Paradoxical association of enhanced cholesterol efflux with increased incident cardiovascular risks

The Gut Microbiome Affects Atherosclerosis by Regulating Reverse Cholesterol Transport

The human system's secret organ, the gut microbiome, has received considerable attention. Emerging research has yielded substantial scientific evidence indicating that changes in gut microbial composition and microbial metabolites may contribute to the development of atherosclerotic cardiovascular disease. The burden of cardiovascular disease on healthcare systems is exacerbated by atherosclerotic cardiovascular disease, which continues to be the leading cause of mortality globally. Reverse cholesterol transport is a powerful protective mechanism that effectively prevents excessive accumulation of cholesterol for atherosclerotic cardiovascular disease. It has been revealed how the gut microbiota modulates reverse cholesterol transport in patients with atherosclerotic risk. In this review, we highlight the complex interactions between microbes, their metabolites, and their potential impacts in reverse cholesterol transport. We also explore the feasibility of modulating gut microbes and metabolites to facilitate reverse cholesterol transport as a novel therapy for atherosclerosis.

Serum opacity factor normalizes erythrocyte morphology in Scarb1-/- mice in an HDL-free cholesterol-dependent way

Compared with WT mice, HDL receptor-deficient (Scarb1-/-) mice have higher plasma levels of free cholesterol (FC)-rich HDL and exhibit multiple pathologies associated with a high mol% FC in ovaries, platelets, and erythrocytes, which are reversed by lowering HDL. Bacterial serum opacity factor (SOF) catalyzes the opacification of plasma by targeting and quantitatively converting HDL to neo HDL (HDL remnant), a cholesterol ester-rich microemulsion, and lipid-free APOA1. SOF delivery with an adeno-associated virus (AAVSOF) constitutively lowers plasma HDL-FC and reverses female infertility in Scarb1-/- mice in an HDL-dependent way. We tested whether AAVSOF delivery to Scarb1-/- mice will normalize erythrocyte morphology in an HDL-FC-dependent way. We determined erythrocyte morphology and FC content (mol%) in three groups-WT, untreated Scarb1-/- (control), and Scarb1-/- mice receiving AAVSOF-and correlated these with their respective HDL-mol% FC. Plasma-, HDL-, and tissue-lipid compositions were also determined. Plasma- and HDL-mol% FC positively correlated across all groups. Among Scarb1-/- mice, AAVSOF treatment normalized reticulocyte number, erythrocyte morphology, and erythrocyte-mol% FC. Erythrocyte-mol% FC positively correlated with HDL-mol% FC and with both the number of reticulocytes and abnormal erythrocytes. AAVSOF treatment also reduced FC of extravascular tissues to a lesser extent. HDL-FC spontaneously transfers from plasma HDL to cell membranes. AAVSOF treatment lowers erythrocyte-FC and normalizes erythrocyte morphology and lipid composition by reducing HDL-mol% FC.

Proteomic Determinants of Variation in Cholesterol Efflux: Observations from the Dallas Heart Study

High-density lipoproteins (HDLs) are promising targets for predicting and treating atherosclerotic cardiovascular disease (ASCVD), as they mediate removal of excess cholesterol from lipid-laden macrophages that accumulate in the vasculature. This functional property of HDLs, termed cholesterol efflux capacity (CEC), is inversely associated with ASCVD. HDLs are compositionally diverse, associating with >250 different proteins, but their relative contribution to CEC remains poorly understood. Our goal was to identify and define key HDL-associated proteins that modulate CEC in humans. The proteomic signature of plasma HDL was quantified in 36 individuals in the multi-ethnic population-based Dallas Heart Study (DHS) cohort that exhibited persistent extremely high (>=90th%) or extremely low CEC (<=10th%) over 15 years. Levels of apolipoprotein (Apo)A-I associated ApoC-II, ApoC-III, and ApoA-IV were differentially correlated with CEC in high (r = 0.49, 0.41, and -0.21 respectively) and low (r = -0.46, -0.41, and 0.66 respectively) CEC groups (p for heterogeneity (pHet) = 0.03, 0.04, and 0.003 respectively). Further, we observed that levels of ApoA-I with ApoC-III, complement C3 (CO3), ApoE, and plasminogen (PLMG) were inversely associated with CEC in individuals within the low CEC group (r = -0.11 to -0.25 for subspecies with these proteins vs. r = 0.58 to 0.65 for subspecies lacking these proteins; p < 0.05 for heterogeneity). These findings suggest that enrichment of specific proteins on HDLs and, thus, different subspecies of HDLs, differentially modulate the removal of cholesterol from the vasculature.

Cell-free, high-density lipoprotein-specific phospholipid efflux assay predicts incident cardiovascular disease

BACKGROUNDCellular cholesterol efflux capacity (CEC) is a better predictor of cardiovascular disease (CVD) events than HDL-cholesterol (HDL-C) but is not suitable as a routine clinical assay.METHODSWe developed an HDL-specific phospholipid efflux (HDL-SPE) assay to assess HDL functionality based on whole plasma HDL apolipoprotein-mediated solubilization of fluorescent phosphatidylethanolamine from artificial lipid donor particles. We first assessed the association of HDL-SPE with prevalent coronary artery disease (CAD): study I included NIH severe-CAD (n = 50) and non-CAD (n = 50) participants, who were frequency matched for sex, BMI, type 2 diabetes mellitus, and smoking; study II included Japanese CAD (n = 70) and non-CAD (n = 154) participants. We also examined the association of HDL-SPE with incident CVD events in the Prevention of Renal and Vascular End-stage Disease (PREVEND) study comparing 340 patients with 340 controls individually matched for age, sex, smoking, and HDL-C levels.RESULTSReceiver operating characteristic curves revealed stronger associations of HDL-SPE with prevalent CAD. The AUCs in study I were as follows: HDL-SPE, 0.68; apolipoprotein A-I (apoA-I), 0.62; HDL-C, 0.63; and CEC, 0.52. The AUCs in study II were as follows: HDL-SPE, 0.83; apoA-I, 0.64; and HDL-C, 0.53. Also longitudinally, HDL-SPE was significantly associated with incident CVD events independent of traditional risk factors with ORs below 0.2 per SD increment in the PREVEND study (P < 0.001).CONCLUSIONHDL-SPE could serve as a routine clinical assay for improving CVD risk assessment and drug discovery.TRIAL REGISTRATIONClinicalTrials.gov NCT01621594.FUNDINGNHLBI Intramural Research Program, NIH (HL006095-06).

Inverse Correlation of Cholesterol Efflux Capacity with Peripheral Plaque Volume Measured by 3D Ultrasound

INTRODUCTION

Cardiovascular disease (CVD) is a systemic multifocal illness called atherosclerosis that causes artery constriction and blockage. By causing cholesterol to build up in the artery wall, hypercholesterolemia is a major factor in the pathophysiology of atherosclerotic plaque development. Reverse cholesterol transport is the process of transporting cholesterol from the periphery back to the liver through cholesterol efflux mediated by high-density lipoprotein (HDL). It was suggested that the cholesterol efflux capacity (CEC), which is inversely linked with cardiovascular risk, can serve as a stand-in measure for reverse cholesterol transport. In this work, we sought to investigate a potential link between the peripheral plaque volume (PV) and CEC.

METHODS

Since lipid-lowering therapy interferes with CEC, we performed a cross-sectional study of 176 patients (48.9% females) with one cardiovascular risk factor or known CVD that did not currently take lipid-lowering medication. CEC was determined using cAMP-treated ³H-cholesterol-labeled J774 cells. Cholesterol ester transfer protein (CETP)-mediated cholesterol ester transfer was measured by quantifying the transfer of cholesterol ester from radiolabeled exogenous HDL cholesterol to Apolipoprotein B-containing lipoproteins. PV in the carotid and the femoral artery, defined as the total PV, was measured using a 3D ultrasound system equipped with semi-automatic software.

RESULTS

In our patients, we discovered an inverse relationship between high total PV and CEC (p = 0.027). However, there was no connection between total PV and low-density lipoprotein cholesterol, lipoprotein (a), or CETP-mediated cholesterol ester transfer.

CONCLUSION

In patients not receiving lipid-lowering treatment, CEC inversely correlates with peripheral atherosclerosis, supporting its role in the pathophysiology of atherosclerosis.

HDL Function and Atherosclerosis: Reactive Dicarbonyls as Promising Targets of Therapy

Epidemiologic studies detected an inverse relationship between HDL (high-density lipoprotein) cholesterol (HDL-C) levels and atherosclerotic cardiovascular disease (ASCVD), identifying HDL-C as a major risk factor for ASCVD and suggesting atheroprotective functions of HDL. However, the role of HDL-C as a mediator of risk for ASCVD has been called into question by the failure of HDL-C-raising drugs to reduce cardiovascular events in clinical trials. Progress in understanding the heterogeneous nature of HDL particles in terms of their protein, lipid, and small RNA composition has contributed to the realization that HDL-C levels do not necessarily reflect HDL function. The most examined atheroprotective function of HDL is reverse cholesterol transport, whereby HDL removes cholesterol from plaque macrophage foam cells and delivers it to the liver for processing and excretion into bile. Indeed, in several studies, HDL has shown inverse associations between HDL cholesterol efflux capacity and ASCVD in humans. Inflammation plays a key role in the pathogenesis of atherosclerosis and vulnerable plaque formation, and a fundamental function of HDL is suppression of inflammatory signaling in macrophages and other cells. Oxidation is also a critical process to ASCVD in promoting atherogenic oxidative modifications of LDL (low-density lipoprotein) and cellular inflammation. HDL and its proteins including apoAI (apolipoprotein AI) and PON1 (paraoxonase 1) prevent cellular oxidative stress and LDL modifications. Importantly, HDL in humans with ASCVD is oxidatively modified rendering HDL dysfunctional and proinflammatory. Modification of HDL with reactive carbonyl species, such as malondialdehyde and isolevuglandins, dramatically impairs the antiatherogenic functions of HDL. Importantly, treatment of murine models of atherosclerosis with scavengers of reactive dicarbonyls improves HDL function and reduces systemic inflammation, atherosclerosis development, and features of plaque instability. Here, we discuss the HDL antiatherogenic functions in relation to oxidative modifications and the potential of reactive dicarbonyl scavengers as a therapeutic approach for ASCVD.

Relationship between circulating adipokines and cholesterol efflux in subjects with severe carotid atherosclerosis

AIMS

Cholesterol efflux capacity (CEC) as a measure of high-density lipoprotein functionality is independently and inversely associated with increased risk of cardiovascular events and mortality, and advanced plaque morphology. Adipokines, adipose tissue-derived factors, can influence systemic lipoprotein metabolism, and participate in the regulation of vascular function and inflammation. We aimed to investigate the association between CEC and circulating adipokine levels (anti-inflammatory adiponectin, and pro-inflammatory chemerin and resistin) in subjects with severe carotid atherosclerotic disease and evaluate its impact on post-surgical outcomes.

METHODS AND RESULTS

This is a cross-sectional study with a 5-year follow-up component. Consecutive patients with severe carotid atherosclerosis scheduled for a carotid endarterectomy were recruited from hospital-based centres in Montreal, Canada (n = 285). Fasting blood samples were collected pre-operatively and used to measure plasma total and high-molecular weight (HMW) adiponectin, chemerin, and resistin, and to perform cholesterol efflux assays in J774 macrophage-like cells. Five-year post-surgery outcomes were obtained through medical chart review. Subjects had a mean age of 70.1 ± 9.4, were 67.0 % male, had various comorbidities (hypercholesterolemia [85.3 %], hypertension [83.5 %], type 2 diabetes [34.5 %], coronary artery disease [38.6 %]), and previously experienced cerebrovascular symptomatology (77.9 %). CEC was independently and positively associated with total and HMW adiponectin levels (ß [95 % confidence interval]; 0.216 [0.134-0.298] and 0.107 [0.037-0.176], respectively) but not with chemerin or resistin. Total adiponectin had the greatest association accounting for 8.3 % of the variance in CEC. Interaction regression models demonstrated a significant interaction between adiponectin and chemerin in increasing CEC. Notably, with each unit increase in CEC there was a 93.9 % decrease in the odds of having an ischemic cerebrovascular event 5 years post-surgery (0.061 [0.007-0.561]).

CONCLUSIONS

Our findings demonstrated circulating adiponectin to have a strong association with increased CEC in subjects with severe carotid atherosclerosis and high CEC to be associated with more favourable post-surgical outcomes. These findings reflect the importance of adipose tissue health in influencing CEC levels and atherosclerotic cardiovascular disease risk.

KLKB1 and CLSTN2 are associated with HDL-mediated cholesterol efflux capacity in a genome-wide association study

BACKGROUND AND AIMS

HDL-mediated cholesterol efflux capacity (CEC) may protect from cardiovascular disease. Thus, we aimed to identify its genetic and non-genetic determinants.

METHODS

We measured CEC to 2% apolipoprotein B-depleted serum using BODIPY-cholesterol and cAMP-stimulated J774A.1 macrophages using serum samples from 4,981 participants in the German Chronic Kidney Disease (GCKD) study. Variance of CEC explained by clinical and biochemical parameters in a multivariable linear regression model was calculated by proportional marginal variance decomposition. A genome-wide association study with 7,746,917 variants was performed based on an additive genetic model. The main model was adjusted for age, sex and principal components 1-10. Further models were selected for sensitivity analysis and to reduce residual variance by known CEC pathways.

RESULTS

Variables that explained 1% and more of the variance of CEC were concentrations of triglycerides (12.9%), HDL-cholesterol (11.8%), LDL-cholesterol (3.0%), apolipoprotein A-IV (2.8%), PCSK9 (1.0%), and eGFR (1.0%). The KLKB1 (chr4) and APOE/C1 (chr19) loci were genome-wide significantly (p < 5x10-8) associated with CEC in our main model (p = 8.8x10-10 and p = 3.3x10-10, respectively). KLKB1 remained significantly associated after additional adjustment for either kidney parameters, HDL-cholesterol, triglycerides or apolipoprotein A-IV concentrations, while the APOE/C1 locus was not significantly associated anymore after adjustment for triglycerides. Adjustment for triglycerides also revealed an association with the CLSTN2 locus (chr3; p = 6.0x10-9).

CONCLUSIONS

We identified HDL-cholesterol and triglycerides as the main determinants of CEC. Furthermore, we newly found a significant association of CEC with the KLKB1 and the CLSTN2 locus and confirmed the association with the APOE/C1 locus, likely mediated by triglycerides.

Compositional and functional properties of high-density lipoproteins in relation to coronary in-stent restenosis

INTRODUCTION

In-stent restenosis (ISR) is an unfavorable outcome that occurs in patients after coronary stenting. Use of drugs such as statins as well as drug-eluting stents has only been partially effective in reducing the rate of ISR. Since low high-density lipoprotein cholesterol (HDL-C) concentration is a pivotal cardiovascular disease risk factor, this study aimed to evaluate the compositional and functional alterations of HDL in individuals with ISR.

MATERIAL AND METHODS

This case-control study included 21 ISR, 26 non-ISR (NISR), 16 angiography-negative, and 18 healthy subjects. Serum HDL2 (d: 1.063-1.125 g/ml) and HDL3 (d: 1.125-1.210 g/ml) subfractions were extracted from each subject using sequential ultracentrifugation. The capacity of HDL to efflux cellular cholesterol from lipid-loaded macrophages as well as to take up free cholesterol (FC) from triglyceride-rich lipoproteins (TGRLs) during lipolysis was assessed.

RESULTS

No difference was found in the HDL2 and HDL3 content of free cholesterol and total protein among the groups. The NISR group showed lower triglyceride content in HDL2 and higher phospholipid content in HDL3 relative to healthy subjects. Strong positive correlations were found between the cholesterol efflux capacity (CEC) of HDL2 and its phospholipid content in the healthy (r = 0.50), angiography-negative (r = 0.55) and ISR (r = 0.52) groups. The capacity of apolipoprotein B (apoB)-depleted serum to take up free cholesterol was not different among the groups.

CONCLUSIONS

Despite some compositional alterations, the capacity of HDL to efflux cholesterol from lipid-loaded macrophages as well as to take up free cholesterol from TGRLs during lipolysis was not associated with ISR in this study.

Predictive value of HDL function in patients with coronary artery disease: relationship with coronary plaque characteristics and clinical events

BACKGROUND

HDL is endowed with several metabolic, vascular, and immunoinflammatory protective functions. Among them, a key property is to promote reverse cholesterol transport from cells back to the liver. The aim of this study was to estimate the association of scavenger receptor class B type I (SR-BI)- and ATP binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux (the two major routes for cholesterol efflux to HDL) with the presence, extent, and severity of coronary artery disease (CAD), vascular wall remodelling processes, coronary plaque characteristics, and the incidence of myocardial infarction in the different subgroups of patients from the CAPIRE study.

METHODS

Patients (n = 525) from the CAPIRE study were divided into two groups: low-risk factors (RF), with 0-1 RF (n = 263), and multiple-RF, with ≥2 RFs; within each group, subjects were classified as no-CAD or CAD based on the segment involvement score (SIS) evaluated by coronary computed tomography angiography (SIS = 0 and SIS > 5, respectively). SR-BI- and ABCA1-mediated cholesterol efflux were measured using the plasma of all patients.

RESULTS

SR-BI-mediated cholesterol efflux was significantly reduced in patients with CAD in both the low-RF and multiple-RF groups, whereas ABCA1-mediated cholesterol efflux was similar among all groups. In CAD patients, multivariable analysis showed that SR-BI-mediated cholesterol efflux <25^th percentile predicted cardiovascular outcome (odds ratio 4.1; 95% CI: 1.3-13.7; p = .019), whereas ABCA-1-mediated cholesterol efflux and HDL-C levels significantly did not. Despite this finding, reduced SR-BI-mediated cholesterol efflux was not associated with changes in high-risk plaque features or changes in the prevalence of elevated total, non-calcified, and low-attenuation plaque volume.

CONCLUSION

SR-BI-mediated cholesterol efflux capacity is lower in patients with diffuse coronary atherosclerosis. In addition, a lower SR-BI-mediated cholesterol efflux capacity is associated with the worst clinical outcomes in patients with CAD, independently of atherosclerotic plaque features. Key MessagesIncreased cholesterol efflux capacity, an estimate of HDL function, is associated with a reduced CVD risk, regardless of HDL-C levels.HDL-C levels are significantly lower in patients with CAD.Lower SR-BI-mediated cholesterol efflux capacity is observed in patients with diffuse coronary atherosclerosis and is associated with the worst clinical outcomes in patients with CAD, independently of atherosclerotic plaque features.

Systemic consequences of abnormal cholesterol handling: Interdependent pathways of inflammation and dyslipidemia

Metabolic conditions such as obesity and associated comorbidities are increasing in prevalence worldwide. In chronically inflamed pathologies, metabolic conditions are linked to early onset cardiovascular disease, which remains the leading cause of death despite decades of research. In recent years, studies focused on the interdependent pathways connecting metabolism and the immune response have highlighted that dysregulated cholesterol trafficking instigates an overactive, systemic inflammatory response, thereby perpetuating early development of cardiovascular disease. In this review, we will discuss the overlapping pathways connecting cholesterol trafficking with innate immunity and present evidence that cholesterol accumulation in the bone marrow may drive systemic inflammation in chronically inflamed pathologies. Lastly, we will review the current therapeutic strategies that target both inflammation and cholesterol transport, and how biologic therapy restores lipoprotein function and mitigates the immune response.

Differential Effects of Genetically Determined Cholesterol Efflux Capacity on Coronary Artery Disease and Ischemic Stroke

Background

Observational studies indicated that cholesterol efflux capacity (CEC) of high-density lipoprotein (HDL) is inversely associated with cardiovascular events, independently of the HDL cholesterol concentration. The aim of the study is to examine the casual relevance of CEC for coronary artery disease (CAD) and myocardial infarction (MI), and compare it with that for ischemic stroke and its subtypes using a Mendelian randomization approach.

Methods

We performed a 2-sample Mendelian randomization to estimate the casual relationship of CEC with the risk of CAD, MI, and ischemic stroke. A CEC-related genetic variant (rs141622900) and other five genetic variants were used as the instrumental variables. Association of genetic variants with CAD were estimated in a GWAS involving 60,801 CAD cases and 123,504 controls. They were then compared with the associations of these variants with ischemic stroke and its subtypes (large vessel, small vessel, and cardioembolic) involving 40,585 ischemic stroke cases and 406,111 controls.

Results

Using the SNP of rs141622900 as the instrument, a 1-SD increase in CEC was associated with 45% lower risk for CAD (odds ratio [OR] 0.55, 95% confidence interval [CI] 0.44–0.69, p < 0.001) and 33% lower risk for MI (odds ratio [OR] 0.67, 95% CI 0.52–0.87, p = 0.002). By contrast, the causal effect of CEC was much weaker for ischemic stroke (odds ratio [OR] 0.79, 95% CI 0.64–0.97, p = 0.02; p for heterogeneity = 0.03) and, in particular, for cardioembolic stroke (p for heterogeneity = 0.006) when compared with that for CAD. Results using five genetic variants as the instrument also indicated consistently weaker effects on ischemic stroke than on CAD.

Conclusion

Genetic predicted higher CEC may be associated with decreased risk of CAD. However, the casual association of CEC with ischemic stroke and specific subtypes would need to be validated in further Mendelian randomization studies.

High-density lipoprotein cholesterol efflux capacity and incidence of coronary artery disease and cardiovascular mortality: a systematic review and meta-analysis

Background

The preventive effect of cholesterol efflux capacity (CEC) on the progression of atherosclerotic lesions has been confirmed in animal models, but findings in the population are inconsistent. Therefore, this meta-analysis aimed to systematically investigate the relationship of CEC with coronary artery disease (CAD) and cardiovascular mortality in a general population.

Methods

Four electronic databases (PubMed, Embase database, Cochrane Library, Web of Science) were searched from inception to February 1st, 2022 for relevant studies, without any language restriction. For continuous variables, the mean and standard deviation (SD), maximum adjusted odds ratios (ORs), relative risks (RRs), or hazard ratios (HRs) and 95% confidence intervals (CIs) were extracted. The random-effects model was adopted to calculate the pooled results, and dose-response analyses were conducted. All pooled results were expressed by standardized mean difference (SMD) and ORs.

Results

Finally, 18 observational studies were included. Compared with the non-CAD group, the CAD group (SMD -0.48, 95% CI − 0.66 to − 0.30; I² 88.9%) had significantly lower CEC. In the high-CEC population, the risks of CAD (OR 0.52, 95% CI 0.37 to 0.71; I² 81%) significantly decreased, and a linear negative dose-response was detected. However, an association between CEC and the risk of cardiovascular mortality was not found (OR 0.44, 95% CI 0.18 to 1.06; I² 83.2%).

Conclusions

This meta-analysis suggests that decreased CEC is strongly associated with the risk of CAD, independent of HDL-C level. However, a decreased CEC seems not to be related to cardiovascular mortality. Meanwhile, CEC is linearly negatively correlated with the risk of CAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01657-3.

Serum Cholesterol Efflux Capacity in Age-Related Macular Degeneration and Polypoidal Choroidal Vasculopathy

Purpose

To investigate serum cholesterol efflux capacity (the ability of the serum to accept cholesterol) and factors that regulate it using nuclear magnetic resonance-quantified measures of lipoprotein particle composition and size and apolipoproteins metrics in patients with age-related macular degeneration (AMD).

Design

Case-control study.

Participants

Four hundred two serum samples from 80 patients with early AMD (eAMD), and 212 patients with neovascular AMD (nAMD), including 80 with typical nAMD (tAMD) and 132 with polypoidal choroidal vasculopathy (PCV), and 110 age- and gender matched control participants.

Methods

Serum from participants showed cholesterol efflux capacity measured using in vitro cell assays and lipoprotein subfractions measured using nuclear magnetic resonance (Nightingale, Ltd). Associations between cholesterol efflux capacity (measured in percentage) and lipid subfractions were investigated in the patients and control participants.

Main Outcome Measures

Cholesterol efflux capacity and lipid subfractions in control, eAMD, and nAMD. Associations between HDL subfractions and cholesterol efflux capacity.

Results

Cholesterol efflux capacity was higher in patients with eAMD (68.0 ± 11.3% [mean ± standard deviation]) and nAMD (75.9 ± 27.7%) than in the control participants (56.9 ± 16.7%) after adjusting for age, gender, and use of lipid-lowering drug (P < 0.0001). Nuclear magnetic resonance lipidomics demonstrated that the mean diameter of HDL was larger both in eAMD (9.96 ± 0.27 mm [mean ± standard deviation]) and PCV (9.97 ± 0.23 mm) compared with that of the control participants (9.84 ± 0.24 mm; P = 0.0001 for both). Among the 28 HDL subfractions, most of the small, medium, and large HDLs, but none of the 7 extra large HDLs fractions, were associated moderately with cholesterol efflux capacity in eAMD and PCV (R = 0.149-0.277).

Conclusions

Serum cholesterol efflux capacity was increased in eAMD and PCV, but not tAMD, possibly reflecting differential underlying pathophysiologic features of lipid dysregulation in tAMD and PCV. Further studies should be directed toward investigating the diverse biological activities of HDL in AMD, including macular pigment transport, regulation of inflammation, and local cholesterol transport system.

HDL Is Not Dead Yet

High-density lipoprotein cholesterol (HDL-C) levels are inversely correlated with coronary heart disease (CHD) in multiple epidemiological studies, but whether HDL is causal or merely associated with CHD is unclear. Recent trials for HDL-raising drugs were either not effective in reducing CHD events or, if beneficial in reducing CHD events, were not conclusive as the findings could be attributed to the drugs’ LDL-reducing activity. Furthermore, the first large Mendelian randomization study did not causally relate HDL-C levels to decreased CHD. Thus, the hypothesis that HDL is protective against CHD has been rightfully challenged. However, subsequent Mendelian randomization studies found HDL characteristics that are causally related to decreased CHD. Many aspects of HDL structure and function, especially in reverse cholesterol transport, may be better indicators of HDL’s protective activity than simply measuring HDL-C. Cholesterol efflux capacity is associated with lower levels of prevalent and incident CHD, even after adjustment for HDL-C and apolipoprotein A-1 levels. Also, subjects with very high levels of HDL-C, including those with rare mutations that disrupt hepatic HDL uptake and reverse cholesterol transport, may be at higher risk for CHD than those with moderate levels. We describe here several cell-based and cell-free in vitro assays of HDL structure and function that may be used in clinical studies to determine which of HDL’s functions are best associated with protection against CHD. We conclude that the HDL hypothesis may need revision based on studies of HDL structure and function, but that the HDL hypothesis is not dead yet.

Cholesterol Efflux Capacity and Its Association With Adverse Cardiovascular Events: A Systematic Review and Meta-Analysis

Background: Serum high-density lipoprotein cholesterol (HDL-C) levels are inversely associated with cardiovascular disease events. Yet, emerging evidence suggests that it is the functional properties of HDL, in particular, reverse cholesterol transport, which is a key protective mechanism mediating cholesterol removal from macrophage cells and reducing plaque lipid content. Cholesterol efflux capacity (CEC) measures the capacity of HDL to perform this function. A systematic review and meta-analysis were conducted to explore the association of CEC and adverse cardiovascular events.

Methods: A comprehensive literature review of Embase, PubMed, and Web of Science Core Collection from inception to September 2019 was performed for all studies that examined the association between CEC and cardiovascular outcomes. The primary outcome was adverse cardiovascular events, which were inclusive of atherosclerotic cardiovascular disease (ASCVD) or mortality.

Results: A total of 20 trials were included. Compared with low CEC levels, high CEC levels were associated with a 37% lower risk of adverse cardiovascular events (crude RR = 0.63; 95% CI, 0.52–0.76; P < 0.00001). Every SD increase of CEC was associated with a 20% lower risk of adverse cardiovascular events (HR = 0.80; 95% CI, 0.66–0.97; P = 0.02). The association remained significant after adjusting for cardiovascular risk factors, medications, and HDL-C levels (HR = 0.76; 95% CI, 0.63–0.91; P = 0.004). A significant CEC-endpoint relationship was observed (P = 0.024) such that for every 0.1 unit increase in CEC, there was a 5% reduced risk for adverse cardiovascular events (RR = 0.95; 95% CI, 0.91–0.99).

Conclusions: Higher CEC is associated with lower adverse cardiovascular outcomes. These findings warrant further research on whether CEC is merely a biomarker or a mechanism that could be targeted as a pharmacologic intervention for improving clinical outcomes.

PROSPERO Registration Number: CRD42020146681; https://www.crd.york.ac.uk/prospero/.

HDL in COVID-19 Patients: Evidence from an Italian Cross-Sectional Study

A number of studies have highlighted important alterations of the lipid profile in COVID-19 patients. Besides the well-known atheroprotective function, HDL displays anti-inflammatory, anti-oxidative, and anti-infectious properties. The aim of this retrospective study was to assess the HDL anti-inflammatory and antioxidant features, by evaluation of HDL-associated Serum amyloid A (SAA) enrichment and HDL-paraoxonase 1 (PON-1) activity, in a cohort of COVID-19 patients hospitalized at the Cardiorespiratory COVID-19 Unit of Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico of Milan. COVID-19 patients reached very low levels of HDL-c (mean ± SD: 27.1 ± 9.7 mg/dL) with a marked rise in TG (mean ± SD: 165.9 ± 62.5 mg/dL). Compared to matched-controls, SAA levels were significantly raised in COVID-19 patients at admission. There were no significant differences in the SAA amount between 83 alive and 22 dead patients for all-cause in-hospital mortality. Similar findings were reached in the case of PON-1 activity, with no differences between alive and dead patients for all-cause in-hospital mortality. In conclusion, although not related to the prediction of in-hospital mortality, reduction in HDL-c and the enrichment of SAA in HDL are a mirror of SARS-CoV-2 positivity even at the very early stages of the infection.

HDL and reverse cholesterol transport in humans and animals: Lessons from pre-clinical models and clinical studies

The ability to accept cholesterol from cells and to promote reverse cholesterol transport (RCT) represents the best characterized antiatherogenic function of HDL. Studies carried out in animal models have unraveled the multiple mechanisms by which these lipoproteins drive cholesterol efflux from macrophages and cholesterol uptake to the liver. Moreover, the influence of HDL composition and the role of lipid transporters have been clarified by using suitable transgenic models or through experimental design employing pharmacological or nutritional interventions. Cholesterol efflux capacity (CEC), an in vitro assay developed to offer a measure of the first step of RCT, has been shown to associate with cardiovascular risk in several human cohorts, supporting the atheroprotective role of RCT in humans as well. However, negative data in other cohorts have raised concerns on the validity of this biomarker. In this review we will present the most relevant data documenting the role of HDL in RCT, as assessed in classical or innovative methodological approaches.

High-density lipoproteins, reverse cholesterol transport and atherogenesis

Plasma HDL-cholesterol concentrations correlate negatively with the risk of atherosclerotic cardiovascular disease (ASCVD). According to a widely cited model, HDL elicits its atheroprotective effect through its role in reverse cholesterol transport, which comprises the efflux of cholesterol from macrophages to early forms of HDL, followed by the conversion of free cholesterol (FCh) contained in HDL into cholesteryl esters, which are hepatically extracted from the plasma by HDL receptors and transferred to the bile for intestinal excretion. Given that increasing plasma HDL-cholesterol levels by genetic approaches does not reduce the risk of ASCVD, the focus of research has shifted to HDL function, especially in the context of macrophage cholesterol efflux. In support of the reverse cholesterol transport model, several large studies have revealed an inverse correlation between macrophage cholesterol efflux to plasma HDL and ASCVD. However, other studies have cast doubt on the underlying reverse cholesterol transport mechanism: in mice and humans, the FCh contained in HDL is rapidly cleared from the plasma (within minutes), independently of esterification and HDL holoparticle uptake by the liver. Moreover, the reversibility of FCh transfer between macrophages and HDL has implicated the reverse process - that is, the transfer of FCh from HDL to macrophages - in the aetiology of increased ASCVD under conditions of very high plasma HDL-FCh concentrations.

High Free Cholesterol Bioavailability Drives the Tissue Pathologies in Scarb1-/- Mice

Objective: Overall and atherosclerosis-associated mortality is elevated in humans with very high HDL (high-density lipoprotein) cholesterol concentrations. Mice with a deficiency of the HDL receptor, Scarb1 (scavenger receptor class B type 1), are a robust model of this phenotype and exhibit several additional pathologies. We hypothesized that the previously reported high plasma concentration of free cholesterol (FC)-rich HDL in Scarb1-/- mice produces a state of high HDL-FC bioavailability that increases whole-body FC and dysfunction in multiple tissue sites. Approach and Results: The higher mol% FC in Scarb1-/- versus WT (wild type) HDL (41.1 versus 16.0 mol%) affords greater FC bioavailability for transfer to multiple sites. Plasma clearance of autologous HDL-FC mass was faster in WT versus Scarb1-/- mice. FC influx from Scarb1-/- HDL to LDL (low-density lipoprotein) and J774 macrophages was greater ([almost equal to]4x) than that from WT HDL, whereas FC efflux capacity was similar. The higher mol% FC of ovaries, erythrocytes, heart, and macrophages of Scarb1-/- versus WT mice is associated with previously reported female infertility, impaired cell maturation, cardiac dysfunction, and atherosclerosis. The FC contents of other tissues were similar in the two genotypes, and these tissues were not associated with any overt pathology. In addition to the differences between WT versus Scarb1-/- mice, there were many sex-dependent differences in tissue-lipid composition and plasma FC clearance rates. Conclusions: Higher HDL-FC bioavailability among Scarb1-/- versus WT mice drives increased FC content of multiple cell sites and is a potential biomarker that is mechanistically linked to multiple pathologies.

The Capacity of APOB-Depleted Plasma in Inducing ATP-Binding Cassette A1/G1-Mediated Macrophage Cholesterol Efflux-But Not Gut Microbial-Derived Metabolites-Is Independently Associated with Mortality in Patients with ST-Segment Elevation Myocardial Infarction

Impaired HDL-mediated macrophage cholesterol efflux and higher circulating concentrations of trimethylamine N-oxide (TMAO) levels are independent risk factors for cardiovascular mortality. The TMAO precursors, γ-butyrobetaine (γBB) and Trimethyllysine (TML), have also been recently associated with cardiovascular death, but their interactions with HDL-mediated cholesterol efflux remain unclear. We aimed to determine the associations between APOB depleted plasma-mediated macrophage cholesterol efflux and plasma TMAO, γBB, and TML concentrations and explore their association with two-year follow-up mortality in patients with acute ST-elevation myocardial infarction (STEMI) and unstable angina (UA). Baseline and ATP-binding cassette transporter ABCA1 and ABCG1 (ABCA1/G1)-mediated macrophage cholesterol efflux to APOB-depleted plasma was decreased in patients with STEMI, and the latter was further impaired in those who died during follow-up. Moreover, the circulating concentrations of TMAO, γBB, and TML were higher in the deceased STEMI patients when compared with the STEMI survivors or UA patients. However, after statistical adjustment, only ABCA1/G1-mediated macrophage cholesterol efflux remained significantly associated with mortality. Furthermore, neither the TMAO, γBB, nor TML levels altered the HDL-mediated macrophage cholesterol efflux in vitro. We conclude that impaired ABCA1/G1-mediated macrophage cholesterol efflux is independently associated with mortality at follow-up in STEMI patients.

Lysis reagents, cell numbers, and calculation method influence high-throughput measurement of HDL-mediated cholesterol efflux capacity

HDL-mediated cholesterol efflux capacity (CEC) may protect against cardiovascular disease. However, CEC assays are not standardized, hampering their application in large cohorts and comparison between studies. To improve standardization, we systematically investigated technical differences between existing protocols that influence assay performance that have not been previously addressed. CEC was measured in 96-well plates using J774A.1 macrophages labeled with BODIPY-cholesterol and incubated for 4 h with 2% apolipoprotein B-depleted human serum. The time zero method, which calculates CEC using control wells, and the per-well method, which calculates CEC based on the actual content of BODIPY-cholesterol in each well, were compared in 506 samples. We showed that the per-well method had a considerably lower sample rejection rate (4.74% vs. 13.44%) and intra-assay (4.48% vs. 5.28%) and interassay coefficients of variation (two controls: 7.85%, 9.86% vs. 13.58%, 15.29%) compared with the time zero method. Correction for plate-to-plate differences using four controls on each plate also improved assay performance of both methods. In addition, we observed that the lysis reagent used had a significant effect. Compared with cholic acid, lysis with sodium hydroxide results in higher (P = 0.0082) and Triton X-100 in lower (P = 0.0028) CEC values. Furthermore, large cell seeding errors (30% variation) greatly biased CEC for both referencing methods (P < 0.0001) as measured by a resazurin assay. In conclusion, lysis reagents, cell numbers, and assay setup greatly impact the quality and reliability of CEC quantification and should be considered when this method is newly established in a laboratory.

Cholesterol efflux promoting function of high-density lipoproteins in calcific aortic valve stenosis

Background and aims

Cholesterol efflux capacity is a functional property of high-density lipoproteins (HDL) reflecting the efficiency of the atheroprotective reverse cholesterol transport process in humans. Its relationship with calcific aortic valve stenosis (CAVS) has not been fully assessed yet.

Methods

We evaluated HDL-CEC in a patient population with varying degrees of aortic valvular calcific disease, assessed using echocardiography and cardiac computed tomography. Measurement of biomarkers that reflect osteogenic and tissue remodeling, along with dietary and gut microbiota-derived metabolites were performed.

Results

Patients with moderate-severe CAVS had significantly lower HDL-CEC compared to both control and aortic sclerosis subjects (mean: 6.09%, 7.32% and 7.26%, respectively). HDL-CEC displayed negative correlations with peak aortic jet velocity and aortic valve calcium score, indexes of CAVS severity (ρ = -0.298, p = 0.002 and ρ = -0.358, p = 0.005, respectively). In multivariable regression model, HDL-CEC had independent association with aortic valve calcium score (B: -0.053, SE: 0.014, p < 0.001), GFR (B: -0.034, SE: 0.012, p = 0.007), as well as with levels of total cholesterol (B: 0.018, SE: 0.005, p = 0.002).

Conclusion

These results indicate an impairment of HDL-CEC in moderate-severe CAVS and may contribute to identify potential novel targets for CAVS management.

Cholesterol Efflux Capacity Associates with the Ankle-Brachial Index but Not All-Cause Mortality in Patients with Peripheral Artery Disease

Background: Cholesterol efflux is an important mechanism by which high-density lipoproteins (HDLs) protect against cardiovascular disease. As peripheral artery disease (PAD) is associated with high mortality rates, mainly due to cardiovascular causes, we investigated whether cholesterol efflux capacity (CEC) of apolipoprotein B (apoB)-depleted plasma, a widely used surrogate of HDL function, may serve as a predictive marker for mortality in this patient population. Methods: In this prospective single-center study (median follow-up time: 9.3 years), apoB-containing lipoproteins were precipitated from plasma of 95 patients with PAD and incubated with J744-macrophages, which were loaded with radiolabeled cholesterol. CEC was defined as the fractional radiolabel released during 4 h of incubation. Results: Baseline CEC was lower in PAD patients that currently smoked (p = 0.015) and had a history of myocardial infarction (p = 0.011). Moreover, CEC showed a significant correlation with HDL-cholesterol (p = 0.003) and apolipoprotein A-I levels (p = 0.001) as well as the ankle-brachial index (ABI, p = 0.018). However, CEC did not differ between survivors and non-survivors. Neither revealed Kaplan–Meier and Cox regression analyses any significant association of CEC with all-cause mortality rates. Conclusion: Taken together, CEC is associated with ABI but does not predict all-cause mortality in patients with PAD.

Cholesterol efflux pathways, inflammation, and atherosclerosis

Plasma levels of high-density lipoprotein (HDL) inversely correlate with the incidence of cardiovascular diseases (CVD). The causal relationship between plasma HDL-cholesterol levels and CVD has been called into question by Mendelian randomization studies and the majority of clinical trials not showing any benefit of plasma HDL-cholesterol raising drugs on CVD. Nonetheless, recent Mendelian randomization studies including an increased number of CVD cases compared to earlier studies have confirmed that HDL-cholesterol levels and CVD are causally linked. Moreover, several studies in large population cohorts have shown that the cholesterol efflux capacity of HDL inversely correlates with CVD. Cholesterol efflux pathways exert anti-inflammatory and anti-atherogenic effects by suppressing proliferation of hematopoietic stem and progenitor cells, and inflammation and inflammasome activation in macrophages. Cholesterol efflux pathways also suppress the accumulation of cholesteryl esters in macrophages, i.e. macrophage foam cell formation. Recent single-cell RNASeq studies on atherosclerotic plaques have suggested that macrophage foam cells have lower expression of inflammatory genes than non-foam cells, probably reflecting liver X receptor activation, upregulation of ATP Binding Cassette A1 and G1 cholesterol transporters and suppression of inflammation. However, when these pathways are defective lesional foam cells may become pro-inflammatory.

Impact of Dietary Lipids on the Reverse Cholesterol Transport: What We Learned from Animal Studies

Reverse cholesterol transport (RCT) is a physiological mechanism protecting cells from an excessive accumulation of cholesterol. When this process begins in vascular macrophages, it acquires antiatherogenic properties, as has been widely demonstrated in animal models. Dietary lipids, despite representing a fundamental source of energy and exerting multiple biological functions, may induce detrimental effects on cardiovascular health. In the present review we summarize the current knowledge on the mechanisms of action of the most relevant classes of dietary lipids, such as fatty acids, sterols and liposoluble vitamins, with effects on different steps of RCT. We also provide a critical analysis of data obtained from experimental models which can serve as a valuable tool to clarify the effects of dietary lipids on cardiovascular disease.

HDL in Atherosclerotic Cardiovascular Disease: In Search of a Role

For a long time, high-density lipoprotein cholesterol (HDL-C) has been regarded as a cardiovascular disease (CVD) protective factor. Recently, several epidemiological studies, while confirming low plasma levels of HDL-C as an established predictive biomarker for atherosclerotic CVD, indicated that not only people at the lowest levels but also those with high HDL-C levels are at increased risk of cardiovascular (CV) mortality. This “U-shaped” association has further fueled the discussion on the pathophysiological role of HDL in CVD. In fact, genetic studies, Mendelian randomization approaches, and clinical trials have challenged the notion of HDL-C levels being causally linked to CVD protection, independent of the cholesterol content in low-density lipoproteins (LDL-C). These findings have prompted a reconsideration of the biological functions of HDL that can be summarized with the word “HDL functionality”, a term that embraces the many reported biological activities beyond the so-called reverse cholesterol transport, to explain this lack of correlation between HDL levels and CVD. All these aspects are summarized and critically discussed in this review, in an attempt to provide a background scenario for the “HDL story”, a lipoprotein still in search of a role.

A Novel Cell-Free Fluorescent Assay for HDL Function: Low Apolipoprotein A1 Exchange Rate Associated with Increased Incident Cardiovascular Events

BACKGROUND

Cholesterol efflux capacity is a tissue culture assay for HDL function that is not amenable for high-throughput monitoring of risk assessment.

METHODS

We devised a cell-free HDL function assay to measure the exchange rate of exogenous apoA1 into serum HDL using NBD/Alexa647 double-labeled apoA1, whose NBD/Alexa647 emission ratio increased upon exchange into HDL. ApoA1 exchange rate (AER) was assayed by incubating labeled apoA1 with human serum, and the rate of the increase of the NBD/Alexa647 ratio over time was calculated as AER.

RESULTS

Fast protein liquid chromatography analysis of serum confirmed that the labeled apoA1 selectively exchanged into the HDL lipoprotein fraction. Characterization studies demonstrated that the AER assay had excellent intra- and inter-day reproducibility, was stable over 3 freeze-thaw cycles, and yielded similar results with serum or plasma. We quantified AER in serum from randomly selected stable subjects undergoing elective diagnostic coronary angiography (n = 997). AER was correlated with HDL-cholesterol (r = 0.58, P < 0.0001) and apoA1 levels (r = 0.56, P < 0.0001). Kaplan-Meier survival plot showed subjects in the lowest quartile of AER experienced a significantly higher rate of incident major adverse cardiovascular events (MACE = myocardial infarction, stroke, or death) (P < 0.0069 log rank). Moreover, compared to subjects in the lowest AER quartile, the remaining subjects showed significantly lower incident (3 year) risk for MACE, even after adjustment for traditional risk factors and apoA1 (HR 0.58; 95% CI 0.40-0.85; P = 0.005).

CONCLUSIONS

In a prospective cohort of stable subjects undergoing elective diagnostic cardiac evaluations, low AER was associated with increased incident risk of MACE.

HDL Dysfunctionality: Clinical Relevance of Quality Rather Than Quantity

High-density lipoproteins (HDLs) represent a class of lipoproteins very heterogeneous in structure, composition, and biological functions, which carry out reverse cholesterol transport, antioxidant, anti-inflammatory, antithrombotic, and vasodilator actions. Despite the evidence suggesting a clear inverse relationship between HDL cholesterol (HDL-c) concentration and the risk for cardiovascular disease, plasma HDL cholesterol levels do not predict the functionality and composition of HDLs. The importance of defining both the amount of cholesterol transported and lipoprotein functionality has recently been highlighted. Indeed, different clinical conditions such as obesity, diabetes mellitus type 2 (T2DM), and cardiovascular disease (CVD) can alter the HDL functionality, converting normal HDLs into dysfunctional ones, undergoing structural changes, and exhibiting proinflammatory, pro-oxidant, prothrombotic, and proapoptotic properties. The aim of the current review is to summarize the actual knowledge concerning the physical-chemical alteration of HDLs related to their functions, which have been found to be relevant in several pathological conditions associated with systemic inflammation and oxidative stress.

Optimization of gamma-aminobutyric acid production by Lactobacillus brevis PML1 in dairy sludge-based culture medium through response surface methodology

Gamma-aminobutyric acid (GABA) is a pharmaceutical, bioactive amino acid that can produce by some species of Lactic Acid Bacteria (LAB). For the first time, we evaluated the production of GABA by Lactobacillus brevis PML1 in the medium that contain the contaminant food bio-product like dairy sludge and soybean meal. GABA production was analyzed by chromatography (TLC, HPLC) and the features of fermented extract which contains this amino acid were evaluated. The results of Response Surface Methodology (RSM) of Central Composite Design (CCD) at p < .05 showed 300 ppm of GABA production in optimal treatment including 14.77% dairy sludge powder, 6.27% soybean meal, and 0.49% ammonium sulfate (32°C for 120 hr fermentation). The results of fermented extract also showed the acceptable antimicrobial, antioxidant, and toxicity (against cancer cell) properties. Also, L. brevis PML1has not shown any hemolytic or DNase activity which confirm its safety aspects. According to the results, this new culture can be used as a cheap substrate to biological production of GABA, by L. brevis PML1 in various food and pharmaceutical formulations.

Low-density lipoproteins cause atherosclerotic cardiovascular disease: pathophysiological, genetic, and therapeutic insights: a consensus statement from the European Atherosclerosis Society Consensus Panel

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(r)HDL in theranostics: how do we apply HDL's biology for precision medicine in atherosclerosis management?

High-density lipoproteins (HDL) are key players in cholesterol metabolism homeostasis since they are responsible for transporting excess cholesterol from peripheral tissues to the liver. Imbalance in this process, due to either excessive accumulation or impaired clearance, results in net cholesterol accumulation and increases the risk of cardiovascular disease (CVD). Therefore, significant effort has been focused on the development of therapeutic tools capable of either directly or indirectly enhancing HDL-guided reverse cholesterol transport (RCT). More recently, in light of the emergence of precision nanomedicine, there has been renewed research interest in attempting to take advantage of the development of advanced recombinant HDL (rHDL) for both therapeutic and diagnostic purposes. In this review, we provide an update on the different approaches that have been developed using rHDL, focusing on the rHDL production methodology and rHDL applications in theranostics. We also compile a series of examples highlighting potential future perspectives in the field.

Safety and Efficacy of Evacetrapib in Patients with Inadequately-controlled Hypercholesterolemia and High Cardiovascular Risk; A meta-analysis of Randomized Placebo-controlled Trials

BACKGROUND

Low-density lipoprotein cholesterol (LDL-C) is causally related to cardiovascular disease. Inhibition of cholesteryl ester transfer protein with Evacetrapib may provide an additional treatment option for patients who do not reach their LDL-C goal with statins or patients who cannot tolerate statins. We aimed to evaluate the safety and efficacy of Evacetrapib in patients with inadequately-controlled hypercholesterolemia and high cardiovascular risk.

METHOD

A computer literature search for PubMed, Scopus, and Science Direct was carried out from inception to 2019 and was updated from January 2019 till March 2021. We included only RCTs. Data were pooled as a mean difference in a random-effect model using the Mantel-Haenzel (M-H) method. We used Open Meta [Analyst] software (by the center of evidence-based medicine, Oxford University, UK).

RESULTS

Five studies (n = 12,937 patients) reported in five articles were included in this meta-analysis. The overall pooled estimate showed that LDL-C was significantly lower in the evacetrapib group than the placebo group (MD -34.07 mg/dL, 95% CI [-40.66, -27.49], p<0.0001). The pooled estimate showed that Apo-B was significantly lower in the evacetrapib130 mg group than the placebo group (MD -22.64 mg/dL, 95% CI [-30.70, -14.58], p<0.0001). HDL-C was significantly higher in the evacetrapib group over the placebo group (MD 93.31 mg/dL, 95% CI [56.07, 130.56], p<0.0001).

CONCLUSION

Current evidence from five RCTs (12,539 participants) suggests that evacetrapib has favorable outcomes in patients with inadequately-controlled Hypercholesterolemia and high cardiovascular risks. Evacetrapib could significantly increase the HDL and Apo-A1 levels and lower the LDL cholesterol and Apo-B levels with an acceptable safety profile.

Fetal High-Density Lipoproteins: Current Knowledge on Particle Metabolism, Composition and Function in Health and Disease

Cholesterol and other lipids carried by lipoproteins play an indispensable role in fetal development. Recent evidence suggests that maternally derived high-density lipoprotein (HDL) differs from fetal HDL with respect to its proteome, size, and function. Compared to the HDL of adults, fetal HDL is the major carrier of cholesterol and has a unique composition that implies other physiological functions. Fetal HDL is enriched in apolipoprotein E, which binds with high affinity to the low-density lipoprotein receptor. Thus, it appears that a primary function of fetal HDL is the transport of cholesterol to tissues as is accomplished by low-density lipoproteins in adults. The fetal HDL-associated bioactive sphingolipid sphingosine-1-phosphate shows strong vasoprotective effects at the fetoplacental vasculature. Moreover, lipoprotein-associated phospholipase A2 carried by fetal-HDL exerts anti-oxidative and athero-protective functions on the fetoplacental endothelium. Notably, the mass and activity of HDL-associated paraoxonase 1 are about 5-fold lower in the fetus, accompanied by an attenuation of anti-oxidative activity of fetal HDL. Cholesteryl ester transfer protein activity is reduced in fetal circulation despite similar amounts of the enzyme in maternal and fetal serum. This review summarizes the current knowledge on fetal HDL as a potential vasoprotective lipoprotein during fetal development. We also provide an overview of whether and how the protective functionalities of HDL are impaired in pregnancy-related syndromes such as pre-eclampsia or gestational diabetes mellitus.

Vasculoprotective properties of plasma lipoproteins from brown bears (Ursus arctos)

Plasma cholesterol and triglyceride (TG) levels are twice as high in hibernating brown bears (Ursus arctos) than healthy humans. Yet, bears display no signs of early stage atherosclerosis development when adult. To explore this apparent paradox, we analyzed plasma lipoproteins from the same 10 bears in winter (hibernation) and summer using size exclusion chromatography, ultracentrifugation, and electrophoresis. LDL binding to arterial proteoglycans (PGs) and plasma cholesterol efflux capacity (CEC) were also evaluated. The data collected and analyzed from bears were also compared with those from healthy humans. In bears, the cholesterol ester, unesterified cholesterol, TG, and phospholipid contents of VLDL and LDL were higher in winter than in summer. The percentage lipid composition of LDL differed between bears and humans but did not change seasonally in bears. Bear LDL was larger, richer in TGs, showed prebeta electrophoretic mobility, and had 5–10 times lower binding to arterial PGs than human LDL. Finally, plasma CEC was higher in bears than in humans, especially the HDL fraction when mediated by ABCA1. These results suggest that in brown bears the absence of early atherogenesis is likely associated with a lower affinity of LDL for arterial PGs and an elevated CEC of bear plasma.

High Density Lipoprotein Cholesterol Efflux Capacity and Atherosclerosis in Cardiovascular Disease: Pathophysiological Aspects and Pharmacological Perspectives

Over the years, the relationship between high-density lipoprotein (HDL) and atherosclerosis, initially highlighted by the Framingham study, has been revealed to be extremely complex, due to the multiple HDL functions involved in atheroprotection. Among them, HDL cholesterol efflux capacity (CEC), the ability of HDL to promote cell cholesterol efflux from cells, has emerged as a better predictor of cardiovascular (CV) risk compared to merely plasma HDL-cholesterol (HDL-C) levels. HDL CEC is impaired in many genetic and pathological conditions associated to high CV risk such as dyslipidemia, chronic kidney disease, diabetes, inflammatory and autoimmune diseases, endocrine disorders, etc. The present review describes the current knowledge on HDL CEC modifications in these conditions, focusing on the most recent human studies and on genetic and pathophysiologic aspects. In addition, the most relevant strategies possibly modulating HDL CEC, including lifestyle modifications, as well as nutraceutical and pharmacological interventions, will be discussed. The objective of this review is to help understanding whether, from the current evidence, HDL CEC may be considered as a valid biomarker of CV risk and a potential pharmacological target for novel therapeutic approaches.

Intracoronary monocyte expression pattern and HDL subfractions after non-ST elevation myocardial infarction

AIMS

Coronary artery disease (CAD) is described as a range of clinical conditions including myocardial infarction (MI) and unstable angina. Lipid and apolipoprotein profiles together with the study of cholesterol deposit and efflux serve to identify novel pre and post infarct scenarios for the treatment of these patients. In (non-ST elevation myocardial infarction) NSTEMI patients, we analysed both systemic and intracoronary serum ability to accept cholesterol as well as cholesterol efflux capacity (CEC) of monocytes in terms of expression of genes involved in the reverse cholesterol transport (RCT).

METHODS AND RESULTS

While HDL-C quantity was similar between systemic and coronary arterial blood, in 21 NSTEMI patients we observed a significant reduction of the preβ-HDL fraction and the levels of Apolipoproteins AI, AII, B and E in coronary versus systemic serum. These data are complemented with the observed reduction of CEC. On the contrary, compared to systemic arterial monocytes, in coronary microenvironment of NSTEMI patients after myocardial infarction, the monocytes exhibited a higher mRNA expression of nuclear receptor LXRα and its targets ABCA1 and APOE, which drive cholesterol efflux capacity.

CONCLUSION

In this cross-sectional study we observe that in the immediate post infarction period, there is a spontaneous bona fide ligand-induced activation of the LXR driven cholesterol efflux capacity of intracoronary monocytes to overcome the reduced serum ability to accept cholesterol and to inhibit the post-infarction pro-inflammatory local microenvironment.

HDL particle size is increased and HDL-cholesterol efflux is enhanced in type 1 diabetes: a cross-sectional study

AIMS/HYPOTHESIS

The prevalence of atherosclerosis is increased in type 1 diabetes despite normal-to-high HDL-cholesterol levels. The cholesterol efflux capacity (CEC) of HDL is a better predictor of cardiovascular events than static HDL-cholesterol. This cross-sectional study addressed the hypothesis that impaired HDL function contributes to enhanced CVD risk within type 1 diabetes.

METHODS

We compared HDL particle size and concentration (by NMR), total CEC, ATP-binding cassette subfamily A, member 1 (ABCA1)-dependent CEC and ABCA1-independent CEC (by determining [³H]cholesterol efflux from J774-macrophages to ApoB-depleted serum), and carotid intima-media thickness (CIMT) in 100 individuals with type 1 diabetes (37.6 ± 1.2 years; BMI 26.9 ± 0.5 kg/m²) and 100 non-diabetic participants (37.7 ± 1.1 years; 27.1 ± 0.5 kg/m²).

RESULTS

Compared with non-diabetic participants, total HDL particle concentration was lower (mean ± SD 31.01 ± 8.66 vs 34.33 ± 8.04 μmol/l [mean difference (MD) -3.32 μmol/l]) in participants with type 1 diabetes. However, large HDL particle concentration was greater (9.36 ± 3.98 vs 6.99 ± 4.05 μmol/l [MD +2.37 μmol/l]), resulting in increased mean HDL particle size (9.82 ± 0.57 vs 9.44 ± 0.56 nm [MD +0.38 nm]) (p < 0.05 for all). Total CEC (14.57 ± 2.47%CEC/4 h vs 12.26 ± 3.81%CEC/4 h [MD +2.31%CEC/4 h]) was greater in participants with type 1 diabetes relative to non-diabetic participants. Increased HDL particle size was independently associated with increased total CEC; however, following adjustment for this in multivariable analysis, CEC remained greater in participants with type 1 diabetes. Both components of CEC, ABCA1-dependent (6.10 ± 2.41%CEC/4 h vs 5.22 ± 2.57%CEC/4 h [MD +0.88%CEC/4 h]) and ABCA1-independent (8.47 ± 1.79% CEC/4 h vs 7.05 ± 1.76% CEC/4 h [MD +1.42% CEC/4 h]) CEC, were greater in type 1 diabetes but the increase in ABCA1-dependent CEC was less marked and not statistically significant in multivariable analysis. CIMT was increased in participants with type 1 diabetes but in multivariable analysis it was only associated negatively with age and BMI.

CONCLUSIONS/INTERPRETATION

HDL particle size but not HDL-cholesterol level is independently associated with enhanced total CEC. HDL particle size is greater in individuals with type 1 diabetes but even after adjusting for this, total and ABCA1-independent CEC are enhanced in type 1 diabetes. Further studies are needed to understand the mechanisms underlying these effects, and whether they help attenuate progression of atherosclerosis in this high-risk group. Graphical abstract.

Cholesterol Efflux and Collateral Circulation in Chronic Total Coronary Occlusion: Effect-Circ Study

Background

The mechanism through which high‐density lipoprotein (HDL) induces cardioprotection is not completely understood. We evaluated the correlation between cholesterol efflux capacity (CEC), a functional parameter of HDL, and coronary collateral circulation (CCC). We additionally investigated whether A1BP (apoA1‐binding protein) concentration correlates with CEC and CCC.

Methods and Results

In this case‐control study, clinical and angiographic data were collected from 226 patients (mean age, 58 years; male, 72%) with chronic total coronary occlusion. CEC was assessed using a radioisotope and J774 cells, and human A1BP concentration was measured using enzyme‐linked immunosorbent assay. Differences between the good and poor CCC groups were compared, and associations between CEC, A1BP, and other variables were evaluated. Predictors of CCC were identified by multivariable logistic regression analysis. The CEC was higher in the good than in the poor CCC group (22.0±4.6% versus 20.2±4.7%; P=0.009). In multivariable analyses including age, sex, HDL‐cholesterol levels, age (odds ratio [OR], 0.96; P=0.003), and CEC (OR, 1.10; P=0.004) were identified as the independent predictors of good CCC. These relationships remained significant after additional adjustment for diabetes mellitus, acute coronary syndrome, and Gensini score. The A1BP levels were not significantly correlated with CCC (300 pg/mL and 283 pg/mL in the good CCC and poor CCC groups, respectively, P=0.25) or CEC.

Conclusions

The relationship between higher CEC and good CCC indicates that well‐functioning HDL may contribute to CCC and may be cardioprotective; this suggests that a specific function of HDL can have biological and clinical consequences.

Perimenopausal transdermal estradiol replacement reduces serum HDL cholesterol efflux capacity but improves cardiovascular risk factors

BACKGROUND

The cardiovascular (CV) safety of estrogen replacement therapy (ERT) in perimenopausal women remains uncertain. Although exogenous estrogens increase HDL cholesterol (HDL-C), estrogen-mediated effects on alternative metrics of HDL that may better predict CV risk are unknown.

OBJECTIVE

To determine the effects of transdermal ERT on HDL composition and cholesterol efflux capacity (CEC), as well as the relationships between these metrics and CV risk factors.

METHODS

Fasting plasma samples were analyzed from 101 healthy, perimenopausal women randomized to receive either transdermal placebo or transdermal estradiol (100 μg/24 h) with intermittent micronized progesterone. At baseline and after 6 months of treatment, serum HDL CEC, HDL particle concentration, HDL protein composition, insulin resistance and brachial artery flow-mediated dilatation (FMD) were measured.

RESULTS

No difference between groups was found for change in plasma HDL-C (p = 0.69). Between-group differences were found for changes in serum HDL total CEC [median change from baseline -5.4 (-17.3,+8.4)% ERT group versus +5.8 (-6.3,+16.9)% placebo group, p = 0.01] and ABCA1-specific CEC [median change from baseline -5.3 (-10.7,+6.7)% ERT group versus +7.4 (-1.5,+18.1)% placebo group, p = 0.0002]. Relative to placebo, transdermal ERT led to reductions in LDL-C (p < 0.0001) and insulin resistance (p = 0.0002). An inverse correlation was found between changes in serum HDL total CEC and FMD (β = -0.26, p = 0.004).

CONCLUSIONS

Natural menopause leads to an increase in serum HDL CEC, an effect that is abrogated by transdermal ERT. However, transdermal ERT leads to favorable changes in major CV risk factors.

Impaired cholesterol efflux capacity in patients with Helicobacter pylori infection and its relation with inflammation

BACKGROUND

Gut microorganisms are associated with atherosclerosis and related cardiovascular disease. Helicobacter pylori (H. pylori) infection is associated with dyslipidemia and inflammation contributing to the progression of atherosclerosis.

OBJECTIVE

Several studies have reported reduced HDL-C levels in H. pylori infected patients, but HDL cholesterol efflux capacity (CEC) as the most important function of HDL has not been evaluated yet.

METHODS

This cross-sectional study was conducted with 44 biopsy confirmed H. pylori patients and 43 controls. ABCA1-mediated, non-ABCA1 and total CEC were measured in ApoB-depleted serum and levels of ApoA-I, ApoB and hsCRP were estimated using ELISA technique.

RESULTS

Total and ABCA1 mediated-CEC were reduced in patients compared to controls, independent of age, sex, body mass index and HDL-C (p < 0.001), while non-ABCA1 CEC indicated no significant change between the groups. In addition, patients showed lower serum levels of ApoA-I but increased levels of hsCRP when compared to controls. Total CEC and ABCA1-mediated CEC positively correlated with ApoA-I and HDL-C, furthermore, ABCA1-mediated CEC as well as ApoA-I inversely correlated with hsCRP.

CONCLUSION

The results of the present study indicate reduced CECs in H. pylori infected patients, especially ABCA1-mediated CEC which is associated with decreased ApoA-I and increased inflammation.

High-Density Lipoprotein Carries Markers That Track With Recovery From Stroke

RATIONALE

Prospective cohort studies question the value of HDL-C (high-density lipoprotein cholesterol) for stroke risk prediction.

OBJECTIVE

Investigate the relationship between long-term functional recovery and HDL proteome and function.

METHODS AND RESULTS

Changes in HDL protein composition and function (cholesterol efflux capacity) in patients after acute ischemic stroke at 2 time points (24 hours, 35 patients; 96 hours, 20 patients) and in 35 control subjects were measured. The recovery from stroke was assessed by 3 months, the National Institutes of Health Stroke Scale and modified Rankin scale scores. When compared with control subject after adjustments for sex and HDL-C levels, 12 proteins some of which participate in acute phase response and platelet activation (APMAP [adipocyte plasma membrane-associated protein], GPLD1 [phosphate inositol-glycan specific phospholipase D], APOE [apolipoprotein E], IHH [Indian hedgehog protein], ITIH4 [inter-alpha-trypsin inhibitor chain H4], SAA2 [serum amyloid A2], APOA4 [apolipoprotein A-IV], CLU [clusterin], ANTRX2 [anthrax toxin receptor 2], PON1 [serum paraoxonase/arylesterase], SERPINA1 [alpha-1-antitrypsin], and APOF [apolipoprotein F]) were significantly (adjusted P<0.05) altered in stroke HDL at 96 hours. The first 8 of these proteins were also significantly altered at 24 hours. Consistent with inflammatory remodeling, cholesterol efflux capacity was reduced by 32% (P<0.001) at both time points. Baseline stroke severity adjusted regression model showed that changes within 96-hour poststroke in APOF, APOL1, APMAP, APOC4 (apolipoprotein C4), APOM (apolipoprotein M), PCYOX1 (prenylcysteine oxidase 1), PON1, and APOE correlate with stroke recovery scores (R2=0.38-0.73, adjusted P<0.05). APOF (R2=0.73) and APOL1 (R2=0.60) continued to significantly correlate with recovery scores after accounting for tPA (tissue-type plasminogen activator) treatment.

CONCLUSIONS

Changes in HDL proteins during early acute phase of stroke associate with recovery. Monitoring HDL proteins may provide clinical biomarkers that inform on stroke recuperation.

Facile Cholesterol Loading with a New Probe ezFlux Allows for Streamlined Cholesterol Efflux Assays

Here, we report a nanoparticle-based probe that affords facile cell labeling with cholesterol in cholesterol efflux (CE) assays. This probe, called ezFlux, was optimized through a screening of multiple nanoformulations engineered with a Förster resonance energy transfer (FRET) reporter. The physicochemical- and bio-similarity of ezFlux to standard semi-synthetic acetylated low-density lipoprotein (acLDL) was confirmed by testing uptake in macrophages, the intracellular route of degradation, and performance in CE assays. A single-step fast self-assembly fabrication makes ezFlux an attractive alternative to acLDL. We also show that CE testing using ezFlux is significantly cheaper than that performed using commercial kits or acLDL. Additionally, we analyze clinical trials that measure CE and show that ezFlux has a place in many research and clinical laboratories worldwide that use CE to assess cellular and lipoprotein function.

ABCA1 Polymorphism Is Associated With the Warfarin-Induced Aortic Stiffness After Coronary Artery Bypass Surgery in the Chinese Population

Warfarin is the most widely prescribed oral anticoagulant and is recommended for patients recovering from coronary artery bypass graft (CABG) with atrial fibrillation. Increasing evidence suggested that warfarin increased arterial stiffness in those patients. We aimed to examine the effect of warfarin therapy on aortic stiffness in patients who underwent CABG with or without postoperative warfarin treatment and explored the potential relationships of warfarin therapy with ABCA1 polymorphisms. This was a retrospect observational study of 24 patients who were continuously treated with warfarin were selected as the warfarin group and matched them by age (±3 years) and gender to 48 patients with nonuse of warfarin as the control group. The aortic stiffness, cholesterol efflux capacity, and plasma level of PIVKA-II were measured. Two ABCA1 polymorphisms were genotyped. Compared with baseline, treatment with warfarin for 1 year significantly increased the plasma level of PIVKA-II and aortic stiffness in pulse pressure and pulse wave velocity in patients after CABG. The increase of pulse wave velocity and plasma PIVKA-II level in the TT genotype was significantly greater than the CC genotype when comparing the -565C/T genotypes. The capacity of cholesterol efflux was significantly lower in the TT genotype at baseline and 1-year follow-up than the CC genotype. Postoperative treatment of warfarin for 1 year significantly increased aortic stiffness in patients who underwent CABG. ABCA1 -565C/T polymorphisms affected the cholesterol efflux capacity and were associated with the vitamin K status and the increased aortic stiffness after warfarin treatment in those patients.

Cardioprotective Properties of HDL: Structural and Functional Considerations

BACKGROUND

As Mendelian Randomization (MR) studies showed no effect of variants altering HDL-cholesterol (HDL-C) levels concerning Cardiovascular Disease (CVD) and novel therapeutic interventions aiming to raise HDL-C resulted to futility, the usefulness of HDL-C is unclear.

OBJECTIVE

As the role of HDL-C is currently doubtful, it is suggested that the atheroprotective functions of HDLs can be attributed to the number of HDL particles, and their characteristics including their lipid and protein components. Scientific interest has focused on HDL function and on the causes of rendering HDL particles dysfunctional, whereas the relevance of HDL subclasses with CVD remains controversial.

METHODS

The present review discusses changes in quality as much as in quantity of HDL in pathological conditions and the connection between HDL particle concentration and cardiovascular disease and mortality. Emphasis is given to the recently available data concerning the cholesterol efflux capacity and the parameters that determine HDL functionality, as well as to recent investigations concerning the associations of HDL subclasses with cardiovascular mortality.

RESULTS

MR studies or pharmacological interventions targeting HDL-C are not in favor of the hypothesis of HDL-C levels and the relationship with CVD. The search of biomarkers that relate with HDL functionality is needed. Similarly, HDL particle size and number exhibit controversial data in the context of CVD and further studies are needed.

CONCLUSION

There is no room for the old concept of HDL as a silver bullet,as HDL-C cannot be considered a robust marker and does not reflect the importance of HDL particle size and number. Elucidation of the complex HDL system, as well as the finding of biomarkers, will allow the development of any HDL-targeted therapy.

Anti-atherogenic Modification of Serum Lipoprotein Function in Patients with Rheumatoid Arthritis after Tocilizumab Treatment, a Pilot Study

Lipid metabolism derangement contributes to increased cardiovascular risk in Rheumatoid Arthritis (RA). It is still debated whether and how tocilizumab, an interleukin-6 receptor inhibitor used in active RA, impacts cardiovascular risk. We studied the effect of tocilizumab on the regulation of macrophage cholesterol homeostasis, measuring patient serum ability to respectively load (cholesterol loading capacity, CLC) and discharge (cholesterol efflux capacity, CEC) cells with cholesterol. Patients with RA (n = 8) were studied before and after 4 and 12 weeks of tocilizumab treatment. CLC was measured by a fluorimetric assay of intracellular cholesterol content in human macrophages and CEC was measured for the three main pathways, mediated by the transporters Scavenger Receptor class B-type I (SR-BI), ATP binding cassette-G1 (ABCG1) and -A1 (ABCA1) in specific cell models. After 12 weeks of tocilizumab treatment, serum LDL cholesterol levels were increased, while CLC was reduced. HDL cholesterol levels were unchanged, but CEC was significantly ameliorated for the SR-BI and ABCG1 pathways with respect to baseline. Tocilizumab reduces LDL pro-atherogenic potential despite increasing their serum levels and increases HDL protective activity in RA. The data of our pilot study suggest that tocilizumab regulates lipoprotein function in selected patient populations and lay the groundwork for future larger studies.