High-density lipoprotein subfractions: current views and clinical practice applications

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.

APOB100 transgenic mice exemplify how the systemic circulation content may affect the retina without altering retinal cholesterol input

Apolipoprotein B (APOB) is a constituent of unique lipoprotein particles (LPPs) produced in the retinal pigment epithelium (RPE), which separates the neural retina from Bruch's membrane (BrM) and choroidal circulation. These LPPs accumulate with age in BrM and contribute to the development of age-related macular degeneration, a major blinding disease. The APOB100 transgenic expression in mice, which unlike humans lack the full-length APOB100, leads to lipid deposits in BrM. Herein, we further characterized APOB100 transgenic mice. We imaged mouse retina in vivo and assessed chorioretinal lipid distribution, retinal sterol levels, retinal cholesterol input, and serum content as well as tracked indocyanine green-bound LPPs in mouse plasma and retina after an intraperitoneal injection. Retinal function and differentially expressed proteins were also investigated. APOB100 transgenic mice had increased serum LDL content and an additional higher density HDL subpopulation; their retinal cholesterol levels (initially decreased) became normal with age. The LPP cycling between the RPE and choroidal circulation was increased. Yet, LPP trafficking from the RPE to the neural retina was limited, and total retinal cholesterol input did not change. There were lipid deposits in the RPE and BrM, and retinal function was impaired. Retinal proteomics provided mechanistic insights. Collectively, our data suggested that the serum LDL/HDL ratio may not affect retinal pathways of cholesterol input as serum LPP load is mainly handled by the RPE, which offloads LPP excess to the choroidal circulation rather than neural retina. Different HDL subpopulations should be considered in studies linking serum LPPs and age-related macular degeneration.

Normal HDL Cholesterol Efflux and Anti-Inflammatory Capacities in Type 2 Diabetes Despite Lipidomic Abnormalities

OBJECTIVE

To assess whether, in type 2 diabetes (T2D) patients, lipidomic abnormalities in high-density lipoprotein (HDL) are associated with impaired cholesterol efflux capacity and anti-inflammatory effect, 2 pro-atherogenic abnormalities.

DESIGN AND METHODS

This is a secondary analysis of the Lira-NAFLD study, including 20 T2D patients at T0 and 25 control subjects. Using liquid chromatography/tandem mass spectrometry, we quantified 110 species of the main HDL phospholipids and sphingolipids. Cholesterol efflux capacity was measured on THP-1 macrophages. The anti-inflammatory effect of HDL was measured as their ability to inhibit the tumor necrosis factor α (TNFα)-induced expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) on human vascular endothelial cells (HUVECs).

RESULTS

The cholesterol-to-triglyceride ratio was decreased in HDL from T2D patients compared with controls (-46%, P = 0.00008). As expressed relative to apolipoprotein AI, the amounts of phosphatidylcholines, sphingomyelins, and sphingosine-1-phosphate were similar in HDL from T2D patients and controls. Phosphatidylethanolamine-based plasmalogens and ceramides (Cer) were, respectively, 27% (P = 0.038) and 24% (P = 0.053) lower in HDL from T2D patients than in HDL from controls, whereas phosphatidylethanolamines were 41% higher (P = 0.026). Cholesterol efflux capacity of apoB-depleted plasma was similar in T2D patients and controls (36.2 ± 4.3 vs 35.5 ± 2.8%, P = 0.59). The ability of HDL to inhibit the TNFα-induced expression of both VCAM-1 and ICAM-1 at the surface of HUVECs was similar in T2D patients and controls (-70.6 ± 16.5 vs -63.5 ± 18.7%, P = 0.14; and -62.1 ± 13.2 vs -54.7 ± 17.7%, P = 0.16, respectively).

CONCLUSION

Despite lipidomic abnormalities, the cholesterol efflux and anti-inflammatory capacities of HDL are preserved in T2D patients.

Association of maternal HDL2-c concentration in the first trimester and the risk of large for gestational age birth

Background

Maternal lipid levels during pregnancy are critical for fetal development. Recent studies revealed that high-density lipoprotein cholesterol (HDL-c) levels during pregnancy were negatively correlated with birthweight. High-density lipoprotein 2 cholesterol (HDL2-c) is one of the major subclasses of HDL-c, and its relationship with birthweight is unclear. Association of HDL2-c concentration in the first trimester and risk of large for gestational age (LGA) was explored.

Methods

This study recruited pregnant women who registered in Fuxing Hospital from October 2018 to January 2020, had regular obstetric examinations during pregnancy, and delivered between June 2019 and September 2020. Finally, 549 participants were recruited for the study. Maternal demographic characteristics and venous blood were collected at the 6th-14th gestational week, and serum total cholesterol (TC), triglyceride (TG), HDL-c, HDL2-c, high-density lipoprotein 3 cholesterol (HDL3-c), and low-density lipoprotein cholesterol (LDL-c) concentrations were detected. Neonatal characteristics were collected at delivery. A logistic regression model was used to explore the relationship between the first trimester HDL2-c concentration and LGA incidence. A nomogram was developed, and the performance was evaluated with a concordance index.

Results

Seventy-five mothers delivered LGA infants, and the LGA incidence was 13.66%. LGA mothers had significantly lower serum HDL-c and HDL2-c concentrations than appropriate for gestational age (AGA) mothers. A logistic regression model showed that HDL2-c concentration was negatively correlated with LGA risk (odds ratio (OR) = 0.237, 95% confidence intervals (CI): 0.099–0.567, P = 0.001) when adjusted for age, prepregnancy body mass index (BMI), and parity. A nomogram was generated using all these risk factors. The area under the curve (AUC) was 0.663 (95% CI: 0.593–0.732).

Conclusions

Maternal HDL2-c concentration in the first trimester was negatively correlated with the risk of LGA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01688-w.

The Levels of Oxidized Phospholipids in High-Density Lipoprotein During the Course of Sepsis and Their Prognostic Value

Purpose

To examine the levels of 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero phosphatidylcholine (POVPC) and 1-palmitoyl-2-glutaroyl-sn-glycero-phosphatidylcholine (PGPC) (the oxidized phosphatidylcholines) in HDL during the course of sepsis and to evaluate their prognostic value.

Materials and Methods

This prospective cohort pilot study enrolled 25 septic patients and 10 healthy subjects from 2020 to 2021. The HDLs were extracted from patient plasmas at day 1, 3 and 7 after sepsis onset and from healthy plasmas (total 81 plasma samples). These HDLs were then subjected to examining POVPC and PGPC by using an ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) system. We further measured the levels of 38 plasma cytokines by Luminex and evaluated the correlation of HDL-POVPC level with these cytokines. Patients were further stratified into survivors and non-survivors to analyze the association of HDL-POVPC level with 28-day mortality.

Results

Septic patients exhibited significant increase of HDL-POVPC at day 1, 3 and 7 after sepsis onset (POVPC-D1, p=0.0004; POVPC-D3, p=0.033; POVPC-D7, p=0.004, versus controls). HDL-PGPC was detected only in some septic patients (10 of 25) but not in healthy controls. Septic patients showed a significant change of the plasma cytokines profile. The correlation assay showed that IL-15 and IL-18 levels were positively correlated with HDL-POVPC level, while the macrophage-derived chemokine (MDC) level was negatively correlated with HDL-POVPC level. Furthermore, HDL-POVPC level in non-survivors was significantly increased versus survivors at day 1 and 3 (POVPC-D1, p=0.002; POVPC-D3, p=0.003). Area under ROC curves of POVPC-D1 and POVPC-D3 in predicting 28-day mortality were 0.828 and 0.851. POVPC-D1and POVPC-D3 were the independent risk factors for the death of septic patients (p=0.046 and 0.035).

Conclusions

HDL-POVPC was persistently increased in the course of sepsis. POVPC-D1 and POVPC-D3 were significantly correlated with 28-mortality and might be valuable to predict poor prognosis.

The Differential Effects of HDL Subpopulations on Lipoprotein Lipase (LPL)-Mediated VLDL Catabolism

High-density lipoprotein (HDL) subpopulations functional assessment is more relevant for HDL anti-atherogenic activity than cholesterol level. The aim of the study was to assess the impact of HDL-2 and HDL-3 on lipoprotein lipase (LPL)-mediated very-low-density lipoprotein (VLDL) catabolism related to hypertriglyceridemia development. VLDL and HDLs were isolated from serum by ultracentrifugation. VLDL was incubated with LPL in the absence and presence of total HDL or HDL subpopulations. Next, VLDL remnants were separated, and their composition and electrophoretic mobility was assessed. Both HDL subpopulations increased the efficiency of triglyceride lipolysis and apolipoprotein CII and CIII removal from VLDL up to ~90%. HDL-3 exerted significantly greater impact than HDL-2 on apolipoprotein E (43% vs. 18%, p < 0.001), free cholesterol (26% vs. 18%, p < 0.05) and phospholipids (53% vs. 43%, p < 0.05) removal from VLDL and VLDL remnant electrophoretic mobility (0.18 vs. 0.20, p < 0.01). A greater release of these components was also observed in the presence of total HDL with a low HDL-2/HDL-3 cholesterol ratio. Both HDL subpopulations affect VLDL composition during lipolysis, but HDL-3 exhibited a greater effect on this process. Altered composition of HDL related to significant changes in the distribution between HDL-2 and HDL-3 can influence the VLDL remnant features, affecting atherosclerosis progression.

SARS-CoV-2 spike protein removes lipids from model membranes and interferes with the capacity of high density lipoprotein to exchange lipids

Cholesterol has been shown to affect the extent of coronavirus binding and fusion to cellular membranes. The severity of Covid-19 infection is also known to be correlated with lipid disorders. Furthermore, the levels of both serum cholesterol and high-density lipoprotein (HDL) decrease with Covid-19 severity, with normal levels resuming once the infection has passed. Here we demonstrate that the SARS-CoV-2 spike (S) protein interferes with the function of lipoproteins, and that this is dependent on cholesterol. In particular, the ability of HDL to exchange lipids from model cellular membranes is altered when co-incubated with the spike protein. Additionally, the S protein removes lipids and cholesterol from model membranes. We propose that the S protein affects HDL function by removing lipids from it and remodelling its composition/structure.

Reconstituted high density lipoprotein (rHDL), a versatile drug delivery nanoplatform for tumor targeted therapy

rHDL is a synthesized drug delivery nanoplatform exhibiting excellent biocompatibility, which possesses most of the advantages of HDL. rHDL shows almost no toxicity and can be degraded to non-toxic substances in vivo. The severe limitation of the application of various antitumor agents is mainly due to their low bioavailability, high toxicity, poor stability, etc. Favorably, antitumor drug-loaded rHDL nanoparticles (NPs), which are known as an important drug delivery system (DDS), help to change the situation a lot. This DDS shows an outstanding active-targeting ability towards tumor cells and improves the therapeutic effect during antitumor treatment while overcoming the shortcomings mentioned above. In the following text, we will mainly focus on the various applications of rHDL in tumor targeted therapy by describing the properties, preparation, receptor active-targeting ability and antitumor effects of antineoplastic drug-loaded rHDL NPs.

Arylesterase activity of paraoxonase 1 (PON1) on HDL3 and HDL2: Relationship with Q192R, C-108T, and L55M polymorphisms

Background

Controversy exists regarding the role of the subfractions of high-density lipoproteins (HDL₂ and HDL₃) in cardiovascular disease. The functionality of these particles, and their protective role, is due in part to the paraoxonase 1 (PON1) presence in them. The polymorphisms rs662 (Q192R, A/G), rs854560 (L55 M, T/A), and rs705379 (C-108T) of the PON1 gene have been related to enzyme activity and, with the anti-oxidative capacity of the HDL. The objective was to determine the arylesterase PON1 activity in HDL₃ and HDL₂ and its relationship with the polymorphisms mentioned, in a young population.

Methods

The polymorphisms were determined through mini-sequencing (SnaPshot). The HDL subpopulations were separated via ionic precipitation, cholesterol was measured with enzymatic methods, and PON1 activity was measured through spectrophotometry.

Results

The results show that the PON1 polymorphisms do not influence the cholesterol in the HDL. A variation between 40.02 and 43.9 mg/dL was in all the polymorphisms without significant differences. Additionally, PON1 activity in the HDL₃ subfractions was greater (62.83 ± 20 kU/L) than with HDL₂ (35.8 ± 20.8 kU/L) in the whole population and in all the polymorphisms (p < 0.001), and it was independent of the polymorphism and differential arylesterase activity in the Q192R polymorphism (QQ > QR > RR). Thus, 115.90 ± 30.7, 88.78 ± 21.3, 65.29 ± 10.2, respectively, for total HDL, with identical behavior for HDL₃ and HDL₂.

Conclusions

PON1 polymorphisms do not influence the HDL_-c, and the PON activity is greater in the HDL₃ than in the HDL₂, independent of the polymorphism, but it is necessary to delve into the functionality of these findings in different populations.

•

PON1 polymorphisms do not influence the cholesterol in the HDL subfractions.

•

PON1 arylesterase activity in the HDL₃ subfractions was greater than with HDL₂.

•

In Q192R, L55 M and C-108T polymorphisms, PON1 activity is always higher in HDL3.

•

This study shows that healthy young people in Colombia have very low HDL cholesterol.

A homogeneous assay to determine high-density lipoprotein subclass cholesterol in serum

Existing methods to measure high-density lipoprotein cholesterol (HDL-C) subclasses (HDL₂-C and HDL₃-C) are complex and require proficiency, and thus there is a need for a convenient, homogeneous assay to determine HDL-C subclasses in serum. Here, cholesterol reactivities in lipoprotein fractions [HDL₂, HDL₃, low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL)] toward polyethylene glycol (PEG)-modified enzymes were determined in the presence of varying concentrations of dextran sulfate and magnesium nitrate. Particle sizes formed in the lipoprotein fractions were measured by dynamic light scattering. We optimized the concentrations of dextran sulfate and magnesium nitrate before assay with PEG-modified enzymes to provide selectivity for HDL₃-C. On addition of dextran sulfate and magnesium nitrate, the sizes of particles of HDL₂, LDL, and VLDL increased, but the size of HDL₃ fraction particles remained constant, allowing only HDL₃-C to participate in coupled reactions with the PEG-modified enzymes. In serum from both healthy volunteers and patients with type 2 diabetes, a good correlation was observed between the proposed assay and ultracentrifugation in the determination of HDL-C subclasses. The assay proposed here enables convenient and accurate determination of HDL-C subclasses in serum on a general automatic analyzer and enables low-cost routine diagnosis without preprocessing.

Genetic determinants of blood lipids and cerebral small vessel disease: role of high-density lipoprotein cholesterol

Blood lipids are causally involved in the pathogenesis of atherosclerosis, but their role in cerebral small vessel disease remains largely elusive. Here, we explored associations of genetic determinants of blood lipid levels, lipoprotein particle components, and targets for lipid-modifying drugs with small vessel disease phenotypes. We selected genetic instruments for blood levels of high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides, for cholesterol and triglycerides components of size-defined lipoprotein particles, and for lipid-modifying drug targets based on published genome-wide association studies (up to 617 303 individuals). Applying two-sample Mendelian randomization approaches we investigated associations with ischaemic and haemorrhagic manifestations of small vessel disease [small vessel stroke: 11 710 cases, 287 067 controls; white matter hyperintensities (WMH): 10 597 individuals; intracerebral haemorrhage: 1545 cases, 1481 controls]. We applied the inverse-variance weighted method and multivariable Mendelian randomization as our main analytical approaches. Genetic predisposition to higher HDL-C levels was associated with lower risk of small vessel stroke [odds ratio (OR) per standard deviation = 0.85, 95% confidence interval (CI) = 0.78-0.92] and lower WMH volume (β = -0.07, 95% CI = -0.12 to -0.02), which in multivariable Mendelian randomization remained stable after adjustments for LDL-C and triglycerides. In analyses of lipoprotein particle components by size, we found these effects to be specific for cholesterol concentration in medium-sized high-density lipoprotein, and not large or extra-large high-density lipoprotein particles. Association estimates for intracerebral haemorrhage were negatively correlated with those for small vessel stroke and WMH volume across all lipid traits and lipoprotein particle components. HDL-C raising genetic variants in the gene locus of the target of CETP inhibitors were associated with lower risk of small vessel stroke (OR: 0.82, 95% CI = 0.75-0.89) and lower WMH volume (β = -0.08, 95% CI = -0.13 to -0.02), but a higher risk of intracerebral haemorrhage (OR: 1.64, 95% CI = 1.26-2.13). Genetic predisposition to higher HDL-C, specifically to cholesterol in medium-sized high-density lipoprotein particles, is associated with both a lower risk of small vessel stroke and lower WMH volume. These analyses indicate that HDL-C raising strategies could be considered for the prevention of ischaemic small vessel disease but the net benefit of such an approach would need to be tested in a randomized controlled trial.

A Novel Role for CETP as Immunological Gatekeeper: Raising HDL to Cure Sepsis?

Raising HDL using cholesteryl ester transfer protein (CETP) inhibitors failed to show a clinically relevant risk reduction of cardiovascular disease in clinical trials, inviting reconsideration of the role of CETP and HDL in human physiology. Based on solid evidence from studies with isolated macrophages, rodents, and humans, we propose that a major function of CETP may be to modulate HDL in order to help resolve bacterial infections. When gram-negative bacteria invade the blood, as occurs in sepsis, Kupffer cells lose their expression of CETP to increase HDL levels. This rise in HDL prevents systemic endotoxemia by binding lipopolysaccharide and induces a systemic proinflammatory response in macrophages to mediate bacterial clearance. This raises the interesting possibility to repurpose CETP inhibitors for the treatment of sepsis.

A Standard Lipid Panel Is Insufficient for the Care of a Patient on a High-Fat, Low-Carbohydrate Ketogenic Diet

High-fat, low-carbohydrate ketogenic diets have recently become popular for weight loss and the treatment of numerous chronic diseases; however, the general medical community still expresses concern regarding the impact of high-fat diets on serum lipids and cardiovascular risk. Herein, we report on a young man who adopted a ketogenic diet to treat his inflammatory bowel disease. Incidentally, changes in his serum lipids that would be considered adverse by current standards were noted. A more critical analysis of his lipid profile suggests that the changes he experienced may not be dangerous and may, at least with regard to several parameters, represent improvements. This case study demonstrates how the manner in which lipid panels are often reported and reviewed can lead to misleading conclusions and highlights that, at least in the care of those on a ketogenic diet, more nuanced analyses of lipid subfractionations should be conducted in order for physicians to provide optimal care and clinical recommendations.

Assessing Atherosclerotic Cardiovascular Disease Risk with Advanced Lipid Testing: State of the Science

Cardiovascular disease is the number one cause of death and disability worldwide. While substantial gains have been made in reducing cardiovascular mortality, future projections suggest that we have reached a nadir and may be at an inflection point, given the rising tide of obesity and diabetes. Evaluation and management of plasma lipids is central to the prevention of atherosclerotic cardiovascular disease. Although the standard lipid panel represents a well-established platform to assess risk, this test alone can be insufficient and/or misleading. Advances in our understanding of atherosclerosis have led to the development of lipid-based biomarkers that help to discriminate the risk of cardiovascular disease when it is unclear. While these biomarkers provide novel information, their implementation into clinical medicine remains difficult given discrepancies in the literature, lack of assay standardisation, poor accessibility and high cost. However, additional measures of atherogenic lipoproteins or their surrogates may offer insight beyond the standard lipid panel, providing a more precise assessment of risk and more accurate assessment of lipid-lowering therapy.

HDL3-C is a Marker of Coronary Artery Disease Severity and Inflammation in Patients on Statin Therapy

INTRODUCTION

Low high-density lipoprotein (HDL-C) and inflammation are risk factors for coronary artery disease (CAD). However, limited data are available determining the role of HDL-C sub-particles HDL₂-C and HDL₃-C for assessing CAD severity in patients on statin therapy.

METHODS

Blood samples were obtained prior to cardiac catheterization in 304 consecutive patients with suspected CAD on statin therapy in this sub-analysis of Multi-Analyte, thrombogenic, and Genetic Markers of Atherosclerosis (MAGMA, NCT01276678) study. Detailed lipid profiling and oxidized LDL (ox-LDL) were analyzed. CAD severity was angiographically defined as severe CAD (>75% luminal diameter stenosis [LDS]) and non-severe CAD (≤75% LDS). Multi-regression analysis was performed to test for statistical significance. Receiver operator curve (ROC) analysis was performed to determine cut-point for predicting severe CAD.

RESULTS

Patients with severe CAD had a significantly lower total-HDL-C, lower HDL₃-C and higher lipoprotein(a) levels. HDL₃-C and lipoprotein(a) cholesterol [Lp(a)-C] retained statistical significance on multiple regression analysis. ROC analysis showed HDL₃-C to have a C-statistic of 0.60 (p = 0.003) and Lp(a)-C to have a C-statistic of 0.61 (p = 0.0007). Patients with HDL₃-C ≤ 33 mg/dL and Lp(a)-C > 7 mg/dL were found to have significantly elevated ox-LDL levels.

CONCLUSION

In patients on statin therapy, HDL₃-C and Lp(a)-C improve prediction of severe CAD compared to a traditional lipid panel. In addition, patients with HDL₃-C ≤ 33 mg/dL and Lp(a)-C > 7 mg/dL have greater inflammation marked by ox-LDL. Further studies are needed to evaluate the utility of these novel biomarkers in predicting CAD severity.

Core lipid, surface lipid and apolipoprotein composition analysis of lipoprotein particles as a function of particle size in one workflow integrating asymmetric flow field-flow fractionation and liquid chromatography-tandem mass spectrometry

Lipoproteins are complex molecular assemblies that are key participants in the intricate cascade of extracellular lipid metabolism with important consequences in the formation of atherosclerotic lesions and the development of cardiovascular disease. Multiplexed mass spectrometry (MS) techniques have substantially improved the ability to characterize the composition of lipoproteins. However, these advanced MS techniques are limited by traditional pre-analytical fractionation techniques that compromise the structural integrity of lipoprotein particles during separation from serum or plasma. In this work, we applied a highly effective and gentle hydrodynamic size based fractionation technique, asymmetric flow field-flow fractionation (AF4), and integrated it into a comprehensive tandem mass spectrometry based workflow that was used for the measurement of apolipoproteins (apos A-I, A-II, A-IV, B, C-I, C-II, C-III and E), free cholesterol (FC), cholesterol esters (CE), triglycerides (TG), and phospholipids (PL) (phosphatidylcholine (PC), sphingomyelin (SM), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and lysophosphatidylcholine (LPC)). Hydrodynamic size in each of 40 size fractions separated by AF4 was measured by dynamic light scattering. Measuring all major lipids and apolipoproteins in each size fraction and in the whole serum, using total of 0.1 ml, allowed the volumetric calculation of lipoprotein particle numbers and expression of composition in molar analyte per particle number ratios. Measurements in 110 serum samples showed substantive differences between size fractions of HDL and LDL. Lipoprotein composition within size fractions was expressed in molar ratios of analytes (A-I/A-II, C-II/C-I, C-II/C-III. E/C-III, FC/PL, SM/PL, PE/PL, and PI/PL), showing differences in sample categories with combinations of normal and high levels of Total-C and/or Total-TG. The agreement with previous studies indirectly validates the AF4-LC-MS/MS approach and demonstrates the potential of this workflow for characterization of lipoprotein composition in clinical studies using small volumes of archived frozen samples.

Mass spectrometry-based approaches to targeted quantitative proteomics in cardiovascular disease

Mass spectrometry-based proteomics methodology has become an important tool in elucidating some of the underlying mechanisms involved in cardiovascular disease. The present review provides details on selected important protein targets where highly selective and specific mass spectrometry-based approaches have led to important new findings and provided new mechanistic information. The role of six proteins involved in the etiology of cardiovascular disease (acetylated platelet cyclooxygenase-1, serum apolipoprotein A1, apolipoprotein C-III, serum C-reactive protein, serum high mobility group box-1 protein, insulin-like growth factor I) and their quantification has been discussed. There are an increasing number of examples where highly selective mass spectrometry-based quantification has provided new important data that could not be obtained with less labor intensive and cheaper immunoassay-based procedures. It is anticipated that these findings will lead to significant advances in a number of important issues related to the role of specific proteins in cardiovascular disease. The availability of a new generation of high-resolution high-sensitivity mass spectrometers will greatly facilitate these studies so that in the future it will be possible to analyze serum proteins of relevance to cardiovascular disease with levels of specificity and/or sensitivity that cannot be attained by immunoassay-based procedures.

Utility of high density lipoprotein particle concentration in predicting future major adverse cardiovascular events among patients undergoing angiography

BACKGROUND

HDL-C is recognized to be inversely associated with cardiovascular (CV) risk. However, attenuation of the association of HDL-C with CV risk may occur after adjustment for other lipoprotein parameters and in various disease states, especially in the setting of acute coronary syndrome (ACS). Recently, the number of HDL particles (HDL-P) has been suggested to improve CV risk prediction.

METHODS AND RESULTS

Patients (n=2999) in the Intermountain Heart Collaborative Study who underwent angiography and had lipoprotein particle measurements determined by nuclear magnetic resonance (NMR) spectroscopy were studied. Multivariable Cox hazard regression was utilized to evaluate the association of HDL-C, HDL-P, and HDL-P subclasses with future major adverse CV events (MACE: death, myocardial infarction, heart failure, and stroke). Patients averaged 64±12years, 66% male, 26% diabetic, and 42% ACS. At angiography, 65% of patients were diagnosed with coronary artery disease (CAD). HDL-C and HDL-P averaged 41±13mg/dL and 28±8μmol/L, respectively. HDL-P (HR=0.903, p=0.001), but not HDL-C (HR=0.947, p=0.102) was significantly associated with MACE. In a model that included all HDL-P subclasses, both small (HR=0.862, p<0.0001) and medium (HR=0.922, p=0.020) were associated with CV risk, but not large HDL-P (HR=1.0042, p=0.185). Small HDL-P continued to be associated with all of the individual components of MACE, but not stroke.

CONCLUSION

In this study of patients undergoing angiography, HDL-P was a strong, independent predictor of future MACE, with the smaller HDL-P accounting for this association.

High-density lipoprotein and inflammation in cardiovascular disease

Great advances are being made at the mechanistic level in the understanding of the structural and functional diversity of high-density lipoprotein (HDL). HDL particle subspecies of different sizes are now known to differ in the protein and lipid cargo they transport, conferring on them the ability to perform different functions that in aggregate would be expected to provide protection against the development of atherosclerosis and its downstream clinical consequences. Exacerbating what is already a very complex system is the finding that inflammation, via alteration of the proteomic and lipidomic composition of HDL subspecies, can modulate at least some of their functional activities. In contrast to the progress being made at the mechanistic level, HDL epidemiologic research has lagged behind, largely because the simple HDL biomarkers used (mainly just HDL cholesterol) lack the needed complexity. To address this deficiency, analyses will need to use multiple HDL subspecies and be conducted in such a way as to eliminate potential sources of confounding. To help account for the modulating influence of inflammation, effective use must also be made of inflammatory biomarkers including searching systematically for HDL-inflammation interactions. Using nuclear magnetic resonance (NMR)-measured HDL subclass data and a novel NMR-derived inflammatory biomarker, GlycA, we offer a case study example of the type of analytic approach considered necessary to advance HDL epidemiologic understanding.

Large high-density lipoprotein particle number is independently associated with microvascular function in patients with well-controlled low-density lipoprotein concentration: A vasodilator stress magnetic resonance perfusion study

BACKGROUND

Abnormalities in total cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides are associated with microvascular dysfunction. Recent studies suggest that lipid subfractions better predict atherogenic burden than a routine lipid panel. We sought to determine, whether lipid subfractions are more strongly associated with microvascular function and subclinical atherosclerosis, than conventional lipid measurements using vasodilator stress cardiovascular magnetic resonance (CMR).

METHODS

Twenty-four adults referred for risk stratification from a lipid clinic with low-density lipoprotein cholesterol (LDL-C) <100 mg/dL underwent vasodilator CMR. Time-intensity curves generated from stress and rest perfusion images were used to determine the area under the curve (AUC) for the mid-ventricular slice myocardium and the left ventricular (LV) cavity. Myocardial perfusion reserve index (MPRi) was defined as stress to rest ratio of mid-ventricular myocardium AUC, normalized to LV cavity AUC. Lipid panels that included subfractions of LDL and high-density lipoprotein (HDL) were measured using nuclear magnetic resonance testing. The association between MPRi and lipid parameters was examined using univariate linear regression; lipid components statistically correlated with MPRi (P < .05) were then subjected to multivariate analysis.

RESULTS

Univariate regression analysis showed MPRi was associated with HDL-C, triglycerides, large HDL-P, and small LDL-P; no association was found between MPRi and total cholesterol, LDL-C, total LDL-P, or total HDL-P. Using multivariate analysis, large HDL-P was independently associated with MPRi.

CONCLUSIONS

In patients with LDL-C <100 mg/dL, large HDL-P is independently associated with CMR-derived myocardial perfusion reserve, a surrogate for microvascular function and subclinical atherosclerosis. Further studies using lipid subfractions to better understand cardiovascular risks are warranted.

Serum uric acid is associated with increased risk of idiopathic venous thromboembolism in high HDL-C population: A case-control study

Many studies have indicated that metabolic disorders are positively correlated with idiopathic venous thromboembolism (VTE), whereas the risk factor serum uric acid (SUA) for idiopathic VTE has yet to be investigated. In this retrospective case-control study, 276 idiopathic VTE patients and 536 gender- and age-matched control subjects were included. The subjects in the case and control groups exhibiting common known VTE risk factors and the patients with a first VTE onset in one month were excluded. For the control group, primary and secondary VTE patients were excluded. High-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol, total cholesterol, fasting blood glucose, and current smoking were significantly associated with idiopathic VTE in the univariate analysis. Hyperuricemia was detected in 56/276 (20.29%) idiopathic patients compared with 71/536 (13.25%) in the control group. HDL-C was considered the most prominent interactive factor for SUA in idiopathic VTE by the interaction analysis. After testing for the interaction terms, SUA was closely associated with idiopathic VTE in the high HDL-C population (P=0.0026 for interaction), while there was no such correlation in the low HDL-C group. The results indicated no obvious correlation between triglyceride and hypertension to idiopathic VTE. In conclusion, SUA is closely associated with an increased risk of idiopathic VTE in the high HDL-C population. The abnormality of SUA may act as an important linkage between atherosclerosis and idiopathic VTE through HDL-C.

High-density lipoprotein subclass measurements improve mortality risk prediction, discrimination and reclassification in a cardiac catheterization cohort

BACKGROUND AND AIMS

Recent failures of HDL cholesterol (HDL-C)-raising therapies to prevent cardiovascular disease (CVD) events have tempered the interest in the role of HDL-C in clinical risk assessment. Emerging data suggest that the atheroprotective properties of HDL depend on specific HDL particle characteristics not reflected by HDL-C. The purpose of this study was to determine the association of HDL particle concentration (HDL-P) and HDL subclasses with mortality in a high-risk cardiovascular population and to examine the clinical utility of these parameters in mortality risk discrimination and reclassification models.

METHODS

Using nuclear magnetic resonance spectroscopy, we measured HDL-P and HDL subclasses in 3972 individuals enrolled in the CATHGEN coronary catheterization biorepository; tested for association with all-cause mortality in robust clinical models; and examined the utility of HDL subclasses in incremental mortality risk discrimination and reclassification.

RESULTS

Over an average follow-up of eight years, 29.6% of the individuals died. In a multivariable model adjusted for ten CVD risk factors, HDL-P [HR, 0.71 (0.67-0.76), p = 1.3e-24] had a stronger inverse association with mortality than did HDL-C [HR 0.93 (0.87-0.99), p = 0.02]. Larger HDL size conferred greater risk and the sum of medium- and small-size HDL particles (MS-HDL-P) conferred less risk. Furthermore, the strong inverse relation of HDL-P levels with mortality was accounted for entirely by MS-HDL-P; HDL-C was not associated with mortality after adjustment for MS-HDL-P. Addition of MS-HDL-P to the GRACE Risk Score significantly improved risk discrimination and risk reclassification.

CONCLUSION

HDL-P and smaller HDL subclasses were independent markers of residual mortality risk and incremental to HDL-C in a high-risk CVD population. These measures should be considered in risk stratification and future development of HDL-targeted therapies in high-risk populations.

Inverse relationship between high-density lipoprotein cholesterol raising and high-sensitivity C-reactive protein reduction in older patients treated with lipid-lowering therapy

BACKGROUND

Little is known regarding relationships between high-sensitivity C-reactive protein (hsCRP) and lipoproteins other than low-density lipoprotein cholesterol (LDL-C). High-density lipoprotein (HDL), with both anti-inflammatory and cholesterol-mediating effects, is of particular interest. This exploratory analysis assessed associations between hsCRP and lipids in older (>65 years) patients with moderate and/or high cardiovascular disease risk, before and after treatment with ezetimibe/simvastatin (E/S) or atorvastatin (ATV).

METHODS

An analysis of a multicenter, randomized, double-blind, 12-week study. Correlations were assessed in 1054 patients with both baseline and 12-week hsCRP ≤ 10 mg/L, pooled across doses of E/S (10/20 and 10/40 mg) and ATV (10, 20, and 40 mg), and combined E/S + ATV treatments. Because of multiple comparisons, observed relationships were considered significant only if P values were < .01.

RESULTS

Correlations between baseline levels of hsCRP and either LDL-C, non-HDL-C, or apolipoprotein B were weak and nonsignificant in the E/S, ATV, and E/S + ATV groups. After 12 weeks of treatment, these correlations increased slightly and significantly in all groups, except for LDL-C in the ATV group. HDL-C was significantly but inversely correlated with hsCRP in the ATV and E/S + ATV groups at baseline, and in all groups at 12 weeks. Only with HDL-C did change correlate with change in hsCRP in both the E/S and combined groups.

CONCLUSIONS

Relationships between hsCRP and lipid factors in older patients were weak at baseline and somewhat stronger after treatment. HDL-C was inversely and consistently correlated with baseline and 12-week on-treatment hsCRP and with therapy-induced changes in HDL-C and hsCRP.

Causal Role of Alcohol Consumption in an Improved Lipid Profile: The Atherosclerosis Risk in Communities (ARIC) Study

INTRODUCTION

Health benefits of low-to-moderate alcohol consumption may operate through an improved lipid profile. A Mendelian randomization (MR) approach was used to examine whether alcohol consumption causally affects lipid levels.

METHODS

This analysis involved 10,893 European Americans (EA) from the Atherosclerosis Risk in Communities (ARIC) study. Common and rare variants in alcohol dehydrogenase and acetaldehyde dehydrogenase genes were evaluated for MR assumptions. Five variants, residing in the ADH1B, ADH1C, and ADH4 genes, were selected as genetic instruments and were combined into an unweighted genetic score. Triglycerides (TG), total cholesterol, high-density lipoprotein cholesterol (HDL-c) and its subfractions (HDL2-c and HDL3-c), low-density lipoprotein cholesterol (LDL-c), small dense LDL-c (sdLDL-c), apolipoprotein B (apoB), and lipoprotein (a) (Lp(a)) levels were analyzed.

RESULTS

Alcohol consumption significantly increased HDL2-c and reduced TG, total cholesterol, LDL-c, sdLDL-c, and apoB levels. For each of these lipids a non-linear trend was observed. Compared to the first quartile of alcohol consumption, the third quartile had a 12.3% lower level of TG (p < 0.001), a 7.71 mg/dL lower level of total cholesterol (p = 0.007), a 10.3% higher level of HDL2-c (p = 0.007), a 6.87 mg/dL lower level of LDL-c (p = 0.012), a 7.4% lower level of sdLDL-c (p = 0.037), and a 3.5% lower level of apoB (p = 0.058, poverall = 0.022).

CONCLUSIONS

This study supports the causal role of regular low-to-moderate alcohol consumption in increasing HDL2-c, reducing TG, total cholesterol, and LDL-c, and provides evidence for the novel finding that low-to-moderate consumption of alcohol reduces apoB and sdLDL-c levels among EA. However, given the nonlinearity of the effect of alcohol consumption, even within the range of low-to-moderate drinking, increased consumption does not always result in a larger benefit.

High-Density Lipoproteins for Therapeutic Delivery Systems

High-density lipoproteins (HDL) are a class of natural nanostructures found in the blood and are composed of lipids, proteins, and nucleic acids (e.g. microRNA). Their size, which appears to be well-suited for both tissue penetration/retention as well as payload delivery, long circulation half-life, avoidance of endosomal sequestration, and potential low toxicity are all excellent properties to model in a drug delivery vehicle. In this review, we consider high-density lipoproteins for therapeutic delivery systems. First we discuss the structure and function of natural HDL, describing in detail its biogenesis and transformation from immature, discoidal forms, to more mature, spherical forms. Next we consider features of HDL making them suitable vehicles for drug delivery. We then describe the use of natural HDL, discoidal HDL analogs, and spherical HDL analogs to deliver various classes of drugs, including small molecules, lipids, and oligonucleotides. We briefly consider the notion that the drug delivery vehicles themselves are therapeutic, constituting entities that exhibit "theralivery." Finally, we discuss challenges and future directions in the field.

APOL1 nephropathy risk variants are associated with altered high-density lipoprotein profiles in African Americans

BACKGROUND

Two independent coding variants in the apolipoprotein L1 gene (APOL1), G1 and G2, strongly associate with nephropathy in African Americans; associations with cardiovascular disease are more controversial. Although APOL1 binds plasma high-density lipoproteins (HDLs), data on APOL1 risk variant associations with HDL subfractions are sparse.

METHODS

Two APOL1 G1 single nucleotide polymorphisms and the G2 insertion/deletion polymorphism were genotyped in 2010 Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study participants with nuclear magnetic resonance spectroscopy-based lipoprotein subfraction measurements. Linear regression was used to model associations between numbers of APOL1 G1/G2 risk variants and HDL subfractions, adjusting for demographic, clinical and ancestral covariates.

RESULTS

Female sex and higher percentage of African ancestry were positively associated with the number of APOL1 G1/G2 risk alleles. In the unadjusted analysis, mean (standard error) small HDL concentrations (μmol/L) for participants with zero, one and two G1/G2 risk alleles were 19.0 (0.2), 19.7 (0.2) and 19.9 (0.4), respectively (P = 0.02). Adjustment for age, sex, diabetes and African ancestry did not change the results but strengthened the statistical significance (P = 0.004). No significant differences in large or medium HDL, very low-density lipoprotein or low-density lipoprotein particle concentrations were observed by APOL1 genotype.

CONCLUSIONS

Greater numbers of APOL1 G1/G2 risk alleles were associated with higher small HDL particle concentrations in African Americans. These results may suggest novel areas of investigation to uncover reasons for the association between APOL1 risk variants with adverse outcomes in African Americans.

Cholesterol-overloaded HDL particles are independently associated with progression of carotid atherosclerosis in a cardiovascular disease-free population: a community-based cohort study

BACKGROUND

Cholesterol-overloaded high-density lipoprotein (HDL) particles exert a negative impact on the antiatherogenic function of HDL in experimental studies. However, it remains unclear whether cholesterol-overloaded HDL particle is involved in the development of atherosclerosis in humans.

OBJECTIVES

The objective of this study was to explore whether cholesterol-overloaded HDL particles are associated with the progression of carotid atherosclerosis in a cardiovascular disease-free population.

METHODS

Baseline HDL particle number was measured using nuclear magnetic resonance spectroscopy in 930 participants ages 45 to 74 years in a community-based cohort study. An estimate of cholesterol molecules per HDL particle (HDL-C/P ratio) was calculated as the ratio of HDL cholesterol to HDL particles. HDL-C/P ratio was categorized as <41.0 (lowest), 41.0 to 46.9, 47.0 to 52.9, and ≥53.0 (highest) using a fixed increment method. Modified Poisson regression was used to assess the association between HDL-C/P ratio and 5-year progression of carotid atherosclerosis as indicated by progression of carotid plaques and change in total plaque area (TPA).

RESULTS

Mean baseline HDL-C/P ratio was 46.4 ± 9.3 (range 23.8 to 86.9). Baseline HDL-C/P ratio was significantly associated with 5-year progression of carotid atherosclerosis. Participants with the highest HDL-C/P ratio had 1.56-fold (95% confidence interval: 1.14 to 2.13; p = 0.006) increased progression compared with those with the lowest level. Among participants without baseline plaque, TPA in re-examination was larger by 9.4 mm(2) in the subgroup with the highest level when compared with the lowest level.

CONCLUSIONS

Our findings suggest that cholesterol-overloaded HDL particles are independently associated with the progression of carotid atherosclerosis. This may explain why in recent trials raising HDL cholesterol was not beneficial. This study strongly suggests that the combination of cholesterol content and particle number determines the antiatherogenic function of HDLs, rather than either parameter alone.

Effect of pistachio consumption on plasma lipoprotein subclasses in pre-diabetic subjects

BACKGROUND AND AIMS

Nuts have been demonstrated to improve several cardiovascular risk factors and the lipid profile in diabetic and pre-diabetic subjects. However, analysis of conventional serum lipid profiles does not completely explain the atherogenic risk associated with pre-diabetes. We therefore investigated whether chronic consumption of pistachio modifies the lipoprotein subclasses to a healthier profile in pre-diabetic subjects.

METHODS AND RESULTS

Randomized cross-over clinical trial in 54 subjects with pre-diabetes. Subjects consumed a pistachio-supplemented diet (PD, 50% carbohydrates, 33% fat, including 57 g/d of pistachios daily) and a control diet (CD, 55% carbohydrates, 30% fat) for 4 months each, separated by a 2-week wash-out. Diets were isocaloric and matched for protein, fiber and saturated fatty acids. Nuclear magnetic resonance (NMR) was performed to determine changes in plasma lipoprotein subclasses. Small low-density lipoprotein particles (sLDL-P) significantly decreased after pistachio consumption compared to the nut-free diet (P = 0.023). The non-high-density lipoprotein particles (non-HDL-P i.e. VLDL-P plus LDL-P) significantly decreased under the PD compared to CD (P = 0.041). The percentage of sHDL-P increased by 2.23% after the PD compared with a reduction of 0.08% after the CD (P = 0.014). Consequently, the overall size of HDL-P significantly decreased in the PD (P = 0.007).

CONCLUSION

Chronic pistachio consumption could modify the lipoprotein particle size and subclass concentrations independently of changes in total plasma lipid profile, which may help to explain the decreased risk of cardiovascular disease and mortality associated with those individuals who frequently consumed nuts.

REGISTRATION NUMBER

This study is registered at www.clinicaltrials.gov as NCT01441921.

ABCA1 and nascent HDL biogenesis

ABCA1 mediates the secretion of cellular free cholesterol and phospholipids to an extracellular acceptor, apolipoprotein AI, to form nascent high-density lipoprotein (HDL). Thus, ABCA1 is a key molecule in cholesterol homeostasis. Functional studies of certain Tangier disease mutations demonstrate that ABCA1 has multiple activities, including plasma membrane remodeling and apoAI binding to cell surface, which participate in nascent HDL biogenesis. Recent advances in our understanding of ABCA1 have demonstrated that ABCA1also mediates unfolding the N terminus of apoAI on the cell surface, followed by lipidation of apoAI and release of nascent HDL. Although ABCA1-mediated cholesterol efflux to apoAI can occur on the plasma membrane, the role of apoAI retroendocytosis during cholesterol efflux may play a role in macrophage foam cells that store cholesterol esters in cytoplasmic lipid droplets.