that consists of apolipoproteins and lower level HDL-associated enzymes. HDL dysfunction is a factor in atherosclerosis and decreases patient survival. Mass spectrometry- (MS-) based proteomics provides a high throughput approach for analyzing the composition and modifications of complex HDL proteins in diseases. HDL can be separated according to size, surface charge, electronegativity, or apoprotein composition. MS-based proteomics on subfractionated HDL then allows investigation of lipoprotein roles in diseases. Herein, we review recent developments in MS-based quantitative proteomic techniques, HDL proteomics and lipoprotein modifications in diseases, and HDL subfractionation studies. We also discuss future directions and perspectives in MS-based proteomics on HDL.

HDL particle subpopulations: Focus on biological function

Low levels of high-density lipoprotein-cholesterol (HDL-C) constitute an independent biomarker of cardiovascular morbi-mortality. However, recent advances have drastically modified the classical and limited view of HDL as a carrier of 'good cholesterol', and have revealed unexpected levels of complexity in the circulating HDL particle pool. HDL particles are indeed highly heterogeneous in structure, intravascular metabolism and biological activity. This review describes recent progress in our understanding of HDL subpopulations and their biological activities, and focuses on relationships between the structural, compositional and functional heterogeneity of HDL particles.

Effects of established hypolipidemic drugs on HDL concentration, subclass distribution, and function

The knowledge of an inverse relationship between plasma high-density lipoprotein cholesterol (HDL-C) concentrations and rates of cardiovascular disease has led to the concept that increasing plasma HDL-C levels would be protective against cardiovascular events. Therapeutic interventions presently available to correct the plasma lipid profile have not been designed to specifically act on HDL, but have modest to moderate effects on plasma HDL-C concentrations. Statins, the first-line lipid-lowering drug therapy in primary and secondary cardiovascular prevention, have quite modest effects on plasma HDL-C concentrations (2-10%). Fibrates, primarily used to reduce plasma triglyceride levels, also moderately increase HDL-C levels (5-15%). Niacin is the most potent available drug in increasing HDL-C levels (up to 30%), but its use is limited by side effects, especially flushing.The present chapter reviews the effects of established hypolipidemic drugs (statins, fibrates, and niacin) on plasma HDL-C levels and HDL subclass distribution, and on HDL functions, including cholesterol efflux capacity, endothelial protection, and antioxidant properties.

High-density lipoprotein subfractions and carotid plaque: the Northern Manhattan Study

OBJECTIVE

The objective of this cross-sectional analysis was to investigate the relation between two major high-density lipoprotein cholesterol (HDL-C) subfractions (HDL2-C and HDL3-C) and carotid plaque in a population based cohort.

METHODS

We evaluated 988 stroke-free participants (mean age 66 ± 8 years; 40% men; 66% Hispanic and 34% Non-Hispanic) with available data on HDL subfractions using precipitation method and carotid plaque area and thickness assessed by a high-resolution 2D ultrasound. The associations between HDL-C subfractions and plaque measurements were analyzed by quantile regression.

RESULTS

Plaque was present in 56% of the study population. Among those with plaque, the mean ± SD plaque area was 19.40 ± 20.46 mm² and thickness 2.30 ± 4.45 mm. The mean ± SD total HDL-C was 46 ± 14 mg/dl, HDL2-C 14 ± 8 mg/dl, and HDL3-C 32 ± 8 mg/dl. After adjusting for demographics and vascular risk factors, there was an inverse association between HDL3-C and plaque area (per mg/dl: beta = -0.26 at the 75th percentile, p = 0.001 and beta = -0.32 at the 90th percentile, p = 0.02). A positive association was observed between HDL2-C and plaque thickness (per mg/dl; beta = 0.02 at the 90% percentile, p = 0.003). HDL-C was associated with plaque area (per mg/dl: beta = -0.18 at the 90th percentile, p = 0.01), but only among Hispanics.

CONCLUSION

In our cohort we observed an inverse association between HDL3-C and plaque area and a positive association between HDL2-C and plaque thickness. HDL-C subfractions may have different contributions to the risk of vascular disease. More studies are needed to fully elucidate HDL-C anti-atherosclerotic functions in order to improve HDL-based treatments in prevention of vascular disease and stroke.

HDL and atherosclerosis: Insights from inherited HDL disorders

Plasma high density lipoproteins (HDL) comprise a highly heterogeneous family of lipoprotein particles, differing in density, size, surface charge, and lipid and protein composition. Epidemiological studies have shown that plasma HDL level inversely correlates with atherosclerotic cardiovascular disease. The most relevant atheroprotective function of HDL is to promote the removal of cholesterol from macrophages within the arterial wall and deliver it to the liver for excretion in a process called reverse cholesterol transport. In addition, HDLs can contribute to the maintenance of endothelial cell homeostasis and have potent antioxidant properties. It has been long suggested that individual HDL subclasses may differ in terms of their functional properties, but which one is the good particle remains to be defined. Inherited HDL disorders are rare monogenic diseases due to mutations in genes encoding proteins involved in HDL metabolism. These disorders are not only characterized by extremely low or high plasma HDL levels but also by an abnormal HDL subclass distribution, and thus represent a unique tool to understand the relationship between plasma HDL concentration, HDL function, and HDL-mediated atheroprotection. This article is part of a Special Issue entitled Linking transcription to physiology in lipodomics.

Association between lipids, lipoproteins composition of HDL particles and triglyceride-rich lipoproteins, and LCAT and CETP activity in post-renal transplant patients

High-density lipoprotein (HDL) remodeling within the plasma compartment and the association between lecithin-cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein (CETP) activity, and lipid, lipoprotein concentrations and composition were investigated. The aim was to examine the high sensitivity of C-reactive protein (hsCRP), lipid, apolipoprotein B (apoB), apoAI, total apoAII, apoAIInonB, apoB-containing apoAII (apoB:AII), total apoCIII, apoCIIInonB, apoB-containing apoCIII (apoB:CIII) concentration and LCAT and CETP activity to gain an insight into the association between them and LCAT and CETP, 57 post-renal transplant (Tx) patients with and without statin therapy and in 15 healthy subjects. Tx patients had moderate hypertriglyceridemia, hypercholesterolemia, and dyslipoproteinemia, disturbed triglyceride-rich lipoproteins (TRLs) and HDL composition, decreased LCAT, and slightly increased hsCRP but no CETP activity. Spearman’s correlation test showed the association between lipids and lipoproteins and LCAT or CETP, and multiple ridge stepwise forward regression showed that immunosuppressive therapy in Tx patients can disturb HDL and TRLs composition. The results suggest that inhibition or activation of LCAT is due, in part, to HDL-associated lipoprotein. Lipoprotein composition of apoAI, apoAIInonB, and apoCIIInonB in HDL particle and apoB:AII TRLs can contribute to decrease LCAT mass in Tx patients. Tx patients without statin and with lower triglycerides but higher HDL cholesterol concentration and disturbed lipoprotein composition of ApoAI and apoAII in HDL particle can decrease LCAT, increase LDL cholesterol, aggravate renal graft, and accelerate atherosclerosis and chronic heart diseases.

Measuring short-term liver metabolism non-invasively: postprandial and post-exercise ¹H and ³¹P MR spectroscopy

OBJECT

The objective of this study was to determine the effects of a standardized fat rich meal and subsequent exercise on liver fat content by ¹H MRS and on liver adenosine triphosphate (ATP) content by ³¹P MRS in healthy subjects.

MATERIALS AND METHODS

Hepatic ¹H and proton decoupled ³¹P MRS were performed on nine healthy subjects on a clinical 3.0 T MR imager three times during a day: after (1) an overnight fast, (2) a following standardized fat rich meal and (3) a subsequent exercise session. Blood parameters were followed during the day to serve as a reference to MRS.

RESULTS

Liver fat content increased gradually over the day (p = 0.0001) with an overall increase of 30 %. Also γ-NTP changed significantly over the day (p = 0.005). γ-NTP/tP decreased by 9 % (p = 0.019, post hoc) from the postprandial to the post-exercise state.

CONCLUSION

Our study shows that in vivo MRS can depict short lived physiological changes; entering of fat into liver cells and consumption of ATP during exercise can be measured non-invasively in healthy subjects. The physiological state may have an impact on fat and energy metabolite levels. Hepatic ¹H and ³¹P MRS studies should be performed under standardized conditions.

Newer therapeutic strategies to alter high-density lipoprotein level and function

Measurements of low levels of high-density lipoprotein (HDL) cholesterol have been identified as a risk factor for premature coronary artery disease, however, to date, current pharmacologic approaches for raising HDL have provided little benefit, if at all, in reducing cardiovascular outcomes. It has been shown that HDL can modify many aspects of plaque pathogenesis. Its most established role is in reverse cholesterol transportation, but HDL can also affect oxidation, inflammation, cellular adhesion, and vasodilatation. Considering these potential benefits of HDL, newer treatments have been developed to modify HDL activity, which include the use of oral cholesteryl ester transfer protein inhibitors, apolipoprotein (apo)A-I infusions, apoA-I mimetics, drugs to increase apoA-I synthesis, and agonists of the liver X receptor. These new therapies are reviewed in this article.

Egg consumption modulates HDL lipid composition and increases the cholesterol-accepting capacity of serum in metabolic syndrome

We recently demonstrated that daily whole egg consumption during moderate carbohydrate restriction leads to greater increases in plasma HDL-cholesterol (HDL-C) and improvements in HDL profiles in metabolic syndrome (MetS) when compared to intake of a yolk-free egg substitute. We further investigated the effects of this intervention on HDL composition and function, hypothesizing that the phospholipid species present in egg yolk modulate HDL lipid composition to increase the cholesterol-accepting capacity of subject serum. Men and women classified with MetS were randomly assigned to consume either three whole eggs (EGG, n = 20) per day or the equivalent amount of egg substitute (SUB, n = 17) throughout a 12-week moderate carbohydrate-restricted (25-30 % of energy) diet. Relative to other HDL lipids, HDL-cholesteryl ester content increased in all subjects, with greater increases in the SUB group. Further, HDL-triacylglycerol content was reduced in EGG group subjects with normal baseline plasma HDL-C, resulting in increases in HDL-CE/TAG ratios in both groups. Phospholipid analysis by mass spectrometry revealed that HDL became enriched in phosphatidylethanolamine in the EGG group, and that EGG group HDL better reflected sphingomyelin species present in the whole egg product at week 12 compared to baseline. Further, macrophage cholesterol efflux to EGG subject serum increased from baseline to week 12, whereas no changes were observed in the SUB group. Together, these findings suggest that daily egg consumption promotes favorable shifts in HDL lipid composition and function beyond increasing plasma HDL-C in MetS.

High-density lipoprotein cholesterol subfractions HDL2 and HDL3 are reduced in women with rheumatoid arthritis and may augment the cardiovascular risk of women with RA: a cross-sectional study

INTRODUCTION

Higher levels of high density lipoprotein (HDL) subfractions HDL3-chol and particularly HDL2-chol protect against cardiovascular disease (CVD), but inflammation reduces the HDL level and may impair its anti-atherogenic effect. Changed HDL composition through the impact of inflammation on HDL subfractions may contribute to the excess risk of CVD in rheumatoid arthritis (RA). In this study, we investigated whether HDL2-chol and HDL3-chol concentrations differ between RA patients and healthy controls, and whether these levels are related to the level of RA disease activity.

METHODS

Non-fasting blood samples were collected from 45 RA patients and 45 healthy controls. None of the participants had a history of CVD, diabetes, or used lipid-lowering drugs. HDL2-chol and HDL3-chol concentrations were obtained by ultracentrifugation. Regression modeling was used to compare HDL subfraction levels between RA patients and healthy controls, and to analyze the effect of disease activity on HDL2-chol and HDL3-chol.

RESULTS

HDL2-chol and HDL3-chol were significantly lower in RA patients compared to healthy controls (P = 0.01, P = 0.005, respectively). The HDL2:HDL3 ratio was significantly lower in patients compared to controls (P = 0.04). Reduced HDL2-chol and HDL3-chol levels were primarily present in female RA patients and not in male RA patients. A modest effect of the disease activity score in 28 joins ( DAS28) on HDL2-chol concentrations was found, after correction for disease duration, glucocorticosteroid use and body mass index (BMI), with a 0.06 mmol/L decrease with every point increase in DAS28 (P = 0.05). DAS28 did not significantly affect HDL3-chol concentrations (P = 0.186).

CONCLUSIONS

Both HDL subfractions but particularly HDL2-chol concentrations were decreased in RA, primarily in women. This seems to be associated with disease activity and is of clinical relevance. The reduction of the HDL subfraction concentrations, particularly the supposedly beneficial HDL2-chol, may negatively impact the cardiovascular risk profile of women with RA.

High-density lipoprotein subclasses and their relationship to cardiovascular disease

OBJECTIVE

To assess the clinical utility of measuring high-density lipoprotein (HDL) subfractions to assess coronary heart disease (CHD) risk.

METHODS

Literature review of 80 published investigations.

RESULTS

Measurements of HDL2b by gradient gel electrophoresis provided more consistent evidence of CHD risk than measurement of HDL2 cholesterol. Five of the seven studies that compared the extent or progression of atherosclerosis with gradient gel electrophoresis estimates of HDL subclasses (71%) assigned statistical significance to HDL2b. Ten of the 11 case-control comparisons (91%) reported lower HDL2b in cases. In contrast, of the 16 association studies relating HDL2 cholesterol and HDL3 cholesterol to extent of disease, five reported no significant relationships with either subfraction, two reported significant relationships with both HDL2 and HDL3 cholesterol, four reported significant relationships with HDL2 but not HDL3 cholesterol, and five reported relationships with HDL3 but not HDL2 cholesterol. Forty-five percent of the case-control comparisons reported that both HDL2 cholesterol and HDL3 cholesterol were significantly lower in cases than controls, 17% failed to find significance for either subfraction, and the remainder reported significantly lower values in cases for HDL2 cholesterol only (26%) or HDL3 cholesterol only (11%). On average, the case-control differences were similar for HDL2 (-0.12 ± 0.01 mmol/L) and HDL3 cholesterol (-0.10 ± 0.02 mmol/L), although relative to controls, the percent reduction was twice as great for HDL2 (-25.7 ± 2.9%) than HDL3 cholesterol (-12.1 ± 1.5%). Eight prospective studies were identified and four reported that both HDL2 and HDL3 predicted lower risk for CHD, one reported reductions in risk for HDL2 but not HDL3 cholesterol, and three reported reductions in risk for HDL3 but not HDL2 cholesterol. None of the prospective studies show that measurements of HDL cholesterol subfractions improve the identification of persons at risk.

CONCLUSIONS

HDL2 and HDL3 cholesterol do not distinguish cardioprotective differences between HDL subclasses. More extensive characterization of HDL particles by one or two dimensional gel electrophoresis, ion mobility, or ultracentrifugation may provide more specific information about CHD risk than the measurement of HDL cholesterol, HDL3 cholesterol, or HDL2 cholesterol.

Association between moderately oxidized low-density lipoprotein and high-density lipoprotein particle subclass distribution in hemodialyzed and post-renal transplant patients

Disturbances in the metabolism of lipoprotein profiles and oxidative stress in hemodialyzed (HD) and post-renal transplant (Tx) patients are proatherogenic, but elevated concentrations of plasma high-density lipoprotein (HDL) reduce the risk of cardiovascular disease. We investigated the concentrations of lipid, lipoprotein, HDL particle, oxidized low-density lipoprotein (ox-LDL) and anti-ox-LDL, and paraoxonase-1 (PON-1) activity in HD (n=33) and Tx (n=71) patients who were non-smokers without active inflammatory disease, liver disease, diabetes, or malignancy. HD patients had moderate hypertriglyceridemia, normocholesterolemia, low HDL-C, apolipoprotein A-I (apoA-I) and HDL particle concentrations as well as PON-1 activity, and increased ox-LDL and anti-ox-LDL levels. Tx patients had hypertriglyceridemia, hypercholesterolemia, moderately decreased HDL-C and HDL particle concentrations and PON-1 activity, and moderately increased ox-LDL and anti-ox-LDL levels as compared to the reference, but ox-LDL and anti-ox-LDL levels and PON-1 activity were more disturbed in HD patients. However, in both patient groups, lipid and lipoprotein ratios (total cholesterol (TC)/HDL-C, LDL-C/HDL-C, triglyceride (TG)/HDL-C, HDL-C/non-HDL-C, apoA-I/apoB, HDL-C/apoA-I, TG/HDL) were atherogenic. The Spearman's rank coefficient test showed that the concentration of ox-LDL correlated positively with HDL particle level (R=0.363, P=0.004), and negatively with TC (R=-0.306, P=0.012), LDL-C (R=-0.283, P=0.020), and non-HDL-C (R=-0.263, P=0.030) levels in Tx patients. Multiple stepwise forward regression analysis in Tx patients demonstrated that ox-LDL concentration, as an independent variable, was associated significantly positively with HDL particle level. The results indicated that ox-LDL and decreased PON-1 activity in Tx patients may give rise to more mildly-oxidized HDLs, which are less stable, easily undergo metabolic remodeling, generate a greater number of smaller pre-β-HDL particles, and thus accelerate reverse cholesterol transport, which may be beneficial for Tx patients. Further studies are necessary to confirm this.

Biological activities of HDL subpopulations and their relevance to cardiovascular disease

The concept of raising high-density lipoprotein (HDL) has been the focus of increasing attention as a strategy to reduce cardiovascular disease. HDL particles are, however, highly heterogeneous in structure, intravascular metabolism and biological activity. In this review, we describe major HDL subpopulations and discuss new findings on the antiatherogenic properties of HDL particles. Across the HDL subpopulation spectrum, small, dense, protein-rich HDLs display potent atheroprotective properties, which can be attributed to specific clusters of proteins and lipids; such activities can be compromised under conditions of atherogenic dyslipidemia. Comprehensive structural and compositional analyses of HDL may provide key information to identify subpopulations displaying specific biological functions and acquiring deficient functionality, with the potential to reveal novel biomarkers of cardiovascular risk and new pharmacological targets.

Metabolic and functional relevance of HDL subspecies

PURPOSE OF REVIEW

Our purpose is to review recent findings highlighting the metabolic and functional diversity of HDL subspecies.

RECENT FINDINGS

HDL heterogeneity - both structural and functional - is the main focus of this review. Recent work indicates that the metabolism and functionality of HDL particles differ greatly among HDL subspecies. With the introduction of new and improved methodology (e.g., proteomics), new aspects of the structural complexity and functionality of HDL have been revealed. It has been confirmed that HDL functions - including, but not limited to decreasing inflammation, apoptosis, macrophage adhesion to the endothelium and insulin resistance - are due to HDL's ability to remove cholesterol from cells (reverse cholesterol transport). A new level of HDL complexity has recently been revealed by investigating the lipid composition of HDL with gas chromatography, gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. There are about 100 different HDL-associated proteins; however, there are many more lipid species potentially associated with HDL particles.

SUMMARY

The most important recent findings disclose that HDL is more complex than previously thought. HDL subclasses differ in physical-chemical properties, protein and lipid composition, metabolism, physiological functions and pathophysiological significance. The staggering complexity of HDL demands significantly more investigation before we can truly begin to understand HDL metabolism and function in humans.

The impact of plasma triglyceride and apolipoproteins concentrations on high-density lipoprotein subclasses distribution

OBJECTIVE

To investigate the effect of triglyceride (TG) integrates with plasma major components of apolipoproteins in HDL subclasses distribution and further elicited the TG-apolipoproteins (apos) interaction in the processes of high density lipoprotein (HDL) mature metabolic and atherosclerosis related diseases.

METHODS

Contents of plasma HDL subclasses were quantities by two-dimensional gel electrophoresis associated with immunodetection in 500 Chinese subjects.

RESULTS

Contents of preβ1-HDL, HDL3a, and apoB-100 level along with apoB-100/A-I ratio were significantly increased, whereas there was a significant reduction in the contents of HDL2, apoA-I level as well as apoC-III/C-II ratio with increased TG concentration. Moreover, preβ1-HDL contents is elevated about 9 mg/L and HDL2b contents can be reduced 21 mg/L for 0.5 mmol/L increment in TG concentration. Moreover, with increase of apoA-I levels, HDL2b contents were marginally elevated in any TG concentration group. Furthermore, despite of in the apoB-100/A-I < 0.9 group, the contents of preβ1-HDL increased, and those of HDL2b decreased significantly for subjects in both high and very high TG levels compared to that in normal TG levels. Similarly, in the apoB-100/A-I ≥ 0.9 group, the distribution of HDL subclasses also showed abnormality for subjects with normal TG levels.

CONCLUSIONS

The particle size of HDL subclasses tend to small with TG levels increased which indicated that HDL maturation might be impeded and efficiency of reverse cholesterol transport(RCT) might be weakened. These data suggest that TG levels were not only significantly associated with but liner with the contents of preβ1-HDL and HDL2b. They also raise the possibility that the TG levels effect on HDL maturation metabolism are subjected to plasma apolipoproteins and apolipoproteins ratios.