HDL Cholesterol Efflux Does Not Predict Cardiovascular Risk in Hemodialysis Patients

Lipid and immunophenotypic profiles in hemodialysis patients with citrate vs. acetate dialysates

Background

Chronic kidney disease (CKD) is a significant cardiovascular (CV) risk factor, with dialysis-dependent CKD (DD-CKD) patients facing high mortality rates. Hypercholesterolemia is another crucial CV risk factor, typically managed with lipid-lowering therapy, though its efficacy in DD-CKD remains uncertain. Evidence shows mixed results regarding the benefits of statins in these patients. Citrate-based dialysates are known to reduce inflammatory biomarkers compared to acetate-based ones, potentially impacting lipid profiles and immune responses. This study aimed to determine the effects of citrate vs. acetate dialysate on lipid profiles and immunophenotypes in DD-CKD patients.

Methods

This unicentric, cross-over, prospective study included 21 hemodialysis patients (10 males, 11 females, average age 62.25 years). Each patient underwent 24 dialysis sessions (12 with each dialysate) and acted as their own control. Lipid profiles, immunological parameters, and nutritional and inflammatory markers were measured before the last session with each dialysate.

Results

After twelve dialysis sessions with citrate dialysate (CD), compared to acetate dialysate (AD), there was a statistically significant decline in TG and remnant cholesterol, with a decrease in HDL and an increase in LDL. Regarding immunology, C3 complement levels were higher, while CD3+ CD8+ and CD16+ 56+ lymphocytes were lower. Finally, total lymphocytes were lower with AD than with CD. We found no difference in predialysis nutritional nor inflammatory parameters except for ESR, which was higher when subjects used CD than AD.

Conclusion

There are significant differences in lipid and immunophenotypic profiles with CD in comparison to AD. Interestingly, there could be an advantageous profile given the reduced amount of remnant cholesterol and TG. However, further studies are needed to understand if the observed changes lead to beneficial hard clinical outcomes in DD-CKD patients.

High density lipoprotein particle size and function associate with new cardiovascular events in patients with chronic kidney disease

Chronic Kidney Disease (CKD) is a risk factor for cardiovascular disease (CVD), and patients with CKD have markedly higher CVD mortality compared to healthy controls. However, the relationship between specific lipoprotein profiles and new CV events in patients with advanced CKD and cardiovascular burden is unknown. We profiled the distribution of High density lipoprotein (HDL) size, particle concentration, and cholesterol and triglyceride content of the baseline plasma of 325 subjects with moderate CKD followed for 2.5 years using nuclear magnetic resonance (NMR) spectroscopy. We used Cox regression models controlled for various clinical factors to characterize the role of specific HDL profiles in predicting CV events in this high-risk population. The cholesterol uptake capacity of HDL from peripheral tissues- cholesterol efflux capacity (CEC) and HDL oxidation were also quantified using standardized assays. Patients with new CV events demonstrated increased HDL size, large HDL particle numbers, and CEC. Increased HDL particle size [HR = 2.56, p = 0.002], large HDL particle numbers [HR = 1.41, p = 0.001], HDL-cholesterol levels [HR = 1.03, p = 0.008], and CEC [HR = 1.46, p = 0.03] associated with CV events. Our study demonstrates that higher HDL particle size associated with new CV events in the CKD population with a high cardiovascular burden independent of CEC and HDL cholesterol. Collectively, the data strongly associate altered lipoprotein metabolism, particularly HDL metabolism, and new CV events in patients with established CKD and CVD, allowing us to risk stratify and potentially reduce mortality and morbidity in this high-risk population.

Serum HDL-C subfractions as predictors of cardiovascular calcification in hemodialysis patients: novel insights and clinical implications

Objective

This study aims to explore the relationship between cardiovascular calcification (CVC) and serum levels of high-density lipoprotein cholesterol (HDL-C) and its subfractions in hemodialysis (HD) patients.

Methods

HD patients and healthy participants were recruited based on specific inclusion and exclusion criteria. Various blood indicators were measured, and demographic information was recorded. HDL-C particle levels were quantified using lipophilic fluorescent dye staining and capillary electrophoresis (microfluidic platform). Coronary artery calcium scores and valve calcification were used to classify HD patients into calcification and non-calcification groups.

Results

Compared to healthy participants, HD patients showed a significant increase in HDL-C, high-density lipoprotein 2 cholesterol (HDL2-C), and high-density lipoprotein 3 cholesterol (HDL3-C) levels (p < 0.001). Further division of HD patients into calcification and non-calcification groups revealed higher serum HDL3-C concentrations (p = 0.002) and a higher HDL3-C/HDL-C ratio (p = 0.04) in the calcification group. Additionally, elevated HDL3-C levels were found to be an independent risk factor for CVC in HD patients (p = 0.040). The ROC curve analysis showed an AUC value of 0.706 for HDL3-C (p = 0.002).

Conclusion

Our study indicates that elevated serum HDL3-C levels in HD patients are an independent risk factor for CVC and can serve as a potential predictor for CVC events. However, more studies need to verify its potential as a predictive indicator..

High-Density Lipoprotein Subclasses and Their Role in the Prevention and Treatment of Cardiovascular Disease: A Narrative Review

The association between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) is controversial. HDL-C is one content type of high-density lipoprotein (HDL). HDL consists of diverse proteins and lipids and can be classified into different subclasses based on size, shape, charge, and density, and can change dynamically in disease states. Therefore, HDL-C levels alone cannot represent HDLs' cardioprotective role. In this review, we summarized the methods for separating HDL subclasses, the studies on the association between HDL subclasses and cardiovascular risk (CVR), and the impact of lipid-modifying medications and nonpharmacological approaches (exercise training, dietary omega fatty acids, and low-density lipoprotein apheresis) on HDL subclasses. As HDL is a natural nanoplatform, recombinant HDLs (rHDLs) have been used as a delivery system in vivo by loading small interfering RNA, drugs, contrast agents, etc. Therefore, we further reviewed the HDL subclasses used in rHDLs and their advantages and disadvantages. This review would provide recommendations and guidance for future studies on HDL subclasses' cardioprotective roles.

Low concentrations of medium-sized HDL particles predict incident CVD in chronic kidney disease patients

Patients with chronic kidney disease (CKD) are at high risk for CVD. However, traditional CVD risk factors cannot completely explain the increased risk. Altered HDL proteome is linked with incident CVD in CKD patients, but it is unclear whether other HDL metrics are associated with incident CVD in this population. In the current study, we analyzed samples from two independent prospective case-control cohorts of CKD patients, the Clinical Phenotyping and Resource Biobank Core (CPROBE) and the Chronic Renal Insufficiency Cohort (CRIC). We measured HDL particle sizes and concentrations (HDL-P) by calibrated ion mobility analysis and HDL cholesterol efflux capacity (CEC) by cAMP-stimulated J774 macrophages in 92 subjects from the CPROBE cohort (46 CVD and 46 controls) and in 91 subjects from the CRIC cohort (34 CVD and 57 controls). We tested associations of HDL metrics with incident CVD using logistic regression analysis. No significant associations were found for HDL-C or HDL-CEC in either cohort. Total HDL-P was only negatively associated with incident CVD in the CRIC cohort in unadjusted analysis. Among the six sized HDL subspecies, only medium-sized HDL-P was significantly and negatively associated with incident CVD in both cohorts after adjusting for clinical confounders and lipid risk factors with odds ratios (per 1-SD) of 0.45 (0.22-0.93, P = 0.032) and 0.42 (0.20-0.87, P = 0.019) for CPROBE and CRIC cohorts, respectively. Our observations indicate that medium-sized HDL-P-but not other-sized HDL-P or total HDL-P, HDL-C, or HDL-CEC-may be a prognostic cardiovascular risk marker in CKD.

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.

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.

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.

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 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.

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.

Lipoproteins and fatty acids in chronic kidney disease: molecular and metabolic alterations

Chronic kidney disease (CKD) induces modifications in lipid and lipoprotein metabolism and homeostasis. These modifications can promote, modulate and/or accelerate CKD and secondary cardiovascular disease (CVD). Lipid and lipoprotein abnormalities - involving triglyceride-rich lipoproteins, LDL and/or HDL - not only involve changes in concentration but also changes in molecular structure, including protein composition, incorporation of small molecules and post-translational modifications. These alterations modify the function of lipoproteins and can trigger pro-inflammatory and pro-atherogenic processes, as well as oxidative stress. Serum fatty acid levels are also often altered in patients with CKD and lead to changes in fatty acid metabolism - a key process in intracellular energy production - that induce mitochondrial dysfunction and cellular damage. These fatty acid changes might not only have a negative impact on the heart, but also contribute to the progression of kidney damage. The presence of these lipoprotein alterations within a biological environment characterized by increased inflammation and oxidative stress, as well as the competing risk of non-atherosclerotic cardiovascular death as kidney function declines, has important therapeutic implications. Additional research is needed to clarify the pathophysiological link between lipid and lipoprotein modifications, and kidney dysfunction, as well as the genesis and/or progression of CVD in patients with kidney disease.

Subpopulations of High-Density Lipoprotein: Friends or Foes in Cardiovascular Disease Risk in Chronic Kidney Disease?

Dyslipidemia is a major traditional risk factor for cardiovascular disease (CVD) in chronic kidney disease (CKD) patients, although the altered lipid profile does not explain the number and severity of CVD events. High-density lipoprotein (HDL) is a heterogeneous (size, composition, and functionality) population of particles with different atherogenic or atheroprotective properties. HDL-cholesterol concentrations per se may not entirely reflect a beneficial or a risk profile for CVD. Large HDL in CKD patients may have a unique proteome and lipid composition, impairing their cholesterol efflux capacity. This lack of HDL functionality may contribute to the paradoxical coexistence of increased large HDL and enhanced risk for CVD events. Moreover, CKD is associated with inflammation, oxidative stress, diabetes, and/or hypertension that are able to interfere with the anti-inflammatory, antioxidative, and antithrombotic properties of HDL subpopulations. How these changes interfere with HDL functions in CKD is still poorly understood. Further studies are warranted to fully clarify if different HDL subpopulations present different functionalities and/or atheroprotective effects. To achieve this goal, the standardization of techniques would be valuable.

Impaired High-Density Lipoprotein Function in Patients With Heart Failure

Background

We recently showed that, in patients with heart failure, lower high‐density lipoprotein (HDL) cholesterol concentration was a strong predictor of death or hospitalization for heart failure. In a follow‐up study, we suggested that this association could be partly explained by HDL proteome composition. However, whether the emerging concept of HDL function contributes to the prognosis of patients with heart failure has not been addressed.

Methods and Results

We measured 3 key protective HDL function metrics, namely, cholesterol efflux, antioxidative capacity, and anti‐inflammatory capacity, at baseline and after 9 months in 446 randomly selected patients with heart failure from BIOSTAT‐CHF (A Systems Biology Study to Tailored Treatment in Chronic Heart Failure). Additionally, the relationship between HDL functionality and HDL proteome composition was determined in 86 patients with heart failure. From baseline to 9 months, HDL cholesterol concentrations were unchanged, but HDL cholesterol efflux and anti‐inflammatory capacity declined (both P<0.001). In contrast, antioxidative capacity increased (P<0.001). Higher HDL cholesterol efflux was associated with lower mortality after adjusting for BIOSTAT‐CHF risk models and log HDL cholesterol (hazard ratio, 0.81; 95% CI, 0.71–0.92; P=0.001). Other functionality measures were not associated with outcome. Several HDL proteins correlated with HDL functionality, mainly with cholesterol efflux. Apolipoprotein A1 emerged as the main protein associated with all 3 HDL functionality measures.

Conclusions

Better HDL cholesterol efflux at baseline was associated with lower mortality during follow‐up, independent of HDL cholesterol. HDL cholesterol efflux and anti‐inflammatory capacity declined during follow‐up in patients with heart failure. Measures of HDL function may provide clinical information in addition to HDL cholesterol concentration in patients with heart failure.

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.

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.

Current Understanding of the Relationship of HDL Composition, Structure and Function to Their Cardioprotective Properties in Chronic Kidney Disease

In the general population, the ability of high-density lipoproteins (HDLs) to promote cholesterol efflux is a predictor of cardiovascular events, independently of HDL cholesterol levels. Although patients with chronic kidney disease (CKD) have a high burden of cardiovascular morbidity and mortality, neither serum levels of HDL cholesterol, nor cholesterol efflux capacity associate with cardiovascular events. Important for the following discussion on the role of HDL in CKD is the notion that traditional atherosclerotic cardiovascular risk factors only partially account for this increased incidence of cardiovascular disease in CKD. As a potential explanation, across the spectrum of cardiovascular disease, the relative contribution of atherosclerotic cardiovascular disease becomes less important with advanced CKD. Impaired renal function directly affects the metabolism, composition and functionality of HDL particles. HDLs themselves are a heterogeneous population of particles with distinct sizes and protein composition, all of them affecting the functionality of HDL. Therefore, a more specific approach investigating the functional and compositional features of HDL subclasses might be a valuable strategy to decipher the potential link between HDL, cardiovascular disease and CKD. This review summarizes the current understanding of the relationship of HDL composition, metabolism and function to their cardio-protective properties in CKD, with a focus on CKD-induced changes in the HDL proteome and reverse cholesterol transport capacity. We also will highlight the gaps in the current knowledge regarding important aspects of HDL biology.

HDL Cholesterol Efflux Capacity is Impaired in Severe Short-Term Hypothyroidism Despite Increased HDL Cholesterol

CONTEXT

Severe hypothyroidism has profound effects on lipoprotein metabolism including high-density lipoprotein (HDL) cholesterol elevations but effects on HDL function metrics are unknown.

OBJECTIVE

To determine the impact of severe short-term hypothyroidism on HDL particle characteristics, HDL cholesterol efflux capacity (CEC), and HDL antioxidative capacity.

DESIGN

Observational study with variables measured during severe short-term hypothyroidism (median TSH 81 mU/L) and after 20 weeks of thyroid hormone supplementation (median TSH 0.03 mU/L) (Netherlands Trial Registry ID 7228).

SETTING

University hospital setting in The Netherlands.

PATIENTS

Seventeen patients who had undergone a total thyroidectomy for differentiated thyroid carcinoma.

MAIN OUTCOME MEASURES

HDL particle characteristics (nuclear magnetic resonance spectrometry), CEC (human THP-1-derived macrophage foam cells and apolipoprotein B-depleted plasma), and HDL anti-oxidative capacity (inhibition of low-density lipoprotein oxidation).

RESULTS

During hypothyroidism plasma total cholesterol, HDL cholesterol and apolipoprotein A-I were increased (P ≤ 0.001). HDL particle concentration was unchanged, but there was a shift in HDL subclasses toward larger HDL particles (P < 0.001). CEC was decreased (P = 0.035), also when corrected for HDL cholesterol (P < 0.001) or HDL particle concentration (P = 0.011). HDL antioxidative capacity did not change.

CONCLUSION

During severe short-term hypothyroidism CEC, an important antiatherogenic metric of HDL function, is impaired. HDL cholesterol and larger HDL particles are increased but HDL particle concentration is unchanged. Combined, these findings suggest that HDL quality and quantity are not improved, reflecting dysfunctional HDL in hypothyroidism.

Preβ1-high-density lipoprotein metabolism is delayed in patients with chronic kidney disease not on hemodialysis

BACKGROUND

Preβ1-high-density lipoprotein (HDL) is a lipid-poor cholesterol acceptor that is converted to lipid-rich HDL by lecithin-cholesterol acyltransferase (LCAT). In patients receiving hemodialysis, preβ1-HDL metabolism is hampered even if HDL cholesterol is normal. Hemodialysis may affect preβ1-HDL metabolism by releasing lipases from the vascular wall due to heparin.

OBJECTIVES

We investigated whether preβ1-HDL metabolism is delayed in patients with chronic kidney disease (CKD) who are not receiving hemodialysis.

METHODS

We examined 44 patients with Stage 3 or higher CKD and 22 healthy volunteers (Control group). The patients with CKD were divided into those without renal replacement therapy (CKD group, n = 22) and those undergoing continuous ambulatory peritoneal dialysis (CAPD group, n = 22). Plasma preβ1-HDL concentrations were determined by immunoassay. During incubation at 37°C, we used 5,5-dithio-bis (2-nitrobenzoic acid) (DTNB) to inhibit LCAT activity and defined the conversion halftime of preβ1-HDL (CHT_preβ1) as the time required for the difference in preβ1-HDL concentration in the presence and absence of 5,5-DTNB to reach half the baseline concentration.

RESULTS

The absolute and relative preβ1-HDL concentrations were higher, and CHT_preβ1 was longer in the CKD and CAPD groups than in the Control group. Preβ1-HDL concentration was significantly correlated with CHT_preβ1 but not with LCAT activity in patients with CKD and CAPD.

CONCLUSION

Preβ1-HDL metabolism is delayed in patients with CKD who are not on hemodialysis. This preβ1-HDL metabolic delay may progress as renal function declines.

Elevated TG/HDL-C and non-HDL-C/HDL-C ratios predict mortality in peritoneal dialysis patients

Background and aims

Dyslipidemia is common in patients with chronic kidney disease and particular prevalent in patients receiving peritoneal dialysis. However, whether markers of atherogenic dyslipidemia correlate with outcomes in dialysis patients as in the general population is uncertain. The aim of this study was to explore the prognostic value of the serum triglyceride/HDL cholesterol (TG/HDL-C) ratio and non-HDL-C/HDL-C ratio to predict mortality in peritoneal dialysis patients.

Methods

Two hundred fourteen peritoneal dialysis patients were retrospectively analyzed from January 2011 to December 2015, with a median follow-up of 59 months. We used receiver operating curves (ROC) to determine the optimal threshold for TG/HDL-C and non-HDL/HDL-C ratios at baseline to predict overall survival during follow-up. Prognostic values were accessed by univariate and multivariate COX regression analysis and Kaplan-Meier curve. A predictive nomogram was developed to predict prognosis for overall survival, and the predictive accuracy was evaluated by concordance index (c-index).

Results

The optimal cut-off values for TG/HDL-C ratio and non-HDL-C/HDL-C ratio to predict mortality were 1.94 and 2.86, respectively. A high TG/HDL-C ratio and a high non-HDL-C/HDL-C ratio strongly correlated with worse overall survival in peritoneal dialysis patients. Multivariate analysis demonstrated that elevated TG/HDL-C ratio (HR 3.57, 95% CI 1.99, 6.39, P < 0.000) as well as non-HDL/HDL-C ratio (HR 2.58, 95%CI 1.39–4.81, P = 0.003) were independent markers to predict reduced OS. A nomogram was constructed to predict overall survival, with a c-index for predictive accuracy of 0.795.

Conclusion

TG/HDL-C ratio and non-HDL-C/HDL-C may serve as potential prognostic biomarkers in PD patients.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

High density lipoprotein functionality and cardiovascular events and mortality: A systematic review and meta-analysis

BACKGROUND AND AIMS

The aim of this systematic review and meta-analysis is to synthesize studies assessing the associations between high-density lipoprotein functionality and risk of cardiovascular disease and mortality.

METHODS

We searched Medline and Embase for the identification of observational studies meeting the inclusion criteria. This meta-analysis was conducted following the PRISMA statement and was registered in PROSPERO (CRD42017065857). We pooled risk estimates with a random-effect model separately for cardiovascular disease (fatal and non-fatal) and all-cause mortality.

RESULTS

Out of 29 manuscripts, 20 articles investigated cholesterol efflux capacity (13 prospective and 7 cross-sectional), 10 antioxidant capacity (7 prospective and 3 cross-sectional) and two anti-inflammatory capacity of high-density lipoprotein (1 prospective and 1 cross-sectional). A greater cholesterol efflux capacity was associated with lower risk of cardiovascular disease in 8 studies (RR for 1SD increase: 0.86; 95% CI: 0.76-0.98) and of mortality in 5 studies (RR for 1SD increase: 0,77; 0.60-1.00). Better antioxidant capacity was non-significantly associated with lower cardiovascular disease risk in 2 studies (RR for 1SD increase 0.70; 0.32-1.53) and significantly with mortality in 3 studies (RR for 1SD increase 0.48; 0.28-0.81). High-density lipoprotein anti-inflammatory ability was associated with a lower cardiovascular disease risk in the only prospective study.

CONCLUSIONS

Greater high-density lipoprotein cholesterol efflux capacity and antioxidant/anti-inflammatory capacities were associated with lower risk of cardiovascular disease. However, the heterogeneity between studies and evidence of publication bias warrants caution and highlights the need for larger prospective studies with standardized assays and specific outcomes.

High-density lipoprotein cholesterol efflux capacity and cardiovascular risk in autoimmune and non-autoimmune diseases

Functional assessment of cholesterol efflux capacity (CEC) to high-density lipoprotein (HDL) is an emerging tool for evaluating morbidity and mortality associated with cardiovascular disease (CVD). By promoting macrophage reverse cholesterol transport (RCT), HDL-mediated CEC is believed to play an important role in atherosclerotic lesion progression in the vessel wall. Furthermore, recent evidence indicates that the typical inverse associations between various forms of CEC and CV events may be strongly modulated by environmental systemic factors and traditional CV risk factors, in addition to autoimmune diseases. These factors influence the complex and dynamic composition of HDL particles, which in turn positively or negatively affect HDL-CEC. Herein, we review recent findings connecting HDL-CEC to traditional CV risk factors and cardiometabolic conditions (non-autoimmune diseases) as well as autoimmune diseases, with a specific focus on how these factors may influence the associations between HDL-CEC and CVD risk.

Dysfunctional High-Density Lipoproteins Are Associated With a Greater Incidence of Acute Coronary Syndrome in a Population at High Cardiovascular Risk: A Nested Case-Control Study

BACKGROUND

Studies have failed to establish a clear link between high-density lipoprotein (HDL) cholesterol and cardiovascular disease, leading to the hypothesis that the atheroprotective role of HDL lies in its biological activity rather than in its cholesterol content. However, to date, the association between HDL functional characteristics and acute coronary syndrome has not been investigated comprehensively.

METHODS

We conducted a case-control study nested within the PREDIMED (Prevención con Dieta Mediterránea) cohort, originally a randomized trial in which participants followed a Mediterranean or low-fat diet. Incident acute coronary syndrome cases (N=167) were individually matched (1:2) to control patients by sex, age, intervention group, body mass index, and follow-up time. We investigated 2 individual manifestations (myocardial infarction, unstable angina) as secondary outcomes. We measured the following functional characteristics: HDL cholesterol concentration (in plasma); cholesterol efflux capacity; antioxidant ability, measured by the HDL oxidative-inflammatory index; phospholipase A2 activity; and sphingosine-1-phosphate, apolipoproteins A-I and A-IV, serum amyloid A, and complement 3 protein (in apolipoprotein B-depleted plasma). We used conditional logistic regression models adjusted for HDL cholesterol levels and cardiovascular risk factors to estimate odds ratios (ORs) between 1-SD increments in HDL functional characteristics and clinical outcomes.

RESULTS

Low values of cholesterol efflux capacity (OR1SD, 0.58; 95% CI, 0.40-0.83) and low levels of sphingosine-1-phosphate (OR1SD, 0.70; 95% CI, 0.52-0.92) and apolipoprotein A-I (OR1SD, 0.58; 95% CI, 0.42-0.79) were associated with higher odds of acute coronary syndrome. Higher HDL oxidative inflammatory index values were marginally linked to acute coronary syndrome risk (OR1SD, 1.27; 95% CI, 0.99-1.63). Low values of cholesterol efflux capacity (OR1SD, 0.33; 95% CI, 0.18-0.61), sphingosine-1-phosphate (OR1SD: 0.60; 95% CI: 0.40-0.89), and apolipoprotein A-I (OR1SD, 0.59; 95% CI, 0.37-0.93) were particularly linked to myocardial infarction, whereas high HDL oxidative-inflammatory index values (OR1SD, 1.53; 95% CI, 1.01-2.33) and low apolipoprotein A-I levels (OR1SD, 0.52; 95% CI, 0.31-0.88) were associated with unstable angina.

CONCLUSIONS

Low cholesterol efflux capacity values, pro-oxidant/proinflammatory HDL particles, and low HDL levels of sphingosine-1-phosphate and apolipoprotein A-I were associated with increased odds of acute coronary syndrome and its manifestations in individuals at high cardiovascular risk.

CLINICAL TRIAL REGISTRATION

URL: https://www.controlled-trials.com/ISRCTN35739639. Unique identifier: ISRCTN35739639.

Lipid-modifying therapy in chronic kidney disease: Pathophysiological and clinical considerations

Chronic kidney disease (CKD), which affects >10% of the population worldwide, is associated with a dramatically increased rate of cardiovascular disease (CVD). More people with CKD will die from CVD than develop end-stage renal disease with dialysis-dependency. However, the contribution of classical atherosclerotic cardiovascular risk factors is less evident than in the general population. Particularly, the relationship between dyslipidemia and CVD morbidity and mortality in CKD patients is not as evident as in the general population. While LDL cholesterol-lowering drugs such as statins significantly reduce the rate of cardiovascular events in the general population, their role in patients with end-stage renal disease has been questioned. This could be caused by a shift from atherosclerotic to non-atherosclerotic CVD in patients with advanced CKD, which cannot be effectively prevented by lipid-lowering drugs. In addition, many lines of evidence suggest that impaired renal function directly affects the metabolism, composition and functionality of lipoproteins, which may affect their responsiveness to pharmacological interventions. In this review, we highlight the challenges for the therapeutic application of lipid-lowering treatment strategies in CKD and discuss why treatment strategies used in the general population cannot be applied uncritically to CKD patients.

HDL Cholesterol Efflux Predicts Incident New-Onset Diabetes After Transplantation (NODAT) in Renal Transplant Recipients Independent of HDL Cholesterol Levels

In renal transplant recipients (RTRs), new-onset diabetes after transplantation (NODAT) is a frequent and serious complication limiting survival of graft and patient. However, the underlying pathophysiology remains incompletely understood. In vitro and in preclinical models, HDL can preserve β-cell function, largely by mediating cholesterol efflux, but this concept has not been evaluated in humans. This study investigated whether baseline cholesterol efflux capacity (CEC) in RTRs is associated with incident NODAT during follow-up. This prospective longitudinal study included 405 diabetes-free RTRs with a functioning graft for >1 year. During a median (interquartile range) follow-up of 9.6 (6.6-10.2) years, 57 patients (14.1%) developed NODAT. HDL CEC was quantified using incubation of human macrophage foam cells with apolipoprotein B-depleted plasma. Baseline CEC was significantly lower in patients developing NODAT during follow-up (median 6.84% [interquartile range 5.84-7.50%]) compared with the NODAT-free group (7.44% [6.46-8.60%]; P = 0.001). Kaplan-Meier analysis showed a lower risk for incident NODAT with increasing sex-stratified tertiles of HDL efflux capacity (P = 0.004). Linear regression analysis indicated that CEC is independently associated with incident NODAT (P = 0.04). In Cox regression analyses, CEC was significantly associated with NODAT (hazard ratio 0.53 [95% CI 0.38-0.76]; P < 0.001), independent of HDL cholesterol levels (P = 0.015), adiposity (P = 0.018), immunosuppressive medication (P = 0.001), and kidney function (P = 0.01). Addition of CEC significantly improved the predictive power of the Framingham Diabetes Risk Score (P = 0.004). This study establishes HDL CEC as a strong predictor of NODAT in RTRs, independent of several other recognized risk factors.

Association of Serum Paraoxonase/Arylesterase Activity With All-Cause Mortality in Maintenance Hemodialysis Patients

CONTEXT

In end-stage renal disease (ESRD), serum high-density lipoprotein cholesterol (HDL-C) level is not an accurate predictor of mortality, partly because it does not necessarily correlate with indices of HDL function. Paraoxonase (PON) is a major enzyme constituent of HDL and a key component of HDL antioxidant activity. Apolipoprotein A-I (Apo A-1) is the core HDL structural protein that plays a major role in various aspects of HDL function.

OBJECTIVE

We sought to examine PON activity and Apo A-I levels in patients with ESRD vs healthy controls.

DESIGN AND SETTING

PON/arylesterase activity was measured in 499 patients with maintenance hemodialysis (MHD) and 24 healthy controls with similar distributions of age, sex, and race/ethnicity. Serum acrolein-modified Apo A-I was measured in 30 patients with MHD and 10 healthy controls.

MAIN OUTCOME MEASURES

Multilevel Cox models were used to assess associations among PON activity, Apo A-I, and HDL-C levels with 12-month all-cause mortality.

RESULTS

PON activity was significantly lower in patients with MHD vs controls. Furthermore, acrolein-modified Apo A-I levels were higher in patients with MHD vs controls. In fully adjusted models, high PON activity was associated with lower 12-month mortality, whereas no difference of mortality risk was observed across HDL-C levels. The combination of high PON and low Apo A-I compared with low PON and low Apo A-I was associated with lower mortality risk.

CONCLUSIONS

In patients with MHD, PON activity had a stronger association with 12-month mortality than HDL-C. Future studies are needed to examine the role of these markers as potential diagnostic and therapeutic tools in ESRD.

Kidney as modulator and target of "good/bad" HDL

The strong inverse relationship between low levels of high-density lipoproteins (HDLs) and atherosclerotic cardiovascular disease (CVD) led to the designation of HDL as the "good" cholesterol. The atheroprotection is thought to reflect HDL's capacity to efflux cholesterol from macrophages, followed by interaction with other lipoproteins in the plasma, processing by the liver and excretion into bile. However, pharmacologic increases in HDL-C levels have not led to expected clinical benefits, giving rise to the concept of dysfunctional HDL, in which increases in serum HDL-C are not beneficial due to lost or altered HDL functions and transition to "bad" HDL. It is now understood that the cholesterol in HDL, measured by HDL-C, is neither a marker nor the mediator of HDL function, including cholesterol efflux capacity. It is also understood that besides cholesterol efflux, HDL functionality encompasses many other potentially beneficial functions, including antioxidant, anti-inflammatory, antithrombotic, anti-apoptotic, and vascular protective effects that may be critical protective pathways for various cells, including those in the kidney parenchyma. This review highlights advances in our understanding of the role kidneys play in HDL metabolism, including the effects on levels, composition, and functionality of HDL particles, particularly the main HDL protein, apolipoprotein AI (apoAI). We suggest that normal apoAI/HDL in the glomerular filtrate provides beneficial effects, including lymphangiogenesis, that promote resorption of renal interstitial fluid and biological particles. In contrast, dysfunctional apoAI/HDL activates detrimental pathways in tubular epithelial cells and lymphatics that lead to interstitial accumulation of fluid and harmful particles that promote progressive kidney damage.

HDL (High-Density Lipoprotein) Cholesterol Efflux Capacity Is Associated With Incident Cardiovascular Disease in the General Population

Objective:

Focus is shifting from HDL-C (high-density lipoprotein cholesterol) as predictive biomarker for cardiovascular disease (CVD) towards antiatherogenic HDL functionalities. Still, limited data exist on the prospective association of HDL function metrics with CVD events. The current work aimed to determine, if baseline HDL-C efflux capacity (CEC) is associated with future CVD events in the general population.

Approach and Results:

We performed a prospective study among participants of the PREVEND (Prevention of Renal and Vascular End-stage Disease) cohort (follow-up, 12 years). From the overall n=8592 subjects 325 with previous CVD events were excluded; of the remaining 8267 eligible participants all subjects with new CVD events during follow-up were selected and individually matched to controls for age, sex, smoking status, and HDL-C levels. CEC at baseline was quantified using human THP-1-derived macrophage foam cells and apolipoprotein B-depleted plasma. Despite identical HDL-C and apoA (apolipoprotein)-I levels between cases (n=351) and controls (n=354) CEC was significantly lower in cases (0.93±0.29 versus 1.01±0.24 arbitrary units; P <0.001). In all subjects combined, CEC correlated positively with HDL-C and apoA-I and negatively with body mass index, hsCRP (high-sensitivity C-reactive protein), and urinary albumin excretion. CEC was inversely associated with incident CVD events, both expressed per quartile and per 1 SD change (odds ratio, 0.73; 95% CI, 0.62–0.86; P <0.001); this association remained significant after adjustments for HDL-C, hsCRP, kidney function, and several other clinical covariates.

Conclusions:

Combined these data demonstrate that in the general population baseline CEC is significantly associated with the future development of CVD events independent of HDL-C and apoA-I plasma levels.

Cholesterol efflux capacity, HDL cholesterol, and risk of coronary heart disease: a nested case-control study in men

The capacity of HDLs to accept cholesterol effluxing from macrophages has been proposed as a new biomarker of HDLs' anti-atherogenic function. Whether cholesterol efflux capacity (CEC) is independent of HDL cholesterol (HDL-C) as a biomarker for coronary heart disease (CHD) risk in a generally healthy primary-prevention population remains unanswered. Therefore, in this nested case-control study, we simultaneously assessed CEC (using J774 cells) and plasma HDL-C levels as predictors of CHD in healthy middle-aged and older men not receiving treatment affecting blood lipid concentrations. We used risk-set sampling of participants free of disease at baseline from the Health Professionals Follow-Up Study, and matched cases (n = 701) to controls 1:1 for age, smoking, and blood sampling date. We applied conditional logistic regression models to calculate the multivariable relative risk and 95% CIs of CHD over 16 years of follow-up. CEC and HDL-C were correlated (r = 0.50, P < 0.0001). The risk (95% CI) of CHD per one SD higher CEC was 0.82 (0.71-0.96), but completely attenuated to 1.08 (0.85-1.37) with HDL-C in the model. The association per one SD between HDL-C and CHD (0.66; 0.58-0.76) was essentially unchanged (0.68; 0.53-0.88) after adjustment for CEC. These findings indicate that CEC's ability to predict CHD may not be independent of HDL-C in a cohort of generally healthy men.

Relationship of Maternal Weight Status Before, During, and After Pregnancy with Breast Milk Hormone Concentrations

OBJECTIVE

The aim of this study was to test associations of prepregnancy BMI, gestational weight gain, oral glucose challenge test results, and postpartum weight loss as predictors of breast milk leptin, insulin, and adiponectin concentrations and whether these relationships vary over time.

METHODS

Milk was collected at 1 and 3 months from 135 exclusively breastfeeding women from the longitudinal Mothers and Infants Linked for Healthy Growth (MILk) study. Hormones were assayed in skimmed samples using ELISA. Mixed-effects linear regression models were employed to assess main effects and effect-by-time interactions on hormone concentrations.

RESULTS

In adjusted models, BMI was positively associated with milk leptin (P < 0.001) and insulin (P = 0.03) and negatively associated with milk adiponectin (P = 0.02); however, the association was stronger with insulin and weaker with adiponectin at 3 months than at 1 month (time interaction P = 0.017 for insulin and P = 0.045 for adiponectin). Gestational weight gain was positively associated and postpartum weight loss was negatively associated with milk leptin (both P < 0.001), independent of BMI. Oral glucose challenge test results were not associated with these milk hormone concentrations.

CONCLUSIONS

Maternal weight status before, during, and after pregnancy contributes to interindividual variation in human milk composition. Continuing work will assess the role of these and other milk bioactive factors in altering infant metabolic outcomes.

From HDL-cholesterol to HDL-function: cholesterol efflux capacity determinants

PURPOSE OF REVIEW

The validity of HDL-cholesterol (HDL-C) elevation as a therapeutic target has been questioned, in comparison to enhancing HDL functionality. Cholesterol efflux capacity (CEC) is an in-vitro assay that measures the ability of an individual's HDL to promote cholesterol efflux from cholesterol donor cells such as macrophages. CEC of HDL is a predictor of cardiovascular risk independent of HDL-C levels. However, molecular determinants of CEC and the effects of diseases and therapeutic interventions on CEC have not been completely defined.

RECENT FINDINGS

We review here recent findings on elevated HDL-C and disease risk, as well as determinants of CEC, from genetics and proteomics to pathophysiology and therapeutic interventions that contribute to our understanding of CEC as a biomarker of HDL functionality.

SUMMARY

Elevated HDL-C levels are not always protective against cardiovascular disease and mortality. CEC is a heritable trait, and genetic polymorphisms in genes involved in HDL and triglycerides metabolism are associated with CEC. Multiple HDL proteins correlate positively with CEC levels and inversely with noncalcified plaque burden. Differences in CEC assays that make comparisons between studies difficult are also emphasized. CEC should be measured in clinical trials of lipid-modifying and anti-inflammatory therapies to determine whether increases are cardioprotective.

Precision Medicine and Personalized Management of Lipoprotein and Lipid Disorders in Chronic and End-Stage Kidney Disease

Precision medicine is an emerging field that calls for individualization of treatment strategies based on characteristics unique to each patient. In lipid management, current guidelines are driven mainly by clinical trial results that presently indicate that patients with non-dialysis-dependent chronic kidney disease (CKD) should be treated with a β-hydroxy β-methylglutaryl-CoA reductase inhibitor, also known as statin therapy. For patients with end-stage kidney disease (ESKD) being treated with hemodialysis, statin therapy has not been shown to successfully reduce poor outcomes in trials and therefore is not recommended. The two major guidelines dissent on whether statin therapy should be of moderate or high intensity in non-dialysis-dependent CKD patients, but often leave the prescribing clinician to make that decision. These decisions often are complicated by the increased concerns for adverse events such as myopathies in patients with advanced kidney disease and ESKD. In the future, there may be an opportunity to further identify CKD and ESKD patients who are more likely to benefit from lipid-modifying therapy as opposed to those who likely will suffer from its side effects using precision medicine tools. For now, data from genetics studies and subgroup analyses may provide insight for future research directions in this field and we review some of the work that has been published in this regard.

Unravelling HDL-Looking beyond the Cholesterol Surface to the Quality Within

High-density lipoprotein (HDL) particles have experienced a turbulent decade of falling from grace with widespread demotion from the most-sought-after therapeutic target to reverse cardiovascular disease (CVD), to mere biomarker status. HDL is slowly emerging from these dark times due to the HDL flux hypothesis wherein measures of HDL cholesterol efflux capacity (CEC) are better predictors of reduced CVD risk than static HDL-cholesterol (HDL-C) levels. HDL particles are emulsions of metabolites, lipids, protein, and microRNA (miR) built on the backbone of Apolipoprotein A1 (ApoA1) that are growing in their complexity due to the higher sensitivity of the respective “omic” technologies. Our understanding of particle composition has increased dramatically within this era and has exposed how our understanding of these particles to date has been oversimplified. Elucidation of the HDL proteome coupled with the identification of specific miRs on HDL have highlighted the “hormonal” characteristics of HDL in that it carries and delivers messages systemically. HDL can dock to most peripheral cells via its receptors, including SR-B1, ABCA1, and ABCG1, which may be a critical step for facilitating HDL-to-cell communication. The composition of HDL particles is, in turn, altered in numerous disease states including diabetes, auto-immune disease, and CVD. The consequence of changes in composition, however, on subsequent biological activities of HDL is currently poorly understood and this is an important avenue for the field to explore in the future. Improving HDL particle quality as opposed to HDL quantity may, in turn, prove a more beneficial investment to reduce CVD risk.

HDL functionality and cardiovascular outcome among nondialysis chronic kidney disease patients

CVD remains the leading cause of morbidity and mortality in patients with chronic kidney disease (CKD). CKD profoundly affects HDL composition and functionality, but whether abnormal HDL independently contributes to cardiovascular events in CKD patients remains elusive. In the present study, we assessed whether compositional and functional properties of HDL predict cardiovascular outcome among 526 nondialysis CKD patients who participate in the CARE FOR HOMe study. We measured HDL cholesterol, the content of HDL-associated proinflammatory serum amyloid A (SAA), and activities of the HDL enzymes paraoxonase and lipoprotein-associated phospholipase A2 (Lp-PLA2). In addition, we assessed the antioxidative activity of apoB-depleted serum. During a mean follow-up of 5.1 ± 2.1 years, 153 patients reached the predefined primary endpoint, a composite of atherosclerotic cardiovascular events including cardiovascular mortality and death of any cause. In univariate Cox regression analyses, lower HDL-cholesterol levels, higher HDL-associated SAA content, and lower paraoxonase activity predicted cardiovascular outcome, while Lp-PLA2 activity and antioxidative capacity did not. HDL-cholesterol and HDL-paraoxonase activity lost their association with cardiovascular outcome after adjustment for traditional cardiovascular and renal risk factors, while SAA lost its association after further adjustment for C-reactive protein. In conclusion, our data suggest that neither HDL quantity nor HDL composition or function independently predict cardiovascular outcome among nondialysis CKD patients.

ESRD-induced dyslipidemia-Should management of lipid disorders differ in dialysis patients?

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Although numerous modifiable risk factors in the pathogenesis of CVD and its associated mortality have been identified, dyslipidemia remains to be a key focus for therapy. In this regard, significant progress has been made in reducing cardiovascular mortality via the use of lipid-lowering agents such as HMG CoA reductase inhibitors (statins). Yet, despite the disproportionate risk of CVD and mortality in patients with advanced chronic and end stage renal disease (ESRD), treatment of dyslipidemia in this patient population has not been associated with a notable improvement in outcomes. Furthermore, observational studies have not consistently found an association between dyslipidemia and poor outcomes in patients with ESRD. However, it is imperative that examination of dyslipidemia and its association with outcomes take place in the context of the many factors that are unique to kidney disease and may contribute to the abnormalities in lipid metabolism in patients with ESRD. Understanding these intricacies and distinct features will be vital not only to the interpretation of the available clinical data in regards to outcomes, but also to the individualization of lipid therapy in ESRD. In this review, we will examine the nature and underlying mechanisms responsible for dyslipidemia, the association of serum lipids and lipoprotein concentrations with outcomes and the results of major trials targeting cholesterol (mainly statins) in patients with ESRD.

High-density lipoprotein cholesterol and causes of death in chronic kidney disease

BACKGROUND

Recent data suggest a U-shaped association between high-density lipoprotein cholesterol (HDL-c) and death in chronic kidney disease (CKD). However, whether the increased mortality in patients with extreme levels is explained by specific causes of death remains unclear.

OBJECTIVES

We studied the associations between HDL-c and cause-specific deaths in CKD.

METHODS

We included 38,377 patients with estimated glomerular filtration rate 15-59 mL/min/1.73 m². We classified deaths into 3 major categories: (1) cardiovascular; (2) malignant; and (3) noncardiovascular/nonmalignant causes. We fitted Cox regression models for overall mortality and separate competing risk models for each major cause of death category to evaluate their respective associations with categories of HDL-c (≤30, 31-40, 41-50 [referent], 51-60, >60 mg/dL). Separate analyses were conducted for men and women.

RESULTS

During a median follow-up of 4.5 years, 9665 patients died. After adjusting for relevant covariates, in both sexes, HDL-c 31 to 40 mg/dL and ≤30 mg/dL were associated with higher risk of all-cause mortality, cardiovascular mortality, malignancy-related deaths, and noncardiovascular/nonmalignancy-related deaths. HDL-c >60 mg/dL was associated with lower all-cause (hazard ratio: 0.75, 95% confidence interval: 0.69, 0.81), cardiovascular, malignancy-related, and noncardiovascular/nonmalignancy-related deaths among women but not in men. Similar results were noted when HDL-c was examined as a continuous measure.

CONCLUSIONS

In a non-dialysis-dependent CKD population, HDL-c ≤40 mg/dL was associated with risk of higher all-cause, cardiovascular, malignant, and noncardiovascular/nonmalignant mortality in men and women. HDL >60 mg/dL was associated with lower risk of all-cause, cardiovascular, malignant, and noncardiovascular/nonmalignant mortality in women but not in men.

HDL in CKD-The Devil Is in the Detail

The picture of HDL cholesterol (HDL-C) as the "good" cholesterol has eroded. This is even more surprising because there exists strong evidence that HDL-C is associated with cardiovascular disease (CVD) in the general population as well as in patients with impairment of kidney function and/or progression of CKD. However, drugs that dramatically increase HDL-C have mostly failed to decrease CVD events. Furthermore, genetic studies took the same line, as genetic variants that have a pronounced influence on HDL-C concentrations did not show an association with cardiovascular risk. For many, this was not surprising, given that an HDL particle is highly complex and carries >80 proteins and several hundred lipid species. Simply measuring cholesterol might not reflect the variety of biologic effects of heterogeneous HDL particles. Therefore, functional studies and the involvement of HDL components in the reverse cholesterol transport, including the cholesterol efflux capacity, have become a further focus of study during recent years. As also observed for other aspects, CKD populations behave differently compared with non-CKD populations. Although clear disturbances have been observed for the "functionality" of HDL particles in patients with CKD, this did not necessarily translate into clear-cut associations with outcomes.

Increments in serum high-density lipoprotein cholesterol over time are not associated with improved outcomes in incident hemodialysis patients

BACKGROUND

Elevated serum high-density lipoprotein cholesterol (HDL-C) has not been associated with better cardiovascular (CV) and all-cause mortality in hemodialysis patients. However, the association between change in HDL over time and mortality has not been fully examined.

OBJECTIVE

In a nationally representative cohort of incident hemodialysis patients who had available HDL data at baseline and 6 months after dialysis initiation, we studied the association of change in HDL-C during the first 6 months of dialysis with all-cause and CV mortality.

METHODS

Associations between HDL-C change and mortality were determined in Cox proportional hazard regression models with adjustment for multiple variables.

RESULTS

In case-mix models, there was a J-shaped association between change in HDL-C and mortality, such that quartiles 1 (<-5 mg/dL) and 4 (≥7 mg/dL) were each associated with higher all-cause (hazard ratio, 1.32 [95% confidence interval, 1.21-1.45] and 1.09 [1.01-1.18]) and CV (1.28 [1.06-1.55] and 1.23 [1.04-1.45]) death risk, respectively. In fully adjusted models that included indices of malnutrition and inflammation, the higher death risk observed in the lowest quartile was attenuated, whereas the highest quartile continued to demonstrate significantly higher all-cause (1.11 [1.02-1.20]) and CV mortality (1.15 [1.00-1.32]). These associations persisted across various subgroups.

CONCLUSIONS

Although malnutrition and inflammation may explain the increased risk for mortality in patients with decreasing serum HDL-C concentrations over time, these indices do not mitigate the elevated risk in patients with rising serum HDL-C. We found that increasing serum HDL-C over time is paradoxically associated with worse outcomes in incident hemodialysis patients.

Association of the TG/HDL-C and Non-HDL-C/HDL-C Ratios with Chronic Kidney Disease in an Adult Chinese Population

BACKGROUND/AIMS

Evidence indicates a role for dyslipidemia in the development of chronic kidney disease (CKD). However, the association of lipid abnormalities and their ratios with kidney disease using the new CKD Epidemiology Collaboration (CKD-EPI) equation is not well understood.

METHODS

This cross-sectional study included 48,054 adult subjects. CKD was defined as an estimated glomerular filtration rate <60 ml/min/1.73 m2 or dipstick-positive proteinuria. Logistic regression models were used to examine the relationship between lipid variables and CKD.

RESULTS

The prevalence of CKD in this study was 3.7%. When the participants exhibited higher serum triglyceride (TG), a higher TG/high-density lipoprotein cholesterol (TG/HDL-c) ratio or a higher non-HDL-c/HDL-c ratio or HDL-c in a lower quartile, the prevalence of CKD tended to be higher. The multivariate adjusted odds ratios for CKD per 1 standard deviation increase in lipid level were 1.17 (1.10-1.23) for TG, 0.86 (0.79-0.93) for HDL-c, 1.21 (1.13-1.31) for the TG/HDL-c ratio, and 1.14 (1.06-1.22) for the non-HDL-c/HDL-c ratio. No significant association was detected between CKD and total cholesterol (TC), non-HDL-c or the low-density lipoprotein cholesterol/HDL-c (LDL-c/HDL-c) ratio.

CONCLUSION

In this relatively healthy adult Chinese population, the CKD-EPI equation determined that the TG/HDL-c and non-HDL-c/HDL-c ratios as well as TG and HDL-c correlate with the prevalence of CKD.

Chronic Kidney Disease and Disproportionally Increased Cardiovascular Damage: Does Oxidative Stress Explain the Burden?

Chronic kidney disease (CKD) patients are among the groups at the highest risk for cardiovascular disease and significantly shortened remaining lifespan. CKD enhances oxidative stress in the organism with ensuing cardiovascular damage. Oxidative stress in uremia is the consequence of higher reactive oxygen species (ROS) production, whereas attenuated clearance of pro-oxidant substances and impaired antioxidant defenses play a complementary role. The pathophysiological mechanism underlying the increased ROS production in CKD is at least partly mediated by upregulation of the intrarenal angiotensin system. Enhanced oxidative stress in the setting of the uremic milieu promotes enzymatic modification of circulating lipids and lipoproteins, protein carbamylation, endothelial dysfunction via disruption of nitric oxide (NO) pathways, and activation of inflammation, thus accelerating atherosclerosis. Left ventricular hypertrophy (LVH) and heart failure are hallmarks of CKD. NADPH oxidase activation, xanthine oxidase, mitochondrial dysfunction, and NO-ROS are the main oxidative pathways leading to LVH and the cardiorenal syndrome. Finally, a subset of antioxidant enzymes, the paraoxonases (PON), deserves special attention due to abundant clinical evidence accumulated regarding reduced serum PON1 activity in CKD as a contributor to the increased burden of cardiovascular disease. Future, meticulously designed studies are needed to assess the effects of antioxidant therapy on patients with CKD.

High-density lipoprotein cholesterol efflux capacity is inversely associated with cardiovascular risk: a systematic review and meta-analysis

Background

A low plasma level of high-density lipoprotein (HDL) cholesterol (HDL-C) is associated with cardiovascular risk. A key cardioprotective property of HDL is cholesterol efflux capacity (CEC), the ability of HDL to accept cholesterol from macrophages. In this study, we aimed to identify the predictive value of CEC for cardiovascular risk.

Methods

The relative risks (RRs) and 95% confidence intervals (CIs) were pooled to analyze the association between CEC and the incidence of cardiovascular events and all-cause mortality. The odds ratios (ORs) and 95% CIs were pooled to estimate the association of CEC and the prevalence of cardiovascular events.

Results

A total of 15 studies were included. Results showed that the highest CEC was significantly associated with a reduced risk of cardiovascular events incidents compared to the lowest CEC (RR, 0.56; 95% CI, 0.37 to 0.85; I², 89%); the pooled RR of cardiovascular risk for per unit SD increase was 0.87 (95% CI, 0.73 to 1.04; I², 67%). Dose-response curve indicated that cardiovascular risk decreased by 39% (RR, 0.61; 95% CI, 0.51 to 0.74) for per unit CEC increase. Similarly, an inverse association was observed between CEC and the prevalence of cardiovascular events (highest vs. lowest, OR, 0.30; 95% CI, 0.17 to 0.5; I² = 63%; per unit SD increase, OR, 0.94; 95% CI, 0.90 to 0.98; I² = 71%). However, based on the current data, CEC was not significantly associated with all-cause mortality.

Conclusions

Findings from this meta-analysis suggest that HDL-mediated CEC is inversely associated with cardiovascular risk, which appears to be independent of HDL concentration. The growing understanding of CEC and its role in cardiovascular risk decrease may improve the accuracy of cardiovascular risk prediction and also open important avenues to develop novel therapeutic targeting HDL metabolism.

Electronic supplementary material

The online version of this article (doi: 10.1186/s12944-017-0604-5) contains supplementary material, which is available to authorized users.

Serum inhibitory factor 1, high-density lipoprotein and cardiovascular diseases

PURPOSE OF REVIEW

The atheroprotective properties of HDL are supported by epidemiological and preclinical research. However, the results of interventional trials paradoxically indicate that drugs increasing HDL-cholesterol (HDL-C) do not reduce coronary artery disease (CAD) risk. Moreover, Mendelian randomization studies have shown no effect of HDL-C-modifying variants on CAD outcome. Thus, the protective effects of HDL particles are more governed by their functional status than their cholesterol content. In this context, any successful clinical exploitation of HDL will depend on the identification of HDL-related biomarkers, better than HDL-C level, for assessing cardiovascular risk and monitoring responses to treatment.

RECENT FINDINGS

Recent studies have enlightened the role of ecto-F1-ATPase as a cell surface receptor for apoA-I, the major apolipoprotein of HDL, involved in the important metabolic and vascular atheroprotective functions of HDL. In the light of these findings, the clinical relevance of ecto-F1-ATPase in humans has recently been supported by the identification of serum F1-ATPase inhibitor (IF1) as an independent determinant of HDL-C, CAD risk and cardiovascular mortality in CAD patients.

SUMMARY

Serum IF1 measurement might be used as a novel HDL-related biomarker to better stratify risk in high-risk populations or to determine pharmacotherapy.

Modified Lipids and Lipoproteins in Chronic Kidney Disease: A New Class of Uremic Toxins

Chronic kidney disease (CKD) is associated with an enhanced oxidative stress and deep modifications in lipid and lipoprotein metabolism. First, many oxidized lipids accumulate in CKD and were shown to exert toxic effects on cells and tissues. These lipids are known to interfere with many cell functions and to be pro-apoptotic and pro-inflammatory, especially in the cardiovascular system. Some, like F2-isoprostanes, are directly correlated with CKD progression. Their accumulation, added to their noxious effects, rendered their nomination as uremic toxins credible. Similarly, lipoproteins are deeply altered by CKD modifications, either in their metabolism or composition. These impairments lead to impaired effects of HDL on their normal effectors and may strongly participate in accelerated atherosclerosis and failure of statins in end-stage renal disease patients. This review describes the impact of oxidized lipids and other modifications in the natural history of CKD and its complications. Moreover, this review focuses on the modifications of lipoproteins and their impact on the emergence of cardiovascular diseases in CKD as well as the appropriateness of considering them as actual mediators of uremic toxicity.