Circulating cholesteryl ester transfer protein and coronary heart disease: mendelian randomization meta-analysis

Cholesteryl Ester Transfer Protein (CETP) Variations in Relation to Lipid Profiles and Cardiovascular Diseases: An Update

Lipid metabolism plays an essential role in the pathogenesis of cardiovascular and metabolic diseases. Cholesteryl ester transfer protein (CETP) is a crucial glycoprotein involved in lipid metabolism by transferring cholesteryl esters (CE) and triglycerides (TG) between plasma lipoproteins. CETP activity results in reduced HDL-C and increased VLDL- and LDL-C concentrations, thus increasing the risk of cardiovascular and metabolic diseases. In this review, we discuss the structure of CETP and its mechanism of action. Furthermore, we focus on recent experiments on animal CETP-expressing models, deciphering the regulation and functions of CETP in various genetic backgrounds and interaction with different external factors. Finally, we discuss recent publications revealing the association of CETP single nucleotide polymorphisms (SNPs) with the risk of cardiovascular and metabolic diseases, lifestyle factors, diet and therapeutic interventions. While CETP SNPs can be used as effective diagnostic markers, diet, lifestyle, gender and ethnic specificity should also be considered for effective treatment.

Novel and future lipid-modulating therapies for the prevention of cardiovascular disease

Lowering the levels of LDL cholesterol in the plasma has been shown to reduce the risk of atherosclerotic cardiovascular disease (ASCVD). Several other lipoproteins, such as triglyceride-rich lipoproteins, HDL and lipoprotein(a) are associated with atherosclerosis and ASCVD, with strong evidence supporting causality for some. In this Review, we discuss novel and upcoming therapeutic strategies targeting different pathways in lipid metabolism to potentially attenuate the risk of cardiovascular events. Key proteins involved in lipoprotein metabolism, such as PCSK9, angiopoietin-related protein 3, cholesteryl ester transfer protein and apolipoprotein(a), have been identified as viable targets for therapeutic intervention through observational and genetic studies. These proteins can be targeted using a variety of approaches, such as protein inhibition or interference, inhibition of translation at the mRNA level (with the use of antisense oligonucleotides or small interfering RNA), and the introduction of loss-of-function mutations through base editing. These novel and upcoming strategies are complementary to and could work synergistically with existing therapies, or in some cases could potentially replace therapies, offering unprecedented opportunities to prevent ASCVD. Moreover, a major challenge in the prevention and treatment of non-communicable diseases is how to achieve safe, long-lasting reductions in causal exposures. This challenge might be overcome with approaches such as small interfering RNAs or genome editing, which shows how far the field has advanced from when the burden of achieving this goal was placed upon patients through rigorous adherence to daily small-molecule drug regimens.

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.

Association of CETP Gene Variants with Atherogenic Dyslipidemia Among Thai Patients Treated with Statin

Objective

Patients treated with statins for dyslipidemia may still have a residual risk of atherosclerotic cardiovascular disease (ASCVD). To determine whether genetic variants in the cholesteryl ester transport protein (CETP), rs3764261 (C>A), rs708272 (G>A), and rs12149545 (G>A) affect ASCVD risk, we studied the association of these variants with dyslipidemia in statin-treated patients.

Patients and Methods

We included 299 adult Thai patients treated with a statin (95 men and 204 women). Genotyping was performed by conducting a TaqMan real-time polymerase chain reaction-based analysis. We used logistic regression models adjusted for potential confounders of age, body mass index, blood pressure, insulin resistance, and statin dosage to analyze the association between CETP variants and atherogenic lipoprotein patterns.

Results

CETP polymorphisms of rs3764261 and rs708272, but not rs12149545, were significantly associated with high-density lipoprotein cholesterol (HDL-C), apoA-I, triglycerides, very low-density lipoprotein (VLDL)-C, and large LDL (LDL1-C) levels as well as mean LDL particle size (all p < 0.020). However, no significant difference was observed in total cholesterol, LDL-C, or apoB levels by CETP variants. Regardless of sex, the combination of rs3764261 (CC genotype) and rs708272 (GG or GA genotypes) showed a stronger association with atherogenic dyslipidemia, including features of decreased HDL-C, elevated triglycerides, and LDL subclass pattern B (odds ratio [OR] = 2.99, 95% confidence interval [CI]: 1.78–5.02) compared with the single variant rs3764261 (OR = 2.11, 95% CI: 1.27–3.50) or rs708272 (OR = 2.12, 95% CI: 1.29–3.49).

Conclusion

The polymorphisms of CETP rs3764261 (CC genotype) and rs708272 (GG and GA genotypes) may have a higher susceptibility to atherogenic dyslipidemia. Testing for CETP rs3764261 and rs708272 may serve as a surrogate marker for lipid management in statin-treated patients, which may help individualize treatment for reducing the residual risk of ASCVD.

Cholesteryl Ester Transfer Protein Genetic Variants Associated with Risk for Type 2 Diabetes and Diabetic Kidney Disease in Taiwanese Population

Cholesteryl ester transfer protein (CETP) plays an important role in lipid metabolism. Low levels of high-density lipoprotein cholesterol (HDL-C) increase the risk of type 2 diabetes (T2D). This study investigated CETP gene variants to assess the risk of T2D and specific complications of diabetic kidney disease (DKD) and diabetic retinopathy. Towards this, a total of 3023 Taiwanese individuals (1383 without T2D, 1640 with T2D) were enrolled in this study. T2D mice (+Lepr^db/+Lepr^db, db/db) were used to determine CETP expression in tissues. The A-alleles of rs3764261, rs4783961, and rs1800775 variants were found to be independently associated with 2.86, 1.71, and 0.91 mg/dL increase in HDL-C per allele, respectively. In addition, the A-allele of rs4783961 was significantly associated with a reduced T2D risk (odds ratio (OR), 0.82; 95% confidence interval (CI), 0.71–0.96)), and the A-allele of rs1800775 was significantly related to a lowered DKD risk (OR, 0.78; 95% CI, 0.64–0.96). CETP expression was significantly decreased in the T2D mice kidney compared to that in the control mice (T2D mice, 0.16 ± 0.01 vs. control mice, 0.21 ± 0.02; p = 0.02). These collective findings indicate that CETP variants in the promoter region may affect HDL-C levels. Taiwanese individuals possessing an allele associated with higher HDL-C levels had a lower risk of T2D and DKD.

CETP (Cholesteryl Ester Transfer Protein) Concentration: A Genome-Wide Association Study Followed by Mendelian Randomization on Coronary Artery Disease

BACKGROUND

We aimed to identify independent genetic determinants of circulating CETP (cholesteryl ester transfer protein) to assess causal effects of variation in CETP concentration on circulating lipid concentrations and cardiovascular disease risk.

METHODS

A genome-wide association discovery and replication study on serum CETP concentration were embedded in the NEO study (Netherlands Epidemiology of Obesity). Based on the independent identified variants, Mendelian randomization was conducted on serum lipids (NEO study) and coronary artery disease (CAD; CARDIoGRAMplusC4D consortium).

RESULTS

In the discovery analysis (n=4248), we identified 3 independent variants (P<5×10^-8) that determine CETP concentration. These single-nucleotide polymorphisms were mapped to CETP and replicated in a separate subpopulation (n=1458). Per-allele increase (SE) in serum CETP was 0.32 (0.02) µg/mL for rs247616-C, 0.35 (0.02) µg/mL for rs12720922-A, and 0.12 (0.02) µg/mL for rs1968905-G. Combined, these 3 variants explained 16.4% of the total variation in CETP concentration. One microgram per milliliter increase in genetically determined CETP concentration strongly decreased high-density lipoprotein cholesterol (-0.23 mmol/L; 95% confidence interval, -0.26 to -0.20), moderately increased low-density lipoprotein cholesterol (0.08 mmol/L; 95% confidence interval, 0.00-0.16), and was associated with an odds ratio of 1.08 (95% confidence interval, 0.94-1.23) for CAD risk.

CONCLUSIONS

This is the first genome-wide association study identifying independent variants that largely determine CETP concentration. Although high-density lipoprotein cholesterol is not a causal risk factor for CAD, it has been unequivocally demonstrated that low-density lipoprotein cholesterol lowering is proportionally associated with a lower CAD risk. Therefore, the results of our study are fully consistent with the notion that CETP concentration is causally associated with CAD through low-density lipoprotein cholesterol.

High-density lipoprotein metabolism and reverse cholesterol transport: strategies for raising HDL cholesterol

A key to effective treatment of cardiovascular disease is to understand the body’s complex lipoprotein transport system. Reverse cholesterol transport (RCT) is the process of cholesterol movement from the extrahepatic tissues back to the liver. Lipoproteins containing apoA-I [high-density lipoprotein (HDL)] are key mediators in RCT, whereas non-high-density lipoproteins (non-HDL, lipoproteins containing apoB) are involved in the lipid delivery pathway. HDL particles are heterogeneous; they differ in proportion of proteins and lipids, size, shape, and charge. HDL heterogeneity is the result of the activity of several factors that assemble and remodel HDL particles in plasma: ATP-binding cassette transporter A1 (ABCA1), lecithin cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP), hepatic lipase (HL), phospholipid transfer protein (PLTP), endothelial lipase (EL), and scavenger receptor class B type I (SR-BI). The RCT pathway consists of the following steps: 1. Cholesterol efflux from peripheral tissues to plasma, 2. LCAT-mediated esterification of cholesterol and remodeling of HDL particles, 3. direct pathway of HDL cholesterol delivery to the liver, and 4. indirect pathway of HDL cholesterol delivery to the liver via CETP-mediated transfer There are several established strategies for raising HDL cholesterol in humans, such as lifestyle changes; use of drugs including fibrates, statins, and niacin; and new therapeutic approaches. The therapeutic approaches include CETP inhibition, peroxisome proliferator-activated receptor (PPAR) agonists, synthetic farnesoid X receptor agonists, and gene therapy. Results of clinical trials should be awaited before further clinical management of atherosclerotic cardiovascular disease.

Development of triglyceride-lowering drugs to address residual cardiovascular risk: strategic and clinical considerations

The prevalence of hypertriglyceridaemia is high and growing in several parts of the world. Hypertriglyceridaemia has a well-defined association with the risk of atherosclerotic cardiovascular (CV) disease and triglycerides represent a potential target for drugs aimed at mitigating CV risk. So far, no triglyceride-lowering pharmacological strategy has succeeded in conclusively showing the ability to modify clinical outcomes. This article discusses strategic and clinical aspects of development of triglyceride-lowering drugs to address CV disease.

CETP inhibition, statins and diabetes

Type 2 diabetes is a causal risk factor for the development of atherosclerotic cardiovascular disease (ASCVD). While treatment with a statin reduces the risk of having an ASCVD event in all people, including those with type-2 diabetes, statin treatment also increases the likelihood of new onset diabetes when given to those with risk factors for developing diabetes. Treatment with the cholesteryl ester transfer protein (CETP) inhibitor, anacetrapib, reduces the risk of having a coronary event over and above that achieved with a statin. However, unlike statins, anacetrapib decreases the risk of developing diabetes. If the reduced risk of new-onset diabetes is confirmed in another CETP inhibitor outcome trial, there will be a case for considering the use of the combination of a statin plus a CETP inhibitor in high ASCVD-risk people who are also at increased risk of developing diabetes.

The Role of High-Density Lipoproteins in Diabetes and Its Vascular Complications

Almost 600 million people are predicted to have diabetes mellitus (DM) by 2035. Diabetic patients suffer from increased rates of microvascular and macrovascular complications, associated with dyslipidaemia, impaired angiogenic responses to ischaemia, accelerated atherosclerosis, and inflammation. Despite recent treatment advances, many diabetic patients remain refractory to current approaches, highlighting the need for alternative agents. There is emerging evidence that high-density lipoproteins (HDL) are able to rescue diabetes-related vascular complications through diverse mechanisms. Such protective functions of HDL, however, can be rendered dysfunctional within the pathological milieu of DM, triggering the development of vascular complications. HDL-modifying therapies remain controversial as many have had limited benefits on cardiovascular risk, although more recent trials are showing promise. This review will discuss the latest data from epidemiological, clinical, and pre-clinical studies demonstrating various roles for HDL in diabetes and its vascular complications that have the potential to facilitate its successful translation.

Cholesteryl ester transfer protein and its inhibitors

Most of the cholesterol in plasma is in an esterified form that is generated in potentially cardioprotective HDLs. Cholesteryl ester transfer protein (CETP) mediates bidirectional transfers of cholesteryl esters (CEs) and triglycerides (TGs) between plasma lipoproteins. Because CE originates in HDLs and TG enters the plasma as a component of VLDLs, activity of CETP results in a net mass transfer of CE from HDLs to VLDLs and LDLs, and of TG from VLDLs to LDLs and HDLs. As inhibition of CETP activity increases the concentration of HDL-cholesterol and decreases the concentration of VLDL- and LDL-cholesterol, it has the potential to reduce atherosclerotic CVD. This has led to the development of anti-CETP neutralizing monoclonal antibodies, vaccines, and antisense oligonucleotides. Small molecule inhibitors of CETP have also been developed and four of them have been studied in large scale cardiovascular clinical outcome trials. This review describes the structure of CETP and its mechanism of action. Details of its regulation and nonlipid transporting functions are discussed, and the results of the large scale clinical outcome trials of small molecule CETP inhibitors are summarized.

A meta-analytic evaluation of cholesteryl ester transfer protein (CETP) C-629A polymorphism in association with coronary heart disease risk and lipid changes

Lipid metabolism plays an essential role in the pathogenesis of atherosclerosis, a major cause for coronary heart disease (CHD). Cholesteryl ester transfer protein (CETP) is an important glycoprotein involved in lipid metabolism by transferring cholesteryl esters to apolipoprotein B-containing lipoproteins in exchange for triglycerides. The objective of this meta-analysis was to evaluate the association of CETP C-629A polymorphism with CHD risk and lipid changes. Four public databases were searched, and data from 17 qualified articles were extracted in duplicate and analyzed by STATA software. Overall association of C-629A with CHD risk was nonsignificant in 5441 patients and 7967 controls. Subgroup analyses by ethnicity revealed significance only in Caucasians, with the odds of CHD being 1.18, 1.43 and 1.41 under allelic, genotypic and dominant models, respectively (P < 0.001). Similarly, the -629C allele increased the corresponding risk of myocardial infarction by 1.23-, 1.28- and 1.29-fold (P < 0.02). The association of C-629A with CHD was significantly strengthened in prospective and large studies. Moreover, carriers of the -629C allele had significant higher levels of circulating CETP (weighted mean difference [WMD]: 0.45 μg/mL; 95% confidence interval [CI]: 0.25 to 0.65; P < 0.001), but lower levels of high-density lipoprotein cholesterol (HDL-C) (WMD: -3.65 mg/dL; 95% CI: -5.59 to -1.70; P < 0.001) relative to the -629AA homozygotes. The probability of publication bias was low. Our meta-analytic findings collectively demonstrate that the -629C allele was significantly associated with an increased risk of CHD in Caucasians, and this association may be mediated by its phenotypic regulation on circulating CETP and HDL-C.

Present therapeutic role of cholesteryl ester transfer protein inhibitors

Therapeutic interventions aimed at increasing high-density lipoprotein (HDL) levels in order to reduce the residual cardiovascular (CV) risk of optimally drug treated patients have not provided convincing results, so far. Transfer of cholesterol from extrahepatic tissues to the liver appears to be the major atheroprotective function of HDL, and an elevation of HDL levels could represent an effective strategy. Inhibition of the cholesteryl ester transfer protein (CETP), raising HDL-cholesterol (HDL-C) and apolipoprotein A-I (apoA-I) levels, reduces low-density lipoprotein-cholesterol (LDL-C) and apoB levels, thus offering a promising approach. Despite the beneficial influence on cholesterol metabolism, off-target effects and lack of reduction in CV events and mortality (with torcetrapib, dalcetrapib and evacetrapib) highlighted the complex mechanism of CETP inhibition. After the failure of the above mentioned inhibitors in phase III clinical development, possibly due to the short duration of the trials masking benefit, the secondary prevention REVEAL trial has recently shown that the inhibitor anacetrapib significantly raised HDL-C (+104%), reduced LDL-C (-18%), with a protective effect on major coronary events (RR, 0.91; 95%CI, 0.85-0.97; p = 0.004). Whether LDL-C lowering fully accounts for the CV benefit or if HDL-C-rise is a crucial factor still needs to be determined, although the reduction of non-HDL (-18%) and Lp(a) (-25%), should be also taken into account. In spite of the positive results of the REVEAL Study, Merck decided not to proceed in asking regulatory approval for anacetrapib. Dalcetrapib (Dal-GenE study) and CKD-519 remain the two molecules within this area still in clinical development.

HDL Cholesterol Metabolism and the Risk of CHD: New Insights from Human Genetics

PURPOSE OF REVIEW

Elevated high-density lipoprotein cholesterol levels in the blood (HDL-C) represent one of the strongest epidemiological surrogates for protection against coronary heart disease (CHD), but recent human genetic and pharmacological intervention studies have raised controversy about the causality of this relationship. Here, we review recent discoveries from human genome studies using new analytic tools as well as relevant animal studies that have both addressed, and in some cases, fueled this controversy.

RECENT FINDINGS

Methodologic developments in genotyping and sequencing, such as genome-wide association studies (GWAS), exome sequencing, and exome array genotyping, have been applied to the study of HDL-C and risk of CHD in large, multi-ethnic populations. Some of these efforts focused on population-wide variation in common variants have uncovered new polymorphisms at novel loci associated with HDL-C and, in some cases, CHD risk. Other efforts have discovered loss-of-function variants for the first time in genes previously implicated in HDL metabolism through common variant studies or animal models. These studies have allowed the genetic relationship between these pathways, HDL-C and CHD to be explored in humans for the first time through analysis tools such as Mendelian randomization. We explore these discoveries for selected key HDL-C genes CETP, LCAT, LIPG, SCARB1, and novel loci implicated from GWAS including GALNT2, KLF14, and TTC39B. Recent human genetics findings have identified new nodes regulating HDL metabolism while reshaping our current understanding of known candidate genes to HDL and CHD risk through the study of critical variants across model systems. Despite their effect on HDL-C, variants in many of the reviewed genes were found to lack any association with CHD. These data collectively indicate that HDL-C concentration, which represents a static picture of a very dynamic and heterogeneous metabolic milieu, is unlikely to be itself causally protective against CHD. In this context, human genetics represent an extremely valuable tool to further explore the biological mechanisms regulating HDL metabolism and investigate what role, if any, HDL plays in the pathogenesis of CHD.

Mendelian randomization analysis of cholesteryl ester transfer protein and subclinical atherosclerosis: A population-based study

BACKGROUND

Several trials to prevent cardiovascular disease by inhibiting cholesteryl ester transfer protein (CETP) have failed, except Randomized EValuation of the Effects of Anacetrapib through Lipid-modification. Thus far, it is unclear to what extent CETP is causally related to measures of atherosclerosis.

OBJECTIVE

The aim of the article was to study the causal relationship between genetically determined CETP concentration and carotid intima-media thickness (cIMT) in a population-based cohort study.

METHODS

In the Netherlands Epidemiology of Obesity study, participants were genotyped, and cIMT was measured by ultrasonography. We examined the relation between a weighted genetic risk score for CETP concentration, based on 3 single-nucleotide polymorphisms that have previously been shown to largely determine CETP concentration and cIMT using Mendelian randomization in the total population and in strata by sex, Framingham 10-year risk, (pre)diabetes, high-density lipoprotein cholesterol, triglycerides, and statin use.

RESULTS

We analyzed 5655 participants (56% women) with a mean age of 56 (range 44-66) years, body mass index of 26 (range 17-61) kg/m², and serum CETP of 2.47 (range 0.68-5.33) μg/mL. There was no evidence for a causal relation between genetically determined CETP and cIMT in the total population, but associations were differently directed in men (16 μm per μg/mL increase in genetically determined CETP; 95% confidence interval: -8, 39) and women (-8 μm; -25, 9). Genetically determined CETP appeared to be associated with cIMT in normoglycemic men (26 μm; -1, 52) and in (pre)diabetic women (48 μm; -2, 98).

CONCLUSION

In this population-based study, there was no causal relation between genetically determined CETP concentration and cIMT in the total population although we observed directionally differing effects in men and women. Stratified results suggested associations in individuals with different cardiometabolic risk factor profiles, which require replication.

Comprehensive lipid and metabolite profiling of children with and without familial hypercholesterolemia: A cross-sectional study

BACKGROUND AND AIMS

Individuals with familial hypercholesterolemia (FH) have elevated low-density lipoprotein cholesterol (LDL-C), accelerated atherosclerosis, and premature cardiovascular disease. Whereas children with lifestyle-induced dyslipidemias often present with complex lipid abnormalities, children with FH have isolated hypercholesterolemia. However, to the best of our knowledge, a comprehensive profiling of FH children is lacking. Therefore, we aimed to characterize the lipid-related and metabolic alterations associated with elevated LDL-C in children with FH and healthy children.

METHODS

We measured plasma metabolites in children with FH (n = 47) and in healthy children (n = 57) using a high-throughput nuclear magnetic resonance (NMR) spectroscopy platform, and compared the differences between FH and healthy children.

RESULTS

Both statin treated (n = 17) and non-statin treated FH children (n = 30) had higher levels of atherogenic ApoB-containing lipoproteins and lipids, and lipid fractions in lipoprotein subclasses, compared to healthy children (n = 57). FH children displayed alterations in HDL particle concentration and lipid content, compared with healthy children. Interestingly, the small HDL particles were characterized by higher content of cholesteryl esters, and lower levels of free cholesterol and phospholipids. Furthermore, plasma fatty acids were higher in non-statin treated FH children, particularly linoleic acid. Finally, acetoacetate and acetate were lower in FH children compared with healthy children.

CONCLUSIONS

Hypercholesterolemia in children associates with diverse metabolic repercussions and is more complex than previously believed. In particular, we found that hypercholesterolemia in FH children was paralleled not only by increased atherogenic ApoB-containing lipoproteins and lipid fractions, but also alterations in HDL subfractions that suggest impaired reverse cholesterol transport.

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.

HDL cholesterol: reappraisal of its clinical relevance

Background

While several lines of evidence prove that elevated concentrations of low-density lipoproteins (LDL) causally contribute to the development of atherosclerosis and its clinical consequences, high-density lipoproteins are still widely believed to exert atheroprotective effects. Hence, HDL cholesterol (HDL-C) is in general still considered as “good cholesterol”. Recent research, however, suggests that this might not always be the case and that a fundamental reassessment of the clinical significance of HDL-C is warranted.

Method

This review article is based on a selective literature review.

Results

In individuals without a history of cardiovascular events, low concentrations of HDL-C are inversely associated with the risk of future cardiovascular events. This relationship may, however, not apply to patients with metabolic disorders or manifest cardiovascular disease. The classical function of HDL is to mobilise cholesterol from extrahepatic tissues for delivery to the liver for excretion. These roles in cholesterol metabolism as well as many other biological functions of HDL particles are dependent on the number as well as protein and lipid composition of HDL particles. They are poorly reflected by the HDL-C concentration. HDL can even exert negative vascular effects, if its composition is pathologically altered. High serum HDL-C is therefore no longer regarded protective. In line with this, recent pharmacological approaches to raise HDL-C concentration have not been able to show reductions of cardiovascular outcomes.

Conclusion

In contrast to LDL cholesterol (LDL-C), HDL-C correlates with cardiovascular risk only in healthy individuals. The calculation of the ratio of LDL-C to HDL-C is not useful for all patients. Low HDL-C should prompt examination of additional metabolic and inflammatory pathologies. An increase in HDL-C through lifestyle change (smoking cessation, physical exercise) has positive effects and is recommended. However, HDL-C is currently not a valid target for drug therapy.

[Clinical importance of HDL cholesterol]

BACKROUND

Each year 16-17 million determinations of high-density lipoprotein cholesterol (HDL-C) are conducted and interpreted in Germany. Recently acquired data have led to a fundamental reassessment of the clinical significance of HDL-C.

METHOD

This review article is based on a selective literature search.

RESULTS

Low HDL‑C levels usually indicate an increased cardiovascular risk, particularly in primary prevention but the epidemiological relationship between HDL‑C and the risk is complex. The HDL plays a role in the back transport and excretion of cholesterol; however, the biological functions of HDL are dependent on the protein and lipid composition, which is not reflected by the HDL‑C concentration. If the composition of HDL is pathologically altered it can also exert negative vascular effects.

CONCLUSION

Compared with low-density lipoprotein cholesterol (LDL-C), HDL‑C is of secondary importance for cardiovascular risk stratification and the calculation of the LDL-C:HDL‑C ratio is not useful for all patients. Low HDL‑C levels should prompt a search for additional metabolic and inflammatory pathologies. An increase in HDL‑C through lifestyle changes (e.g. smoking cessation and physical exercise) has positive effects and is recommended; however, HDL‑C is currently not a valid target for drug therapy.

New Era of Lipid-Lowering Drugs

There are several established lipid-modifying agents, including statins, fibrates, niacin, and ezetimibe, that have been shown in randomized clinical outcome trials to reduce the risk of having an atherosclerotic cardiovascular event. However, in many people, the risk of having an event remains unacceptably high despite treatment with these established agents. This has stimulated the search for new therapies designed to reduce residual cardiovascular risk. New approaches that target atherogenic lipoproteins include: 1) inhibition of proprotein convertase subtilisin/kexin type 9 to increase removal of atherogenic lipoproteins from plasma; 2) inhibition of the synthesis of apolipoprotein (apo) B, the main protein component of atherogenic lipoproteins; 3) inhibition of microsomal triglyceride transfer protein to block the formation of atherogenic lipoproteins; 4) inhibition of adenosine triphosphate citrate lyase to inhibit the synthesis of cholesterol; 5) inhibition of the synthesis of lipoprotein(a), a factor known to cause atherosclerosis; 6) inhibition of apoC-III to reduce triglyceride-rich lipoproteins and to enhance high-density lipoprotein (HDL) functionality; and 7) inhibition of cholesteryl ester transfer protein, which not only reduces the concentration of atherogenic lipoproteins but also increases the level and function of the potentially antiatherogenic HDL fraction. Other new therapies that specifically target HDLs include infusions of reconstituted HDLs, HDL delipidation, and infusions of apoA-I mimetic peptides that mimic some of the functions of HDLs. This review describes the scientific basis and rationale for developing these new therapies and provides a brief summary of established therapies.

HDLs in crises

PURPOSE OF REVIEW

The clinical utility of HDLs has been scrutinized upon the publication of Mendelian randomization studies showing no effect of HDL-cholesterol (HDL-C) modifying variants on cardiovascular disease (CVD) outcome. The failures of randomized controlled HDL-C-directed intervention trials have further fueled this skepticism. This general criticism originates from oversimplification that has equated 'HDL-C' with 'HDL' and misconceived both as the 'good cholesterol'.

RECENT FINDINGS

HDL particles are heterogeneous and carry hundreds of different lipids, proteins, and microRNAs. Many of them but not cholesterol, that is, HDL-C, contributes to the multiple protective functions of HDLs that probably evolved to manage potentially life-threatening crises. Inflammatory processes modify the composition of HDL particles as well as their individual protein and lipid components, and, as a consequence, also their functionality. Gain of dominant-negative functions makes dysfunctional HDL a part rather than a solution of the endangering situation. Quantification of HDL particle numbers, distinct proteins or lipids, and modifications thereof as well as bioassays of HDL functionality are currently explored toward their diagnostic performance in risk prediction and monitoring of treatment response.

SUMMARY

Any successful clinical exploitation of HDLs will depend on the identification of the most relevant (dys)functions and their structural correlates. Stringent or prioritized structure-(dys)function relationships may provide biomarkers for better risk assessment and monitoring of treatment response. The most relevant agonists carried by either functional or dysfunctional HDLs as well as their cellular responders are interesting targets for drug development.

Cholesteryl Ester Transfer Protein Inhibition Is Not Yet Dead—Pro

Cholesteryl ester transfer protein (CETP) transfers cholesteryl esters from nonatherogenic high-density lipoproteins to potentially proatherogenic non–high-density lipoprotein fractions. Human genetic studies and human cohort studies have concluded that CETP gene polymorphisms associated with decreased CETP activity are accompanied by a significantly lower risk of atherosclerotic cardiovascular disease. Inhibition of CETP in rabbits reduces development of diet-induced atherosclerosis. Inhibition of CETP in humans reduces non–high-density lipoprotein cholesterol while increasing high-density lipoproteins cholesterol, consistent with a reduced risk of having an atherosclerotic cardiovascular disease event. The failure of randomized human clinical outcome trials with 3 different CETP inhibitors may have been the consequence of either off-target adverse effects of the drug used or problems with the design of the trials. The hypothesis that CETP inhibition reduces atherosclerotic cardiovascular disease risk is still untested. The future of CETP inhibition as a cardio-protective strategy will depend on the outcome of the ongoing Randomized Evaluation of the Effects of Anacetrapib Through Lipid-Modification (REVEAL) trial with the CETP inhibitor, anacetrapib.

Genetically lowered concentrations of circulating sRAGE might cause an increased risk of cancer: Meta-analysis using Mendelian randomization

Objectives

To undertake a systematic meta-analysis of all variants in the gene encoding receptor for advanced glycation end products (RAGE) to summarize their associations with cancer risk and changes in the levels of circulating soluble RAGE (sRAGE), with the aim of determining possible causality between circulating sRAGE and cancer risk.

Methods

Articles written in English were retrieved from MEDLINE® and EMBASE® databases. Two researchers independently identified eligible articles and extracted the data (analysed using STATA® software version 12.0).

Results

Fifteen articles qualified for inclusion in the meta-analysis of the RAGE–cancer association and three examined the RAGE–sRAGE relationship. The 82Ser/82Ser genotype was significantly associated with overall cancer risk compared with the 82Gly/Gly genotype (odds ratio 1.75, 95% confidence interval [CI] 1.46, 2.10). Carriers of the 82Ser/82Ser genotype had significantly reduced circulating sRAGE concentrations compared with the 82Gly/82Gly genotype. Mendelian randomization analysis demonstrated that a reduction of 100, 200 and 300 pg/ml in circulating sRAGE concentrations was associated with a 1.11-fold (95% CI 1.06, 1.25), 1.24-fold (95% CI 1.11, 1.57) and 1.38-fold (95% CI 1.18, 1.96) increased risk of developing cancer, respectively.

Conclusions

Genetically lowered concentrations of circulating sRAGE might cause an increased risk of cancer.

Cholesteryl ester transfer protein gene polymorphism (I405V) and premature coronary artery disease in an Iranian population

The effect of human cholesteryl ester transfer protein (CETP) expression on atherogenesis is still under debate. The rs5882 (I405V) polymorphism affect CETP function. We aimed to examine the relationship between the rs5882 polymorphism and the risk of angiographically determined coronary artery disease (CAD). To define premature CAD (PCAD), an age cutoff of 55 years for women and 45 years for men was used. An age- and sex-matched case-control study was conducted in 560 patients with newly diagnosed angiographically documented PCAD (≥50% luminal stenosis of any coronary vessel) and an equal number of control patients with normal coronary arteries (no luminal stenosis at coronary arteries). The severity of CAD was determined by vessel score and Gensini score. A real-time polymerase chain reaction (PCR) and high resolution melting analysis were used to distinguish between genotypes. The I405V genotype distributions were not statistically different in CAD and non-CAD groups in univariate and multivariable-adjusted logistic regression analyzes. The median and inter-quartile range for Gensini score was not significantly different among the AA (43, 24 to 73), AG (40, 20 to 66), and GG (45, 25 to 72) genotypes (p = 0.097). Furthermore, the distribution of vessel score did not statistically differ between these genotypes (p = 0.691). Our results suggest that there is no significant association between CETP I405V polymorphism and the risk of PCAD presence and severity. Larger prospective studies are needed to investigate such associations in different populations.