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

High-density lipoprotein in diabetes: Structural and functional relevance

Low levels of high-density lipoprotein-cholesterol (HDL-C) is considered a major cardiovascular risk factor. However, recent studies have suggested a more U-shaped association between HDL-C and cardiovascular disease. It has been shown that the cardioprotective effect of HDL is related to the functions of HDL particles rather than their cholesterol content. HDL particles are highly heterogeneous and have multiple functions relevant to cardiometabolic conditions including cholesterol efflux capacity, anti-oxidative, anti-inflammatory, and vasoactive properties. There are quantitative and qualitative changes in HDL as well as functional abnormalities in both type 1 and type 2 diabetes. Non-enzymatic glycation, carbamylation, oxidative stress, and systemic inflammation can modify the HDL composition and therefore the functions, especially in situations of poor glycemic control. Studies of HDL proteomics and lipidomics have provided further insights into the structure-function relationship of HDL in diabetes. Interestingly, HDL also has a pleiotropic anti-diabetic effect, improving glycemic control through improvement in insulin sensitivity and β-cell function. Given the important role of HDL in cardiometabolic health, HDL-based therapeutics are being developed to enhance HDL functions rather than to increase HDL-C levels. Among these, recombinant HDL and small synthetic apolipoprotein A-I mimetic peptides may hold promise for preventing and treating diabetes and cardiovascular disease.

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.

ANGPTL3 is a novel HDL component that regulates HDL function

BACKGROUND

Angiopoietin-like protein 3 (ANGPTL3) is secreted by hepatocytes and inhibits lipoprotein lipase and endothelial lipase activity. Previous studies reported the correlation between plasma ANGPTL3 levels and high-density lipoprotein (HDL). Recently ANGPTL3 was found to preferentially bind to HDL in healthy human circulation. Here, we examined whether ANGPTL3, as a component of HDL, modulates HDL function and affects HDL other components in human and mice with non-diabetes or type 2 diabetes mellitus.

METHODS

HDL was isolated from the plasma of female non-diabetic subjects and type-2 diabetic mellitus (T2DM) patients. Immunoprecipitation, western blot, and ELISA assays were used to examine ANGPTL3 levels in HDL. Db/m and db/db mice, AAV virus mediated ANGPTL3 overexpression and knockdown models and ANGPTL3 knockout mice were used. The cholesterol efflux capacity induced by HDL was analyzed in macrophages preloaded with fluorescent cholesterol. The anti-inflammation capacity of HDL was assessed using flow cytometry to measure VCAM-1 and ICAM-1 expression levels in TNF-α-stimulated endothelial cells pretreated with HDL.

RESULTS

ANGPTL3 was found to bind to HDL and be a component of HDL in both non-diabetic subjects and T2DM patients. Flag-ANGPTL3 was found in the HDL of transgenic mice overexpressing Flag-ANGPTL3. ANGPLT3 of HDL was positively associated with cholesterol efflux in female non-diabetic controls (r = 0.4102, p = 0.0117) but not in female T2DM patients (r = - 0.1725, p = 0.3224). Lower ANGPTL3 levels of HDL were found in diabetic (db/db) mice compared to control (db/m) mice and were associated with reduced cholesterol efflux and inhibition of VCAM-1 and ICAM-1 expression in endothelial cells (p < 0.05 for all). Following AAV-mediated ANGPTL3 cDNA transfer in db/db mice, ANGPTL3 levels were found to be increased in HDL, and corresponded to increased cholesterol efflux and decreased ICAM-1 expression. In contrast, knockdown of ANGPTL3 levels in HDL by AAV-mediated shRNA transfer led to a reduction in HDL function (p < 0.05 for both). Plasma total cholesterol, total triglycerides, HDL-c, protein components of HDL and the cholesterol efflux function of HDL were lower in ANGPTL3-/- mice than ANGPTL3+/+ mice, suggesting that ANGPTL3 in HDL may regulate HDL function by disrupting the balance of protein components in HDL.

CONCLUSION

ANGPTL3 was identified as a component of HDL in humans and mice. ANGPTL3 of HDL regulated cholesterol efflux and the anti-inflammatory functions of HDL in T2DM mice. Both the protein components of HDL and cholesterol efflux capacity of HDL were decreased in ANGPTL3-/- mice. Our findings suggest that ANGPTL3 in HDL may regulate HDL function by disrupting the balance of protein components in HDL. Our study contributes to a more comprehensive understanding of the role of ANGPTL3 in lipid metabolism.

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).

Sugar and Dyslipidemia: A Double-Hit, Perfect Storm

The availability of sugar has expanded over the past 50 years, due to improved industrial processes and corn subsidies, particularly in the form of sweetened beverages. This correlates with a surge in the prevalence of cardiometabolic disorders, which has brought this issue back into the spotlight for public health. In this narrative review, we focus on the role of fructose in the genesis of cardiometabolic dyslipidemia (an increase in serum triglyceride-rich lipoproteins (TRL): VLDL, chylomicrons (CM), and their remnants) bringing together the most recent data on humans, which demonstrates the crucial interaction between glucose and fructose, increasing the synthesis while decreasing the catabolism of these particles in a synergistic downward spiral. After reviewing TRL metabolism, we discuss the fundamental principles governing the metabolism of fructose in the intestine and liver and the effects of dysregulated fructolysis, in conjunction with the activation of carbohydrate-responsive element-binding protein (ChREBP) by glucose and the resulting crosstalk. The first byproduct of fructose catabolism, fructose-1-P, is highlighted for its function as a signaling molecule that promotes fat synthesis. We emphasize the role of fructose/glucose interaction in the liver, which enhances de novo lipogenesis, triglyceride (TG) synthesis, and VLDL production. In addition, we draw attention to current research that demonstrates how fructose affects the activity of lipoprotein lipase by increasing the concentration of inhibitors such as apolipoprotein CIII (apoCIII) and angiopoietin-like protein 3 (ANGPTL3), which reduce the catabolism of VLDL and chylomicrons and cause the building up of their atherogenic remnants. The end outcome is a dual, synergistic, and harmful action that encourages atherogenesis. Thus, considering the growing concerns regarding the connection between sugar consumption and cardiometabolic disease, current research strongly supports the actions of public health organizations aimed at reducing sugar intake, including dietary guidance addressing "safe" limits for sugar consumption.

HDL Cholesterol Efflux and the Complement System Are Linked in Systemic Lupus Erythematosus

Cholesterol efflux capacity (CEC), the ability of high-density lipoprotein (HDL) cholesterol to accept cholesterol from macrophages, has been linked to cardiovascular events. Systemic lupus erythematosus (SLE) is characterized by the consumption of complement (C) proteins and has been associated with an increased risk of cardiovascular disease. CEC is reduced in SLE patients compared to controls. In the present work, our objective was to analyze whether the disruption of C influences CEC in patients with SLE. New-generation functional assays of the three pathways of the C system were performed in 207 patients with SLE. Additionally, serum levels of inactive (C1q, C2, C3, C4, and factor D) and activated (C3a) molecules, and regulators (C1-inhibitor and factor H) of C system were measured. CEC, using an in vitro assay, and lipoprotein serum concentrations were assessed. Multivariable linear regression analysis was performed to assess the relationship between C system and CEC. After full multivariable analysis, the alternative C cascade functional test showed a significant and negative relationship with CEC. This was also the case for C2 and C3, in which the associations were found to be positive and statistically significant, after adjustment for covariates. In conclusion, C system and CEC are interconnected in patients with SLE.

The Association of Physical Activity and Sedentary Behavior with Maternal and Cord Blood Anti-Oxidative Capacity and HDL Functionality: Findings of DALI Study

Obesity is one of the most common health issues in pregnancy with short and long-term consequences for both mother and her offspring. Promoting moderate to vigorous physical activity (MVPA) and decreasing sedentary time (ST) could have a positive impact on weight and obesity management, and therefore adiposity-induced oxidative stress, inflammation, and atherogenesis. However, the effects of MVPA and ST on anti-oxidative and anti-atherogenic markers in pregnancy have not been studied to date. This study aimed to assess the association of longitudinally and objectively measured MVPA and ST in 122 overweight/obese women (BMI ≥ 29 kg/m2) with maternal and cord blood markers of oxidative stress measured by advanced oxidation protein products (AOPP), anti-oxidative capacity, as well as high-density lipoproteins (HDL) related paraoxonase-1 (PON-1) activity and cholesterol efflux. Linear regression models showed no associations of MVPA and ST with outcomes in maternal blood. In contrast, MVPA at <20 weeks and 24–28 weeks of gestation were positively associated with anti-oxidative capacity, as well as PON-1 activity of HDL in cord blood. MVPA at 35–37 weeks correlated with higher AOPP, as well as higher anti-oxidative capacity. ST <20 weeks was also positively associated with inhibition of oxidation in cord blood. We speculate that increasing MVPA of overweight/obese women during pregnancy attenuates the oxidative stress state in the new-born.

Additive Effects of Drinking Habits and a Susceptible Genetic Polymorphism on Cholesterol Efflux Capacity

AIMS

High levels of high-density lipoprotein cholesterol (HDL-C) are not necessarily effective in preventing atherosclerotic cardiovascular disease, and cholesterol efflux capacity (CEC) has attracted attention regarding HDL functionality. We aimed to elucidate whether drinking habits are associated with CEC levels, while also paying careful attention to confounding factors including serum HDL-C levels, other life style factors, and rs671 (^＊2), a genetic polymorphism of the aldehyde dehydrogenase 2 (ALDH2) gene determining alcohol consumption habit.

METHODS

A cross-sectional study was performed in 505 Japanese male subjects who were recruited from a health screening program. Associations of HDL-C and CEC levels with drinking habits and ALDH2 genotypes were examined.

RESULTS

The genotype frequencies of ALDH2 ^＊1/^＊1 (homozygous wild-type genotype), ^＊1/^＊2 and ^＊2/^＊2 (homozygous mutant genotype) were 55%, 37% and 8%, respectively. Both HDL-C and CEC levels were higher in ALDH2 ^＊1/^＊1 genotype carriers than in ^＊2 allele carriers. Although HDL-C levels were higher in subjects who had a drinking habit than in non-drinkers, CEC levels tended to be lower in subjects with ≥ 46 g/day of alcohol consumption than in non-drinkers. Furthermore, CEC levels tended to be lower in ALDH2 ^＊1/^＊1 genotype carriers with a drinking habit of ≥ 46 g/day than non-drinkers, while for ^＊2 allele carriers, CEC levels tended to be lower with a drinking habit of 23-45.9 g/day compared to no drinking habit.

CONCLUSIONS

Our results suggest that heavy drinking habits may tend to decrease CEC levels, and in the ALDH2 ^＊2 allele carriers, even moderate drinking habits may tend to decrease CEC levels.

High-density lipoprotein cholesterol efflux capacity in patients with obstructive sleep apnea and its relation with disease severity

Background

Obstructive sleep apnea (OSA) is linked to an accelerated risk of cardiovascular disease (CVD). Some key CVD risk factors are present in patients suffering from OSA such as hypertension, inflammation, oxidative stress, and dyslipidemia. High-density lipoprotein (HDL) cholesterol efflux capacity (CEC) is proposed as a reliable biomarker of HDL function and the present study aimed to quantify this biomarker in patients with OSA.

Methods

ATP binding cassette subfamily A member 1 (ABCA1), non-ABCA1, and total CEC were determined in 69 polysomnographic-confirmed OSA patients and 23 controls. Moreover, paraoxonase (PON) activities, high-sensitivity C-reactive protein (hsCRP), apolipoprotein B (apo B), and apolipoprotein A-I (apo A-I) circulating levels were quantified in the studied population.

Results: All CEC measures were reduced in the OSA group compared to the control group. Strikingly, ABCA1 CEC was diminished in severe OSA in comparison with mild OSA. Furthermore, PON activities and apo A-I showed lower levels, while hsCRP and apo B were elevated in OSA patients compared to controls. Moreover, ABCA1 CEC showed an inverse association with hsCRP and a positive association with apo A-I, while non-ABCA1 CEC presented an association with HDL-C.

Conclusion

These results suggest the presence of an impaired HDL function in OSA. In particular, ABCA1 CEC was associated with disease severity and inflammation which could be a factor increasing the risk of CVD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01723-w.

A Modern Approach to Dyslipidemia

Lipid disorders involving derangements in serum cholesterol, triglycerides, or both are commonly encountered in clinical practice and often have implications for cardiovascular risk and overall health. Recent advances in knowledge, recommendations, and treatment options have necessitated an updated approach to these disorders. Older classification schemes have outlived their usefulness, yielding to an approach based on the primary lipid disturbance identified on a routine lipid panel as a practical starting point. Although monogenic dyslipidemias exist and are important to identify, most individuals with lipid disorders have polygenic predisposition, often in the context of secondary factors such as obesity and type 2 diabetes. With regard to cardiovascular disease, elevated low-density lipoprotein cholesterol is essentially causal, and clinical practice guidelines worldwide have recommended treatment thresholds and targets for this variable. Furthermore, recent studies have established elevated triglycerides as a cardiovascular risk factor, whereas depressed high-density lipoprotein cholesterol now appears less contributory than was previously believed. An updated approach to diagnosis and risk assessment may include measurement of secondary lipid variables such as apolipoprotein B and lipoprotein(a), together with selective use of genetic testing to diagnose rare monogenic dyslipidemias such as familial hypercholesterolemia or familial chylomicronemia syndrome. The ongoing development of new agents-especially antisense RNA and monoclonal antibodies-targeting dyslipidemias will provide additional management options, which in turn motivates discussion on how best to incorporate them into current treatment algorithms.

Role of ABCA1 in Cardiovascular Disease

Cholesterol homeostasis plays a significant role in cardiovascular disease. Previous studies have indicated that ATP-binding cassette transporter A1 (ABCA1) is one of the most important proteins that maintains cholesterol homeostasis. ABCA1 mediates nascent high-density lipoprotein biogenesis. Upon binding with apolipoprotein A-I, ABCA1 facilitates the efflux of excess intracellular cholesterol and phospholipids and controls the rate-limiting step of reverse cholesterol transport. In addition, ABCA1 interacts with the apolipoprotein receptor and suppresses inflammation through a series of signaling pathways. Thus, ABCA1 may prevent cardiovascular disease by inhibiting inflammation and maintaining lipid homeostasis. Several studies have indicated that post-transcriptional modifications play a critical role in the regulation of ABCA1 transportation and plasma membrane localization, which affects its biological function. Meanwhile, carriers of the loss-of-function ABCA1 gene are often accompanied by decreased expression of ABCA1 and an increased risk of cardiovascular diseases. We summarized the ABCA1 transcription regulation mechanism, mutations, post-translational modifications, and their roles in the development of dyslipidemia, atherosclerosis, ischemia/reperfusion, myocardial infarction, and coronary heart disease.

HDL as Bidirectional Lipid Vectors: Time for New Paradigms

The anti-atherogenic properties of high-density lipoproteins (HDL) have been explained mainly by reverse cholesterol transport (RCT) from peripheral tissues to the liver. The RCT seems to agree with most of the negative epidemiological correlations between HDL cholesterol levels and coronary artery disease. However, therapies designed to increase HDL cholesterol failed to reduce cardiovascular risk, despite their capacity to improve cholesterol efflux, the first stage of RCT. Therefore, the cardioprotective role of HDL may not be explained by RCT, and it is time for new paradigms about the physiological function of these lipoproteins. It should be considered that the main HDL apolipoprotein, apo AI, has been highly conserved throughout evolution. Consequently, these lipoproteins play an essential physiological role beyond their capacity to protect against atherosclerosis. We propose HDL as bidirectional lipid vectors carrying lipids from and to tissues according to their local context. Lipid influx mediated by HDL appears to be particularly important for tissue repair right on site where the damage occurs, including arteries during the first stages of atherosclerosis. In contrast, the HDL-lipid efflux is relevant for secretory cells where the fusion of intracellular vesicles drastically enlarges the cytoplasmic membrane with the potential consequence of impairment of cell function. In such circumstances, HDL could deliver some functional lipids and pick up not only cholesterol but an integral part of the membrane in excess, restoring the viability of the secretory cells. This hypothesis is congruent with the beneficial effects of HDL against atherosclerosis as well as with their capacity to induce insulin secretion and merits experimental exploration.

Update on dyslipidemia in hypothyroidism: the mechanism of dyslipidemia in hypothyroidism

Hypothyroidism is often associated with elevated serum levels of total cholesterol, LDL-C and triglycerides. Thyroid hormone (TH) affects the production, clearance and transformation of cholesterol, but current research shows that thyroid-stimulating hormone (TSH) also participates in lipid metabolism independently of TH. Therefore, the mechanism of hypothyroidism-related dyslipidemia is associated with the decrease of TH and the increase of TSH levels. Some newly identified regulatory factors, such as proprotein convertase subtilisin/kexin type 9, angiogenin-like proteins and fibroblast growth factors are the underlying causes of dyslipidemia in hypothyroidism. HDL serum concentration changes were not consistent, and its function was reportedly impaired. The current review focuses on the updated understanding of the mechanism of hypothyroidism-related dyslipidemia.

Triglycerides and low HDL cholesterol predict coronary heart disease risk in patients with stable angina

We assessed whether high triglycerides (TG) and low high-density lipoprotein cholesterol (HDL-C) levels, expressed by an increased TG/HDL-C ratio, predict coronary atherosclerotic disease (CAD) outcomes in patients with stable angina. We studied 355 patients (60 ± 9 years, 211 males) with stable angina who underwent coronary computed tomography angiography (CTA), were managed clinically and followed for 4.5 ± 0.9 years. The primary composite outcome was all-cause mortality and non-fatal myocardial infarction. At baseline, the proportion of males, patients with metabolic syndrome, diabetes and obstructive CAD increased across TG/HDL-C ratio quartiles, together with markers of insulin resistance, hepatic and adipose tissue dysfunction and myocardial damage, with no difference in total cholesterol or LDL-C. At follow-up, the global CTA risk score (HR 1.06, 95% confidence interval (CI) 1.03–1.09, P = 0.001) and the IV quartile of the TG/HDL-C ratio (HR 2.85, 95% CI 1.30–6.26, P < 0.01) were the only independent predictors of the primary outcome. The TG/HDL-C ratio and the CTA risk score progressed over time despite increased use of lipid-lowering drugs and reduction in LDL-C. In patients with stable angina, high TG and low HDL-C levels are associated with CAD related outcomes independently of LDL-C and treatments.

Trial registration. EVINCI study: ClinicalTrials.gov NCT00979199, registered September 17, 2009; SMARTool study: ClinicalTrials.gov NCT04448691, registered June 26, 2020.

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.

Molecular Patterns of Extreme and Persistent Cholesterol Efflux Capacity

Objective: Cholesterol efflux capacity (CEC), the ability of extracellular acceptors to pick-up cholesterol from macrophages, is a clinically relevant cardiovascular biomarker. CEC is inversely associated with incident atherosclerotic cardiovascular disease events. However, CEC is only modestly associated with HDL-C (high-density lipoprotein cholesterol) levels, which may explain the failure of HDL-C raising therapies to improve atherosclerotic cardiovascular disease outcomes. Determinants of variation in CEC are not well understood. Thus, we sought to establish whether extreme high and low CEC is a robust persistent phenotype and to characterize associations with cholesterol, protein, and phospholipids across the particle size distribution. Approach and Results: CEC was previously measured in 2924 participants enrolled in the Dallas Heart Study, a multi-ethnic population-based study from 2000 to 2002. We prospectively recruited those who were below the 10th and above 90th percentile of CEC. Our study revealed that extreme low and high CEC are persistent, robust phenotypes after 15 years of follow-up. Using size exclusion chromatography, CEC to fractionated plasma depleted of apolipoprotein B (fraction-specific CEC) demonstrated significant differences in CEC patterns between persistent high and low efflux groups. Fraction-specific CEC was correlated with fraction-specific total phospholipid but not apolipoprotein A-I, cholesterol, or total protein. These correlations varied across the size distribution and differed among persistent high versus low efflux groups. Conclusions: Extreme high and low CEC are persistent and robust phenotypes. CEC patterns in fractionated plasma reveal marked variation across the size distribution. Future studies are warranted to determine specific molecular species linked to CEC in a size-specific manner.

The Endothelium Is Both a Target and a Barrier of HDL's Protective Functions

The vascular endothelium serves as a barrier between the intravascular and extravascular compartments. High-density lipoproteins (HDL) have two kinds of interactions with this barrier. First, bloodborne HDL must pass the endothelium to access extravascular tissues, for example the arterial wall or the brain, to mediate cholesterol efflux from macrophages and other cells or exert other functions. To complete reverse cholesterol transport, HDL must even pass the endothelium a second time to re-enter circulation via the lymphatics. Transendothelial HDL transport is a regulated process involving scavenger receptor SR-BI, endothelial lipase, and ATP binding cassette transporters A1 and G1. Second, HDL helps to maintain the integrity of the endothelial barrier by (i) promoting junction closure as well as (ii) repair by stimulating the proliferation and migration of endothelial cells and their progenitor cells, and by preventing (iii) loss of glycocalix, (iv) apoptosis, as well as (v) transmigration of inflammatory cells. Additional vasoprotective functions of HDL include (vi) the induction of nitric oxide (NO) production and (vii) the inhibition of reactive oxygen species (ROS) production. These vasoprotective functions are exerted by the interactions of HDL particles with SR-BI as well as specific agonists carried by HDL, notably sphingosine-1-phophate (S1P), with their specific cellular counterparts, e.g., S1P receptors. Various diseases modify the protein and lipid composition and thereby the endothelial functionality of HDL. Thorough understanding of the structure-function relationships underlying the multiple interactions of HDL with endothelial cells is expected to elucidate new targets and strategies for the treatment or prevention of various diseases.

[Plasma high density lipoproteins phospholipds as an indirect indicator of their cholesterol efflux capacity - new suspected atherosclerosis risk factor]

High density lipoproteins (HDL) are a unique natural structure, protecting the body from the development of atherosclerotic vascular lesions and cardiovascular diseases due to this ability to remove cholesterol from cells. Plasma HDL level estimated by their cholesterol content, is a common lipid parameter, and its decrease is considered as an established atherosclerosis risk factor. However, a number of studies have shown the absence of positive clinical effects after drug-induced increase in HDL cholesterol. There is increasing evidence that not only HDL concentration, but also HDL properties, considered in this review are important. Many studies showed the decrease of HDL cholesterol efflux capacity in patients with coronary heart diseases and its association with disease severity. Some authors consider a decrease of this HDL capacity as a new additional risk factor of atherosclerosis. The review summarizes existing information on various protein and lipid components of HDL with a primary emphasis on the HDL. Special attention is paid to correlation between the HDL cholesterol efflux capacity and HDL phospholipids and the ratio "phospholipids/free cholesterol". The accumulated information indicates importance of evaluation in the HDL fraction not only in terms of their cholesterol, but also phospholipids. In addition to the traditionally used lipid criteria, this would provide more comprehensive information about the activity of the reverse cholesterol transport process in the body and could contribute to the targeted correction of the detected disorders.

Role of Adenylate Cyclase 9 in the Pharmacogenomic Response to Dalcetrapib: Clinical Paradigm and Molecular Mechanisms in Precision Cardiovascular Medicine

Following the neutral results of the dal-OUTCOMES trial, a genome-wide study identified the rs1967309 variant in the adenylate cyclase type 9 (ADCY9) gene on chromosome 16 as being associated with the risk of future cardiovascular events only in subjects taking dalcetrapib, a CETP (cholesterol ester transfer protein) modulator. Homozygotes for the minor A allele (AA) were protected from recurrent cardiovascular events when treated with dalcetrapib, while homozygotes for the major G allele (GG) had increased risk. Here, we present the current state of knowledge regarding the impact of rs1967309 in ADCY9 on clinical observations and biomarkers in dalcetrapib trials and the effects of mouse ADCY9 gene inactivation on cardiovascular physiology. Finally, we present our current model of the interaction between dalcetrapib and ADCY9 gene variants in the arterial wall macrophage, based on the intracellular role of CETP in the transfer of complex lipids from endoplasmic reticulum membranes to lipid droplets. Briefly, the concept is that dalcetrapib would inhibit CETP-mediated transfer of cholesteryl esters, resulting in a progressive inhibition of cholesteryl ester synthesis and free cholesterol accumulation in the endoplasmic reticulum. Reduced ADCY9 activity, by paradoxically leading to higher cyclic AMP levels and in turn increased cellular cholesterol efflux, could impart cardiovascular protection in rs1967309 AA patients. The ongoing dal-GenE trial recruited 6145 patients with the protective AA genotype and will provide a definitive answer to whether dalcetrapib will be protective in this population.

Atherosclerosis Regression and Cholesterol Efflux in Hypertriglyceridemic Mice

[Figure: see text].

Relationship of Para and Perirenal Fat and High-Density Lipoprotein and Its Function in Patients with Type 2 Diabetes Mellitus

BACKGROUND

Para and perirenal fat is a fat pad surrounding the kidneys. Recent studies showed the association between para and perirenal fat and cardiovascular diseases including atherosclerosis and hypertension. We aimed to assess the relationship between para-perirenal ultrasonographic fat thickness and serum high-density lipoprotein (HDL) level and cholesterol efflux capacity of HDL in patients with type 2 diabetes mellitus (T2DM).

METHODS

We recruited 58 subjects with T2DM and collected anthropometric indices including height, weight, waist circumference, and other clinical data. Para-perirenal ultrasonographic fat thickness (PUFT) was measured via ultrasound. Serum lipid profile and other metabolic indices were determined as well. Correlation analysis and regression analysis were performed to analyze the relationship between PUFT and HDL level and cholesterol efflux capacity in all patients and subgroups.

RESULTS

Patients with higher PUFT have lower serum HDL level but increased cholesterol efflux capacity. Further analysis showed that PUFT negatively correlated with the serum HDL level in all patients, with no difference in groups divided by body mass index (BMI). In addition, PUFT was positively correlated with cholesterol efflux capacity in all patients. Multiple stepwise regression analysis showed an independent association of PUFT and serum HDL level and cholesterol efflux capacity.

CONCLUSIONS

PUFT is closely correlated with the serum HDL level and cholesterol efflux capacity in patients with T2DM.

OX-HDL: A Starring Role in Cardiorenal Syndrome and the Effects of Heme Oxygenase-1 Intervention

In this review, we will evaluate how high-density lipoprotein (HDL) and the reverse cholesterol transport (RCT) pathway are critical for proper cardiovascular-renal physiology. We will begin by reviewing the basic concepts of HDL cholesterol synthesis and pathway regulation, followed by cardiorenal syndrome (CRS) pathophysiology. After explaining how the HDL and RCT pathways become dysfunctional through oxidative processes, we will elaborate on the potential role of HDL dysfunction in CRS. We will then present findings on how HDL function and the inducible antioxidant gene heme oxygenase-1 (HO-1) are interconnected and how induction of HO-1 is protective against HDL dysfunction and important for the proper functioning of the cardiovascular-renal system. This will substantiate the proposal of HO-1 as a novel therapeutic target to prevent HDL dysfunction and, consequently, cardiovascular disease, renal dysfunction, and the onset of CRS.

Rationale and design of the expanded combination of evolocumab plus empagliflozin in diabetes: EXCEED-BHS3 trial

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) remain at increased cardiovascular residual risk and endothelial dysfunction, even after optimizing metabolic control and treatment by sodium-glucose-2 transporter inhibitors (SGLT2-is). The present study was based on the hypothesis that proprotein convertase subtilisin/kexin 9 inhibitor (PCSK9i) therapy may mitigate endothelial dysfunction in T2DM patients who are on regular treatment by SGLT2-i.

METHODS

The EXCEED-BHS3 is a prospective, single-center, investigator-blinded, open-label, randomized clinical trial. Participants (n = 110) will be randomized (1:1) to either empagliflozin 25 mg/day alone or empagliflozin 25 mg/day plus evolocumab 140 mg every 2 weeks in addition to optimal medical care. The primary endpoint was defined as the change in the 1-min flow-mediated dilation (FMD) after 16 weeks of treatment. The secondary endpoint is the FMD change after ischemia/reperfusion injury protocol (reserve FMD) after 16 weeks of treatment. Exploratory outcomes comprise the change in FMD and reserve FMD after 8 weeks of treatment and the change after 16 weeks of treatment in the following parameters: plasma levels of nitric oxide, vascular cell adhesion molecule-1 and isoprostane, high-density lipoprotein (HDL) and low-density lipoprotein subfractions profile, HDL function, blood pressure, body mass index, waist circumference and adipokines.

CONCLUSION

This will be the first study to evaluate the add-on effect of PCSK9i on endothelial function of T2DM patients under regular use of empagliflozin.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03932721.

Structure-function relationships of HDL in diabetes and coronary heart disease

High-density lipoproteins (HDL) contain hundreds of lipid species and proteins and exert many potentially vasoprotective and antidiabetogenic activities on cells. To resolve structure-function-disease relationships of HDL, we characterized HDL of 51 healthy subjects and 98 patients with diabetes (T2DM), coronary heart disease (CHD), or both for protein and lipid composition, as well as functionality in 5 cell types. The integration of 40 clinical characteristics, 34 nuclear magnetic resonance (NMR) features, 182 proteins, 227 lipid species, and 12 functional read-outs by high-dimensional statistical modeling revealed, first, that CHD and T2DM are associated with different changes of HDL in size distribution, protein and lipid composition, and function. Second, different cellular functions of HDL are weakly correlated with each other and determined by different structural components. Cholesterol efflux capacity (CEC) was no proxy of other functions. Third, 3 potentially novel determinants of HDL function were identified and validated by the use of artificially reconstituted HDL, namely the sphingadienine-based sphingomyelin SM 42:3 and glycosylphosphatidylinositol-phospholipase D1 for the ability of HDL to inhibit starvation-induced apoptosis of human aortic endothelial cells and apolipoprotein F for the ability of HDL to promote maximal respiration of brown adipocytes.

Novel Associations between Related Proteins and Cellular Effects of High-Density Lipoprotein

BACKGROUND AND OBJECTIVES

Recent studies have examined the structure-function relationship of high-density lipoprotein (HDL). This study aimed to identify and rank HDL-associated proteins involved in several biological function of HDL.

METHODS

HDLs isolated from 48 participants were analyzed. Cholesterol efflux capacity, effect of HDL on nitric oxide production, and vascular cell adhesion molecule-1 expression were assessed. The relative abundance of identified proteins in the highest vs. lowest quartile was expressed using the normalized spectral abundance factor ratio.

RESULTS

After adjustment by multiple testing, six proteins, thyroxine-binding globulin, alpha-1B-glycoprotein, plasma serine protease inhibitor, vitronectin, angiotensinogen, and serum amyloid A-4, were more abundant (relative abundance ratio ≥2) in HDLs with the highest cholesterol efflux capacity. In contrast, three proteins, complement C4-A, alpha-2-macroglobulin, and immunoglobulin mu chain C region, were less abundant (relative abundance ratio <0.5). In terms of nitric oxide production and vascular cell adhesion molecule-1 expression, no proteins showed abundance ratios ≥2 or <0.5 after adjustment. Proteins correlated with the functional parameters of HDL belonged to diverse biological categories.

CONCLUSIONS

In summary, this study ranked proteins showing higher or lower abundance in HDLs with high functional capacities and newly identified multiple proteins linked to cholesterol efflux capacity.