Hepatic lipase, genetically elevated high-density lipoprotein, and risk of ischemic cardiovascular disease

Expression of microbial lipase in filamentous fungus Aspergillus niger: a review

Lipase has high economic importance and is widely used in biodiesel, food, detergents, cosmetics, and pharmaceutical industries. The rapid development of synthetic biology and system biology has not only paved the way for comprehensively understanding the efficient operation mechanism of Aspergillus niger cell factories but also introduced a new technological system for creating and optimizing high-efficiency A. niger cell factories. In this review, all relevant data on microbial lipase enzyme sources and general properties are gathered and updated. The relationship between A. niger strain morphology and protein production is discussed. The safety of A. niger strain is investigated to ensure product safety. The biotechnologies and factors influencing lipase expression in A. niger are summarized. This review focuses on various strategies to improve lipase expression in A. niger. The summary of these methods and the application of the gene editing technology CRISPR/Cas9 system can further improve the efficiency of constructing the engineered lipase-producing A. niger.

Genetic variants in the adenosine triphosphate-binding cassette transporter A1 and risk of age-related macular degeneration

Genetic variants in ABCA1 are associated with higher concentrations of high-density lipoprotein (HDL) cholesterol. Higher HDL cholesterol concentrations are observationally and genetically associated with higher risk of age-related macular degeneration (AMD). However, whether amino acid-changing genetic variants in ABCA1 associated with high HDL cholesterol concentrations confer a higher risk of AMD in the general population is currently unknown. We tested this hypothesis. The study included 80,972 individuals (1,370 AMD cases) from the Copenhagen General Population Study (CGPS) and 9,584 individuals (142 AMD cases) from the Copenhagen City Heart Study (CCHS) with 10 to 18 years of follow-up. We created an HDL cholesterol weighted allele score based on amino acid-changing ABCA1 variants with a minor allele frequency above 0.001 and divided it into tertiles. The study included 55% women. Mean age was 58 years. The ABCA1 allele score for the third versus the first tertile was associated with HRs (95% confidence intervals (CIs)) of 1.30 (1.14-1.49) for all-cause AMD, 1.26 (1.06-1.50) for nonneovascular AMD, and 1.31 (1.12-1.53) for neovascular AMD in a multivariable adjusted model. On a continuous scale, higher concentrations of genetically determined HDL cholesterol were associated with higher risk of all-cause AMD, nonneovascular AMD, and neovascular AMD in an age- and sex adjusted model and in a multivariable adjusted model. In conclusion, amino acid-changing genetic variants in ABCA1 associated with higher HDL cholesterol concentrations were also associated with higher risk of AMD, suggesting a role for ABCA1 in AMD pathogenesis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Identification of a Gain-of-Function LIPC Variant as a Novel Cause of Familial Combined Hypocholesterolemia

BACKGROUND

Atherosclerotic cardiovascular disease is the main cause of mortality worldwide and is strongly influenced by circulating low-density lipoprotein (LDL) cholesterol levels. Only a few genes causally related to plasma LDL cholesterol levels have been identified so far, and only 1 gene, ANGPTL3, has been causally related to combined hypocholesterolemia. Here, our aim was to elucidate the genetic origin of an unexplained combined hypocholesterolemia inherited in 4 generations of a French family.

METHODS

Using next-generation sequencing, we identified a novel dominant rare variant in the LIPC gene, encoding for hepatic lipase, which cosegregates with the phenotype. We characterized the impact of this LIPC-E97G variant on circulating lipid and lipoprotein levels in family members using nuclear magnetic resonance-based lipoprotein profiling and lipidomics. To uncover the mechanisms underlying the combined hypocholesterolemia, we used protein homology modeling, measured triglyceride lipase and phospholipase activities in cell culture, and studied the phenotype of APOE*3.Leiden.CETP mice after LIPC-E97G overexpression.

RESULTS

Family members carrying the LIPC-E97G variant had very low circulating levels of LDL cholesterol and high-density lipoprotein cholesterol, LDL particle numbers, and phospholipids. The lysophospholipids/phospholipids ratio was increased in plasma of LIPC-E97G carriers, suggestive of an increased lipolytic activity on phospholipids. In vitro and in vivo studies confirmed that the LIPC-E97G variant specifically increases the phospholipase activity of hepatic lipase through modification of an evolutionarily conserved motif that determines substrate access to the hepatic lipase catalytic site. Mice overexpressing human LIPC-E97G recapitulated the combined hypocholesterolemic phenotype of the family and demonstrated that the increased phospholipase activity promotes catabolism of triglyceride-rich lipoproteins by different extrahepatic tissues but not the liver.

CONCLUSIONS

We identified and characterized a novel rare variant in the LIPC gene in a family who presents with dominant familial combined hypocholesterolemia. This gain-of-function variant makes LIPC the second identified gene, after ANGPTL3, causally involved in familial combined hypocholesterolemia. Our mechanistic data highlight the critical role of hepatic lipase phospholipase activity in LDL cholesterol homeostasis and suggest a new LDL clearance mechanism.

Early and late recurrent cardiovascular events among high-risk patients with an acute coronary syndrome: Meta-analysis of phase III studies and implications on trial design

Background

Despite low‐density lipoprotein cholesterol‐lowering therapies and other standard‐of‐care therapy, there remains a substantial residual atherosclerotic risk among patients with an acute coronary syndrome (ACS). This study aims to estimate the risk of early and late recurrent major adverse cardiovascular events (MACE) and address its implications on trial design.

Methods

A literature search was performed to collect phase III interventional trials on high‐risk ACS patients. Pooled event rates at 90 and 360 days were estimated by fitting random‐effects models using the DerSimonian–Laird method. Under the assumption of a total sample size of 10,000 and 1:1 allocation at a one‐sided alpha of 0.025 using the log‐rank test, the relationship between power and relative risk reduction (RRR) or absolute risk reduction (ARR) was explored for early versus late MACE endpoint.

Results

Seven trials representing 82,727 recent ACS patients were analyzed. The pooled rates of recurrent MACE were 4.1% and 8.3% at 90 and 360 days. Approximately 49% of events occurred within the first 90 days. Based on the estimated risks at 90 and 360 days, to attain 90% statistical power, a lower magnitude of RRR is required for late MACE than early MACE (22% vs. 30%), whereas a lower magnitude of ARR is required for early MACE than late MACE (1.2% vs. 1.8%).

Conclusion

The initial 90‐day window after ACS represents a vulnerable period for recurrent events. From a trial design perspective, determining a clinically important benefit by RRR versus ARR may influence the decision between early and late MACE as the study endpoint.

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

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

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

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

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

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

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.

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.

Association between Endothelial nitric oxide synthase and Hepatic lipase gene polymorphisms with the risk of coronary artery disease in Southern Iran population - A case control study

Coronary artery disease is a multifactorial genetic disease caused by the interaction between genetic and environmental factors. Angiography is the gold standard method for the diagnosis and determining the stage of cardiac disorder. The rs1800588 at the Hepatic Lipase gene and rs1799983 at the endothelial nitric oxide synthase (eNOS) gene are two candidate SNP that result in increased risk of this disease. The aim of this study was to find out the associations of the two mentioned polymorphisms with angiographically proven coronary artery patients in a southern Iranian population. In this study, this two polymorphisms in 287 patients and 229 matched controls were confirmed by angiography and analyzed. Genotype analysis was carried out by PCR and RFLP. Data showed that a significant difference for the eNOS gene polymorphism (p = 0.004) and a non-significant difference for the Hepatic lipase polymorphism (p = 0.261) and increasing severity of angiographic evidences of coronary artery disease were observed. Conclusively the significant association of the G894T with the narrowing of two or three coronary vessels of this patients in an Iranian population have been detected.

From genome-wide association studies to Mendelian randomization: novel opportunities for understanding cardiovascular disease causality, pathogenesis, prevention, and treatment

The Mendelian randomization approach is an epidemiological study design incorporating genetic information into traditional epidemiological studies to infer causality of biomarkers, risk factors, or lifestyle factors on disease risk. Mendelian randomization studies often draw on novel information generated in genome-wide association studies on causal associations between genetic variants and a risk factor or lifestyle factor. Such information can then be used in a largely unconfounded study design free of reverse causation to understand if and how risk factors and lifestyle factors cause cardiovascular disease. If causation is demonstrated, an opportunity for prevention of disease is identified; importantly however, before prevention or treatment can be implemented, randomized intervention trials altering risk factor levels or improving deleterious lifestyle factors needs to document reductions in cardiovascular disease in a safe and side-effect sparse manner. Documentation of causality can also inform on potential drug targets, more likely to be successful than prior approaches often relying on animal or cell studies mainly. The present review summarizes the history and background of Mendelian randomization, the study design, assumptions for using the design, and the most common caveats, followed by a discussion on advantages and disadvantages of different types of Mendelian randomization studies using one or more samples and different levels of information on study participants. The review also provides an overview of results on many of the risk factors and lifestyle factors for cardiovascular disease examined to date using the Mendelian randomization study design.

CETP, LIPC, and SCARB1 variants in individuals with extremely high high-density lipoprotein-cholesterol levels

The concentration of high-density lipoprotein-cholesterol (HDL-C) in humans is partially determined by genetic factors; however, the role of these factors is incompletely understood. The aim of this study was to examine the prevalence and characteristics of CETP, LIPC, and SCARB1 variants in Korean individuals with extremely high HDL-C levels. We also analysed associations between these variants and cholesterol efflux capacity (CEC), reactive oxygen species (ROS) generation, and vascular cell adhesion molecule-1 (VCAM-1) expression. Of 13,545 participants in the cardiovascular genome cohort, 42 subjects with HDL-C levels >100 mg/dL were analysed. The three target genes were sequenced by targeted next-generation sequencing, the functional effects of detected variants were predicted, and CEC was assessed using a radioisotope and apolipoprotein B-depleted sera. We observed two rare variants of CETP in 13 individuals (rare variant c.A1196G [p.D399G] of CETP was discovered in 12 subjects) and one rare variant of SCARB1 in one individual. Furthermore, all subjects had at least one of four common variants (one CETP and three LIPC variants). Two additional novel CETP variants of unknown frequency were found in two subjects. However, the identified variants did not show significant associations with CEC, ROS generation, or VCAM-1 expression. Our study provides additional insights into the role of genetics in individuals with extremely high HDL-C.

Modified and Dysfunctional Lipoproteins in Atherosclerosis: Effectors or Biomarkers?

Atherosclerotic diseases are the leading cause of mortality in industrialized countries. Correspondingly, studying the pathogenesis of atherosclerosis and developing new methods for its diagnostic and treatment remain in the focus of current medicine and health care. This review aims to discuss the mechanistic role of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in atherogenesis. In particular, the generally accepted hypothesis about the key role of oxidized LDL in atherogenesis is questioned, and an alternative concept of multiple modification of LDL is presented. The fundamental question discussed in this review is whether LDL and HDL are effectors or biomarkers, or both. This is important for understanding whether lipoproteins are a therapeutic target or just diagnostic indicators.

Trials in "True" Dyslipidemic Patients Are Urged to Reconsider Comprehensive Lipid Management as a Means to Reduce Residual Cardiovascular Risk

Randomized cardiovascular trials aimed to reduce the excessive residual risk in high‐risk patients through a more aggressive low‐density lipoprotein‐cholesterol control or targeting triglycerides or high‐density lipoprotein‐cholesterol levels have shown a null or, at best, limited incremental benefit. In some cases, the treatment produced meaningful effects only in study subgroups. As a consequence, some compounds were withdrawn (e.g., nicotinic acid derivatives and cholesteryl ester transfer protein inhibitors), whereas others (fibrates) are utilized with reluctance due to the low level of evidence‐based data. By reviewing these trials analytically, we identified a common feature that might explain their meager results: most of them involved patients generically at high cardiovascular risk with normal or near normal lipid levels and not patients with “true” dyslipidemia, who would receive the treatment if it were part of usual care. These observations may warrant re‐examining a central criterion of pragmatism, eligibility, in the outline of forthcoming cardiovascular trials with novel lipid‐modifying drugs.

Mendelian randomization reveals unexpected effects of CETP on the lipoprotein profile

According to the current dogma, cholesteryl ester transfer protein (CETP) decreases high-density lipoprotein (HDL)-cholesterol (C) and increases low-density lipoprotein (LDL)-C. However, detailed insight into the effects of CETP on lipoprotein subclasses is lacking. Therefore, we used a Mendelian randomization approach based on a genetic score for serum CETP concentration (rs247616, rs12720922 and rs1968905) to estimate causal effects per unit (µg/mL) increase in CETP on 159 standardized metabolic biomarkers, primarily lipoprotein subclasses. Metabolic biomarkers were measured by nuclear magnetic resonance (NMR) in 5672 participants of the Netherlands Epidemiology of Obesity (NEO) study. Higher CETP concentrations were associated with less large HDL (largest effect XL-HDL-C, P = 6 × 10^-22) and more small VLDL components (largest effect S-VLDL cholesteryl esters, P = 6 × 10^-6). No causal effects were observed with LDL subclasses. All these effects were replicated in an independent cohort from European ancestry (MAGNETIC NMR GWAS; n ~20,000). Additionally, we assessed observational associations between ELISA-measured CETP concentration and metabolic measures. In contrast to results from Mendelian randomization, observationally, CETP concentration predominantly associated with more VLDL, IDL and LDL components. Our results show that CETP is an important causal determinant of HDL and VLDL concentration and composition, which may imply that the CETP inhibitor anacetrapib decreased cardiovascular disease risk through specific reduction of small VLDL rather than LDL. The contrast between genetic and observational associations might be explained by a high capacity of VLDL, IDL and LDL subclasses to carry CETP, thereby concealing causal effects on HDL.

A robust method to estimate regional polygenic correlation under misspecified linkage disequilibrium structure

Complex traits can share a substantial proportion of their polygenic heritability. However, genome-wide polygenic correlations between pairs of traits can mask heterogeneity in their shared polygenic effects across loci. We propose a novel method (weighted maximum likelihood-regional polygenic correlation [RPC]) to evaluate polygenic correlation between two complex traits in small genomic regions using summary association statistics. Our method tests for evidence that the polygenic effect at a given region affects two traits concurrently. We show through simulations that our method is well calibrated, powerful, and more robust to misspecification of linkage disequilibrium than other methods under a polygenic model. As small genomic regions are more likely to harbor specific genetic effects, our method is ideal to identify heterogeneity in shared polygenic correlation across regions. We illustrate the usefulness of our method by addressing two questions related to cardiometabolic traits. First, we explored how RPC can inform on the strong epidemiological association between high-density lipoprotein cholesterol and coronary artery disease (CAD), suggesting a key role for triglycerides metabolism. Second, we investigated the potential role of PPARγ activators in the prevention of CAD. Our results provide a compelling argument that shared heritability between complex traits is highly heterogeneous across loci.

HDL as a Causal Factor in Atherosclerosis: Insights from Human Genetics

High-density lipoprotein cholesterol (HDL-C) levels are inversely related to risk of atherosclerotic cardiovascular disease (ASCVD). However, the simplistic assumption that HDL-C levels directly and causally impact atherogenesis has been challenged in recent years. The purpose of this article is to review the current state of knowledge regarding genetically determined HDL-C levels and ASCVD risk and determine what insight these studies provide into the causal relationship between HDL and atherosclerosis.

En route to precision medicine through the integration of biological sex into pharmacogenomics

Frequently, pharmacomechanisms are not fully elucidated. Therefore, drug use is linked to an elevated interindividual diversity of effects, whether therapeutic or adverse, and the role of biological sex has as yet unrecognized and underestimated consequences. A pharmacogenomic approach could contribute towards the development of an adapted therapy for each male and female patient, considering also other fundamental features, such as age and ethnicity. This would represent a crucial step towards precision medicine and could be translated into clinical routine. In the present review, we consider recent results from pharmacogenomics and the role of sex in studies that are relevant to cardiovascular therapy. We focus on genome-wide analyses, because they have obvious advantages compared with targeted single-candidate gene studies. For instance, genome-wide approaches do not necessarily depend on prior knowledge of precise molecular mechanisms of drug action. Such studies can lead to findings that can be classified into three categories: first, effects occurring in the pharmacokinetic properties of the drug, e.g. through metabolic and transporter differences; second, a pharmacodynamic or drug target-related effect; and last diverse adverse effects. We conclude that the interaction of sex with genetic determinants of drug response has barely been tested in large, unbiased, pharmacogenomic studies. We put forward the theory that, to contribute towards the realization of precision medicine, it will be necessary to incorporate sex into pharmacogenomics.

Genetic determinants of inherited susceptibility to hypercholesterolemia - a comprehensive literature review

Hypercholesterolemia is a strong determinant of mortality and morbidity associated with cardiovascular diseases and a major contributor to the global disease burden. Mutations in four genes (LDLR, APOB, PCSK9 and LDLRAP1) account for the majority of cases with familial hypercholesterolemia. However, a substantial proportion of adults with hypercholesterolemia do not have a mutation in any of these four genes. This indicates the probability of having other genes with a causative or contributory role in the pathogenesis of hypercholesterolemia and suggests a polygenic inheritance of this condition. Here in, we review the recent evidence of association of the genetic variants with hypercholesterolemia and the three lipid traits; total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C), their biological pathways and the associated pathogenetic mechanisms. Nearly 80 genes involved in lipid metabolism (encoding structural components of lipoproteins, lipoprotein receptors and related proteins, enzymes, lipid transporters, lipid transfer proteins, and activators or inhibitors of protein function and gene transcription) with single nucleotide variants (SNVs) that are recognized to be associated with hypercholesterolemia and serum lipid traits in genome-wide association studies and candidate gene studies were identified. In addition, genome-wide association studies in different populations have identified SNVs associated with TC, HDL-C and LDL-C in nearly 120 genes within or in the vicinity of the genes that are not known to be involved in lipid metabolism. Over 90% of the SNVs in both these groups are located outside the coding regions of the genes. These findings indicates that there might be a considerable number of unrecognized processes and mechanisms of lipid homeostasis, which when disrupted, would lead to hypercholesterolemia. Knowledge of these molecular pathways will enable the discovery of novel treatment and preventive methods as well as identify the biochemical and molecular markers for the risk prediction and early detection of this common, yet potentially debilitating condition.

The association of lipoprotein(a) with incident heart failure hospitalization: Atherosclerosis Risk in Communities study

BACKGROUND AND AIMS

Lipoprotein(a) [Lp(a)] is a proatherogenic lipoprotein associated with coronary heart disease, ischemic stroke, and more recently aortic stenosis and heart failure (HF). We examined the association of Lp(a) levels with incident HF hospitalization in the Atherosclerosis Risk in Communities (ARIC) study. We also assessed the relationship between Lp(a) levels and arterial stiffness as a potential mechanism for development of HF.

METHODS

Lp(a) was measured in 14,154 ARIC participants without prevalent HF at ARIC visit 1 (1987-1989). The association of Lp(a) quintiles with incident HF hospitalization was assessed using Cox proportional-hazards models. Arterial stiffness parameters were stratified based on Lp(a) quintiles, and p-trend was calculated across ordered groups.

RESULTS

At a median follow-up of 23.4 years, there were 2605 incident HF hospitalizations. Lp(a) levels were directly associated with incident HF hospitalization in models adjusted for age, race, gender, systolic blood pressure, history of hypertension, diabetes, smoking status, body mass index, heart rate, and high-density lipoprotein cholesterol (quintile 5 vs. quintile 1: hazard ratio [HR] 1.24, 95% confidence interval [CI] 1.09-1.41; p-trend across increasing quintiles <0.01), but not after excluding prevalent and incident myocardial infarction cases (HR 1.07, 95% CI 0.91-1.27; p-trend = 0.70). When adjusted for age, gender, and race, Lp(a) quintiles were not significantly associated with arterial stiffness parameters.

CONCLUSIONS

Increased Lp(a) levels were associated with increased risk of incident HF hospitalization. After excluding prevalent and incident myocardial infarction, the association was no longer significant. Lp(a) levels were not associated with arterial stiffness parameters.

Triglycerides and Triglyceride-Rich Lipoproteins in the Causal Pathway of Cardiovascular Disease

Epidemiologic and clinical studies suggest that elevated triglyceride levels are a biomarker of cardiovascular (CV) risk. Consistent with these findings, recent genetic evidence from mutational analyses, genome-wide association studies, and Mendelian randomization studies provide robust evidence that triglycerides and triglyceride-rich lipoproteins are in the causal pathway for atherosclerotic CV disease, indicating that they may play a pathogenic role, much like low-density lipoprotein cholesterol (LDL-C). Although statins are the cornerstone of dyslipidemia management, high triglyceride levels may persist in some patients despite statin therapy. Several triglyceride-lowering agents are available, including fibrates, niacin, and omega-3 fatty acids, of which prescription omega-3 fatty acids have the best tolerability and safety profile. In clinical studies, omega-3 fatty acids have been shown to reduce triglyceride levels, but products containing both eicosapentaenoic acid and docosahexaenoic acid may increase LDL-C levels. Icosapent ethyl, a high-purity eicosapentaenoic acid-only product, does not raise LDL-C levels and also reduces triglyceride, non-high-density lipoprotein cholesterol, and triglyceride-rich lipoprotein levels. In conclusion, omega-3 fatty acids are currently being evaluated in large CV outcome studies in statin-treated patients; these studies should help to elucidate the causative role of triglycerides in atherosclerotic CV disease.

High-Density Lipoprotein, Lecithin: Cholesterol Acyltransferase, and Atherosclerosis

Epidemiological data clearly show the existence of a strong inverse correlation between plasma high-density lipoprotein cholesterol (HDL-C) concentrations and the incidence of coronary heart disease. This relation is explained by a number of atheroprotective properties of HDL, first of all the ability to promote macrophage cholesterol transport. HDL are highly heterogeneous and are continuously remodeled in plasma thanks to the action of a number of proteins and enzymes. Among them, lecithin:cholesterol acyltransferase (LCAT) plays a crucial role, being the only enzyme able to esterify cholesterol within lipoproteins. LCAT is synthetized by the liver and it has been thought to play a major role in reverse cholesterol transport and in atheroprotection. However, data from animal studies, as well as human studies, have shown contradictory results. Increased LCAT concentrations are associated with increased HDL-C levels but not necessarily with atheroprotection. On the other side, decreased LCAT concentration and activity are associated with decreased HDL-C levels but not with increased atherosclerosis. These contradictory results confirm that HDL-C levels per se do not represent the functionality of the HDL system.

HDL functionality in reverse cholesterol transport--Challenges in translating data emerging from mouse models to human disease

Whereas LDL-derived cholesterol accumulates in atherosclerotic lesions, HDL particles are thought to facilitate removal of cholesterol from the lesions back to the liver thereby promoting its fecal excretion from the body. Because generation of cholesterol-loaded macrophages is inherent to atherogenesis, studies on the mechanisms stimulating the release of cholesterol from these cells and its ultimate excretion into feces are crucial to learn how to prevent lesion development or even induce lesion regression. Modulation of this key anti-atherogenic pathway, known as the macrophage-specific reverse cholesterol transport, has been extensively studied in several mouse models with the ultimate aim of applying the emerging knowledge to humans. The present review provides a detailed comparison and critical analysis of the various steps of reverse cholesterol transport in mouse and man. We attempt to translate this in vivo complex scenario into practical concepts, which could serve as valuable tools when developing novel HDL-targeted therapies.

Perhexiline activates KLF14 and reduces atherosclerosis by modulating ApoA-I production

Recent genome-wide association studies have revealed that variations near the gene locus encoding the transcription factor Krüppel-like factor 14 (KLF14) are strongly associated with HDL cholesterol (HDL-C) levels, metabolic syndrome, and coronary heart disease. However, the precise mechanisms by which KLF14 regulates lipid metabolism and affects atherosclerosis remain largely unexplored. Here, we report that KLF14 is dysregulated in the liver of 2 dyslipidemia mouse models. We evaluated the effects of both KLF14 overexpression and genetic inactivation and determined that KLF14 regulates plasma HDL-C levels and cholesterol efflux capacity by modulating hepatic ApoA-I production. Hepatic-specific Klf14 deletion in mice resulted in decreased circulating HDL-C levels. In an attempt to pharmacologically target KLF14 as an experimental therapeutic approach, we identified perhexiline, an approved therapeutic small molecule presently in clinical use to treat angina and heart failure, as a KLF14 activator. Indeed, in WT mice, treatment with perhexiline increased HDL-C levels and cholesterol efflux capacity via KLF14-mediated upregulation of ApoA-I expression. Moreover, perhexiline administration reduced atherosclerotic lesion development in apolipoprotein E-deficient mice. Together, these results provide comprehensive insight into the KLF14-dependent regulation of HDL-C and subsequent atherosclerosis and indicate that interventions that target the KLF14 pathway should be further explored for the treatment of atherosclerosis.

Residual Cardiovascular Risk in Chronic Kidney Disease: Role of High-density Lipoprotein

Although reducing low-density lipoprotein-cholesterol (LDL-C) levels with lipid-lowering agents (statins) decreases cardiovascular disease (CVD) risk, a substantial residual risk (up to 70% of baseline) remains after treatment in most patient populations. High-density lipoprotein (HDL) is a potential contributor to residual risk, and low HDL-cholesterol (HDL-C) is an established risk factor for CVD. However, in contrast to conventional lipid-lowering therapies, recent studies show that pharmacologic increases in HDL-C levels do not bring about clinical benefits. These observations have given rise to the concept of dysfunctional HDL where increases in serum HDL-C may not be beneficial because HDL loss of function is not corrected by or even intensified by the therapy. Chronic kidney disease (CKD) increases CVD risk, and patients whose CKD progresses to end-stage renal disease (ESRD) requiring dialysis are at the highest CVD risk of any patient type studied. The ESRD population is also unique in its lack of significant benefit from standard lipid-lowering interventions. Recent studies indicate that HDL-C levels do not predict CVD in the CKD population. Moreover, CKD profoundly alters metabolism and composition of HDL particles and impairs their protective effects on functions such as cellular cholesterol efflux, endothelial protection, and control of inflammation and oxidation. Thus, CKD-induced perturbations in HDL may contribute to the excess CVD in CKD patients. Understanding the mechanisms of vascular protection in renal disease can present new therapeutic targets for intervention in this population.

Mendelian randomization of blood lipids for coronary heart disease

AIMS

To investigate the causal role of high-density lipoprotein cholesterol (HDL-C) and triglycerides in coronary heart disease (CHD) using multiple instrumental variables for Mendelian randomization.

METHODS AND RESULTS

We developed weighted allele scores based on single nucleotide polymorphisms (SNPs) with established associations with HDL-C, triglycerides, and low-density lipoprotein cholesterol (LDL-C). For each trait, we constructed two scores. The first was unrestricted, including all independent SNPs associated with the lipid trait identified from a prior meta-analysis (threshold P < 2 × 10(-6)); and the second a restricted score, filtered to remove any SNPs also associated with either of the other two lipid traits at P ≤ 0.01. Mendelian randomization meta-analyses were conducted in 17 studies including 62,199 participants and 12,099 CHD events. Both the unrestricted and restricted allele scores for LDL-C (42 and 19 SNPs, respectively) associated with CHD. For HDL-C, the unrestricted allele score (48 SNPs) was associated with CHD (OR: 0.53; 95% CI: 0.40, 0.70), per 1 mmol/L higher HDL-C, but neither the restricted allele score (19 SNPs; OR: 0.91; 95% CI: 0.42, 1.98) nor the unrestricted HDL-C allele score adjusted for triglycerides, LDL-C, or statin use (OR: 0.81; 95% CI: 0.44, 1.46) showed a robust association. For triglycerides, the unrestricted allele score (67 SNPs) and the restricted allele score (27 SNPs) were both associated with CHD (OR: 1.62; 95% CI: 1.24, 2.11 and 1.61; 95% CI: 1.00, 2.59, respectively) per 1-log unit increment. However, the unrestricted triglyceride score adjusted for HDL-C, LDL-C, and statin use gave an OR for CHD of 1.01 (95% CI: 0.59, 1.75).

CONCLUSION

The genetic findings support a causal effect of triglycerides on CHD risk, but a causal role for HDL-C, though possible, remains less certain.

HDL biogenesis, remodeling, and catabolism

In this chapter, we review how HDL is generated, remodeled, and catabolized in plasma. We describe key features of the proteins that participate in these processes, emphasizing how mutations in apolipoprotein A-I (apoA-I) and the other proteins affect HDL metabolism. The biogenesis of HDL initially requires functional interaction of apoA-I with the ATP-binding cassette transporter A1 (ABCA1) and subsequently interactions of the lipidated apoA-I forms with lecithin/cholesterol acyltransferase (LCAT). Mutations in these proteins either prevent or impair the formation and possibly the functionality of HDL. Remodeling and catabolism of HDL is the result of interactions of HDL with cell receptors and other membrane and plasma proteins including hepatic lipase (HL), endothelial lipase (EL), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP), apolipoprotein M (apoM), scavenger receptor class B type I (SR-BI), ATP-binding cassette transporter G1 (ABCG1), the F1 subunit of ATPase (Ecto F1-ATPase), and the cubulin/megalin receptor. Similarly to apoA-I, apolipoprotein E and apolipoprotein A-IV were shown to form discrete HDL particles containing these apolipoproteins which may have important but still unexplored functions. Furthermore, several plasma proteins were found associated with HDL and may modulate its biological functions. The effect of these proteins on the functionality of HDL is the topic of ongoing research.

Elevated remnant cholesterol in 25-hydroxyvitamin D deficiency in the general population: Mendelian randomization study

BACKGROUND

Low plasma 25-hydroxyvitamin D [25(OH)D] levels are associated with high cardiovascular risk. This may be because that low 25(OH)D levels are associated with high levels of atherogenic lipoproteins, but whether these 2 risk factors are genetically associated is unknown. We tested this hypothesis.

METHODS AND RESULTS

Using a Mendelian randomization approach, potential genetic associations between plasma levels of atherogenic lipoproteins and 25(OH)D were examined in ≤85,868 white, Danish individuals in whom we genotyped for variants affecting plasma levels of 25(OH)D, nonfasting remnant cholesterol, low-density lipoprotein-cholesterol, and high-density lipoprotein-cholesterol. Lipoprotein levels were measured in all and 25(OH)D levels in 31,435. A doubling in nonfasting remnant cholesterol levels was observationally and genetically associated with -6.0%(95% confidence interval [CI], -6.5% to -5.5%) and -8.9% (95% CI, -15% to -2.3%) lower plasma 25(OH)D levels. For low-density lipoprotein-cholesterol levels, corresponding values were -4.6% (95% CI, -5.4% to -3.7%) observationally and -11% (95% CI, -29% to +6.9%) genetically. In contrast, a halving in high-density lipoprotein-cholesterol levels was observationally associated with -1.5% (95% CI, -2.2% to -0.7%) lower but genetically associated with +20% (95% CI, +7.4% to +34%) higher plasma 25(OH)D levels. Plasma levels of lipoprotein(a) and 25(OH)D did not associate. Finally, low 25(OH)D levels did not associate genetically with levels of remnant and low-density lipoprotein-cholesterol.

CONCLUSIONS

Genetically elevated nonfasting remnant cholesterol is associated with low 25(OH)D levels, whereas genetically reduced high-density lipoprotein-cholesterol is not associated with low 25(OH)D levels. These findings suggest that low 25(OH)D levels observationally is simply a marker for elevated atherogenic lipoproteins and question a role for vitamin D supplementation in the prevention of cardiovascular disease.

HDL and atherosclerosis: Insights from inherited HDL disorders

Plasma high density lipoproteins (HDL) comprise a highly heterogeneous family of lipoprotein particles, differing in density, size, surface charge, and lipid and protein composition. Epidemiological studies have shown that plasma HDL level inversely correlates with atherosclerotic cardiovascular disease. The most relevant atheroprotective function of HDL is to promote the removal of cholesterol from macrophages within the arterial wall and deliver it to the liver for excretion in a process called reverse cholesterol transport. In addition, HDLs can contribute to the maintenance of endothelial cell homeostasis and have potent antioxidant properties. It has been long suggested that individual HDL subclasses may differ in terms of their functional properties, but which one is the good particle remains to be defined. Inherited HDL disorders are rare monogenic diseases due to mutations in genes encoding proteins involved in HDL metabolism. These disorders are not only characterized by extremely low or high plasma HDL levels but also by an abnormal HDL subclass distribution, and thus represent a unique tool to understand the relationship between plasma HDL concentration, HDL function, and HDL-mediated atheroprotection. This article is part of a Special Issue entitled Linking transcription to physiology in lipodomics.

Loss-of-function mutations in APOC3 and risk of ischemic vascular disease

BACKGROUND

High plasma levels of nonfasting triglycerides are associated with an increased risk of ischemic cardiovascular disease. Whether lifelong low levels of nonfasting triglycerides owing to mutations in the gene encoding apolipoprotein C3 (APOC3) are associated with a reduced risk of ischemic cardiovascular disease in the general population is unknown.

METHODS

Using data from 75,725 participants in two general-population studies, we first tested whether low levels of nonfasting triglycerides were associated with reduced risks of ischemic vascular disease and ischemic heart disease. Second, we tested whether loss-of-function mutations in APOC3, which were associated with reduced levels of nonfasting triglycerides, were also associated with reduced risks of ischemic vascular disease and ischemic heart disease. During follow-up, ischemic vascular disease developed in 10,797 participants, and ischemic heart disease developed in 7557 of these 10,797 participants.

RESULTS

Participants with nonfasting triglyceride levels of less than 1.00 mmol per liter (90 mg per deciliter) had a significantly lower incidence of cardiovascular disease than those with levels of 4.00 mmol per liter (350 mg per deciliter) or more (hazard ratio for ischemic vascular disease, 0.43; 95% confidence interval [CI], 0.35 to 0.54; hazard ratio for ischemic heart disease, 0.40; 95% CI, 0.31 to 0.52). Heterozygosity for loss-of-function mutations in APOC3, as compared with no APOC3 mutations, was associated with a mean reduction in nonfasting triglyceride levels of 44% (P<0.001). The cumulative incidences of ischemic vascular disease and ischemic heart disease were reduced in heterozygotes as compared with noncarriers of APOC3 mutations (P=0.009 and P=0.05, respectively), with corresponding risk reductions of 41% (hazard ratio, 0.59; 95% CI, 0.41 to 0.86; P=0.007) and 36% (hazard ratio, 0.64; 95% CI, 0.41 to 0.99; P=0.04).

CONCLUSIONS

Loss-of-function mutations in APOC3 were associated with low levels of triglycerides and a reduced risk of ischemic cardiovascular disease. (Funded by the European Union and others.).

Genetics of lipid traits: Genome-wide approaches yield new biology and clues to causality in coronary artery disease

A wealth of novel lipid loci have been identified through a variety of approaches focused on common and low-frequency variation and collaborative metaanalyses in multiethnic populations. Despite progress in identification of loci, the task of determining causal variants remains challenging. This work will undoubtedly be enhanced by improved understanding of regulatory DNA at a genomewide level as well as new methodologies for interrogating the relationships between noncoding SNPs and regulatory regions. Equally challenging is the identification of causal genes at novel loci. Some progress has been made for a handful of genes and comprehensive testing of candidate genes using multiple model systems is underway. Additional insights will be gleaned from focusing on low frequency and rare coding variation at candidate loci in large populations. This article is part of a Special Issue entitled: From Genome to Function.

Bone marrow-derived HL mitigates bone marrow-derived CETP-mediated decreases in HDL in mice globally deficient in HL and the LDLr

The objective of this study was to determine the combined effects of HL and cholesteryl ester transfer protein (CETP), derived exclusively from bone marrow (BM), on plasma lipids and atherosclerosis in high-fat-fed, atherosclerosis-prone mice. We transferred BM expressing these proteins into male and female double-knockout HL-deficient, LDL receptor-deficient mice (HL(-/-)LDLr(-/-)). Four BM chimeras were generated, where BM-derived cells expressed 1) HL but not CETP, 2) CETP and HL, 3) CETP but not HL, or 4) neither CETP nor HL. After high-fat feeding, plasma HDL-cholesterol (HDL-C) was decreased in mice with BM expressing CETP but not HL (17 ± 4 and 19 ± 3 mg/dl, female and male mice, respectively) compared with mice with BM expressing neither CETP nor HL (87 ± 3 and 95 ± 4 mg/dl, female and male mice, respectively, P < 0.001 for both sexes). In female mice, the presence of BM-derived HL mitigated this CETP-mediated decrease in HDL-C. BM-derived CETP decreased the cholesterol component of HDL particles and increased plasma cholesterol. BM-derived HL mitigated these effects of CETP. Atherosclerosis was not significantly different between BM chimeras. These results suggest that BM-derived HL mitigates the HDL-lowering, HDL-modulating, and cholesterol-raising effects of BM-derived CETP and warrant further studies to characterize the functional properties of these protein interactions.

Low Nonfasting Triglycerides and Reduced All-Cause Mortality: A Mendelian Randomization Study

BACKGROUND

Increased nonfasting plasma triglycerides marking increased amounts of cholesterol in remnant lipoproteins are important risk factors for cardiovascular disease, but whether lifelong reduced concentrations of triglycerides on a genetic basis ultimately lead to reduced all-cause mortality is unknown. We tested this hypothesis.

METHODS

Using individuals from the Copenhagen City Heart Study in a mendelian randomization design, we first tested whether low concentrations of nonfasting triglycerides were associated with reduced all-cause mortality in observational analyses (n = 13 957); second, whether genetic variants in the triglyceride-degrading enzyme lipoprotein lipase, resulting in reduced nonfasting triglycerides and remnant cholesterol, were associated with reduced all-cause mortality (n = 10 208).

RESULTS

During a median 24 and 17 years of 100% complete follow-up, 9991 and 4005 individuals died in observational and genetic analyses, respectively. In observational analyses compared to individuals with nonfasting plasma triglycerides of 266–442 mg/dL (3.00–4.99 mmol/L), multivariably adjusted hazard ratios for all-cause mortality were 0.89 (95% CI 0.78–1.02) for 177–265 mg/dL (2.00–2.99 mmol/L), 0.74 (0.65–0.84) for 89–176 mg/dL (1.00–1.99 mmol/L), and 0.59 (0.51–0.68) for individuals with nonfasting triglycerides &lt;89 mg/dL (&lt;1.00 mmol/L). The odds ratio for a genetically derived 89-mg/dL (1-mmol/L) lower concentration in nonfasting triglycerides was 0.50 (0.30–0.82), with a corresponding observational hazard ratio of 0.87 (0.85–0.89). Also, the odds ratio for a genetically derived 50% lower concentration in nonfasting triglycerides was 0.43 (0.23–0.80), with a corresponding observational hazard ratio of 0.73 (0.70–0.77).

CONCLUSIONS

Genetically reduced concentrations of nonfasting plasma triglycerides are associated with reduced all-cause mortality, likely through reduced amounts of cholesterol in remnant lipoproteins.

Effects of lipid-lowering drugs on high-density lipoprotein subclasses in healthy men-a randomized trial

CONTEXT AND OBJECTIVE

Investigating the effects of lipid-lowering drugs on HDL subclasses has shown ambiguous results. This study assessed the effects of ezetimibe, simvastatin, and their combination on HDL subclass distribution.

DESIGN AND PARTICIPANTS

A single-center randomized parallel 3-group open-label study was performed in 72 healthy men free of cardiovascular disease with a baseline LDL-cholesterol of 111±30 mg/dl (2.9±0.8 mmol/l) and a baseline HDL-cholesterol of 64±15 mg/dl (1.7±0.4 mmol/l). They were treated with ezetimibe (10 mg/day, n = 24), simvastatin (40 mg/day, n = 24) or their combination (n = 24) for 14 days. Blood was drawn before and after the treatment period. HDL subclasses were determined using polyacrylamide gel-tube electrophoresis. Multivariate regression models were used to determine the influence of treatment and covariates on changes in HDL subclass composition.

RESULTS

Baseline HDL subclasses consisted of 33±10% large, 48±6% intermediate and 19±8% small HDL. After adjusting for baseline HDL subclass distribution, body mass index, LDL-C and the ratio triglycerides/HDL-C, there was a significant increase in large HDL by about 3.9 percentage points (P<0.05) and a decrease in intermediate HDL by about 3.5 percentage points (P<0.01) in both simvastatin-containing treatment arms in comparison to ezetimibe. The parameters obtained after additional adjustment for the decrease in LDL-C indicated that about one third to one half of these effects could be explained by the extent of LDL-C-lowering.

CONCLUSIONS

In healthy men, treatment with simvastatin leads to favorable effects on HDL subclass composition, which was not be observed with ezetimibe. Part of these differential effects may be due to the stronger LDL-C-lowering effects of simvastatin.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00317993.

Genetics of lipid traits and relationship to coronary artery disease

Despite the critical importance of plasma lipoproteins in the development of atherosclerosis, varying degrees of evidence surround the causal associations of lipoproteins with coronary artery disease (CAD). These causal contributions can be assessed by employing genetic variants as unbiased proxies for lipid levels. A relatively large number of low-density lipoprotein cholesterol (LDL-C) variants strongly associate with CAD, confirming the causal impact of this lipoprotein on atherosclerosis. Although not as firmly established, genetic evidence supporting a causal role of triglycerides (TG) in CAD is growing. Conversely, high-density lipoprotein cholesterol (HDL-C) variants not associated with LDL-C or TG have not yet been shown to be convincingly associated with CAD, raising questions about the causality of HDL-C in atherosclerosis. Finally, genetic variants at the LPA locus associated with lipoprotein(a) [Lp(a)] are decisively linked to CAD, indicating a causal role for Lp(a). Translational investigation of CAD-associated lipid variants may identify novel regulatory pathways with therapeutic potential to alter CAD risk.

Treating low high-density lipoprotein cholesterol: what is the evidence?

Epidemiological studies have shown an inverse association between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) risk. However, genetic and interventional studies have failed to consistently support this relationship. There is an increasing body of evidence that the function of HDL, including its antiatherogenic properties and its reverse cholesterol transport activity, has a greater impact on CVD risk compared with levels of HDL alone. Targeting HDL has become a growing interest. Nevertheless, raising HDL pharmacologically has failed to show a considerable, if any, impact on cardiovascular outcome. Efforts should focus on improving HDL quality in addition to raising HDL levels when developing new therapies. Ongoing and future research will help determine the most safe and effective approach to improve cardiovascular outcome and establish the safety, efficacy and impact on atherosclerosis of the emerging HDL-raising therapies.

Common variants associated with plasma triglycerides and risk for coronary artery disease

Triglycerides are transported in plasma by specific triglyceride-rich lipoproteins; in epidemiologic studies, increased triglyceride levels correlate with higher risk for coronary artery disease (CAD). However, it is unclear whether this association reflects causal processes. We used 185 common variants recently mapped for plasma lipids (P<5×10⁻⁸ for each) to examine the role of triglycerides on risk for CAD. First, we highlight loci associated with both low-density lipoprotein cholesterol (LDL-C) and triglycerides, and show that the direction and magnitude of both are factors in determining CAD risk. Second, we consider loci with only a strong magnitude of association with triglycerides and show that these loci are also associated with CAD. Finally, in a model accounting for effects on LDL-C and/or high-density lipoprotein cholesterol, a polymorphism's strength of effect on triglycerides is correlated with the magnitude of its effect on CAD risk. These results suggest that triglyceride-rich lipoproteins causally influence risk for CAD.

High-density lipoprotein cholesterol, size, particle number, and residual vascular risk after potent statin therapy

BACKGROUND

Chemically measured high-density lipoprotein cholesterol (HDL-C) may not be the best clinical measure of HDL. Little is known about alternative HDL measures such as HDL size or particle number (HDL-P) as determinants of residual risk after potent statin therapy.

METHODS AND RESULTS

In Justification for the Use of statins in Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER), HDL size and HDL-P were measured by nuclear magnetic resonance spectroscopy, and HDL-C and apolipoprotein A-I (apoA-I) were chemically assayed in 10 886 participants without cardiovascular disease (CVD) before and after random allocation to rosuvastatin 20 mg/d or placebo. Levels were examined with first CVD (n=234). HDL-P correlated better with apoA-I (Spearman r=0.69, P<0.0001) than with HDL-C (r=0.55, P<0.0001). Rosuvastatin lowered low-density lipoprotein cholesterol (49%) and raised HDL-C (6.1%), apoA-I (2.1%), HDL-P (3.8%), and HDL size (1.2%); all P<0.0001. Among placebo-allocated individuals, on-treatment HDL-C, apoA-I, and HDL-P had similar inverse associations with CVD (risk factor-adjusted hazard ratio and 95% confidence interval per 1 standard deviation: 0.79 [0.63-0.98], 0.75 [0.62-0.92], and 0.81 [0.67-0.97], respectively). Among rosuvastatin-allocated individuals, on-treatment HDL-P had a statistically significant and somewhat stronger association with CVD (0.73, 0.57-0.93, P=0.01) than HDL-C (0.82, 0.63-1.08, P=0.16) or apoA-I (0.86, 0.67-1.10, P=0.22). Among rosuvastatin-allocated individuals, on-treatment HDL-P remained significant (0.72, 0.53-0.97, P=0.03) after additionally adjusting for HDL-C. In risk factor-adjusted models, HDL size showed no significant association with CVD.

CONCLUSIONS

In the setting of potent statin therapy, HDL particle number may be a better marker of residual risk than chemically measured HDL-C or apoA-I. This has potential implications for evaluating novel therapies targeting HDL.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT00239681.

HDL cholesterol and cardiovascular outcomes: what is the evidence?

The relationship between low concentrations of high density lipoprotein cholesterol (HDL-C) and heightened risk for cardiovascular (CV) disease has been known for decades. Despite the consistent inverse relationship among epidemiological studies, the linkage between a residual low HDL-C among patients treated with statins and excess cardiovascular risk is less clearly established. Encouraging results from trials using niacin over the past 40 years have not been validated among more recent trials in patients taking contemporary anti-atherosclerotic therapy. Emerging evidence suggests that certain subsets of HDL particles may be more protective and/or more closely associated with CV disease than others, which may impact therapeutic benefits. Ongoing clinical trials will clarify whether raising HDL-C per se directly translates into a reduction in hard CV events. Until those results are available, the clinician is left with only weak evidence to support whether or not to target treatment of HDL-C with pharmacological therapy.

Importance of high-density lipoprotein quality: evidence from chronic kidney disease

PURPOSE OF REVIEW

This review will examine advances in our understanding of the association between high-density lipoprotein (HDL) function and cardiovascular disease (CVD) in patients with chronic kidney disease (CKD).

RECENT FINDINGS

Large randomized statin trials and related meta-analyses confirm that lipid-lowering therapy benefits patients with mild to moderate CKD, leaving a degree of residual cardiovascular risk similar to that documented in the general population. However, patients with advanced CKD on dialysis show little to no cardiovascular benefits from lipid-lowering therapy and have an exaggerated residual cardiovascular risk. HDL quantity and functionality may explain some of the residual risk. CKD modulates the level, composition and functionality of HDL, including impaired cholesterol acceptor function and pro-inflammatory effects. Although these abnormalities prevail in CKD, they do not track together and thus support the idea of separate and distinct mechanistic pathways for each of these critical functions of HDL.

SUMMARY

CKD-induced perturbations in HDL composition, metabolism and functionality may contribute to the excess CVD in patients with CKD and present new therapeutic targets for intervention in this population.

HDL--is it too big to fail?

The HDL hypothesis has suffered damage in the past few years. Clinical trials have shown that raising HDL cholesterol levels does not improve cardiovascular disease (CVD) outcomes. In addition, Mendelian randomization studies have shown that DNA variants that alter HDL cholesterol levels in populations are unrelated to incident CVD events. Balancing this deluge of negative data are substantial basic science data supporting the concept that raising HDL cholesterol levels reduces CVD risk. Also, functionally relevant HDL subfractions might be more important determinants of risk than overall HDL cholesterol levels. But, while wobbly, the HDL hypothesis is still standing, seemingly too big to fail owing to past intellectual, economic and psychological investments in the idea.