Cholesteryl ester transfer protein (CETP) deficiency and CETP inhibitors

Revisiting high-density lipoprotein cholesterol in cardiovascular disease: Is too much of a good thing always a good thing?

Cardiovascular disease (CVD) continues to be a leading cause of global mortality and morbidity. Various established risk factors are linked to CVD, and modifying these risk factors is fundamental in CVD management. Clinical studies underscore the association between dyslipidemia and CVD, and therapeutic interventions that target low-density lipoprotein cholesterol elicit clear benefits. Despite the correlation between low high-density lipoprotein cholesterol (HDLC) and heightened CVD risk, HDL-raising therapies have yet to showcase significant clinical benefits. Furthermore, evidence from epidemiological and genetic studies reveals that not only low HDL-C levels, but also very high levels of HDL-C are linked to increased risk of CVD. In this review, we focus on HDL metabolism and delve into the relationship between HDL and CVD, exploring HDL functions and the observed alterations in its roles in disease. Altogether, the results discussed herein support the conventional wisdom that "too much of a good thing is not always a good thing". Thus, our recommendation is that a careful reconsideration of the impact of high HDL-C levels is warranted, and shall be revisited in future research.

The Role of Triglyceride-rich Lipoproteins and Their Remnants in Atherosclerotic Cardiovascular Disease

Atherosclerotic cardiovascular disease (ASCVD) is the world's leading cause of death. ASCVD has multiple mediators that therapeutic interventions target, such as dyslipidaemia, hypertension, diabetes and heightened systemic inflammatory tone, among others. LDL cholesterol is one of the most well-studied and established mediators targeted for primary and secondary prevention of ASCVD. However, despite the strength of evidence supporting LDL cholesterol reduction by multiple management strategies, ASCVD events can still recur, even in patients whose LDL cholesterol has been very aggressively reduced. Hypertriglyceridaemia and elevated levels of triglyceride-rich lipoproteins (TRLs) may be key contributors to ASCVD residual risk. Several observational and genetic epidemiological studies have highlighted the causal role of triglycerides within the TRLs and/or their remnant cholesterol in the development and progression of ASCVD. TRLs consist of intestinally derived chylomicrons and hepatically synthesised very LDL. Lifestyle modification has been considered the first line intervention for managing hypertriglyceridaemia. Multiple novel targeted therapies are in development, and have shown efficacy in the preclinical and clinical phases of study in managing hypertriglyceridaemia and elevated TRLs. This comprehensive review provides an overview of the biology, pathogenicity, epidemiology, and genetics of triglycerides and TRLs, and how they impact the risk for ASCVD. In addition, we provide a summary of currently available and novel emerging triglyceride-lowering therapies in development.

Gender Differences in the Association between Cholesteryl Esters Transfer Protein Polymorphism (rs708272) and Plasma Lipid Levels in Hyperlipidaemic Participants at Hospital Universiti Sains Malaysia

Background

Single nucleotide polymorphism (SNP) in the cholesteryl esters transfer protein (CETP) gene (rs708272) was reported to affect statin efficacy. This study investigated the association between CETP rs708272 and statin's lipid-lowering effects in hyperlipidaemic participants at Hospital Universiti Sains Malaysia, Kelantan.

Methods

A total of 229 hyperlipidaemic statin users (96.1% Malays) were recruited, and a single blood sample (3 mL) was obtained for DNA extraction. The genotypes were determined using PCR-RFLP method and validated by sequencing analysis.

Results

The minor allele frequency for rs708272 in all participants was 0.391, with no difference between females and males. At the baseline, the SNP was associated with different low-density lipoprotein (LDL-c) and triglyceride (TG) levels in females, but not males, when the GG and GA+AA genotypes were compared using a dominant genetic model. Regardless of the genotype, the total cholesterol and LDL-c levels decreased significantly (P < 0.001) in both genders after statin treatment, but the TG levels decreased exclusively in females with the GG genotypes. In both genders, high density lipoprotein levels were unaffected before and after the statin treatment.

Conclusion

To improve the management of hyperlipidaemia, future research should consider patient gender when assessing the CETP rs708272 impact on LDL-c and TG.

Structure-based mechanism and inhibition of cholesteryl ester transfer protein

PURPOSE OF REVIEW

Cholesteryl ester transfer proteins (CETP) regulate plasma cholesterol levels by transferring cholesteryl esters (CEs) among lipoproteins. Lipoprotein cholesterol levels correlate with the risk factors for atherosclerotic cardiovascular disease (ASCVD). This article reviews recent research on CETP structure, lipid transfer mechanism, and its inhibition.

RECENT FINDINGS

Genetic deficiency in CETP is associated with a low plasma level of low-density lipoprotein cholesterol (LDL-C) and a profoundly elevated plasma level of high-density lipoprotein cholesterol (HDL-C), which correlates with a lower risk of atherosclerotic cardiovascular disease (ASCVD). However, a very high concentration of HDL-C also correlates with increased ASCVD mortality. Considering that the elevated CETP activity is a major determinant of the atherogenic dyslipidemia, i.e., pro-atherogenic reductions in HDL and LDL particle size, inhibition of CETP emerged as a promising pharmacological target during the past two decades. CETP inhibitors, including torcetrapib, dalcetrapib, evacetrapib, anacetrapib and obicetrapib, were designed and evaluated in phase III clinical trials for the treatment of ASCVD or dyslipidemia. Although these inhibitors increase in plasma HDL-C levels and/or reduce LDL-C levels, the poor efficacy against ASCVD ended interest in CETP as an anti-ASCVD target. Nevertheless, interest in CETP and the molecular mechanism by which it inhibits CE transfer among lipoproteins persisted. Insights into the structural-based CETP-lipoprotein interactions can unravel CETP inhibition machinery, which can hopefully guide the design of more effective CETP inhibitors that combat ASCVD. Individual-molecule 3D structures of CETP bound to lipoproteins provide a model for understanding the mechanism by which CETP mediates lipid transfer and which in turn, guide the rational design of new anti-ASCVD therapeutics.

Is microRNA-33 an Appropriate Target in the Treatment of Atherosclerosis?

The maintenance of cholesterol homeostasis is a complicated process involving regulation of cholesterol synthesis, dietary uptake and bile acid synthesis and excretion. Reverse cholesterol transport, described as the transfer of cholesterol from non-hepatic cells, including foam cells in atherosclerotic plaques, to the liver and then its excretion in the feces is important part of this regulation. High-density lipoproteins are the key mediators of reverse cholesterol transport. On the other hand, microRNA-33 was identified as a key regulator of cholesterol homeostasis. Recent studies indicate the impact of microRNA-33 not only on cellular cholesterol efflux and HDL production but also on bile metabolism in the liver. As proper coordination of cholesterol metabolism is essential to human health, discussion of recent findings in this field may open new perspectives in the microRNA-dependent treatment of a cholesterol imbalance.

Translating atherosclerosis research from bench to bedside: navigating the barriers for effective preclinical drug discovery

Cardiovascular disease (CVD) remains the leading cause of death worldwide. An ongoing challenge remains the development of novel pharmacotherapies to treat CVD, particularly atherosclerosis. Effective mechanism-informed development and translation of new drugs requires a deep understanding of the known and currently unknown biological mechanisms underpinning atherosclerosis, accompanied by optimization of traditional drug discovery approaches. Current animal models do not precisely recapitulate the pathobiology underpinning human CVD. Accordingly, a fundamental limitation in early-stage drug discovery has been the lack of consensus regarding an appropriate experimental in vivo model that can mimic human atherosclerosis. However, when coupled with a clear understanding of the specific advantages and limitations of the model employed, preclinical animal models remain a crucial component for evaluating pharmacological interventions. Within this perspective, we will provide an overview of the mechanisms and modalities of atherosclerotic drugs, including those in the preclinical and early clinical development stage. Additionally, we highlight recent preclinical models that have improved our understanding of atherosclerosis and associated clinical consequences and propose model adaptations to facilitate the development of new and effective treatments.

Lipid and Lipoprotein Metabolism

The exogenous lipoprotein pathway starts with the incorporation of dietary lipids into chylomicrons in the intestine. Chylomicron triglycerides are metabolized in muscle and adipose tissue and chylomicron remnants are formed, which are removed by the liver. The endogenous lipoprotein pathway begins in the liver with the formation of very low-density lipoprotein particles (VLDL). VLDL triglycerides are metabolized in muscle and adipose tissue forming intermediate-density lipoprotein (IDL), which may be taken up by the liver or further metabolized to low-density lipoprotein (LDL). Reverse cholesterol transport begins with the formation of nascent high-density lipoprotein (HDL) by the liver and intestine that acquire cholesterol from cells resulting in mature HDL. The HDL then transports the cholesterol to the liver either directly or indirectly by transferring the cholesterol to VLDL or LDL.

Association of lipid metabolism-related gene promoter methylation with risk of coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is a complex disease that is influenced by environmental and genetic factors. Lipid levels are regarded as a major risk factor for CAD, and epigenetic mechanisms might be involved in the regulation of CAD development. This study was designed to investigate the association between the DNA methylation status of 8 lipid metabolism-related genes and the risk of CAD in the Chinese Han population.

METHODS

A total of 260 individuals were sampled in this study, including 120 CAD cases and 140 normal healthy controls. DNA methylation status was tested via targeted bisulfite sequencing.

RESULTS

The results indicated a significant association between hypomethylation of the APOC3, CETP and APOC1 gene promoters and the risk of CAD. Individuals with higher methylation levels of the APOA5 and LIPC gene promoters had increased risks for CAD. In addition, ANGPTL4 methylation level was significantly associated with CAD in males but not females. There were no significant differences in the methylation levels of the APOB and PCSK9 gene promoters between CAD patients and controls.

CONCLUSIONS

The methylation status of the APOC3, APOA5, LIPC, CETP and APOC1 gene promoters may be associated with the development of CAD.

Anti-Hyperlipidemia, Hypoglycemic, and Hepatoprotective Impacts of Pearl Millet (Pennisetum glaucum L.) Grains and Their Ethanol Extract on Rats Fed a High-Fat Diet

This study tested the anti-hyperlipidemic, hypoglycemic, hepatoprotective, and anti-inflammatory effects of whole pearl millet grain powder (MPG) and its ethanol extract (MPGethaolE) in obese rats fed a high-fat diet. The rats were divided into eight groups based on the treatments they received: control, high fat diet (HFD), HFD + MGE (25 mg/Kg), HFD + MPGethaolE (50 mg/Kg), HFD + MPGethaolE (100 mg/Kg), HFD + MPG (10%), HFD + MPG (20%), and HFD + MPG (30%). The final body weight, visceral, epididymal fat pads, and the liver weight were significantly decreased, in a dose-dependent manner, in HFD fed rats that were co-administered either the MPG powder or MPGethaolE. In the same line, serum levels of triglycerides (TGs), cholesterol (CHOL), and low-density lipoprotein-cholesterol (LDL-c), as well as fasting glucose, insulin, HOMA-IR, and serum levels of lipopolysaccharides (LPS), interleukine-6 (IL-6), interleukine-10 (IL-10), C-reactive protein (CRP), tumor necrosis factor (TNF-α), and adiponectin were progressively decreased while serum levels of high-density lipoproteins (HDL-c) were significantly increased when increasing the doses of both treatments. In conclusion, both the raw powder and ethanolic extract of MP have a comparative dose-dependent anti-obesity, hypoglycemic, hypolipidemic, anti-inflammatory, and anti-steatotic in HFD-fed rats.

The APOEε3/ε4 Genotype Drives Distinct Gene Signatures in the Cortex of Young Mice

Introduction

Restrictions on existing APOE mouse models have impacted research toward understanding the strongest genetic risk factor contributing to Alzheimer’s disease (AD) and dementia, APOEε4, by hindering observation of a key, common genotype in humans – APOEε3/ε4. Human studies are typically underpowered to address APOEε4 allele risk as the APOEε4/ε4 genotype is rare, which leaves human and mouse research unsupported to evaluate the APOEε3/ε4 genotype on molecular and pathological risk for AD and dementia.

Methods

As a part of MODEL-AD, we created and validated new versions of humanized APOEε3/ε3 and APOEε4/ε4 mouse strains that, due to unrestricted breeding, allow for the evaluation of the APOEε3/ε4 genotype. As biometric measures are often translatable between mouse and human, we profiled circulating lipid concentrations. We also performed transcriptional profiling of the cerebral cortex at 2 and 4 months (mos), comparing APOEε3/ε4 and APOEε4/ε4 to the reference APOEε3/ε3 using linear modeling and WGCNA. Further, APOE mice were exercised and compared to litter-matched sedentary controls, to evaluate the interaction between APOEε4 and exercise at a young age.

Results

Expression of human APOE isoforms were confirmed in APOEε3/ε3, APOEε3/ε4 and APOEε4/ε4 mouse brains. At two mos, cholesterol composition was influenced by sex, but not APOE genotype. Results show that the APOEε3/ε4 and APOEε4/ε4 genotype exert differential effects on cortical gene expression. APOEε3/ε4 uniquely impacts ‘hormone regulation’ and ‘insulin signaling,’ terms absent in APOEε4/ε4 data. At four mos, cholesterol and triglyceride levels were affected by sex and activity, with only triglyceride levels influenced by APOE genotype. Linear modeling revealed APOEε3/ε4, but not APOEε4/ε4, affected ‘extracellular matrix’ and ‘blood coagulation’ related terms. We confirmed these results using WGCNA, indicating robust, yet subtle, transcriptional patterns. While there was little evidence of APOE genotype by exercise interaction on the cortical transcriptome at this young age, running was predicted to affect myelination and gliogenesis, independent of APOE genotype with few APOE genotype-specific affects identified.

Discussion

APOEε4 allele dosage-specific effects were observed in circulating lipid levels and cortical transcriptional profiles. Future studies are needed to establish how these data may contribute to therapeutic development in APOEε3/ε4 and APOEε4/ε4 dementia patients.

Genetics of Familial Combined Hyperlipidemia (FCHL) Disorder: An Update

Familial combined hyperlipidemia (FCHL) is one of the most common familial lipoprotein disorders of the lipoproteins, with a prevalence of 0.5% to 2% in different populations. About 10% of these patients suffer from cardiovascular disease and this number is increased by up to 11.3% in the young survivors of myocardial infarction and by 40% among all the survivors of myocardial infarction. Although initially thought to be that FCHL has an inheritance pattern of monogenic, the disease's etiology is still not fully understood and it appears that FCHL has a complex pattern related to genetic variants, environmental factors, and lifestyles. Two strategies have been used to identify its complex genetic background: candidate gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL with a variable degree of scientific evidence. Until now, more than 30 different genetic variants have been identified related to FCHL. In this study, we aimed to review the individual genes that have been described in FCHL and how these genes and variants can be related to the current concept of metabolic pathways resulting in familial combined hyperlipidemia.

Mechanism of Glycans Modulating Cholesteryl Ester Transfer Protein: Unveiled by Molecular Dynamics Simulation

Inhibition of the cholesteryl ester transfer protein (CETP) has been considered as a promising way for the treatment of cardiovascular disease (CVD) for three decades. However, clinical trials of several CETP inhibitors with various potencies have been marginally successful at best, raising doubts on the target drugability of CETP. The in-depth understanding of the glycosylated CETP structure could be beneficial to more definitive descriptions of the CETP function and the underlying mechanism. In this work, large-scale molecular dynamics simulations were performed to thoroughly explore the mechanism of glycans modulating CETP. Here, the extensive simulation results intensely suggest that glycan88 tends to assist CETP in forming a continuous tunnel throughout interacting with the upper-right region of the N-barrel, while it also could prevent the formation of a continuous tunnel by swinging toward the right-rear of the N-barrel. Furthermore, glycan240 formed stable H-bonds with Helix-B and might further stabilize the central cavity of CETP. Furthermore, the nonspecific involvement of the hydroxyl groups from the various glycans with protein core interactions and the similar influence of different glycans trapped at similar regions on the protein structure suggest that physiological glycan may lead to a similar effect. This study would provide valuable insights into devising novel methods for CVD treatment targeting CETP and functional studies about glycosylation for other systems.

Atherosclerotic cardiovascular disease in hyperalphalipoproteinemia due to LIPG variants

BACKGROUND

High density lipoprotein cholesterol (HDL-C) concentration correlates inversely with atherosclerotic cardiovascular disease (ASCVD) risk and is included in risk calculations. Endothelial lipase (EL) is a phospholipase that remodels HDL. Deficiency of EL due to mutations in its gene, LIPG, is associated with hyperalphalipoproteinemia. The effects of EL on HDL function and ASCVD risk remain poorly understood.

OBJECTIVES

To determine whether hyperalphalipoproteinemia due to EL deficiency is protective against ASCVD.

METHODS

We identified LIPG variants amongst patients with severe hyperalphalipoproteinemia (HDL-C >2.5 mmol/L) attending a referral lipid clinic in the Western Cape Province of South Africa. We analysed the clinical and biochemical phenotypes amongst primary hyperalphalipoproteinemia cases (males HDL-C >1.6 mmol/L; females HDL-C >1.8 mmol/L) due to LIPG variants, and the distribution of variants in normal and hyperalphalipoproteinemia ranges of HDL-C.

RESULTS

1007 patients with HDL-C concentration ranging from 1.2 to 4.5 mmol/L were included. Seventeen females had primary hyperalphalipoproteinemia. Vascular disease was prominent, but not associated with HDL-C concentration, LDL-C concentration or carotid artery intima media thickness. Two novel and three known LIPG variants were identified in severe hyperalphalipoproteinemia. Four additional variants were identified in the extended cohort. Two common variants appeared normally distributed across the HDL-C concentration range, while six less-common variants were found only at higher HDL-C concentrations. One rare variant had a moderate effect.

CONCLUSION

Hyperalphalipoproteinemia due to LIPG variants is commoner in females and may not protect against ASCVD. Use of current risk calculations may be inappropriate in patients with hyperalphalipoproteinemia due to EL deficiency. Our study cautions targeting EL to reduce risk.

Cholesteryl ester transfer protein inhibitors in precision medicine

Dyslipidemia is associated with atherosclerosis and cardiovascular disease development, posing serious risks to human health. Cholesteryl ester transfer protein (CETP) is responsible for exchange of neutral lipids, such as cholesteryl ester and TG, between plasma high density lipoprotein (HDL) particles and Apolipoprotein B-100 (ApoB-100) containing lipoprotein particles. Genetic studies suggest that single-nucleotide polymorphism (SNPs) with loss of activity CETP is associated with increased HDL-C, reduced LDL-C, and cardiovascular risk. In animal studies, mostly in rabbits, which have similar CETP activity to humans, inhibition of CETP through antisense oligonucleotides reduced aortic arch atherosclerosis. Concerning this notion, inhibiting the CETP is considered as a promise approach to reduce cardiovascular events, and several CETP inhibitors have been recently studied as a cholesterol modifying agent to reduce cardiovascular mortality in high risk cardiovascular disease patients. However, in Phase III cardiovascular outcome trials, three CETP inhibitors, named Torcetrapib, Dalcetrapib, and Evacetrapib, did not provide expected cardiovascular benefits and failed to improve outcomes of patient with cardiovascular diseases (CVD). Although REVEAL trail has recently shown that Anacetrapib could reduce major coronary events, it was also shown to induce excessive lipid accumulation in adipose tissue; thereby, the further regulatory approval will not be sought. On the other hand, growing evidence indicated that the function of CETP inhibitors on modulating the cardiovascular events are determined by correlated single nucleotide polymorphism (SNP) in the ADCY9 gene. However, the underlying mechanisms whereby CETP inhibitors interact with the genotype are not yet elucidated, which could potentially be related to the genotype-dependent cholesterol efflux capacity of HDL particles. In the present review, we summarize the current understanding of the functions of CETP and the outcomes of the phase III randomized controlled trials of CETP inhibitors. In addition, we also put forward the implications from results of the trials which potentially suggest that the CETP inhibitors could be a promising precise therapeutic medicine for CVD based on genetic background.

The Effect of Smoking on the Association between Long-Term Alcohol Consumption and Dyslipidemia in a Middle-Aged and Older Population

AIMS

The joint effects of chronic alcohol consumption and smoking on dyslipidemia remain unclear in a prospective design. This study examined the effect of smoking on the association between long-term alcohol consumption and risk of incident dyslipidemia.

METHODS

A total of 4467 participants (1866 men and 2601women) aged 40-69 years without dyslipidemia were recruited at baseline. Alcohol consumption was assessed biennially using a questionnaire and classified as light, moderate or heavy drinker. Smoking status was examined at baseline and categorized into non-smokers and current smokers. Dyslipidemia was defined as the presence of one or more of following: hypertriglyceridemia (triglyceride ≥200 mg/dL), hypercholesterolemia (total cholesterol ≥240 mg/dL), low high-density lipoprotein-cholesterol (HDL-C) < 40 mg/dL, or high low-density lipoprotein cholesterol ≥160 mg/dL.

RESULTS

During a follow-up period of 12 years, 2872 (64.3%) participants developed dyslipidemia. In non-smoking men, light or moderate alcohol consumption was associated with a lower risk of incident dyslipidemia such as hypertriglyceridemia and hypercholesterolemia, whereas this association was not observed in current smoking men. Unlike non-smokers, the duration of alcohol drinking > 10 years was associated with a higher risk of hypertriglyceridemia in current smoking men (hazard ratio = 1.57, 95% confidence interval: 1.07-2.30, P = 0.020). In addition, alcohol consumption was inversely associated with low HDL-C regardless of smoking status. In women, alcohol consumption was inversely associated with dyslipidemia hypercholesterolemia and low HDL-C regardless of alcohol amount.

CONCLUSION

Smoking crucially confounds the association between long-term alcohol consumption and dyslipidemia, particularly in hypertriglyceridemia and hypercholesterolemia.

Association between Small Dense Low-Density Lipoproteins and High-Density Phospolipid Content in Patients with Coronary Artery Disease with or without Diabetes

OBJECTIVE

To evaluate the phospholipid profile in total plasma, non-high-density lipoprotein (HDL), and HDL fractions. We tried to correlate the phospholipid profile to low-density lipoprotein (LDL) size, as reflected by cholesterol content in each LDL subclass.

METHODS

We measured small dense LDL-C levels after heparin-magnesium precipitation and measured high-density lipoprotein phospholipid (HDL-P) levels using a colorimetric enzymatic method.

RESULTS

The correlation of the phospholipid profile to small dense LDL-C (sdLDL-C) in patients with coronary problems showed a negative association between small dense low-density lipoprotein (sdLDL) and HDL-P (r = -0.73; P = .02). Moreover, a strong positive correlation was detected between TG and the ratio HDL-P/HDL-C (r = 0.83; P <.001).

CONCLUSIONS

HDL phospholipid has an antiatherogenic effect in coronary artery disease with or without diabetes. Further, large LDL modulation seems to be associated with diabetes rather than coronaropathy.

Paradoxical Hypercholesterolemia in an Otherwise Healthy Adult Man

Hypercholesterolemia is characterized by serum cholesterol levels greater than 5 mmol per L. However, the distribution of cholesterol among lipoprotein classes has a significant bearing on diagnosis: high-low-density lipoprotein (LDL) cholesterol suggests familial hypercholesterolemia, whereas high-high-density lipoprotein (HDL) cholesterol is associated with hyperalphalipoproteinemia. On routine screening, a 23-year-old man presented with a total cholesterol level of 7.6 mmol per L but was subsequently found to have an HDL cholesterol level of 5.6 mmol per L. The clinical picture was confounded by his use of red yeast rice extract, a popular health supplement with hypolipidemic effects. In this case individual, the use of red yeast rice extract caused a hyperlipidemic state, ostensibly through downregulation of cholesteryl ester transfer protein. This case emphasizes the extended role of laboratory medicine in complex cases of hyperlipidemia.

Genomics of hypertriglyceridemia

With regard to heritability of phenotypes, the serum triglyceride level is considered to be highly heritable, with approximately 50% of its variability estimated to derive from parents. Thus, approximately 50% could be modifiable via environmental factors, including lifestyle and medications. Lipoproteins are definitive risk factors for atherosclerotic cardiovascular disease (ASCVD); among these, low-density lipoprotein (LDL) particles have been established as a causal factor for the development of ASCVD. Recently, triglyceride-rich lipoproteins have emerged as additional lipoproteins, which should be considered as residual targets for ASCVD risk reduction by LDL-lowering therapies. Compared with LDL particles, triglyceride-rich lipoproteins are significantly increased in the postprandial state, making it difficult to assess their clinical relevance. However, numerous pieces of evidence suggest that fasting and non-fasting triglycerides are associated with ASCVD. In addition, a recent meta-analysis of a Mendelian randomization study suggests that consideration of apolipoprotein B (APOB) might be better than considering LDL and triglyceride-rich lipoproteins separately. In this review, we examine (1) how triglyceride levels are determined by genetics, (2) lessons from extreme cases exhibiting severe hypertriglyceridemia, and (3) why triglycerides are important, by highlighting clinical and genetic evidence of their associations with ASCVD risk.

A transcriptome-wide association study based on 27 tissues identifies 106 genes potentially relevant for disease pathology in age-related macular degeneration

Genome-wide association studies (GWAS) for late stage age-related macular degeneration (AMD) have identified 52 independent genetic variants with genome-wide significance at 34 genomic loci. Typically, such an approach rarely results in the identification of functional variants implicating a defined gene in the disease process. We now performed a transcriptome-wide association study (TWAS) allowing the prediction of effects of AMD-associated genetic variants on gene expression. The TWAS was based on the genotypes of 16,144 late-stage AMD cases and 17,832 healthy controls, and gene expression was imputed for 27 different human tissues which were obtained from 134 to 421 individuals. A linear regression model including each individuals imputed gene expression data and the respective AMD status identified 106 genes significantly associated to AMD variants in at least one tissue (Q-value < 0.001). Gene enrichment analysis highlighted rather systemic than tissue- or cell-specific processes. Remarkably, 31 of the 106 genes overlapped with significant GWAS signals of other complex traits and diseases, such as neurological or autoimmune conditions. Taken together, our study highlights the fact that expression of genes associated with AMD is not restricted to retinal tissue as could be expected for an eye disease of the posterior pole, but instead is rather ubiquitous suggesting processes underlying AMD pathology to be of systemic nature.

Cholesteryl ester transfer protein: the physiological and molecular characteristics in the pathogenesis of atherosclerosis and Alzheimer’s disease

Cholesteryl ester transfer protein (CETP) is involved in reverse cholesterol transport, mediates the exchange of cholesteryl esters for triglycerides between high-density lipoproteinsand low-density lipoproteins/very low-density lipoproteins. Lipid transfer mechanism by CETP is unknown. Two main models have been proposed for the mechanism of action of CETP: shuttle and tunnel mechanisms. The variants of CETP gene affect activity and level of protein, thus they are associated with lipid profile and risk of many diseases. Some clinical studies reported that polymorphisms of CETP, including TaqIB and I405V, are associated with risk of atherosclerosis and/or Alzheimer’s disease. CETP plays important role an in the metabolism of cholesterol, thus is correlated with pathomechanism of coronary artery disease. Inhibition of CETP can be an effective strategy to improve the lipid profile and reduce risk of cardiovascular diseases. Therefore, new therapeutic strategies to reduce activity of CETP or decrease its level are developed. Effectiveness of following pharmacological methods of modulation of CETP activity was studied: anti-CETP vaccines, antisense oligonucleotide and small molecule inhibitors of CETP. This article presents an overview of the literature on the correlation between cardiovascular diseases and CETP protein/CETP gene. Furthermore, it discusses the impact of CETP on pathogenesis of Alzheimer’s disease.

Role of HDL function and LDL atherogenicity on cardiovascular risk: A comprehensive examination

BACKGROUND

High-density lipoprotein (HDL) functionality and low-density lipoprotein (LDL) atherogenic traits can describe the role of both particles on cardiovascular diseases more accurately than HDL- or LDL-cholesterol levels. However, it is unclear how these lipoprotein properties are particularly affected by different cardiovascular risk factors.

OBJECTIVE

To determine which lipoprotein properties are associated with greater cardiovascular risk scores and each cardiovascular risk factor.

METHODS

In two cross-sectional baseline samples of PREDIMED trial volunteers, we assessed the associations of HDL functionality (N = 296) and LDL atherogenicity traits (N = 210) with: 1) the 10-year predicted coronary risk (according to the Framingham-REGICOR score), and 2) classical cardiovascular risk factors.

RESULTS

Greater cardiovascular risk scores were associated with low cholesterol efflux values; oxidized, triglyceride-rich, small HDL particles; and small LDLs with low resistance against oxidation (P-trend<0.05, all). After adjusting for the rest of risk factors; 1) type-2 diabetic individuals presented smaller and more oxidized LDLs (P<0.026, all); 2) dyslipidemic participants had smaller HDLs with an impaired capacity to metabolize cholesterol (P<0.035, all); 3) high body mass index values were associated to lower HDL and LDL size and a lower HDL capacity to esterify cholesterol (P<0.037, all); 4) men presented a greater HDL oxidation and lower HDL vasodilatory capacity (P<0.046, all); and 5) greater ages were related to small, oxidized, cytotoxic LDL particles (P<0.037, all).

CONCLUSIONS

Dysfunctional HDL and atherogenic LDL particles are present in high cardiovascular risk patients. Dyslipidemia and male sex are predominantly linked to HDL dysfunctionality, whilst diabetes and advanced age are associated with LDL atherogenicity.

Biological Consequences of Dysfunctional HDL

Epidemiological studies have suggested an inverse correlation between high-density lipoprotein (HDL) cholesterol levels and the risk of cardiovascular disease. HDLs promote reverse cholesterol transport (RCT) and possess several putative atheroprotective functions, associated to the anti-inflammatory, anti-thrombotic and anti-oxidant properties as well as to the ability to support endothelial physiology. The assumption that increasing HDL-C levels would be beneficial on cardiovascular disease (CVD), however, has been questioned as, in most clinical trials, HDL-C-raising therapies did not result in improved cardiovascular outcomes. These findings, together with the observations from Mendelian randomization studies showing that polymorphisms mainly or solely associated with increased HDL-C levels did not decrease the risk of myocardial infarction, shift the focus from HDL-C levels toward HDL functional properties. Indeed, HDL from atherosclerotic patients not only exhibit impaired atheroprotective functions but also acquire pro-atherogenic properties and are referred to as "dysfunctional" HDL; this occurs even in the presence of normal or elevated HDL-C levels. Pharmacological approaches aimed at restoring HDL functions may therefore impact more significantly on CVD outcome than drugs used so far to increase HDL-C levels. The aim of this review is to discuss the pathological conditions leading to the formation of dysfunctional HDL and their role in atherosclerosis and beyond.

Diabetes alters the association between high-density lipoprotein subfractions and carotid intima-media thickness: The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

INTRODUCTION

High-density lipoprotein cholesterol comprises a group of heterogeneous subfractions that might have differential effects on atherosclerosis. Moreover, prior investigations suggest that the presence of diabetes (T2D) modifies the impact of some subfractions on atherosclerosis. In this study, we aimed to evaluate the association between high-density lipoprotein cholesterol subfractions and carotid intima-media thickness in the baseline assessment of the Brazilian Longitudinal Study of Adult Health participants from the São Paulo investigation centre.

METHODS

We evaluated 3930 individuals between 35 and 74 years without previous cardiovascular disease not using lipid-lowering drugs. High-density lipoprotein cholesterol subfractions (HDL₂-C and HDL₃-C) were measured by vertical ultracentrifugation (vertical auto profile). The relationship between each high-density lipoprotein cholesterol subfraction and carotid intima-media thickness was analysed by multiple linear regression models.

RESULTS

Total high-density lipoprotein cholesterol, as well as HDL₂-C and HDL₃-C, was negatively associated with carotid intima-media thickness after adjustment for demographic data (all p < 0.001) and traditional risk factors (all p < 0.05). When stratified by T2D status, the HDL₂-C/HDL₃-C ratio showed a negative association with carotid intima-media thickness in participants with T2D ( p = 0.032), even after fully controlling for confounding variables, including total high-density lipoprotein cholesterol.

CONCLUSION

HDL₂-C, HDL₃-C and HDL₂/HDL₃-C ratio are inversely associated with carotid intima-media thickness after adjustment for traditional risk factors. Association of the HDL₂-C/HDL₃-C ratio is modified by the presence of diabetes, being more pronounced in diabetic individuals.

A mega-analysis of expression quantitative trait loci (eQTL) provides insight into the regulatory architecture of gene expression variation in liver

Genome-wide association studies (GWAS) have identified numerous genetic variants in the human genome associated with diseases and traits. Nevertheless, for most loci the causative variant is still unknown. Expression quantitative trait loci (eQTL) in disease relevant tissues is an excellent approach to correlate genetic association with gene expression. While liver is the primary site of gene transcription for two pathways relevant to age-related macular degeneration (AMD), namely the complement system and cholesterol metabolism, we explored the contribution of AMD associated variants to modulate liver gene expression. We extracted publicly available data and computed the largest eQTL data set for liver tissue to date. Genotypes and expression data from all studies underwent rigorous quality control. Subsequently, Matrix eQTL was used to identify significant local eQTL. In total, liver samples from 588 individuals revealed 202,489 significant eQTL variants affecting 1,959 genes (Q-Value < 0.001). In addition, a further 101 independent eQTL signals were identified in 93 of the 1,959 eQTL genes. Importantly, our results independently reinforce the notion that high density lipoprotein metabolism plays a role in AMD pathogenesis. Taken together, our study generated a first comprehensive map reflecting the genetic regulatory landscape of gene expression in liver.

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.

Design, Synthesis and Biological Evaluation of N,N-Substituted Amine Derivatives as Cholesteryl Ester Transfer Protein Inhibitors

N,N-Substituted amine derivatives were designed by utilizing a bioisosterism strategy. Consequently, twenty-two compounds were synthesized and evaluated for their inhibitory activity against CETP. Structure-activity relationship (SAR) studies indicate that hydrophilic groups at the 2-position of the tetrazole and 3,5-bistrifluoromethyl groups on the benzene ring provide important contributions to the potency. Among these compounds, compound 17 exhibited excellent CETP inhibitory activity (IC₅₀ = 0.38 ± 0.08 μM) in vitro. Furthermore, compound 17 was selected for an in vitro metabolic stability study.

Plasma lipoprotein subfraction concentrations are associated with lipid metabolism and age-related macular degeneration

Disturbance in lipid metabolism has been suggested as a major pathogenic factor for age-related macular degeneration (AMD). Conventional lipid measures have been inconsistently associated with AMD. Other factors that can alter lipid metabolism include lipoprotein phenotype and genetic mutations. We performed a case-control study to examine the association between lipoprotein profile and neovascular AMD (nAMD) and whether the cholesterylester transfer protein (CETP) D442G mutation modulates these associations. Patients with nAMD had significantly higher concentrations of HDL and IDL compared with controls. The increase in HDL particles in nAMD patients was driven by an excess of medium-sized particles. Concurrently, patients with nAMD also had lower Apo A-1, lower VLDL and chylomicron lipoprotein. Many of these associations showed a dose-dependent association between controls, early AMD cases, and nAMD cases. Adjustment for the presence of the D442G mutation at the CETP locus did not significantly alter the increased AMD risk associated with HDL particle concentration. AMD is associated with variation in many lipoprotein subclasses, including increased HDL and IDL particles and decreased Apo A-1, VLDL, and chylomicron particles. These data suggest widespread systemic disturbance in lipid metabolism in the pathogenesis of AMD, including possible alterations in lipoprotein carrier capacity.

Serum Lipid Transfer Proteins in Hypothyreotic Patients Are Inversely Correlated with Thyroid-Stimulating Hormone (TSH) Levels

Background

Plasma cholesteryl ester transfer protein (CETP) activity is often decreased in patients with hypothyroidism, whereas less is known about the phospholipid transfer protein (PLTP). We aimed to evaluate simultaneously serum CETP and PLTP activity in patients diagnosed with hypothyroidism.

Material/Methods

The selection criteria for control group members (without thyroid dysfunction) in this case to case study were levels of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides similar to those in study group patients (101 patients diagnosed with hypothyroidism). Serum CETP and PLTP activities were measured by homogenous fluorometric assays using synthetic donor particle substrates.

Results

Serum CETP and PLTP activities in hypothyreotic patients were lower (p<0.001) compared with those in healthy subjects. This lowering was associated with significant changes in HDL-C subclasses: decrease in HDL₂- and increase in HDL₃ cholesterol levels. Multiple linear regression analyses adjusted for age, sex, body mass index, smoking habits, and alcohol drinking showed a strong association between hypothyroidism and activity of lipid transfer proteins. A linear inverse relationship between thyroid-stimulating hormone (TSH) and CETP (r=−0.21; p<0.01) and between TSH and PLTP (r=−0.24; p<0.001) was shown. There also was a positive correlation (p<0.001) between CETP and HDL₂ cholesterol (r=0.27) and between PLTP and HDL₂ cholesterol (r=0.37). A negative correlation between CETP and HDL₃ cholesterol (r=−0.22: p<0.01) and between PLTP and HDL₃ cholesterol (r=−0.24; p<0.001) has been demonstrated as well.

Conclusions

The decreased HDL₂ and increased HDL₃ cholesterol levels in subjects with hypothyroidism are consequences of decreased activity of lipid transfer proteins. These changes are early symptoms of lipid disturbances in hypothyroidism.

Serum CETP and PLTP activity in middle-aged men living in urban or rural area of the Lower Silesia region. PURE Poland sub-study

INTRODUCTION

The dependence of lipid transfer proteins on significant pro-atherogenic factors is unclear. The aim of the study was to evaluate serum cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activity in relation to lipid disturbances in men living in an urban or rural area.

MATERIAL AND METHODS

A group of 427 men, volunteers for the Prospective Urban Rural Epidemiology (PURE) sub-study - 263 urban inhabitants (aged 51.9 ±6.0) and 164 residents of villages (aged 51.1 ±5.9) - were examined. In the multivariable linear regression model, the following factors were included as potential confounders: age, body mass index (BMI), smoking, alcohol consumption, hs-C-reactive protein reaction (hs-CRP) and co-existence of chronic diseases.

RESULTS

In multiple linear regression models, site of residence (urban or rural area) was the most important independent and consistent predictor of CETP and PLTP activity; β coefficients (95% CI) for CETP (0.18) and PLTP (-0.29) were significant at levels of p < 0.001. Three-way analysis of variance showed no effect of smoking or moderate alcohol consumption on lipid transfer proteins; however, CETP activity showed an interaction effect between these risk factors. In the group of all men, CETP activity was significantly and positively correlated with total cholesterol (r = 0.24), low-density lipoprotein cholesterol (r = 0.18), and non-high density lipoprotein cholesterol (r = 0.21), whereas PLTP activity was correlated with BMI (r = 0.12). Body mass index in rural men was higher than in the urban male population.

CONCLUSIONS

Increased PLTP activity, recognized as a pro-atherogenic factor, and decreased CETP activity, known as a protective factor, both observed in men living in rural areas, are probably conditioned by nutritional and/or genetic factors.

Design, synthesis and biological evaluation of novel cholesteryl ester transfer protein inhibitors bearing a cycloalkene scaffold

Cholesteryl ester transfer protein (CETP) is a potential target for cardiovascular disease therapy as inhibition of CETP leads to increased HDL-C in humans. Based on the structure of Merck's biphenyl CETP inhibitor, we designed novel N,N-substituted-cycloalkenyl-methylamine scaffold derivatives by utilizing core replacement and conformational restriction strategies. Consequently, twenty-eight compounds were synthesized and evaluated for their inhibitory activity against CETP. Their preliminary structure-activity relationships (SARs) studies indicate that polar substituents were tolerated in moiety A and hydrophobic alkyl groups at the 5-position of cyclohexene were critical for potency. Among them, compound 17a, bearing an N-(5-pyrazolyl-pyrimidin-2-yl)-cycloalkenyl- methylamine scaffold, exhibited excellent CETP inhibitory activity (IC50 = 0.07 μM) in vitro. Furthermore, it showed an acceptable pharmacokinetic profile in S-D rats and efficient HDL-C increase in high-fat fed hamsters.

The controversy over the use of cholesteryl ester transfer protein inhibitors: is there some light at the end of the tunnel?

BACKGROUND

According to epidemiological studies, there is no clear relationship between the plasma cholesteryl ester transfer protein (CETP) concentration and the development of atherosclerosis in human populations. Although some studies suggest that increased CETP activity relates to undesirable profiles of plasma lipoproteins, promoting an anti-atherogenic plasma lipoprotein profile by drugs that inhibit CETP has not succeeded in preventing atherosclerosis in humans.

MATERIALS AND METHODS

This review describes 28 investigations in human populations dealing with plasma CETP, 11 in mice that express human CETP and seven in animals (six in rabbits and one in mice) in which plasma CETP activity was inhibited by drugs.

RESULTS

Present review shows that models in mice expressing human CETP are not illuminating because they report increase as well reduction of atherosclerosis. However, investigations in rabbits and mice that develop severe hypercholesterolaemia clearly indicate that impairment of the plasma CETP activity elicits protection against the development of atherosclerosis; in all of these experiments are attained substantial reductions of the atherogenic lipoproteins, namely, plasma apoB containing lipoproteins.

CONCLUSION

These models are strong indicators that the benefit in preventing atherosclerosis should be earned in cases of hyperlipidemia by CETP inhibitors.

Dysfunctional High-Density Lipoprotein: An Innovative Target for Proteomics and Lipidomics

High-Density Lipoprotein-Cholesterol (HDL-C) is regarded as an important protective factor against cardiovascular disease, with abundant evidence of an inverse relationship between its serum levels and risk of cardiovascular disease, as well as various antiatherogenic, antioxidant, and anti-inflammatory properties. Nevertheless, observations of hereditary syndromes featuring scant HDL-C concentration in absence of premature atherosclerotic disease suggest HDL-C levels may not be the best predictor of cardiovascular disease. Indeed, the beneficial effects of HDL may not depend solely on their concentration, but also on their quality. Distinct subfractions of this lipoprotein appear to be constituted by specific protein-lipid conglomerates necessary for different physiologic and pathophysiologic functions. However, in a chronic inflammatory microenvironment, diverse components of the HDL proteome and lipid core suffer alterations, which propel a shift towards a dysfunctional state, where HDL-C becomes proatherogenic, prooxidant, and proinflammatory. This heterogeneity highlights the need for further specialized molecular studies in this aspect, in order to achieve a better understanding of this dysfunctional state; with an emphasis on the potential role for proteomics and lipidomics as valuable methods in the search of novel therapeutic approaches for cardiovascular disease.