A review of CETP and its relation to atherosclerosis

Adaptive dysfunction of selenoproteins from the perspective of the triage theory: why modest selenium deficiency may increase risk of diseases of aging

The triage theory proposes that modest deficiency of any vitamin or mineral (V/M) could increase age-related diseases. V/M-dependent proteins required for short-term survival and/or reproduction (i.e., "essential") are predicted to be protected on V/M deficiency over other "nonessential" V/M-dependent proteins needed only for long-term health. The result is accumulation of insidious damage, increasing disease risk. We successfully tested the theory against published evidence on vitamin K. Here, we review about half of the 25 known mammalian selenoproteins; all of those with mouse knockout or human mutant phenotypes that could be used as criteria for a classification of essential or nonessential. Five selenoproteins (Gpx4, Txnrd1, Txnrd2, Dio3, and Sepp1) were classified as essential and 7 (Gpx1, Gpx 2, Gpx 3, Dio1, Dio2, Msrb1, and SelN) nonessential. On modest selenium (Se) deficiency, nonessential selenoprotein activities and concentrations are preferentially lost, with one exception (Dio1 in the thyroid, which we predict is conditionally essential). Mechanisms include the requirement of a special form of tRNA sensitive to Se deficiency for translation of nonessential selenoprotein mRNAs except Dio1. The same set of age-related diseases and conditions, including cancer, heart disease, and immune dysfunction, are prospectively associated with modest Se deficiency and also with genetic dysfunction of nonessential selenoproteins, suggesting that Se deficiency could be a causal factor, a possibility strengthened by mechanistic evidence. Modest Se deficiency is common in many parts of the world; optimal intake could prevent future disease.

Cholesterol ester transfer protein and apolipoprotein E gene polymorphisms in hyperlipidemic Asian Indians in North India

We determined the distribution of the polymorphic variants of CETP TaqIB and ApoE genes and their association with lipid and anthropometric parameters in hyperlipidemic and normolipidemic Asian Indians in North India. CETP TaqIB and ApoE polymorphism were assayed by PCR-RFLP in hyperlipidemic (n = 220) and normolipidemic (n = 367) subjects. Plasma lipids levels were estimated using commercially available kits from Randox (USA). The distribution of CETP TaqIB genotypes and alleles did not differ between the two groups. The frequency of ApoE ε4 allele was significantly higher in hyperlipidemic than normolipidemic subjects. Serum lipid levels were comparable between subjects with the different CETP TaqIB and ApoE genotypes in the two groups. Multivariate analysis after adjusting for age, sex, BMI, WHR, and total skinfold thickness showed that subjects with the Ε3Ε4 genotype and ε4 allele carriers were at significantly higher odds to develop hyperlipidemia [2.07 (1.29-3.30) and 2.05 (1.30-3.24), respectively] as compared to the other genotypes. ApoE ε4 allele and E3E4 genotype emerged as important genetic markers for hyperlipidemia in this study population.

Anacetrapib and dalcetrapib: two novel cholesteryl ester transfer protein inhibitors

OBJECTIVE

To evaluate the role of cholesteryl ester transfer protein (CETP) in the cholesterol transport system and review the pharmacology, pharmacokinetic properties, efficacy, and adverse effects of the CETP inhibitors, anacetrapib and dalcetrapib, for the treatment of dyslipidemia.

DATA SOURCES

A literature search was conducted in Ovid/MEDLINE (1950 to week 4 December 2010), PubMed/MEDLINE (up to December 2010), EMBASE (2000 to December 2010), and International Pharmaceutical Abstracts (1970 to December 2010) using the MeSH terms and key words anacetrapib, MK 0859, dalcetrapib, and JTT 705. The search was limited to publications in English.

STUDY SELECTION AND DATA EXTRACTION

Studies evaluating the pharmacology, pharmacokinetics, safety, and efficacy of anacetrapib and dalcetrapib for the treatment of dyslipidemia were included. Clinical reviews evaluating the characterization of CETP and its inhibition as a mechanism for reducing cardiovascular risk were also included.

DATA SYNTHESIS

Anacetrapib and dalcetrapib represent a novel treatment option for patients who have dyslipidemia and low levels of high-density lipoprotein cholesterol (HDL-C). Anacetrapib and dalcetrapib increase HDL-C by inhibiting CETP-mediated transfer of cholesteryl ester and triglyceride. Studies evaluating the safety and efficacy of anacetrapib and dalcetrapib concluded that both agents safely and effectively augment HDL-C. Their mechanism of action, potential for significant raising of HDL-C, once-daily dosing regimen, and favorable lipid-altering effects when added to hydroxymethylglutaryl-CoA reductase inhibitors are key elements. Anacetrapib and dalcetrapib are well tolerated, with mild gastrointestinal complaints reported more than with placebo. Although another CETP inhibitor, torcetrapib, was withdrawn from clinical development secondary to increased morbidity and mortality, neither anacetrapib nor dalcetrapib has demonstrated the adverse off-target effects portrayed with torcetrapib.

CONCLUSIONS

Inhibition of CETP by anacetrapib and dalcetrapib represents an encouraging development in the management of dyslipidemia, particularly in patients with low HDL-C levels. Results of future trials are much anticipated, as these will clarify the role of anacetrapib and dalcetrapib in reduction of cardiovascular disease.

Pro-inflammatory and atherogenic circulating factors in non-alcoholic fatty liver disease associated to metabolic syndrome

BACKGROUND

It is not elucidated if liver fat deposits associated to metabolic syndrome (MS) aggravate the atherogenic state. We evaluated, in MS patients, if the presence of non-alcoholic hepatic steatosis (HS) determines differences in inflammatory markers and VLDL characteristics.

METHODS

Seventy-five patients with MS were divided into 2 groups depending on the presence or absence of HS, assessed by ultrasound. Lipid profile, free fatty acids (FFA), VLDL composition, adiponectin, tumor necrosis factor-alpha (TNF-α), high sensitivity C-reactive protein (hs-CRP), and soluble adhesion molecules (sVCAM-1 and sICAM-1) were measured.

RESULTS

HS patients presented increased triglycerides levels, HOMA-IR and FFA. Patients with HS showed a reduction in adiponectin (p = 0.04) and increase in hs-CRP (p = 0.02), independently of insulin-resistance (IR). FFA correlated positively with TNF-α (p = 0.04) and inversely with adiponectin (p = 0.01). hs-CRP correlated with all inflammatory markers, independently of IR: TNF-α (r = 0.34, p = 0.02), sVCAM-1 (r = 0.29 p = 0.03), sICAM-1 (r = 0.56, p = 0.01), adiponectin (r = -0.34, p = 0.04). HS patients presented higher VLDL mass and number of particles. Adiponectin correlated with VLDL cholesterol content (r = -0.47, p = 0.04), independently of IR. VLDL, once secreted, would suffer from changes, becoming more atherogenic.

CONCLUSIONS

Simple HS would play an important role increasing cardiovascular risk, independently of IR. hs-CRP may represent a useful biomarker of this condition.

Genetic Determinants of Major Blood Lipids in Pakistanis Compared With Europeans

Background—

Evidence is sparse about the genetic determinants of major lipids in Pakistanis.

Methods and Results—

Variants (n=45 000) across 2000 genes were assessed in 3200 Pakistanis and compared with 2450 Germans using the same gene array and similar lipid assays. We also did a meta-analysis of selected lipid-related variants in Europeans. Pakistani genetic architecture was distinct from that of several ethnic groups represented in international reference samples. Forty-one variants at 14 loci were significantly associated with levels of HDL-C, triglyceride, or LDL-C. The most significant lipid-related variants identified among Pakistanis corresponded to genes previously shown to be relevant to Europeans, such as CETP associated with HDL-C levels (rs711752; P <10 −13 ), APOA5/ZNF259 (rs651821; P <10 −13 ) and GCKR (rs1260326; P <10 −13 ) with triglyceride levels; and CELSR2 variants with LDL-C levels (rs646776; P <10 −9 ). For Pakistanis, these 41 variants explained 6.2%, 7.1%, and 0.9% of the variation in HDL-C, triglyceride, and LDL-C, respectively. Compared with Europeans, the allele frequency of rs662799 in APOA5 among Pakistanis was higher and its impact on triglyceride concentration was greater ( P -value for difference <10 −4 ).

Conclusions—

Several lipid-related genetic variants are common to Pakistanis and Europeans, though they explain only a modest proportion of population variation in lipid concentration. Allelic frequencies and effect sizes of lipid-related variants can differ between Pakistanis and Europeans.

Impact of combined deficiency of hepatic lipase and endothelial lipase on the metabolism of both high-density lipoproteins and apolipoprotein B-containing lipoproteins

RATIONALE

Hepatic lipase (HL) and endothelial lipase (EL) are extracellular lipases that both hydrolyze triglycerides and phospholipids and display potentially overlapping or complementary roles in lipoprotein metabolism.

OBJECTIVE

We sought to dissect the overlapping roles of HL and EL by generating mice deficient in both HL and EL (HL/EL-dko) for comparison with single HL-knockout (ko) and EL-ko mice, as well as wild-type mice.

METHODS AND RESULTS

Reproduction and viability of the HL/EL-dko mice were impaired compared with the single-knockout mice. The plasma levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, non-HDL cholesterol, and phospholipids in the HL/EL-dko mice were markedly higher than those in the single-knockout mice. Most notably, the HL/EL-dko mice exhibited an unexpected substantial increase in small low-density lipoproteins. Kinetic studies with [(3)H]cholesteryl ether-labeled very-low-density lipoproteins demonstrated that the HL/EL-dko mice accumulated counts in the smallest low-density lipoprotein-sized fractions, as assessed by size exclusion chromatography, suggesting that it arises from lipolysis of very-low-density lipoproteins. HDL from all 3 lipase knockout models had an increased cholesterol efflux capacity but reduced clearance of HDL cholesteryl esters versus control mice. Despite their higher HDL cholesterol levels, neither HL-ko, EL-ko, nor HL/EL-dko mice demonstrated an increased rate of macrophage reverse cholesterol transport in vivo.

CONCLUSIONS

These studies reveal an additive effect of HL and EL on HDL metabolism but not macrophage reverse cholesterol transport in mice and an unexpected redundant role of HL and EL in apolipoprotein B lipoprotein metabolism.

Genetic causes of high and low serum HDL-cholesterol

Plasma levels of HDL cholesterol (HDL-C) have a strong inherited basis with heritability estimates of 40-60%. The well-established inverse relationship between plasma HDL-C levels and the risk of coronary artery disease (CAD) has led to an extensive search for genetic factors influencing HDL-C concentrations. Over the past 30 years, candidate gene, genome-wide linkage, and most recently genome-wide association (GWA) studies have identified several genetic variations for plasma HDL-C levels. However, the functional role of several of these variants remains unknown, and they do not always correlate with CAD. In this review, we will first summarize what is known about HDL metabolism, monogenic disorders associated with both low and high HDL-C levels, and candidate gene studies. Then we will focus this review on recent genetic findings from the GWA studies and future strategies to elucidate the remaining substantial proportion of HDL-C heritability. Comprehensive investigation of the genetic factors conferring to low and high HDL-C levels using integrative approaches is important to unravel novel pathways and their relations to CAD, so that more effective means of diagnosis, treatment, and prevention will be identified.

Novel tetrahydrochinoline derived CETP inhibitors

In the course of our efforts to identify orally active cholesteryl ester transfer protein (CETP) inhibitors, we have continued to explore tetrahydrochinoline derivatives. Based on BAY 19-4789 structural modifications led to the discovery of novel cycloalkyl substituted compounds. Thus, example 11b is a highly potent CETP inhibitor both in vitro and in vivo in transgenic mice with favourable pharmacokinetic properties for clinical development.

Association of circulating cholesteryl ester transfer protein activity with incidence of cardiovascular disease in the community

BACKGROUND

Plasma high-density lipoprotein cholesterol concentration is related inversely to the risk of cardiovascular disease (CVD). Inhibiting cholesteryl ester transfer protein (CETP) activity raises high-density lipoprotein cholesterol and may be cardioprotective, but an initial clinical trial with a CETP inhibitor was stopped prematurely because of increased CVD in treated patients, raising concerns about this approach. Data relating circulating CETP concentrations to CVD incidence in the community are conflicting.

METHODS AND RESULTS

Plasma CETP activity was measured in 1978 Framingham Heart Study participants (mean age, 51 years; 54% women) who attended a routine examination in 1987-1990 and were free of CVD. On follow-up (mean, 15.1 years), 320 participants experienced a first CVD event (fatal or nonfatal coronary heart disease, cerebrovascular disease, peripheral vascular disease, or heart failure). In multivariable analyses adjusted for standard risk factors including high-density lipoprotein cholesterol, plasma CETP activity was related inversely to the incidence of CVD events (hazard ratio for activity, at or above the median of 0.72; 95% confidence interval, 0.57 to 0.90; P=0.004 [compared with below median]; hazard ratio per SD increment, 0.86; 95% confidence interval, 0.76 to 0.97; P=0.01). The inverse association of CETP activity with CVD incidence remained robust in time-dependent models updating standard risk factors every 4 years and was maintained in analyses of incident "hard" CVD events (myocardial infarction, stroke, or heart failure).

CONCLUSIONS

In our prospective investigation of a community-based sample, lower plasma CETP activity was associated with greater CVD risk. These observations, if confirmed, challenge the concept that CETP inhibition may lower CVD risk.

Current and emerging strategies for treating dyslipidemia and macrovascular disease

Statins, inhibitors of hydroxymethylglutaryl CoA (HMG-CoA) reductase, have been in clinical use for over 20 years. The widespread use of these agents has left doubt of the efficacy of cholesterol-lowering therapy to prevent cardiovascular disease. In spite of the widespread use of these agents and the successful lowering of circulating cholesterol together with reduction of cardiovascular-related deaths, there is consensus that further improvements in therapy are needed. Cardiovascular disease remains a major cause of premature death and continues to exert an extensive drain on the health-care costs. This chapter outlines some of the emerging strategies for discovering and developing novel treatments of dyslipidemia and macrovascular disease. Mechanisms considered include alternate ways to lower total cholesterol through inhibition of synthesis, limitation of absorption, or recycling. Other approaches include the modification of circulating forms of cholesterol and changes in gene expression at the key sites of storage, utilization, and pathology. The next successful strategy will likely be one that works well in concert with existing statins.

Fine mapping and association studies of a high-density lipoprotein cholesterol linkage region on chromosome 16 in French-Canadian subjects

Low levels of high-density lipoprotein cholesterol (HDL-C) are an independent risk factor for cardiovascular disease. To identify novel genetic variants that contribute to HDL-C, we performed genome-wide scans and quantitative association studies in two study samples: a Quebec-wide study consisting of 11 multigenerational families and a study of 61 families from the Saguenay-Lac St-Jean (SLSJ) region of Quebec. The heritability of HDL-C in these study samples was 0.73 and 0.49, respectively. Variance components linkage methods identified a LOD score of 2.61 at 98 cM near the marker D16S515 in Quebec-wide families and an LOD score of 2.96 at 86 cM near the marker D16S2624 in SLSJ families. In the Quebec-wide sample, four families showed segregation over a 25.5-cM (18 Mb) region, which was further reduced to 6.6 Mb with additional markers. The coding regions of all genes within this region were sequenced. A missense variant in CHST6 segregated in four families and, with additional families, we observed a P value of 0.015 for this variant. However, an association study of this single-nucleotide polymorphism (SNP) in unrelated Quebec-wide samples was not significant. We also identified an SNP (rs11646677) in the same region, which was significantly associated with a low HDL-C (P=0.016) in the SLSJ study sample. In addition, RT-PCR results from cultured cells showed a significant difference in the expression of CHST6 and KIAA1576, another gene in the region. Our data constitute additional evidence for a locus on chromosome 16q23-24 that affects HDL-C levels in two independent French-Canadian studies.

Apolipoprotein AI tertiary structures determine stability and phospholipid-binding activity of discoidal high-density lipoprotein particles of different sizes

Human high-density lipoprotein (HDL) plays a key role in the reverse cholesterol transport pathway that delivers excess cholesterol back to the liver for clearance. In vivo, HDL particles vary in size, shape and biological function. The discoidal HDL is a 140-240 kDa, disk-shaped intermediate of mature HDL. During mature spherical HDL formation, discoidal HDLs play a key role in loading cholesterol ester onto the HDL particles by activating the enzyme, lecithin:cholesterol acyltransferase (LCAT). One of the major problems for high-resolution structural studies of discoidal HDL is the difficulty in obtaining pure and, foremost, homogenous sample. We demonstrate here that the commonly used cholate dialysis method for discoidal HDL preparation usually contains 5-10% lipid-poor apoAI that significantly interferes with the high-resolution structural analysis of discoidal HDL using biophysical methods. Using an ultracentrifugation method, we quickly removed lipid-poor apoAI. We also purified discoidal reconstituted HDL (rHDL) into two pure discoidal HDL species of different sizes that are amendable for high-resolution structural studies. A small rHDL has a diameter of 7.6 nm, and a large rHDL has a diameter of 9.8 nm. We show that these two different sizes of discoidal HDL particles display different stability and phospholipid-binding activity. Interestingly, these property/functional differences are independent from the apoAI alpha-helical secondary structure, but are determined by the tertiary structural difference of apoAI on different discoidal rHDL particles, as evidenced by two-dimensional NMR and negative stain electron microscopy data. Our result further provides the first high-resolution NMR data, demonstrating a promise of structural determination of discoidal HDL at atomic resolution using a combination of NMR and other biophysical techniques.

Safety and tolerability of dalcetrapib

Efficacy and safety data for dalcetrapib (RO4607381/JTT-705) are presented, following a report of increased mortality and cardiac events with another cholesteryl ester transfer protein inhibitor, torcetrapib, associated with off-target adverse effects (hypertension and the activation of the renin-angiotensin-aldosterone system). The efficacy and clinical safety of dalcetrapib 300, 600, and 900 mg or placebo were assessed (n = 838) in 4 pooled 4-week phase IIa trials (1 monotherapy, n = 193; 3 statin combination, n = 353) and 1 12-week phase IIb trial (with pravastatin, n = 292). Nonclinical safety, assessed by the induction of aldosterone production and aldosterone synthase (cytochrome P450 11B2) messenger ribonucleic acid, was measured in human adrenocarcinoma (H295R) cells exposed to dalcetrapib or torcetrapib. Dalcetrapib increased high-density lipoprotein cholesterol by up to 36% and apolipoprotein A-I by up to 16%. The incidence of adverse events (AEs) was similar between placebo (42%) and dalcetrapib 300 mg (50%) and 600 mg (42%), with more events with dalcetrapib 900 mg (58%) (p <0.05, pooled 4-week studies). Six serious AEs (3 with placebo, 1 with dalcetrapib 300 mg, and 2 with dalcetrapib 600 mg) were considered "unrelated" to treatment. Cardiovascular AEs were similar across treatment groups, with no dose-related trends and no clinically relevant changes in blood pressure or electrocardiographic results. Findings were similar in the 12-week study. In vitro, torcetrapib but not dalcetrapib increased aldosterone production and cytochrome P450 11B2 messenger ribonucleic acid levels. In conclusion, dalcetrapib alone or in combination with statins was effective at increasing high-density lipoprotein cholesterol and was well tolerated, without clinically relevant changes in blood pressure or cardiovascular AEs and no effects on aldosterone production as assessed nonclinically.

A Translational Medicine perspective of the development of torcetrapib: Does the failure of torcetrapib development cast a shadow on future development of lipid modifying agents, HDL elevation strategies or CETP as a viable molecular target for atherosclerosis? A case study of the use of biomarkers and Translational Medicine in atherosclerosis drug discovery and development

Although the relationship between HDL (high density lipoprotein) function and cardiovascular (CV) risk has been extensively explored, the premise that HDL elevation is linked to reduced CV risks and that high HDL cholesterol (HDL-C) might be a potential surrogate biomarker for reduced CV risk remains controversial. Substantial genetic, molecular, biochemical and preclinical evidence have raised the hope that HDL-C elevation via CETP inhibition might generate clinical benefits. However, four large-scale clinical trials with the CETP inhibitor torcetrapib failed to demonstrate benefits on CV clinical outcomes. Likewise, biomarkers that were supposed to predict vascular risk reduction provided disappointing results. The sad tale of torcetrapib development emphasizes the need for a paradigm shift from the conventional drug development mode to a biomarker-based Translational Medicine (TMed) strategy. Emergence of further CETP inhibitors encourage continued development of such compounds for cardiovascular risk management. However, there is a need to adopt biomarker-driven TMed strategies in target validation, target-compound interaction, pharmacodynamic activities, disease modification and patient selection to guide future drug development efforts. This commentary analyzes the issues surrounding the demise of torcetrapib and proposes a TMed-based road map towards successful development of new CETP inhibitors.

Mechanism of inhibition defines CETP activity: a mathematical model for CETP in vitro

Because cholesteryl ester transfer protein (CETP) inhibition is a potential HDL-raising therapy, interest has been raised in the mechanisms and consequences of CETP activity. To explore these mechanisms and the dynamics of CETP in vitro, a mechanistic mathematical model was developed based upon the shuttle mechanism for lipid transfer. Model parameters were estimated from eight published experimental datasets, and the resulting model captures observed dynamics of CETP in vitro. Simulations suggest the shuttle mechanism yields behaviors consistent with experimental observations. Three key findings predicted from model simulations are: 1) net CE transfer activity from HDL to VLDL and LDL can be significantly altered by changing the balance of homoexchange versus heteroexchange of neutral lipids via CETP; 2) lipemia-induced increases in CETP activity are more likely caused by increases in lipoprotein particle size than particle number; and 3) the inhibition mechanisms of the CETP inhibitors torcetrapib and JTT-705 are significantly more potent than a classic competitive inhibition mechanism with the irreversible binding mechanism having the most robust response. In summary, the model provides a plausible representation of CETP activity in vitro, corroborates strong evidence for the shuttle hypothesis, and provides new insights into the consequences of CETP activity and inhibition on lipoproteins.

Receptor complementation and mutagenesis reveal SR-BI as an essential HCV entry factor and functionally imply its intra- and extra-cellular domains

HCV entry into cells is a multi-step and slow process. It is believed that the initial capture of HCV particles by glycosaminoglycans and/or lipoprotein receptors is followed by coordinated interactions with the scavenger receptor class B type I (SR-BI), a major receptor of high-density lipoprotein (HDL), the CD81 tetraspanin, and the tight junction protein Claudin-1, ultimately leading to uptake and cellular penetration of HCV via low-pH endosomes. Several reports have indicated that HDL promotes HCV entry through interaction with SR-BI. This pathway remains largely elusive, although it was shown that HDL neither associates with HCV particles nor modulates HCV binding to SR-BI. In contrast to CD81 and Claudin-1, the importance of SR-BI has only been addressed indirectly because of lack of cells in which functional complementation assays with mutant receptors could be performed. Here we identified for the first time two cell types that supported HCVpp and HCVcc entry upon ectopic SR-BI expression. Remarkably, the undetectable expression of SR-BI in rat hepatoma cells allowed unambiguous investigation of human SR-BI functions during HCV entry. By expressing different SR-BI mutants in either cell line, our results revealed features of SR-BI intracellular domains that influence HCV infectivity without affecting receptor binding and stimulation of HCV entry induced by HDL/SR-BI interaction. Conversely, we identified positions of SR-BI ectodomain that, by altering HCV binding, inhibit entry. Finally, we characterized alternative ectodomain determinants that, by reducing SR-BI cholesterol uptake and efflux functions, abolish HDL-mediated infection-enhancement. Altogether, we demonstrate that SR-BI is an essential HCV entry factor. Moreover, our results highlight specific SR-BI determinants required during HCV entry and physiological lipid transfer functions hijacked by HCV to favor infection.

More than 180 million people are chronically infected by hepatitis C virus (HCV), a leading cause of liver failure and cancer, stimulating the need to fully define the biology of HCV infection for developing novel and effective therapeutics. During the first steps of infection, the virus is taken up and penetrates hepatocytes. HCV entry is thought to be a coordinated multi-step process mediated by specific factors, including CD81, Claudin-1, and the scavenger receptor BI (SR-BI). Whereas the involvement of CD81 and Claudin-1 was demonstrated by rendering susceptible cells that are otherwise refractory, SR-BI complementation assays were lacking, raising questions as to its functions during HCV entry. Here, we identify one hepatoma rat cell line, in which SR-BI complementation assay and targeted mutagenesis could be performed. We therefore demonstrate that SR-BI is an essential HCV entry factor. Our results shed light on SR-BI intracellular domain functions in HCV entry, and, further, emphasize the remarkable capacity of HCV to hijack the lipid transfer function of SR-BI, hence favoring infection.

HDL-replacement therapy: mechanism of action, types of agents and potential clinical indications

HDL-replacement therapy is a promising new treatment strategy involving the acute administration of HDL to rapidly stabilize patients at imminent risk for developing a myocardial infarction, such as those with acute coronary syndrome. This review will first focus on the anti-atherogenic mechanisms for HDL, such as the stimulation of the reverse cholesterol transport pathway, and then discuss the other potential beneficial biological effects of HDL on atherosclerosis. The various types of HDL-replacement therapies that are being investigated and developed will be reviewed and ongoing clinical trials and other possible clinical indications for HDL-replacement therapy besides the prevention of myocardial infarction will also be described. Finally, HDL-replacement therapy will be put into perspective by summarizing the current gaps in our knowledge of HDL metabolism and identifying challenges for future research in this area.

A novel homozygous mutation in CETP gene as a cause of CETP deficiency in a Caucasian kindred

OBJECTIVE

To analyze the cholesteryl ester transfer protein (CETP) gene and the plasma HDL phenotype in a Caucasian subject with extremely elevated plasma high density lipoprotein-cholesterol (HDL-C).

METHODS AND RESULTS

The proband, a 63-year-old male of Swedish ancestry with elevated HDL-C (208mg/dl) and apoA-I (and 272mg/dl), was found to be homozygous for a point mutation in exon 2 of CETP gene (c.109 C>T) resulting in a premature termination codon (R37X). Plasma CETP mass and activity were undetectable. Plasma HDL were characterized by predominance of large HDL with enhanced prebeta-HDL content. The proband's sons, heterozygotes for the mutation, had reduced plasma CETP activity and moderately elevated HDL-C. Serum of CETP deficient subjects showed a normal or enhanced cholesterol efflux capacity via ABCG1/SR-BI; cholesterol efflux via ABCA1 and macrophage cholesterol removal were lower than normal. The proband was healthy and had no atherosclerotic plaques in carotid or femoral arteries.

CONCLUSION

Complete CETP deficiency caused by mutations in CETP gene is exceedingly rare in Caucasians; the description of this single case indicates that CETP deficiency does not predispose to atherosclerosis in the absence of major cardiovascular risk factors.

One common polymorphism of cholesteryl ester transfer protein gene in Iranian subjects with and without primary hypertriglyceridemia

Primary hypertriglyceridemia is considered to be a major risk factor for pancreatitis, atherosclerosis and coronary heart disease. Cholesteryl ester transfer protein gene polymorphisms known to be associated with changes in lipid levels. This study was performed by using polymerase chain reaction and restriction fragment length polymorphisms. Genotype distribution and allelic frequencies of polymorphism were determined and compared in primary hypertriglyceridemic and normotriglyceridemic subjects. The results showed that plasma cholesteryl ester transfer protein activity was significantly higher in primary hypertriglyceridemia than in controls (p = 0.001). In this study all individuals with B2B2 genotype had lower plasma cholesteryl ester transfer protein activity, higher high-density lipoprotein than B1B1 and B1B2 genotypes, whereas triglyceride was significantly decreased in this genotype. The genotype and allelic frequencies for this polymorphism differed significantly between primary hypertriglyceridemic patients and controls (p = 0.014 and p = 0.027, respectively). In both groups, CETP Taq 1B polymorphism (presence of B2 allele) correlated significantly with HDL-C (r = 0.207 and 0.300 in control and patient groups, respectively) and CETP activity (r = -0.193 for controls and r = -0.132 for patients). Taq 1B polymorphism of cholesteryl ester transfer protein gene was associated with changes in lipids profile and plasma cholesteryl ester transfer protein activity in the selected population.

HDL remodeling during the acute phase response

OBJECTIVE

The purpose of this study was to examine the interactive action of serum amyloid A (SAA), group IIA secretory phospholipase A(2) (sPLA(2)-IIA), and cholesteryl ester transfer protein (CETP) on HDL remodeling and cholesterol efflux during the acute phase (AP) response elicited in humans after cardiac surgery.

METHODS AND RESULTS

Plasma was collected from patients before (pre-AP), 24 hours after (AP-1 d), and 5 days after cardiac surgery (AP-5 d). SAA levels were increased 16-fold in AP-1 d samples. The activity of sPLA(2)-IIA was increased from 77.7+/-38.3 U/mL (pre-AP) to 281.4+/-57.1 U/mL (AP-1 d; P<0.001). CETP mass and activity reduction was commensurate to the reduction of HDL cholesterol levels. The combined action of SAA, sPLA(2)-IIA, and CETP in vitro markedly remodeled HDL with the generation of lipid-poor apoA-I from both pre-AP and AP-1 d HDL. The net result of this remodeling was a relative preservation of ABCA1- and ABCG1-dependent cholesterol efflux during the acute phase response.

CONCLUSIONS

Our results show that the many and complex changes in plasma proteins during the acute phase response markedly remodel HDL with functional implications, particularly the relative retention of cholesterol efflux capacity.

High density lipoprotein cholesterol: an evolving target of therapy in the management of cardiovascular disease

Since the pioneering work of John Gofman in the 1950s, our understanding of high density lipoprotein cholesterol (HDL-C) and its relationship to coronary heart disease (CHD) has grown substantially. Numerous clinical trials since the Framingham Study in 1977 have demonstrated an inverse relationship between HDL-C and one’s risk of developing CHD. Over the past two decades, preclinical research has gained further insight into the nature of HDL-C metabolism, specifically regarding the ability of HDL-C to promote reverse cholesterol transport (RCT). Recent attempts to harness HDL’s ability to enhance RCT have revealed the complexity of HDL-C metabolism. This review provides a detailed update on HDL-C as an evolving therapeutic target in the management of cardiovascular disease.

Cholesteryl ester transfer protein (CETP) genetic variation and early onset of non-fatal myocardial infarction

Although Cholesteryl Ester Transfer Protein (CETP) mediates the transfer of cholesteryl esters and triglycerides between lipoprotein particles and thus plays a crucial role in reverse cholesterol transport, the association of variations in the CETP gene with acute myocardial infarction (MI) remains unclear. In this study we examined whether common genetic variation in the CETP gene is related to early-onset non-fatal MI risk in a population-based case-control study from western Washington State. Genotyping for the CETP -2708 G/A, -971 A/G, -629 A/C, Intron-I TaqI G/A and exon-14 A/G (I405V) SNPs was performed in 578 cases with first acute non-fatal MI and in 666 demographically similar controls, free of clinical cardiovascular disease, identified randomly from the community. In-person interviews and non-fasting blood specimens provided data on coronary heart disease risk factors. In men, there was little evidence for an association between single SNPs and MI risk, but in women the age- and race-adjusted OR was found to be significant in 4 out of the 5 CETP single variants. Haplotype analysis revealed two haplotypes associated with MI risk among men. As compared to men homozygous for the most common haplotype D (-2708 G, -971 G, -629 C, TaqI G and exon-14 A), the fully-adjusted multiplicative model identified haplotype G (-2708 G, -971 A, -629 A, TaqI G and exon-14 G) was associated with a 4.0-6.0-fold increased risk of MI for each additional copy; [95%CI 2.4-14.8] and haplotype B (-2708 G, -971 G, -629 A, TaqI A and exon-14 A) showed a significant decreased risk for early onset MI [OR = 0.18; 95%CI 0.04 - 0.75]. An evolutionary-based haplotype analysis indicated that the two haplotypes associated with the MI risk are most evolutionarily divergent from the other haplotypes. Variation at the CETP gene locus is associated with the risk of early-onset non-fatal MI. This association was found to be independent of HDL-C levels. These data and the sex-specific findings require confirmation in other populations.

Cholesteryl ester transfer protein inhibition and HDL increase: has the dream ended?

Statins effectively lower plasma low-density lipoprotein cholesterol (LDL-C) levels and reduce the risk of vascular events. However, this benefit might be improved by dealing with other vascular risk factors such as high-density lipoprotein cholesterol (HDL-C). It follows that there has been an interest in drugs that raise plasma HDL-C levels. Among these drugs are the cholesteryl ester transfer protein (CETP) inhibitors. The first CETP inhibitor to be evaluated in an event-based trial was torcetrapib. This drug can considerably elevate serum HDL-C levels (e.g., by 72%). However, a recently published trial (ILLUMINATE) showed that torcetrapib used in combination with atorvastatin was associated with significantly more vascular events and deaths than atorvastatin alone. This finding resulted in the discontinuation of the torcetrapib development programme. The cause(s) of the adverse outcome remain speculative. It has been suggested that a significant rise in systolic blood pressure and possibly the quality of the HDL produced may be relevant. Despite this disappointing outcome it seems to be too early to close the book on CETP inhibitors because two other members of this class are being evaluated. These drugs (JTT-705 and anacetrapib) may be devoid of the adverse effect on systolic blood pressure. Eventually only appropriately designed, event-based trials, will settle the issue of whether CETP inhibitors are clinically useful.

The importance of treating cardiometabolic risk factors in patients with type 2 diabetes

Cardiometabolic risk factors are the combined vascular and metabolic components of risk that may lead to a cardiovascular event. There are numerous such factors. Underlying the concept of cardiometabolic risk is an association with excess visceral fat, leading to the dysregulation of the adipokines, the signalling proteins derived from adipose tissue. Changes in the levels of the adipokines - tumour necrosis factor-alpha, cholesteryl ester transfer protein and adiponectin, for example - can lead to alterations in insulin sensitivity and high-density lipoprotein cholesterol metabolism. At present, specific cardiometabolic risk factors are commonly managed on an individual basis. We are now moving from the era of single risk factor intervention, however, to multiple risk factor intervention in people at high cardiovascular risk, with the additional possibility of using new drug classes to target the underlying cardiometabolic problems more effectively.

Hepatic insulin resistance is sufficient to produce dyslipidemia and susceptibility to atherosclerosis

Insulin resistance plays a central role in the development of the metabolic syndrome, but how it relates to cardiovascular disease remains controversial. Liver insulin receptor knockout (LIRKO) mice have pure hepatic insulin resistance. On a standard chow diet, LIRKO mice have a proatherogenic lipoprotein profile with reduced high-density lipoprotein (HDL) cholesterol and very low-density lipoprotein (VLDL) particles that are markedly enriched in cholesterol. This is due to increased secretion and decreased clearance of apolipoprotein B-containing lipoproteins, coupled with decreased triglyceride secretion secondary to increased expression of Pgc-1 beta (Ppargc-1b), which promotes VLDL secretion, but decreased expression of Srebp-1c (Srebf1), Srebp-2 (Srebf2), and their targets, the lipogenic enzymes and the LDL receptor. Within 12 weeks on an atherogenic diet, LIRKO mice show marked hypercholesterolemia, and 100% of LIRKO mice, but 0% of controls, develop severe atherosclerosis. Thus, insulin resistance at the level of the liver is sufficient to produce the dyslipidemia and increased risk of atherosclerosis associated with the metabolic syndrome.

Prevention challenges: the era of atherosclerosis regression

Statins slow atherosclerosis progression and can even induce atherosclerosis regression. The reduction of cardiovascular events with statins by approximately one-third demonstrates not only their clinical efficacy but also the unmet clinical need. The aging of the population and the epidemics of the metabolic syndrome and diabetes contribute to the increasing burden of atherosclerosis in society, and fuel the need for novel complementary therapies to further improve clinical outcomes. Some targets, such as acyl-coenzyme A:cholesterol acyltransferase inhibition, have yielded disappointing clinical results. In contrast, there is strong evidence linking lower high density lipoprotein (HDL) cholesterol levels and greater cardiovascular risk, thus providing the rationale for targeting HDL in the prevention and treatment of cardiovascular diseases. Therapeutic approaches include direct infusions of HDL cholesterol or HDL-mimetic agents, as well as the inhibition of cholesteryl ester transfer protein (CETP). CETP inhibition appears to be one particularly promising strategy. The CETP inhibitor torcetrapib increases plasma HDL cholesterol levels by 40% to 60%, while modestly decreasing low density lipoprotein (LDL) cholesterol. Combining the HDL cholesterol-elevating properties of a CETP inhibitor with the LDL cholesterol-lowering properties of a statin may offer improved outcomes over targeting LDL cholesterol alone. This hypothesis is being extensively evaluated in a comprehensive program that involves several imaging studies and a large-scale clinical end point trial. The additional cardiovascular protection required for patients with atherosclerosis or risk equivalents will likely be provided by therapies that go beyond LDL reduction.

Reliance of host cholesterol metabolic pathways for the life cycle of hepatitis C virus

Hepatitis C virus (HCV), a single-stranded positive-sense RNA virus of the Flaviviridae family, infects more than 170 million people worldwide and is the leading cause of liver failure in the United States. A unique feature of HCV is that the viral life cycle depends on cholesterol metabolism in host cells. This review summarizes the cholesterol metabolic pathways that are required for the replication, secretion, and entry of HCV. The potential application of drugs that alter host cholesterol metabolism in treating HCV infection is also discussed.

CETP genotypes and HDL-cholesterol phenotypes in the HERITAGE Family Study

Associations between cholesteryl ester transfer protein (CETP) polymorphisms and high-density lipoprotein cholesterol (HDL-c) levels before and after 20 wk of endurance training were investigated in the HERITAGE Family Study. Plasma HDL-c, HDL2-c, HDL3-c, and apolipoprotein (apo)A1 levels were measured, and 13 CETP single nucleotide polymorphisms (SNPs) were genotyped in 265 blacks and 486 whites. Three haplotypes defined by SNPs at the −1337, −971, and −629 sites were strongly associated with baseline HDL-c levels in whites. Both C−1337T and C−629A were associated with baseline HDL-c ( P < 0.001) and apoA1 ( P < 0.01) when tested separately. However, only C−629A remained significant in a combined model. G−971A was not associated with HDL phenotypes, but showed significant interactions with C−629A ( P = 0.002) on baseline traits. Genotype-by-sex interactions were observed at the −629 locus for HDL3-c ( P = 0.004) and apoA1 ( P = 0.02) training responses in whites. In women, the −629 A/A homozygotes showed greater increases in HDL3-c ( P = 0.02) and apoA1 ( P = 0.02) levels than the other genotypes. Finally, apolipoprotein E (APOE) genotype and the CETP C−629A locus contributed independently and in additive fashion to the HDL traits, explaining 6.0–8.8% of the variance. The CETP −1337T and −629A alleles are associated with higher baseline HDL-c and apoA1 levels. The beneficial effects of endurance training on plasma HDL3-c and apoA1 levels are evident in white women homozygous for the −629A allele. The CETP and APOE genotypes account for up to 9% of the variance in HDL-c phenotypes in the HERITAGE Family Study.

Expression of cholesteryl ester transfer protein in mice promotes macrophage reverse cholesterol transport

BACKGROUND

Cholesteryl ester transfer protein (CETP) transfers cholesteryl esters from high-density lipoproteins to apolipoprotein (apo) B-containing lipoproteins and in humans plays an important role in lipoprotein metabolism. However, the role that CETP plays in mediation of reverse cholesterol transport (RCT) remains unclear. We used a validated in vivo assay of macrophage RCT to test the effect of CETP expression in mice (which naturally lack CETP) on macrophage RCT, including in mice that lack the low-density lipoprotein receptor or the scavenger receptor class B, type I.

METHOD AND RESULTS

A vector based on adeno-associated virus serotype 8 (AAV8) with a liver-specific thyroglobulin promoter was used to stably express human CETP in livers of mice and was compared with an AAV8-lacZ control vector. The RCT assay was performed 4 weeks after vector injection and involved the intraperitoneal injection of acetylated low-density lipoprotein cholesterol-loaded and 3H-cholesterol-labeled J774 macrophages in mice with plasma sampling at several time points, liver and bile sampling at 48 hours, and continuous fecal collection to measure 3H-sterol as an integrated readout of macrophage RCT. In apobec-1-null mice, CETP expression reduced plasma high-density lipoprotein cholesterol levels but significantly increased fecal 3H-sterol excretion. In low-density lipoprotein receptor/apobec-1 double-null mice, CETP expression reduced high-density lipoprotein cholesterol levels and had no effect on fecal 3H-sterol excretion. Finally, in scavenger receptor class B, type I-null mice, CETP expression reduced high-density lipoprotein cholesterol levels and significantly increased fecal 3H-sterol excretion.

CONCLUSION

The present results demonstrate that CETP expression promotes macrophage RCT in mice, that this effect is dependent on the low-density lipoprotein receptor, and that CETP expression restores to normal the impaired RCT in mice deficient in scavenger receptor class B, type I.

Genome-wide scan for interacting loci affecting human cholesteryl ester transfer protein-induced hypercholesterolemia in transgenic human cholesteryl ester transfer protein F2-intercross rats

OBJECTIVE

We documented susceptibility in Dahl S rats to coronary atherosclerosis upon the transgenic expression of human cholesteryl ester transfer protein (hCETP) producing severe combined hyperlipidemia, as detected in Tg[hCETP]53 (Tg53) Dahl S rats. In other genetic backgrounds (i.e. Dahl R, spontaneously hypertensive rat strains) transgene expression does not lead to severe combined hyperlipidemia. This study aimed to identify genetic loci that modify the effect of hCETP on hypercholesterolemia observed in different genetic contexts.

METHODS

To identify quantitative trait loci (QTL) that affect hCETP-mediated hyperlipidemia in Tg53 Dahl S rats in contrast to Tg53 Dahl R rats we performed a genome-wide scan for QTL affecting plasma total cholesterol in an F2[Tg (R x S)]-intercross male population (n = 159) that are transgenic for the Tg[hCETP]53 transgene. Hybrids were genotyped with 121 informative polymorphic markers.

RESULTS

We detected three novel hCETP-dependent QTL for hypercholesterolemia: one on chromosome 3 with suggestive linkage [logarithm of odds score derived from likelihood ratio statistic using a factor of 4.6 (LOD) 2.26]; one on chromosome 9 with significant linkage (LOD 4.15), and one on chromosome 11 with significant linkage (LOD 3.48) that have not been detected in other rat intercrosses.

CONCLUSION

Three cholesteryl ester transfer protein (CETP)-interacting loci were identified in a Tg53 Dahl S rat intercross study affecting cholesterol metabolism. These results could partly explain the controversy regarding the atherogenic role of CETP in humans, suggesting the hypothesis that putative CETP interacting genes confound or play an important role in CETP-mediated pro-atherogenic susceptibility in humans. Overall, these observations reiterate the key role of epistasis in complex, multifactorial traits.

Inhibition of CETP activity by torcetrapib reduces susceptibility to diet-induced atherosclerosis in New Zealand White rabbits

Cholesteryl ester transfer protein (CETP) inhibitors increase high density lipoprotein-cholesterol (HDL-C) in animals and humans, but whether CETP inhibition will be antiatherogenic is still uncertain. We tested the CETP inhibitor torcetrapib in rabbits fed an atherogenic diet at a dose sufficient to increase HDL-C by at least 3-fold (207 +/- 32 vs. 57 +/- 6 mg/dl in controls at 16 weeks). CETP activity was inhibited by 70-80% throughout the study. Non-HDL-C increased in both groups, but there was no difference apparent by the study's end. At 16 weeks, aortic atherosclerosis was 60% lower in torcetrapib-treated animals (16.4 +/- 3.4% vs. 39.8 +/- 5.4% in controls) and aortic cholesterol content was reduced proportionally. Sera from a separate group of rabbits administered torcetrapib effluxed 48% more cholesterol from Fu5AH cells than did sera from control animals, possibly explaining the reduced aortic cholesterol content. Regression analyses indicated that lesion area in the torcetrapib-treated group was strongly correlated with the ratio of total plasma cholesterol to HDL-C but not with changes in other lipid or lipoprotein levels. CETP inhibition with torcetrapib retards atherosclerosis in rabbits, and the reduced lesion area is associated with increased levels of HDL-C.

Interaction effects of high-density lipoprotein metabolism gene variation and alcohol consumption on coronary heart disease risk: the atherosclerosis risk in communities study

OBJECTIVE

Light to moderate alcohol consumption has been widely established to be protective against coronary heart disease (CHD), whereas heavy alcohol consumption has been shown to have a potential detrimental effect. The reduction in risk of CHD associated with light and moderate alcohol intake is generally attributed to the beneficial effects of alcohol on high-density lipoprotein (HDL) cholesterol levels. Previous research in the Atherosclerosis Risk in Communities (ARIC) study showed all levels of alcohol consumption to be protective against CHD in whites but to be associated with an increased risk of CHD in black men. We investigated the ARIC cohort to determine whether risk of incident CHD is influenced by an interaction effect between alcohol intake and genetic variation involved in the regulation of HDL cholesterol. Genes of interest included cholesterol ester transfer protein (CETP), lipoprotein lipase (LPL), hepatic lipase (HL), and paraoxonase-1 (PON1).

METHOD

Participants were selected from the ARIC study, a prospective investigation of atherosclerosis and its clinical sequelae, involving 15,792 individuals, ages 45-64 years at recruitment (1987-1989). Incident CHD was identified through annual telephone calls and hospital and death certificate surveillance. Because of ethnic differences in the alcohol-CHD relationship observed in the ARIC cohort and pattern of alcohol consumption differences, statistical analyses were evaluated separately for each race-gender stratum (white men/women, black men/women).

RESULTS

Genotype modified the relationship between heavy drinking and CHD risk but did not modify this relationship for light or moderate drinking. Interaction analyses were significant for heavy alcohol intake and PON1 genotype (p=.02) in black men, with a suggested interaction for heavy alcohol intake and CETP genotype (p=.06) in black men. Heavy drinking was associated with an increased risk for CHD in black men with the PON1 QQ and CETP GG genotypes (PON1 hazard rate ratio [HRR]=17.3, 95% confidence interval [CI]: 1.76-170.2; CETP HRR=2.23, 95% CI: 1.01-4.91).

CONCLUSIONS

Results from the current study suggest that interaction effects between alcohol consumption and HDL cholesterol metabolism gene variation influence the risk of incident CHD in black men. Additional studies are warranted to confirm these findings.