High-Density Lipoprotein Cholesterol and Cause-Specific Mortality in Individuals Without Previous Cardiovascular Conditions

High-density lipoprotein revisited: biological functions and clinical relevance

Previous interest in high-density lipoproteins (HDLs) focused on their possible protective role in atherosclerotic cardiovascular disease (ASCVD). Evidence from genetic studies and randomized trials, however, questioned that the inverse association of HDL-cholesterol (HDL-C) is causal. This review aims to provide an update on the role of HDL in health and disease, also beyond ASCVD. Through evolution from invertebrates, HDLs are the principal lipoproteins, while apolipoprotein B-containing lipoproteins first developed in vertebrates. HDLs transport cholesterol and other lipids between different cells like a reusable ferry, but serve many other functions including communication with cells and the inactivation of biohazards like bacterial lipopolysaccharides. These functions are exerted by entire HDL particles or distinct proteins or lipids carried by HDL rather than by its cholesterol cargo measured as HDL-C. Neither does HDL-C measurement reflect the efficiency of reverse cholesterol transport. Recent studies indicate that functional measures of HDL, notably cholesterol efflux capacity, numbers of HDL particles, or distinct HDL proteins are better predictors of ASCVD events than HDL-C. Low HDL-C levels are related observationally, but also genetically, to increased risks of infectious diseases, death during sepsis, diabetes mellitus, and chronic kidney disease. Additional, but only observational, data indicate associations of low HDL-C with various autoimmune diseases, and cancers, as well as all-cause mortality. Conversely, extremely high HDL-C levels are associated with an increased risk of age-related macular degeneration (also genetically), infectious disease, and all-cause mortality. HDL encompasses dynamic multimolecular and multifunctional lipoproteins that likely emerged during evolution to serve several physiological roles and prevent or heal pathologies beyond ASCVD. For any clinical exploitation of HDL, the indirect marker HDL-C must be replaced by direct biomarkers reflecting the causal role of HDL in the respective disease.

The associations between exercise and lipid biomarkers

Cardiovascular diseases (CVD) remain the leading cause of death globally, and further efforts are being undertaken to understand and modify CVD risk factors, such as dyslipidemia (DLD), hypertension, and diabetes. The sedentary lifestyle of most individuals today contributes to the prevalence of these conditions. Uncontrolled dyslipidemia serves as a fertile ground for atherosclerotic plaque formation, while lipoproteins (Lp) act as cofactors for inflammatory processes that cause plaque destabilization leading to subsequent CVD events. As such, many health experts and institutions continue to emphasize the importance of cardiorespiratory fitness (CRF) and muscular strength (MusS) with the intent to reduce atherogenic lipoproteins and proprotein convertase subtilisin kexin type 9 (PCSK-9) expression. Concordantly, the two modes of exercise training (ET), such as aerobic ET (aET) and resistance ET (rET) have both demonstrated to improve CRF and MusS, respectively. Although both modes of ET were shown to independently reduce mortality, participation in both forms resulted in a more pronounced improvement in cholesterol levels and CVD-related mortality. Though reduction of adiposity is not a pre-requisite to achieve better control of DLD through increased CRF and MusS, the beneficial effects of physical activity on the inflammatory processes linked to atherosclerosis are almost always associated with a simultaneous decrease in overall adiposity. It is therefore essential to promote both aET and rET, including weight loss in order to attenuate the risks stemming from atherosclerosis and its proinflammatory components.

Strength of association of classical vascular risk factors in young patients with ischaemic stroke: a case-control study

INTRODUCTION

Recent studies have reported an increasing incidence of ischaemic stroke among young adults. However, the strength of the association between traditional vascular risk factors has not been fully established.

METHODS

We compared 120 patients with a first ischaemic stroke before the age of 55 years admitted to the stroke unit of our centre with 600 healthy non-stroke controls from a population-based cohort study (HERMEX), matched for sex. Risk factors assessed included: hypertension, obesity, auricular fibrillation, current smoking, estimated glomerular filtration rate (eGFR), total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglycerides, high-density lipoprotein cholesterol (HDL-C) and diabetes mellitus. We used logistic regression analysis and calculated population attributable risk. We performed an overall analysis, by sex and aetiological subgroup.

RESULTS

Using logistic regression analysis, we found that overall, the significant risk factors were: hypertension (OR: 1.58; 95%CI: 1.01-2.50), atrial fibrillation (OR: 4.77; 95%CI: 1.20-19.00), low eGFR (OR: 4.74; 95%CI: 1.3-21.94) and low HDL-C (OR: 5.20; 95%CI: 3.29-8.21), as well as smoking for males (OR: 1.86; 95%CI: 1.14-3.03). LDL-C showed an inverse association with stroke. The population attributable risk for HDL-C was 37.8% and for hypertension 21.1%. In terms of aetiological subgroups, only low HDL-C was associated with stroke of undetermined aetiology.

CONCLUSIONS

Hypertension, auricular fibrillation, low eGFR, and low HDL-C, plus tobacco use in men, are the main risk factors among patients under 55 years of age with a first ischaemic stroke. We believe that it would be of particular interest to further explore the management of low HDL-C levels as part of preventive strategies in young stroke patients.

Crosstalk between high-density lipoproteins and endothelial cells in health and disease: Insights into sex-dependent modulation

Atherosclerotic cardiovascular disease is the leading cause of death worldwide. Intense research in vascular biology has advanced our knowledge of molecular mechanisms of its onset and progression until complications; however, several aspects of the patho-physiology of atherosclerosis remain to be further elucidated. Endothelial cell homeostasis is fundamental to prevent atherosclerosis as the appearance of endothelial cell dysfunction is considered the first pro-atherosclerotic vascular modification. Physiologically, high density lipoproteins (HDLs) exert protective actions for vessels and in particular for ECs. Indeed, HDLs promote endothelial-dependent vasorelaxation, contribute to the regulation of vascular lipid metabolism, and have immune-modulatory, anti-inflammatory and anti-oxidative properties. Sex- and gender-dependent differences are increasingly recognized as important, although not fully elucidated, factors in cardiovascular health and disease patho-physiology. In this review, we highlight the importance of sex hormones and sex-specific gene expression in the regulation of HDL and EC cross-talk and their contribution to cardiovascular disease.

High HDL (High-Density Lipoprotein) Cholesterol Increases Cardiovascular Risk in Hypertensive Patients

BACKGROUND

Emerging evidence suggests that elevated circulating levels of HDL-C (high-density lipoprotein cholesterol) could be linked to an increased mortality risk. However, to the best of our knowledge, the relationship between HDL-C and specific cardiovascular events has never been investigated in patients with hypertension.

METHODS

To fill this knowledge gap, we analyzed the relationship between HDL-C levels and cardiovascular events in hypertensive patients within the Campania Salute Network in Southern Italy.

RESULTS

We studied 11 987 patients with hypertension, who were followed for 25 534 person-years. Our population was divided in 3 groups according to the HDL-C plasma levels: HDL-C<40 mg/dL (low HDL-C); HDL-C between 40 and 80 mg/dL (medium HDL-C); and HDL-C>80 mg/dL (high HDL-C). At the follow-up analysis, adjusting for potential confounders, we observed a total of 245 cardiovascular events with a significantly increased risk of cardiovascular events in the low HDL-C group and in the high HDL-C arm compared with the medium HDL-C group. The spline analysis revealed a nonlinear U-shaped association between HDL-C levels and cardiovascular outcomes. Interestingly, the increased cardiovascular risk associated with high HDL-C was not confirmed in female patients.

CONCLUSIONS

Our data demonstrate that there is a U-shaped association between HDL-C and the risk of cardiovascular events in male patients with hypertension.

Associations of HDL-C/LDL-C with myocardial infarction, all-cause mortality, haemorrhagic stroke and ischaemic stroke: a longitudinal study based on 384 093 participants from the UK Biobank

OBJECTIVE

To explore the correlations of high-density lipoprotein cholesterol (HDL-C)/low-density lipoprotein cholesterol (LDL-C) with myocardial infarction (MI), all-cause mortality, haemorrhagic stroke and ischaemic stroke, as well as the joint association of genetic susceptibility and HDL-C/LDL-C with the MI risk.

METHODS AND RESULTS

This study selected 384 093 participants from the UK Biobank (UKB) database. First, restricted cubic splines indicated non-linear associations of HDL-C/LDL-C with MI, ischaemic stroke and all-cause mortality. Second, a Cox proportional-hazards model indicated that compared with HDL-C/LDL-C=0.4-0.6, HDL-C/LDL-C<0.4 and >0.6 were correlated with all-cause mortality (HR=0.97 for HDL-C/LDL-C<0.4, 95% CI=0.939 to 0.999, p<0.05; HR=1.21 for HDL-C/LDL-C>0.6, 95% CI=1.16 to 1.26, p<0.001) after full multivariable adjustment. HDL-C/LDL-C<0.4 was correlated with a higher MI risk (HR=1.36, 95% CI=1.28 to 1.44, p<0.05) and ischaemic stroke (HR=1.12, 95% CI=1.02 to 1.22, p<0.05) after full multivariable adjustment. HDL-C/LDL-C>0.6 was associated with higher risk haemorrhagic stroke risk after full multivariable adjustment (HR=1.25, 95% CI=1.03 to 1.52, p<0.05). Third, after calculating the coronary heart disease Genetic Risk Score (CHD-GRS) of each participant, the Cox proportional-hazards model indicated that compared with low CHD-GRS and HDL-C/LDL-C=0.4-0.6, participants with a combination of high CHD-GRS and HDL-C/LDL-C<0.4 were associated with the highest MI risk (HR=2.45, 95% CI=2.15 to 2.8, p<0.001). Participants with HDL-C/LDL-C<0.4 were correlated with a higher MI risk regardless of whether they had a high, intermediate or low CHD-GRS.

CONCLUSION

In UKB participants, HDL-C/LDL-C ratio of 0.4-0.6 was correlated with lower MI risk, all-cause mortality, haemorrhagic stroke and ischaemic stroke. Participants with HDL-C/LDL-C<0.4 were correlated with a higher MI risk regardless of whether they had a high, intermediate or low CHD-GRS. The clinical significance and impact of HDL-C/LDL-C need to be further verified in future studies.

Association of cluster determinant 36, scavenger receptor class B type 1, and major facilitator superfamily domain containing the 2a genetic polymorphism with serum lipid profile in aging population with type 2 diabetes mellitus

Background

Lipid metabolism disorder commonly happens in subjects with Type 2 diabetes mellitus (T2DM) which may be linked to genetic variants of lipid metabolism-related genes. However, few studies have explored the relationship between lipid metabolism-related gene polymorphism and serum lipid profile in aging subjects with T2DM. The present study was designed to explore the impact of genetic polymorphism of cluster determinant 36 (CD36) (rs1049673, rs1054516, rs2151916), scavenger receptor class B type 1 (SCARB1) (rs5888), and major facilitator superfamily domain containing the 2a (MFSD2A) (rs12083239, rs4233508, rs12072037) on the relationship between circulating lipids in aging subjects with T2DM.

Methods

205 T2DM patients and 205 age and gender matched control subjects were recruited. Information on demographic characteristics was collected by using a self-administered questionnaire. Fasting venous blood samples were taken for lipid-related gene genotyping and serum lipid profile measurement. The Chi-square test was used to compare percentage differences and to calculate P-value for Hardy-Weinberg equilibrium. Logistic regression and multiple linear regression were used to explore the risk or correlation between variables, and general linear model (GLM) was used to compare the means of serum lipids between the groups.

Results

In T2DM group, CD36 rs1054516 and MFSD2A rs12072037 were correlated with serum TC level. In control group, CD36 rs1049673 was correlated with serum HDL-C level. Meanwhile, T2DM subjects with MFSD2A rs12083239 (CG), MFSD2A rs4233508 (TT), and MFSD2A rs12072037 (AA) had higher TG level than control subjects. T2DM subjects with CD36 rs1049673 (CG, GG), CD36 rs1054516 (CT), CD36 rs2151916 (TT, CT), SCARB1 rs5888 (GG), MFSD2A rs12083239 (GG, CG), MFSD2A rs4233508 (TT), and MFSD2A rs12072037 (CA, AA) had lower HDL-C level than control subjects. T2DM subjects with MFSD2A rs12072037 (AA) had lower LDL-C level than control subjects. In dominant model, major genotype (GG) of SCARB1 gene was associated with the risk of T2DM (OR = 0.636, P = 0.032).

Conclusion

The genetic polymorphism of CD36 (rs1049673, rs1054516, rs2151916), SCARB1 (rs5888), and MFSD2A (rs12083239, rs4233508, rs12072037) were associated with serum lipids in T2DM subjects. The SCARB1 rs5888 major genotype (GG) was a protective factor for T2DM. Large scale cohort study is required to determine the relationship between lipid metabolism-related gene polymorphism, serum lipid profile and T2DM in aging subjects.

High-Density Lipoprotein and Cardiovascular Disease-Where do We Stand?

Decades of research have shown that high-density lipoprotein cholesterol (HDL-C) levels in humans are associated with atherosclerotic cardiovascular disease (ASCVD). This association is strong and coherent across populations and remains after the elimination of covariates. Animal studies show that increasing HDL particles prevent atherosclerosis, and basic work on the biology of HDL supports a strong biological plausibility for a therapeutic target. This enthusiasm is dampened by Mendelian randomization data showing that HDL-C may not be causal in ASCVD. Furthermore, drugs that increase HDL-C have largely failed to prevent or treat ASCVD.

Prevalence and Treatment of Familial Hypercholesterolemia and Severe Hypercholesterolemia in Older Adults in Ontario, Canada

Background

A simplified Canadian definition was recently developed to enable identification of individuals with familial hypercholesterolemia (FH) and severe hypercholesterolemia in the general population. Our objective was to use a modified version of this new definition to assess contemporary disease prevalence, treatment patterns, and low-density lipoprotein cholesterol (LDL-C) control in Ontario, Canada.

Methods

We identified individuals aged 66 to 105 years who were alive as of January 1, 2011, using the Cardiovascular Health in Ambulatory Care Research Team (CANHEART) database, which was created by linking 19 population-based health databases in Ontario. Hypercholesterolemia was identified using LDL-C values. Cholesterol reduction and lipid-lowering treatment were assessed at time of diagnosis and after at least 2 and 5 years’ follow-up.

Results

Among 922,464 individuals, 2440 (0.26%) met criteria for definite or probable FH, and 72,893 (7.90%) for severe hypercholesterolemia. At diagnosis, mean LDL-C concentration was 9.52 mmol/L for those with definite FH, 5.83 mmol/L for those with probable FH, 5.73 mmol/L for those with severe hypercholesterolemia, and 3.33 mmol/L for all other individuals. After > 5 years, LDL-C concentration remained elevated at 3.58 mmol/L for those with definite FH, 2.72 mmol/L for those with probable FH, and 2.93 mmol/L for those with severe hypercholesteremia. Use of statin therapy was initially high (83% of those with definite FH, 78% of those with probable FH, 62% of those with severe hypercholesterolemia); however, fewer patients remained on statins at follow-up at > 5 years (62% of those with definite FH, 67% of those with probable FH, 58% of those with severe hypercholesterolemia).

Conclusions

Among older Ontarians, we estimated that 1 in 378 individuals had FH, and 1 in 13 had severe hypercholesterolemia. Despite being at substantially increased cardiovascular risk, these patients acheived suboptimal LDL-C level control and fewer were on medical therapy at follow-up.

Integrating Health Data-Driven Machine Learning Algorithms to Evaluate Risk Factors of Early Stage Hypertension at Different Levels of HDL and LDL Cholesterol

Purpose: Cardiovascular disease (CVD) is a major worldwide health burden. As the risk factors of CVD, hypertension, and hyperlipidemia are most mentioned. Early stage hypertension in the population with dyslipidemia is an important public health hazard. This study was the application of data-driven machine learning (ML), demonstrating complex relationships between risk factors and outcomes and promising predictive performance with vast amounts of medical data, aimed to investigate the association between dyslipidemia and the incidence of early stage hypertension in a large cohort with normal blood pressure at baseline. Methods: This study analyzed annual health screening data for 71,108 people from 2005 to 2017, including data for 27 risk-related indicators, sourced from the MJ Group, a major health screening center in Taiwan. We used five machine learning (ML) methods—stochastic gradient boosting (SGB), multivariate adaptive regression splines (MARS), least absolute shrinkage and selection operator regression (Lasso), ridge regression (Ridge), and gradient boosting with categorical features support (CatBoost)—to develop a multi-stage ML algorithm-based prediction scheme and then evaluate important risk factors at the early stage of hypertension, especially for groups with high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) levels within or out of the reference range. Results: Age, body mass index, waist circumference, waist-to-hip ratio, fasting plasma glucose, and C-reactive protein (CRP) were associated with hypertension. The hemoglobin level was also a positive contributor to blood pressure elevation and it appeared among the top three important risk factors in all LDL-C/HDL-C groups; therefore, these variables may be important in affecting blood pressure in the early stage of hypertension. A residual contribution to blood pressure elevation was found in groups with increased LDL-C. This suggests that LDL-C levels are associated with CPR levels, and that the LDL-C level may be an important factor for predicting the development of hypertension. Conclusion: The five prediction models provided similar classifications of risk factors. The results of this study show that an increase in LDL-C is more important than the start of a drop in HDL-C in health screening of sub-healthy adults. The findings of this study should be of value to health awareness raising about hypertension and further discussion and follow-up research.

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.

Mathematical Modelling of Material Transfer to High-Density Lipoprotein (HDL) upon Triglyceride Lipolysis by Lipoprotein Lipase: Relevance to Cardioprotective Role of HDL

High-density lipoprotein (HDL) contributes to lipolysis of triglyceride-rich lipoprotein (TGRL) by lipoprotein lipase (LPL) via acquirement of surface lipids, including free cholesterol (FC), released upon lipolysis. According to the reverse remnant-cholesterol transport (RRT) hypothesis recently developed by us, acquirement of FC by HDL is reduced at both low and extremely high HDL concentrations, potentially underlying the U-shaped relationship between HDL-cholesterol and cardiovascular disease. Mechanisms underlying impaired FC transfer however remain indeterminate. We developed a mathematical model of material transfer to HDL upon TGRL lipolysis by LPL. Consistent with experimental observations, mathematical modelling showed that surface components of TGRL, including FC, were accumulated in HDL upon lipolysis. The modelling successfully reproduced major features of cholesterol accumulation in HDL observed experimentally, notably saturation of this process over time and appearance of a maximum as a function of HDL concentration. The calculations suggested that the both phenomena resulted from competitive fluxes of FC through the HDL pool, including primarily those driven by FC concentration gradient between TGRL and HDL on the one hand and mediated by lecithin-cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) on the other hand. These findings provide novel opportunities to revisit our view of HDL in the framework of RRT.

Sex-Specific U-Shaped Relationships Between High-Density Lipoprotein Cholesterol Levels and 10-year Major Adverse Cardiovascular Events: A Nationwide Cohort Study of 5.7 Million South Koreans

Background

High-density lipoprotein cholesterol (HDL-C) is a well-known predictor of atherosclerotic cardiovascular diseases (ASCVD). We explored the relationships between HDL-C levels and 10-year major adverse cardiovascular events (MACE) and provided sex-specific upper reference limits for HDL-C levels.

Methods

Based on the Korean National Health Insurance Sharing Service, we identified 5,703,897 subjects (women, 48%) with age ≥40 years, eligible HDL-C results, and no prior ASCVD in 2009. We investigated the distribution of 10-year MACE according to HDL-C levels in 10 mg/dL (0.26 mmol/L) intervals and in three HDL-C groups (low: men <40 mg/dL [1.03 mmol/L], women <50 mg/dL [1.29 mmol/L]; high: between low and extremely high levels; and extremely high: >90 mg/dL [2.33 mmol/L]).

Results

There were U-shaped relationships between HDL-C levels and 10-year MACE with later inflection in women than in men (nadir: 80-99 mg/dL [2.07-2.56 mmol/L] and 50-59 mg/dL [1.29-1.53 mmol/L], respectively). In men, the extremely high HDL-C group showed significantly higher 10-year MACE than the high group (28.1% vs. 24.6%, P< 0.0001). In women, the extremely high group showed the lowest 10-year MACE; if the extremely high starting point was raised to 130 mg/dL, it became similar to that in men and showed higher 10-year MACE than the high group (25.6% vs. 20.1%, P<0.0001).

Conclusions

The 10-year MACE showed U-shaped relationships with HDL-C levels, and extremely high HDL-C level at 90 mg/dL (2.33 mmol/L) in men was corresponding in risk to 130 mg/dL (3.36 mmol/L) in women.

Association Between High-Density Lipoprotein Cholesterol Levels and Adverse Cardiovascular Outcomes in High-risk Populations

Importance

Previous studies have shown lower cardiovascular risk with higher high-density lipoprotein cholesterol (HDL-C) levels. However, recent data in the general population have shown increased risk of adverse outcomes at very high HDL-C concentrations.

Objective

To study the association between very high HDL-C levels (>80 mg/dL) and mortality in patients with coronary artery disease (CAD) and to investigate the association of known HDL-C genotypes with high HDL-C level outcomes.

Design, Setting, and Participants

This prospective, multicenter, cohort study, conducted from 2006 to present in the UK and from 2003 to present in Atlanta, Georgia, recruited patients with CAD from the UK Biobank (UKB) and the Emory Cardiovascular Biobank (EmCAB), respectively. Patients without confirmed CAD were excluded from the study. Data analyses were conducted from May 10, 2020, to April 28, 2021.

Exposure

High HDL-C levels (>80 mg/dL).

Main Outcomes and Measures

The primary outcome was all-cause death. The secondary outcome was cardiovascular death.

Results

A total of 14 478 participants (mean [SD] age, 62.1 [5.8] years; 11 034 men [76.2%]) from the UKB and 5467 participants (mean [SD] age, 63.8 [12.3] years; 3632 men [66.4%]) from the EmCAB were included in the study. Over a median follow-up of 8.9 (IQR, 8.0-9.7) years in the UKB and 6.7 (IQR, 4.0-10.8) years in the EmCAB, a U-shaped association with outcomes was observed with higher risk in those with both low and very high HDL-C levels compared with those with midrange values. Very high HDL-C levels (>80 mg/dL) were associated with increased risk of all-cause death (hazard ratio [HR], 1.96; 95% CI, 1.42-2.71; P < .001) and cardiovascular death (HR, 1.71; 95% CI, 1.09-2.68; P = .02) compared with those with HDL-C levels in the range of 40 to 60 mg/dL in the UKB after adjustment for confounding factors. These results were replicated in the EmCAB. These associations persisted after adjustment for the HDL-C genetic risk score within the UKB. Sensitivity analyses demonstrated that the risk of all-cause mortality in the very high HDL-C group was higher among men than women in the UKB (HR, 2.63; 95% CI, 1.75-3.95; P < .001 vs HR, 1.39; 95% CI, 0.82-2.35; P = .23).

Conclusions and Relevance

Results of this cohort study suggest that very high HDL-C levels are paradoxically associated with higher mortality risk in individuals with CAD. This association was independent of the common polymorphisms associated with high HDL-C levels.

Macrophage SR-B1 in atherosclerotic cardiovascular disease

PURPOSE OF REVIEW

Scavenger receptor class B type 1 (SR-B1) promotes atheroprotection through its role in HDL metabolism and reverse cholesterol transport in the liver. However, evidence indicates that SR-B1 may impact atherosclerosis through nonhepatic mechanisms.

RECENT FINDINGS

Recent studies have brought to light various mechanisms by which SR-B1 affects lesional macrophage function and protects against atherosclerosis. Efferocytosis is efficient in early atherosclerotic lesions. At this stage, and beyond its role in cholesterol efflux, SR-B1 promotes free cholesterol-induced apoptosis of macrophages through its control of apoptosis inhibitor of macrophage (AIM). At more advanced stages, macrophage SR-B1 binds and mediates the removal of apoptotic cells. SR-B1 also participates in the induction of autophagy which limits necrotic core formation and increases plaque stability.

SUMMARY

These studies shed new light on the atheroprotective role of SR-B1 by emphasizing its essential contribution in macrophages during atherogenesis as a function of lesion stages. These new findings suggest that macrophage SR-B1 is a therapeutic target in cardiovascular disease.

Lymphocyte activation gene-3-associated protein networks are associated with HDL-cholesterol and mortality in the Trans-omics for Precision Medicine program

Deficiency of the immune checkpoint lymphocyte activation gene-3 (LAG3) protein is significantly associated with both elevated HDL-cholesterol (HDL-C) and myocardial infarction risk. We determined the association of genetic variants within ±500 kb of LAG3 with plasma LAG3 and defined LAG3-associated plasma proteins with HDL-C and clinical outcomes. Whole genome sequencing and plasma proteomics were obtained from the Multi-Ethnic Study of Atherosclerosis (MESA) and the Framingham Heart Study (FHS) cohorts as part of the Trans-Omics for Precision Medicine program. In situ Hi-C chromatin capture was performed in EBV-transformed cell lines isolated from four MESA participants. Genetic association analyses were performed in MESA using multivariate regression models, with validation in FHS. A LAG3-associated protein network was tested for association with HDL-C, coronary heart disease, and all-cause mortality. We identify an association between the LAG3 rs3782735 variant and plasma LAG3 protein. Proteomics analysis reveals 183 proteins significantly associated with LAG3 with four proteins associated with HDL-C. Four proteins discovered for association with all-cause mortality in FHS shows nominal associations in MESA. Chromatin capture analysis reveals significant cis interactions between LAG3 and C1S, LRIG3, TNFRSF1A, and trans interactions between LAG3 and B2M. A LAG3-associated protein network has significant associations with HDL-C and mortality.

Rodriguez et al. use whole genome sequencing and plasma proteomics from the Multi-Ethnic Study of Atherosclerosis (MESA) and the Framingham Heart Study (FHS) cohorts of the Trans-Omics for Precision Medicine program and perform in situ Hi-C chromatin capture in cell lines isolated from four MESA participants. They demonstrate that lymphocyte activation gene-3 protein networks are associated with HDL-cholesterol and mortality, which could guide the development of precision medicine.

Monocyte-to-high-density lipoprotein-cholesterol ratio (MHR) and the risk of all-cause and cardiovascular mortality: a nationwide cohort study in the United States

Background

Elevated monocyte-to-high-density lipoprotein-cholesterol ratio (MHR) is relevant to higher all-cause and cardiovascular mortality in patients with coronary artery disease and other comorbidities. However, the predictive values of MHR for mortality in the general population have been underutilized. This study investigated the association of MHR with all-cause and cardiovascular mortality in the adult population of the United States.

Methods

This study included 34,335 participants (≥20 years) from the National Health and Nutrition Examination Survey 1999–2014 that were grouped according to MHR tertiles. Kaplan-Meier plots and long-rank tests were employed to investigate differences in survival among the groups. Moreover, the relationship of MHR with all-cause and cardiovascular mortality was further explored using multivariate Cox regression and restricted cubic spline analysis.

Results

During the average follow-up of 93.5 ± 56 months, 4310 (12.6%) participants died, with 754 (2.2%) deaths attributed to cardiovascular diseases. Kaplan-Meier analysis revealed statistically obvious differences in all-cause and cardiovascular mortality among the MHR tertiles (log-rank test: all P < 0.001). In multi-adjusted models, participants in the highest tertile of MHR had an increased risk of all-cause (hazard ratio [HR] = 1.19, 95% confidence interval [CI] 1.10–1.29) and cardiovascular mortality (HR = 1.44, 95% CI 1.17–1.77), compared to those in the lowest tertile. Furthermore, the restricted cubic spline curve indicated that MHR had a non-linear association with all-cause mortality (P < 0.001), and the inflection point of MHR was 0.006. Each 2-fold change in MHR exhibited a 32% decrease (HR = 0.68, 95%CI 0.58–0.82) and a 20% increase (HR = 1.20, 95%CI 1.13–1.27) in the risk of all-cause mortality on the left and right flanks of the inflection point, respectively. Additionally, the risk of cardiovascular mortality increased by 21% per 2-fold change in MHR (HR = 1.21, 95%CI 1.07–1.36) in a linear manner.

Conclusions

MHR was significantly related to all-cause and cardiovascular mortality in the general population independent of established risk factors.

Very High High-Density Lipoprotein Cholesterol Levels and Cardiovascular Mortality

Previous studies have shown reduced cardiovascular risk with increasing high-density lipoprotein cholesterol (HDL-C) levels. However, recent data in the general population have shown increased risk of adverse outcomes at very high concentrations of HDL-C. Thus, we aimed to study the gender-specific relation between very high HDL-C levels (>80, >100 mg/100 ml) and adverse cardiovascular outcomes and the genetic basis in the general population enrolled in the United Kingdom Biobank. A total of 415,416 participants enrolled in the United Kingdom Biobank without coronary artery disease were included in this prospective cohort study, with a median follow-up of 9 years. A high HDL-C level >80 mg/100 ml was associated with increased risk of all-cause death (Hazard ratio [HR] 1.11, confidence interval [CI] 1.03 to 1.20, p = 0.005) and cardiovascular death (HR 1.24, CI 1.05 to 1.46, p = 0.01) after adjustment for age, gender, race, body mass index, hypertension, smoking, triglycerides, LDL-C, stroke history, heart attack history, diabetes, eGFR, and frequent alcohol use (defined as ≥3 times/week) using Cox proportional hazard and Fine and Gray's subdistribution hazard models, respectively. In gender-stratified analyses, such associations were only observed in men (all-cause death HR 1.79, CI 1.59 to 2.02, p <0.0001; cardiovascular death HR 1.92, CI 1.52 to 2.42, p <0.0001), but not in women (all-cause death HR 0.97, CI 0.88 to 1.06, p = 0.50; cardiovascular death HR 1.04, CI 0.83 to 1.31, p = 0.70). The findings persisted after adjusting for the genetic risk score comprised of known HDL-C-associated single nucleotide polymorphisms. Very high HDL-C levels are associated with an increased risk of all-cause death and cardiovascular death among men but not in women in the general population free of coronary artery disease.

HDL maturation and remodelling

Cholesterol in the circulation is mostly transported in an esterified form as a component of lipoproteins. The majority of these cholesteryl esters are produced in nascent, discoidal high density lipoproteins (HDLs) by the enzyme, lecithin:cholesterol acyltransferase (LCAT). Discoidal HDLs are discrete populations of particles that consist of a phospholipid bilayer, the hydrophobic acyl chains of which are shielded from the aqueous environment by apolipoproteins that also confer water solubility on the particles. The progressive LCAT-mediated accumulation of cholesteryl esters in discoidal HDLs generates the spherical HDLs that predominate in normal human plasma. Spherical HDLs contain a core of water insoluble, neutral lipids (cholesteryl esters and triglycerides) that is surrounded by a surface monolayer of phospholipids with which apolipoproteins associate. Although spherical HDLs all have the same basic structure, they are extremely diverse in size, composition, and function. This review is concerned with how the biogenesis of discoidal and spherical HDLs is regulated and the mechanistic basis of their size and compositional heterogeneity. Current understanding of the impact of this heterogeneity on the therapeutic potential of HDLs of varying size and composition is also addressed in the context of several disease states.

U-Shaped Relationship of High-Density Lipoprotein Cholesterol and Incidence of Total, Ischemic and Hemorrhagic Stroke: A Prospective Cohort Study

BACKGROUND

We aimed to investigate the association between serially measured HDL-C (high-density lipoprotein cholesterol) levels and stroke risk in a prospective cohort study.

METHODS

We included 96 258 individuals (79.6% men, mean age 51.5 years) without a history of stroke, myocardial infarction, or cancer at baseline from the Kailuan Study, with repeated measurements of HDL-C in 2006, 2008, 2010, 2012, 2014, and 2016. Cumulatively, averaged HDL-C concentrations were calculated using all available HDL-C measurements before incidence stroke or end of follow-up (December 31, 2017). Incident stroke cases were confirmed by review of medical records and further subclassified into ischemic or hemorrhagic stroke. Cox proportional hazards regression and restricted cubic splines were used to examine these associations.

RESULTS

During a median follow-up of 10.7 years, 5012 incident stroke cases occurred. Restricted cubic splines analysis suggested a U-shaped association between concentrations of cumulatively averaged HDL-C and risk of stroke (P_nonlinearity <0.001), with the nadir of risk at 1.29 mmol/L. After adjustment for cardiovascular risk factors, individuals with cumulatively averaged HDL-C ≤1.06 mmol/L or ≥2.05 mmol/L had hazard ratios for total stroke of 1.31 (95% CI, 1.15-1.49) and 1.85 (1.63-2.09) compared with those with HDL-C of 1.26 to 1.39 mmol/L. Corresponding hazard ratios were 1.29 (1.11-1.48) and 1.84 (1.60-2.11) for ischemic stroke and 1.54 (1.12-2.12) and 2.29 (1.73-3.04) for hemorrhagic stroke, respectively.

CONCLUSIONS

Both low and high cumulatively averaged HDL-C were associated with an increased risk of ischemic and hemorrhagic strokes.

A New Look at Novel Cardiovascular Risk Biomarkers: The Role of Atherogenic Lipoproteins and Innovative Antidiabetic Therapies

The presence of residual cardiovascular disease (CVD) risk is a current dilemma in clinical practice; indeed, despite optimal management and treatment, a considerable proportion of patients still undergo major CV events. Novel lipoprotein biomarkers are suggested as possible targets for improving the outcomes of patients at higher risk for CVD, and their impact on major CV events and mortality have previously been investigated. Innovative antidiabetic therapies have recently shown a significant reduction in atherogenic lipoproteins, beyond their effects on glucose parameters; it has also been suggested that such anti-atherogenic effect may represent a valuable mechanistic explanation for the cardiovascular benefit of, at least, some of the novel antidiabetic agents, such as glucagon-like peptide-1 receptor agonists. This emphasizes the need for further research in the field in order to clearly assess the effects of innovative treatments on different novel biomarkers, including atherogenic lipoproteins, such as small dense low-density lipoprotein (LDL), lipoprotein(a) (Lp(a)) and dysfunctional high-density lipoprotein (HDL). The current article discusses the clinical importance of novel lipid biomarkers for better management of patients in order to overcome residual cardiovascular risk.

HDL Is Not Dead Yet

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

High-density lipoprotein cholesterol and cardiovascular mortality: a prospective cohort study among 15.8 million adults

AIMS

We aimed to investigate whether the associations between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) mortality and the optimal range differ by age and CVD subtypes.

METHODS AND RESULTS

Korean adults (n = 15,859,501) with no CVD/cancer who received routine health examinations during 2009-2010 were followed until 2018 for CVD mortality. During a mean 8.8 years of follow-up, 108,123 individuals died from CVD. U-curve associations were found between HDL-C and CVD mortality, regardless of sex, age, and CVD subtype. The optimal range was 50-79 mg/dL (1.29-2.06 mmol/L), while it was 40-69 (1.03-1.80), 50-79 (1.29-2.06), and 60-89 (1.55-2.32) mg/dL (mmol/L) in adults aged <45 years, 45-64 years, and 65-99 years, respectively. Assuming linear associations <60 mg/dL, the multivariable-adjusted hazard ratios (HRs) per 39 mg/dL (1 mmol/L) higher level were 0.58 (95% CI = 0.56-0.60), and they were 0.61 (0.52-0.72), 0.58 (0.54-0.62), and 0.59 (0.56-0.61) in individuals aged 18-44, 45-64, and 65-99 years, respectively (P  interaction[age]=0.845). Assuming linear associations in the 60-150 mg/dL range, HDL-C was positively associated with CVD mortality (HR = 1.09, 1.04-1.14). The strongest association was for sudden cardiac death (HR = 1.37), followed by heart failure (HR = 1.20) and intracerebral hemorrhage (HR = 1.13). The HRs were 1.47 (1.23-1.76), 1.17 (1.08-1.28), and 1.03 (0.97-1.08) in individuals aged 18-44, 45-64, and 65-99 years, respectively (P  interaction[age]<0.001).

CONCLUSIONS

Both low and high levels of HDL-C were associated with increased mortality from CVD in the general population, especially sudden cardiac death, heart failure, and intracerebral hemorrhage. High HDL-C levels are not necessarily a sign of good cardiovascular health, especially in younger adults.

The association of apolipoproteins with later-life all-cause and cardiovascular mortality: a population-based study stratified by age

Midlife lipid levels are important predictors of cardiovascular diseases, yet their association with mortality in older adults is less clear. We aimed to (1) identify lipid profiles based on cholesterol, triglycerides, and apolipoproteins using cluster analysis, and (2) investigate how lipid profiles and lipid levels at different ages are associated with later-life all-cause and cardiovascular mortality. We used data from 98,270 individuals in the Swedish AMORIS cohort who had blood measurements between 1985-1996 and were followed until 2012. Over the follow-up (mean 18.0 years), 30,730 (31.3%) individuals died. Three lipid profiles were identified. Compared with reference profile, a high lipid profile (low ApoA-I and high total cholesterol (TC), triglycerides, ApoB, and ApoB/ApoA-I ratio) at ages 39-59 or 60-79 was associated with higher all-cause mortality. A high lipid profile at ≥ 80 years, however, did not confer higher mortality. For the specific markers, high TC (≥ 7.25 mmol/L) was associated with higher all-cause mortality in ages 39-59 but lower mortality in ages 60-79 and ≥ 80. Low ApoA-I (< 1.28 g/L) and high ApoB/ApoA-I ratio (≥ 1.18), on the other hand, were associated with higher cardiovascular mortality regardless of age at lipid measurement, highlighting their potential relevance for survival in both young and older individuals.

High-density lipoprotein cholesterol to apolipoprotein A1 ratio and all-cause mortality among incident peritoneal dialysis patients

BACKGROUND AND AIMS

The ratio of high-density lipoprotein cholesterol to apolipoprotein A1 (HAR) is associated with all-cause mortality in nonchronic kidney disease patients, but its role in predicting all-cause mortality in patients undergoing peritoneal dialysis (PD) is still unclear. The purpose of this study was to investigate the relationship between HAR and all-cause mortality in patients with PD.

METHODS AND RESULTS

The medical records of 1199 patients with PD from November 1, 2005, to August 31, 2019, were collected retrospectively. The main outcome was defined as all-cause mortality. The HAR was divided into three groups by X-tile software. The association between HAR and all-cause mortality was evaluated by Cox models. The Kaplan-Meier method was used for the survival curve. The median follow-up period was 35 months (interquartile range: 20-57 months), with a total of 326 deaths recorded. After multiple adjustments, the risk of all-cause mortality in the high HAR group was 1.96-fold higher than that in the low HAR group (hazard ratio: 1.96; 95% CI, 1.22 to 3.15; P = 0.005). The restricted cubic splines showed that the risk of all-cause mortality increased gradually when HAR was >0.37. In the stratified analysis, a high HAR was linked to a high risk of all-cause mortality in males, patients under 55 years old, and patients without diabetes or cardiovascular disease (CVD).

CONCLUSION

This study suggests that HAR is independently related to all-cause mortality in PD patients, especially in males, patients under 55 years old, and patients without diabetes or CVD.

High-density Lipoprotein Cholesterol as a Risk Factor of Health-Related Quality of Life in 50–70-Year-Old Community-Dwelling Women

BACKGROUND: The prevalence of dyslipidemia, a risk factor of cardiovascular disease, is at present sufficiently high, particularly in the elderly. Health-related quality of life (HRQoL) is also an important outcome in the treatment of dyslipidemia, which is currently more targeted at lowering the low-density lipoprotein cholesterol (LDL-C) concentration. AIM: The aim of this study was to determine the relationship between the high-density lipoprotein cholesterol (HDL-C) concentration and HRQoL in community-dwelling women aged 50–70 years. METHODS: A cross-sectional study involving 137 women aged 50–70 years who underwent blood sampling for determining the concentrations of hemoglobin, total cholesterol (TC), LDL-C, and HDL-C. A questionnaire was given to all subjects regarding data on age, menopausal status, level of education, and also another questionnaire of SF-36 for evaluation HRQoL. Bivariate and multivariate logistic regression analysis was used to identify risk factors associated with HRQoL. RESULTS: In bivariate logistic regression analysis, age, menopausal status, education level, anemia, TC, and LDL-C were found to have non-statistically significant association with HRQoL, but HDL-C was significantly associated with HRQoL (odds ratio = 0.44; 95% Confidence interval [CI] = 0.20–0.97; p = 0.042). In multivariate analysis, menopausal status and education level have a non-statistically significant association with HRQoL, but those normal level of HDL cholesterol was found 0.18 times less likely to be associated with poor HRQoL (Adjusted odds ratio 0.18; 95% CI = 0.03–0.91; p = 0.038). CONCLUSION: This study showed that HDL-C levels were risk factors of HRQoL in women 50–70 years of age.

Association of Serum High-Density Lipoprotein Cholesterol with High Blood Pressures at Checkup: Results of Kanagawa Investigation of Total Checkup Data from the National Database-9 (KITCHEN-9)

BACKGROUND

although high-density lipoprotein has cardioprotective effects, the association between serum high-density lipoprotein cholesterol (HDL-C) and hypertension is poorly understood. Therefore, we investigated whether high and low concentrations of HDL-C are associated with high blood pressure (HBP) using a large healthcare dataset.

METHODS

in a community-based cross-sectional study of 1,493,152 Japanese people (830,669 men and 662,483 women) aged 40-74 years who underwent a health checkup, blood pressures automatically measured at healthcare center were investigated in nine HDL-C groups (20-110 mg/dL or over).

RESULTS

crude U-shaped relationship were observed between the nine HDL-C and blood pressures in both men and women. Logistic regression analysis showed left-to-right inverted J-shaped relationships between HDL-C and odds ratios for HBP (≥140/90 mmHg and/or pharmacotherapy), with lower limits of 90-99 mg/dL in both sexes, which were unchanged after adjusting for confounding factors. However, further adjustment for body mass index and serum triglyceride concentration revealed positive linear associations between HDL-C and HBP, although blunt U-shaped associations remained in nonalcohol drinkers.

CONCLUSION

both low and extremely high HDL-C concentrations are associated with HBP. The former association might be dependent on excess fat mass concomitant with low HDL-C, whereas the latter association may be largely dependent on frequent alcohol consumption.

High density lipoprotein in atherosclerosis and coronary heart disease: Where do we stand today?

Epidemiological studies during the last five years suggest that a relation between high density lipoprotein cholesterol (HDL-C) levels and the risk for cardiovascular disease (CVD) does exist but follows rather a "U-shaped" curve with an optimal range of HDL-C concentration between 40 and 70 mg/dl for men and 50-70 mg/dl for women. Moreover, as research in the field of lipoproteins progresses it becomes increasingly apparent that HDL particles possess different attributes and depending on their structural and functional characteristics, they may be "antiatherogenic" or "proatherogenic". In light of this information, it is highly doubtful that the choice of experimental drugs and the design of respective clinical trials that put the HDL-C raising hypothesis at test, were the most suitable. Here, we compile the existing literature on HDL, providing a critical up-to-date view that focuses on key data from the biochemistry, epidemiology and pharmacology of HDL, including data from clinical trials. We also discuss the most up-to-date information on the contribution of HDL structure and function to the prevention of atherosclerosis. We conclude by summarizing important differences between mouse models and humans, that may explain why pharmacological successes in mice turn out to be failures in humans.

HDL cholesterol concentrations and risk of atherosclerotic cardiovascular disease - Insights from randomized clinical trials and human genetics

Through seven decades the inverse association between HDL cholesterol concentrations and risk of atherosclerotic cardiovascular disease (ASCVD) has been observed in case-control and prospective cohort studies. This robust inverse association fuelled the enthusiasm towards development of HDL cholesterol increasing drugs, exemplified by the cholesteryl ester transfer protein (CETP) inhibitor trials and the extended-release niacin HPS2-THRIVE trial. These HDL cholesterol increasing trials were launched without conclusive evidence from human genetics, and despite discrepant species dependent evidence from animal studies. Evidence from human genetics and from randomized clinical trials over the last 13 years now point in the direction that concentrations of HDL cholesterol, do not appear to be a viable future path to target therapeutically for prevention of ASCVD. A likely explanation for the strong observational association between low HDL cholesterol and high ASCVD risk is the concomitant inverse association between HDL cholesterol and atherogenic triglyceride-rich lipoproteins. The purpose of the present review is to bring HDL cholesterol increasing trials into a human genetics context exemplified by candidate gene studies of key players in HDL biogenesis as well as by HDL cholesterol related genome-wide association studies.

High-density lipoproteins (HDL): Novel function and therapeutic applications

The failure of high-density lipoprotein (HDL)-raising agents to reduce cardiovascular disease (CVD) together with recent findings of increased cardiovascular mortality in subjects with extremely high HDL-cholesterol levels provide new opportunities to revisit our view of HDL. The concept of HDL function developed to explain these contradictory findings has recently been expanded by a role played by HDL in the lipolysis of triglyceride-rich lipoproteins (TGRLs) by lipoprotein lipase. According to the reverse remnant-cholesterol transport (RRT) hypothesis, HDL critically contributes to TGRL lipolysis via acquirement of surface lipids, including free cholesterol, released from TGRL. Ensuing cholesterol transport to the liver with excretion into the bile may reduce cholesterol influx in the arterial wall by accelerating removal from circulation of atherogenic, cholesterol-rich TGRL remnants. Such novel function of HDL opens wide therapeutic applications to reduce CVD in statin-treated patients, which primarily involve activation of cholesterol flux upon lipolysis.

Genetics and regulation of HDL metabolism

The inverse association between plasma HDL cholesterol (HDL-C) levels and risk for cardiovascular disease (CVD) has been demonstrated by numerous epidemiological studies. However, efforts to reduce CVD risk by pharmaceutically manipulating HDL-C levels failed and refused the HDL hypothesis. HDL-C levels in the general population are highly heterogeneous and are determined by a combination of genetic and environmental factors. Insights into the causes of HDL-C heterogeneity came from the study of monogenic HDL deficiency syndromes but also from genome wide association and Μendelian randomization studies which revealed the contribution of a large number of loci to low or high HDL-C cases in the general or in restricted ethnic populations. Furthermore, HDL-C levels in the plasma are under the control of transcription factor families acting primarily in the liver including members of the hormone nuclear receptors (PPARs, LXRs, HNF-4) and forkhead box proteins (FOXO1-4) and activating transcription factors (ATFs). The effects of certain lipid lowering drugs used today are based on the modulation of the activity of specific members of these transcription factors. During the past decade, the roles of small or long non-coding RNAs acting post-transcriptionally on the expression of HDL genes have emerged and provided novel insights into HDL regulation and new opportunities for therapeutic interventions. In the present review we summarize recent progress made in the genetics and the regulation (transcriptional and post-transcriptional) of HDL metabolism.

High-density lipoproteins, reverse cholesterol transport and atherogenesis

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

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

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

The Effects of Exercise on Lipid Biomarkers

The World Health Organization has declared obesity to be a global epidemic that increases cardiovascular disease (CVD) mortality risk factors, such as hypertension, diabetes, dyslipidemia, and atherosclerosis. The increasing ratio of time spent in sedentary activities to that spent performing physically demanding tasks increases the trends to obesity and susceptibility to these risk factors. Dyslipidemia is the foundation of atherosclerotic buildup and lipoproteins serve as cofactors to the inflammatory processes that destabilize plaques. Increasing cardiorespiratory fitness and muscular strength helps attenuate concentrations of low-density lipoproteins (LDLs), such as LDL cholesterol, and increase levels of high-density lipoprotein cholesterol, as well as reduce proprotein convertase subtilisin kexin type 9 expression. Effects of physical activity on the inflammatory pathways of atherosclerosis, specifically C-reactive protein, are more closely related to reducing the levels of adiposity in tandem with increasing fitness, than with exercise training alone. The purpose of this review is to describe the physiology of dyslipidemia and relate it to CVD and exercise therapies.

Different associations between HDL cholesterol and cardiovascular diseases in people with diabetes mellitus and people without diabetes mellitus: a prospective community-based study

BACKGROUND

Experimental studies have found that the functionality of HDL cholesterol may be lost in the presence of diabetes mellitus (DM).

OBJECTIVES

We aimed to elucidate whether DM modified the association between HDL-cholesterol concentrations and cardiovascular disease (CVD) outcomes.

METHODS

Included were 91,354 Chinese adults (8244 participants with DM and 83,110 participants without DM) free of CVD or cancer at baseline (2006) and without use of lipid-lowering drugs at baseline and during follow-up. The primary endpoint of interest was a composite of CVDs (myocardial infarction, ischemic stroke, and hemorrhagic stroke). Cumulative average HDL-cholesterol concentrations were calculated from all available HDL-cholesterol measures at baseline (2006) and during the follow-up period (2008, 2010, 2012, and 2014).

RESULTS

During a mean of 10.4 y of follow-up, there were 5076 CVD events identified. There was a significant interaction between DM and HDL-cholesterol concentrations on CVD risk (Pinteraction = 0.003). The association between HDL-cholesterol concentrations and CVD followed a U-shaped curve in individuals without DM (Pnonlinearity < 0.001). The adjusted HR of CVD was 1.26 (95% CI: 1.07, 1.48) for HDL-cholesterol concentrations < 1.04 mmol/L and 1.76 (95% CI: 1.53, 2.03) for HDL-cholesterol concentrations > 2.07 mmol/L, relative to the lowest-risk group (HDL-cholesterol concentrations of 1.30-1.42 mmol/L). In participants with DM, higher HDL-cholesterol concentrations were associated with a higher risk of CVD, in a dose-response manner (Pnonlinearity = 0.44; Ptrend < 0.001). The adjusted HR of CVD was 1.62 (95% CI: 1.19, 2.20) for HDL-cholesterol concentrations >2.07 mmol/L, relative to HDL-cholesterol concentrations of 1.30-1.42 mmol/L.

CONCLUSIONS

High HDL-cholesterol concentrations were paradoxically associated with high risk of composite CVD outcomes in individuals with or without DM. However, low HDL-cholesterol concentrations failed to predict future CVD risk in individuals with DM.

HDL and type 2 diabetes: the chicken or the egg?

HDL is a complex macromolecular cluster of various components, such as apolipoproteins, enzymes and lipids. Quality evidence from clinical and epidemiological studies led to the principle that HDL-cholesterol (HDL-C) levels are inversely correlated with the risk of CHD. Nevertheless, the failure of many cholesteryl ester transfer protein inhibitors to protect against CVD casts doubts on this principle and highlights the fact that HDL functionality, as dictated by its proteome and lipidome, also plays an important role in protecting against metabolic disorders. Recent data indicate that HDL-C levels and HDL particle functionality are correlated with the pathogenesis and prognosis of type 2 diabetes mellitus, a major risk factor for CVD. Hyperglycaemia leads to reduced HDL-C levels and deteriorated HDL functionality, via various alterations in HDL particles' proteome and lipidome. In turn, reduced HDL-C levels and impaired HDL functionality impact the performance of key organs related to glucose homeostasis, such as pancreas and skeletal muscles. Interestingly, different structural alterations in HDL correlate with distinct metabolic abnormalities, as indicated by recent data evaluating the role of apolipoprotein A1 and lecithin-cholesterol acyltransferase deficiency in glucose homeostasis. While it is becoming evident that not all HDL disturbances are causatively associated with the development and progression of type 2 diabetes, a bidirectional correlation between these two conditions exists, leading to a perpetual self-feeding cycle.

High Density Lipoproteins: Is There a Comeback as a Therapeutic Target?

Low plasma levels of High Density Lipoprotein (HDL) cholesterol (HDL-C) are associated with increased risks of atherosclerotic cardiovascular disease (ASCVD). In cell culture and animal models, HDL particles exert multiple potentially anti-atherogenic effects. However, drugs increasing HDL-C have failed to prevent cardiovascular endpoints. Mendelian Randomization studies neither found any genetic causality for the associations of HDL-C levels with differences in cardiovascular risk. Therefore, the causal role and, hence, utility as a therapeutic target of HDL has been questioned. However, the biomarker "HDL-C" as well as the interpretation of previous data has several important limitations: First, the inverse relationship of HDL-C with risk of ASCVD is neither linear nor continuous. Hence, neither the-higher-the-better strategies of previous drug developments nor previous linear cause-effect relationships assuming Mendelian randomization approaches appear appropriate. Second, most of the drugs previously tested do not target HDL metabolism specifically so that the futile trials question the clinical utility of the investigated drugs rather than the causal role of HDL in ASCVD. Third, the cholesterol of HDL measured as HDL-C neither exerts nor reports any HDL function. Comprehensive knowledge of structure-function-disease relationships of HDL particles and associated molecules will be a pre-requisite, to test them for their physiological and pathogenic relevance and exploit them for the diagnostic and therapeutic management of individuals at HDL-associated risk of ASCVD but also other diseases, for example diabetes, chronic kidney disease, infections, autoimmune and neurodegenerative diseases.

HDL-C, longitudinal change and risk of mortality in a Chinese cohort study

BACKGROUND AND AIMS

High-density lipoprotein cholesterol (HDL-C) concentration and variability are both important factors of cardiovascular disease (CVD) and mortality. We aimed to explore the associations of HDL-C and longitudinal change in HDL-C with risk of mortality.

METHODS AND RESULTS

We recruited a total of 69,163 participants aged ≥40 years and had medical examination records of HDL-C during 2010-2014 from the Yinzhou District, Ningbo, China. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression models. We observed a non-linear association of HDL-C with risks of non-accidental and CVD mortality. Compared with the moderate concentration group (1.4-1.6 mmol/L), HDL-C <1 mmol/L was associated with a higher risk of non-accidental mortality (HR: 1.13 (95% CI: 1.01-1.27)) and both HDL-C <1 mmol/L and ≥2 mmol/L were associated with a higher risk of CVD mortality (HRs: 1.23 (95% CI: 1.01-1.50) and 1.37 (95% CI: 1.03-1.82), respectively). Compared with the stable group ([-0.1, +0.1 mmol/L]), a large decrease ([-0.5, -0.3 mmol/L]) and very large decrease (<-0.5 mmol/L) in HDL-C were associated with a higher risk of non-accidental mortality (HRs: 1.40 (95% CI: 1.21-1.63) and 1.78 (95% CI: 1.44-2.20), respectively). Similar results were observed for CVD mortality and cancer mortality.

CONCLUSION

Extremely low or high HDL-C and a large decrease or very large decrease in HDL-C were associated with a higher risk of cause-specific mortality. Monitoring of HDL-C may have utility in identifying individuals at higher risk of mortality.

Is a High HDL-Cholesterol Level Always Beneficial?

The specific interest concerning HDL cholesterol (HDL-C) is related to its ability to uptake and return surplus cholesterol from peripheral tissues back to the liver and, therefore, to its role in the prevention of cardiovascular diseases, such as atherosclerosis and myocardial infarction, but also transient ischemic attack and stroke. Previous epidemiological studies have indicated that HDL-C concentration is inversely associated with the risk of cardiovascular disease and that it can be used for risk prediction. Some genetic disorders are characterized by markedly elevated levels of HDL-C; however, they do not translate into diminished cardiovascular risk. The search of the potential causative relationship between HDL-C and adverse events has shifted the attention of researchers towards the composition and function of the HDL molecule/subfractions. HDL possesses various cardioprotective properties. However, currently, it appears that higher HDL-C is not necessarily protective against cardiovascular disease, but it can even be harmful in extremely high quantities.

Inflammation Alters Relationship Between High-Density Lipoprotein Cholesterol and Cardiovascular Risk in Patients With Chronic Kidney Disease: Results From KNOW-CKD

Background

The function of high‐density lipoprotein can change from protective to proatherosclerotic under inflammatory conditions. Herein, we studied whether inflammation could modify the relationship between high‐density lipoprotein level and risk of adverse outcomes in patients with chronic kidney disease .

Methods and Results

In total, 1864 patients from the prospective KNOW‐CKD (Korean Cohort Study for Outcome in Patients With Chronic Kidney Disease) were enrolled. The main predictor was high‐density lipoprotein cholesterol (HDL‐C) level. Presence of inflammation was defined by hs‐CRP (high‐sensitivity C‐reactive protein) level of ≥1.0 mg/L. The primary outcome was extended major adverse cardiovascular events. During 9231.2 person‐years of follow‐up, overall incidence of the primary outcome was 15.8 per 1000 person‐years. In multivariable Cox analysis after adjusting for confounders, HDL‐C level was not associated with the primary outcome. There was a significant interaction between the inflammatory status and HDL‐C for risk of extended major adverse cardiovascular events (P=0.003). In patients without inflammation, the hazard ratios (HRs) (95% CIs) for HDL‐C levels <40, 50 to 59, and ≥60 mg/dL were 1.10 (0.50–1.82), 0.95 (0.50–1.82), and 0.42 (0.19–0.95), respectively, compared with HDL‐C of 40 to 49 mg/dL. However, the significant association for HDL‐C ≥60 mg/dL was not seen after Bonferroni correction. In patients with inflammation, we observed a trend toward increased risk of extended major adverse cardiovascular events in higher HDL‐C groups (HRs [95% CIs], 0.73 [0.37–1.43], 1.24 [0.59–2.61], and 1.56 [0.71–3.45], respectively), but without statistical significance.

Conclusions

The association between HDL‐C level and adverse cardiovascular outcomes showed reverse trends based on inflammation status in Korean patients with chronic kidney disease.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT01630486.

Multitrait GWAS to connect disease variants and biological mechanisms

Genome-wide association studies (GWASs) have uncovered a wealth of associations between common variants and human phenotypes. Here, we present an integrative analysis of GWAS summary statistics from 36 phenotypes to decipher multitrait genetic architecture and its link with biological mechanisms. Our framework incorporates multitrait association mapping along with an investigation of the breakdown of genetic associations into clusters of variants harboring similar multitrait association profiles. Focusing on two subsets of immunity and metabolism phenotypes, we then demonstrate how genetic variants within clusters can be mapped to biological pathways and disease mechanisms. Finally, for the metabolism set, we investigate the link between gene cluster assignment and the success of drug targets in randomized controlled trials.

High-density lipoprotein cholesterol and all-cause mortality by sex and age: a prospective cohort study among 15.8 million adults

BACKGROUND

The associations between high-density lipoprotein cholesterol (HDL-C) levels and all-cause mortality are unclear in young adults (<45 years) and in Asian populations.

METHODS

In total, 15 860 253 Korean adults underwent routine health examinations during 2009-10 and were followed until June 2018 for all-cause mortality. Hazard ratios (HRs) were calculated using Cox proportional hazard models.

RESULTS

During a mean 8.4 years of follow-up, 555 802 individuals died. U-curve associations were found between HDL-C levels and mortality, irrespective of sex or age. The HDL-C ranges associated with the lowest mortality were 40-59 and 50-69 mg/dL (1.03-1.54 and 1.29-1.80 mmol/L) in men aged <65 and ≥65 years, respectively, and the corresponding ranges were 40-69 and 50-79 mg/dL (1.03-1.80 and 1.29-2.06 mmol/L) in women aged <45 and ≥45 years, respectively. For HDL-C ranges of 60-149 mg/dL (1.55-3.86 mmol/L), each 39 mg/dL (1 mmol/L) increase in HDL-C was associated with higher mortality [men: HR = 1.39; 95% confidence interval (CI) = 1.36-1.42; women: HR = 1.15, 95% CI = 1.11-1.18], adjusting for age. These positive associations were generally stronger at younger than older ages, whereas inverse associations for HDL-C ranges <60 mg/dL (1.55 mmol/L) were strongest in middle age (45-64 years). The U-curve associations were generally unchanged after adjustment for various confounders.

CONCLUSIONS

Korean adults showed U-curve associations of HDL-C with mortality, regardless of sex, and age. Younger adults had a lower optimal range and a stronger positive association with mortality than older adults in the high HDL-C range. Even moderately high HDL-C levels are not necessarily a sign of good health, especially in young adults.

Biomarker Discovery in Atherosclerotic Diseases Using Quantitative Nuclear Magnetic Resonance Metabolomics

Despite great progress in the management of atherosclerosis (AS), its subsequent cardiovascular disease (CVD) remains the leading cause of morbidity and mortality. This is probably due to insufficient risk detection using routine lipid testing; thus, there is a need for more effective approaches relying on new biomarkers. Quantitative nuclear magnetic resonance (qNMR) metabolomics is able to phenotype holistic metabolic changes, with a unique advantage in regard to quantifying lipid-protein complexes. The rapidly increasing literature has indicated that qNMR-based lipoprotein particle number, particle size, lipid components, and some molecular metabolites can provide deeper insight into atherogenic diseases and could serve as novel promising determinants. Therefore, this article aims to offer an updated review of the qNMR biomarkers of AS and CVD found in epidemiological studies, with a special emphasis on lipoprotein-related parameters. As more researches are performed, we can envision more qNMR metabolite biomarkers being successfully translated into daily clinical practice to enhance the prevention, detection and intervention of atherosclerotic diseases.

HDL in Atherosclerotic Cardiovascular Disease: In Search of a Role

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