Identification of patients and plaques vulnerable to future coronary events with near-infrared spectroscopy intravascular ultrasound imaging: a prospective, cohort study.

BACKGROUND: Near-infrared spectroscopy (NIRS) intravascular ultrasound imaging can detect lipid-rich plaques (LRPs). LRPs are associated with acute coronary syndromes or myocardial infarction, which can result in revascularisation or cardiac death. In this study, we aimed to establish the relationship between LRPs detected by NIRS-intravascular ultrasound imaging at unstented sites and subsequent coronary events from new culprit lesions. METHODS: In this prospective, cohort study (LRP), patients from 44 medical centres were enrolled in Italy, Latvia, Netherlands, Slovakia, UK, and the USA. Patients with suspected coronary artery disease who underwent cardiac catheterisation with possible ad hoc percutaneous coronary intervention were eligible to be enrolled. Enrolled patients underwent scanning of non-culprit segments using NIRS-intravascular ultrasound imaging. The study had two hierarchal primary hypotheses, patient and plaque, each testing the association between maximum 4 mm Lipid Core Burden Index (maxLCBI4mm) and non-culprit major adverse cardiovascular events (NC-MACE). Enrolled patients with large LRPs (≥250 maxLCBI4mm) and a randomly selected half of patients with small LRPs (<250 maxLCBI4mm) were followed up for 24 months. This study is registered with ClinicalTrials.gov, NCT02033694. FINDINGS: Between Feb 21, 2014, and March 30, 2016, 1563 patients were enrolled. NIRS-intravascular ultrasound device-related events were seen in six (0·4%) patients. 1271 patients (mean age 64 years, SD 10, 883 [69%] men, 388 [31%]women) with analysable maxLCBI4mm were allocated to follow-up. The 2-year cumulative incidence of NC-MACE was 9% (n=103). Both hierarchical primary hypotheses were met. On a patient level, the unadjusted hazard ratio (HR) for NC-MACE was 1·21 (95% CI 1·09-1·35; p=0·0004) for each 100-unit increase maxLCBI4mm) and adjusted HR 1·18 (1·05-1·32; p=0·0043). In patients with a maxLCBI4mm more than 400, the unadjusted HR for NC-MACE was 2·18 (1·48-3·22; p<0·0001) and adjusted HR was 1·89 (1·26-2·83; p=0·0021). At the plaque level, the unadjusted HR was 1·45 (1·30-1·60; p<0·0001) for each 100-unit increase in maxLCBI4mm. For segments with a maxLCBI4mm more than 400, the unadjusted HR for NC-MACE was 4·22 (2·39-7·45; p<0·0001) and adjusted HR was 3·39 (1·85-6·20; p<0·0001). INTERPRETATION: NIRS imaging of non-obstructive territories in patients undergoing cardiac catheterisation and possible percutaneous coronary intervention was safe and can aid in identifying patients and segments at higher risk for subsequent NC-MACE. NIRS-intravascular ultrasound imaging adds to the armamentarium as the first diagnostic tool able to detect vulnerable patients and plaques in clinical practice. FUNDING: Infraredx.

Evacetrapib and Cardiovascular Outcomes in High-Risk Vascular Disease.

BACKGROUND: The cholesteryl ester transfer protein inhibitor evacetrapib substantially raises the high-density lipoprotein (HDL) cholesterol level, reduces the low-density lipoprotein (LDL) cholesterol level, and enhances cellular cholesterol efflux capacity. We sought to determine the effect of evacetrapib on major adverse cardiovascular outcomes in patients with high-risk vascular disease. METHODS: In a multicenter, randomized, double-blind, placebo-controlled phase 3 trial, we enrolled 12,092 patients who had at least one of the following conditions: an acute coronary syndrome within the previous 30 to 365 days, cerebrovascular atherosclerotic disease, peripheral vascular arterial disease, or diabetes mellitus with coronary artery disease. Patients were randomly assigned to receive either evacetrapib at a dose of 130 mg or matching placebo, administered daily, in addition to standard medical therapy. The primary efficacy end point was the first occurrence of any component of the composite of death from cardiovascular causes, myocardial infarction, stroke, coronary revascularization, or hospitalization for unstable angina. RESULTS: At 3 months, a 31.1% decrease in the mean LDL cholesterol level was observed with evacetrapib versus a 6.0% increase with placebo, and a 133.2% increase in the mean HDL cholesterol level was seen with evacetrapib versus a 1.6% increase with placebo. After 1363 of the planned 1670 primary end-point events had occurred, the data and safety monitoring board recommended that the trial be terminated early because of a lack of efficacy. After a median of 26 months of evacetrapib or placebo, a primary end-point event occurred in 12.9% of the patients in the evacetrapib group and in 12.8% of those in the placebo group (hazard ratio, 1.01; 95% confidence interval, 0.91 to 1.11; P=0.91). CONCLUSIONS: Although the cholesteryl ester transfer protein inhibitor evacetrapib had favorable effects on established lipid biomarkers, treatment with evacetrapib did not result in a lower rate of cardiovascular events than placebo among patients with high-risk vascular disease. (Funded by Eli Lilly; ACCELERATE ClinicalTrials.gov number, NCT01687998 .).

The impact of proprotein convertase subtilisin-kexin type 9 serine protease inhibitors on lipid levels and outcomes in patients with primary hypercholesterolaemia: a network meta-analysis.

AIMS: We performed a network meta-analysis of randomized controlled trials (RCTs) in patients with primary hypercholesterolaemia to compare the impact of proprotein convertase subtilisin-kexin type 9 serine protease (PCSK9) inhibitors with placebo and ezetimibe on lipid levels and outcomes. METHODS AND RESULTS: MEDLINE/PubMed, Cochrane CENTRAL, and ClinicalTrials.gov were searched for RCTs assessing PCSK9 inhibitors vs. other therapies in patients with primary hypercholesterolaemia. Network meta-analysis with both a frequentist approach and a Bayesian framework was performed to directly and indirectly compare PCSK9 inhibition on lipid levels with ezetimibe and placebo. Odds ratios with 95% confidence intervals (OR [95% CIs]) were generated with random-effects models to compare outcomes. Our meta-analysis included 17 RCTs with 13 083 patients that were randomized to PCSK9 inhibitors (n = 8250), placebo (n = 3957), ezetimibe (n = 846), or PCSK9 inhibitors and ezetimibe (n = 30). The mean age was 59 ± 10, 52% were male, 34% had coronary artery disease, 51% had hypertension, 19% had diabetes mellitus, baseline LDL of 122 ± 36 mg/dL, total cholesterol of 199 ± 39 mg/dL, and HDL of 51 ± 14 mg/dL. inhibitors significantly reduced LDL cholesterol by 57% relative to placebo (P < 0.001) and 36.1% relative to ezetimibe (P < 0.001). Proprotein convertase subtilisin-kexin type 9 serine protease inhibitors reduced the incidence of all-cause mortality [OR 0.43 (95% CI 0.22-0.82), P = 0.01] but was associated with an increased incidence of neurocognitive adverse events [OR 2.34 (95% CI 1.11-4.93), I(2) = 4%, P = 0.02] when compared with placebo. CONCLUSION: Proprotein convertase subtilisin-kexin type 9 serine protease inhibition significantly improved lipid profiles and reduced the incidence of all-cause mortality compared with placebo but had a higher rate of neurocognitive adverse events. Thus, PCSK9 inhibitor therapy may serve as an alternative for patients with statin intolerance and for those who do not respond to other lipid reduction therapy.

Cholesterol ester transfer protein inhibition by TA-8995 in patients with mild dyslipidaemia (TULIP): a randomised, double-blind, placebo-controlled phase 2 trial.

BACKGROUND: Dyslipidaemia remains a significant risk factor for cardiovascular disease and additional lipid-modifying treatments are warranted to further decrease the cardiovascular disease burden. We assessed the safety, tolerability and efficacy of a novel cholesterol esterase transfer protein (CETP) inhibitor TA-8995 in patients with mild dyslipidaemia. METHODS: In this randomised, double-blind, placebo-controlled, parallel-group phase 2 trial, we recruited patients (aged 18-75 years) from 17 sites (hospitals and independent clinical research organisations) in the Netherlands and Denmark with fasting LDL cholesterol levels between 2·5 mmol/L and 4·5 mmol/L, HDL cholesterol levels between 0·8 and 1·8 mmol/L and triglyceride levels below 4·5 mmol/L after washout of lipid-lowering treatments. Patients were randomly allocated (1:1) by a computer-generated randomisation schedule to receive one of the following nine treatments: a once a day dose of 1 mg, 2·5 mg, 5 mg, or 10 mg TA-8995 or matching placebo; 10 mg TA-8995 plus 20 mg atorvastatin; 10 mg TA-8995 plus 10 mg rosuvastatin or 20 mg atorvastatin or 10 mg rosuvastatin alone. We overencapsulated statins to achieve masking. The primary outcome was percentage change in LDL cholesterol and HDL cholesterol from baseline at week 12, analysed by intention to treat. This study is registered with ClinicalTrials.gov, number NCT01970215. FINDINGS: Between Aug 15, 2013, and Jan 10, 2014, 364 patients were enrolled. At week 12, LDL cholesterol levels were reduced by 27·4% in patients assigned to the 1 mg dose, 32·7% in patients given the 2·5 mg dose, 45·3% in those given the 5 mg dose, and 45·3% in those given the 10 mg dose (p<0·0001). LDL cholesterol levels were reduced by 68·2% in patients given 10 mg TA-8995 plus atorvastatin, and by 63·3% in patients given rosuvastatin plus 10 mg TA-8995 (p<0·0001). A daily dose of 1 mg TA-8995 increased HDL cholesterol levels by 75·8%, 2·5 mg by 124·3%, 5 mg by 157·1%, and 10 mg dose by 179·0% (p<0·0001). In patients receiving 10 mg TA-8995 and 20 mg atorvastatin HDL cholesterol levels increased by 152·1% and in patients receiving 10 mg TA-8995 and 10 mg rosuvastatin by 157·5%. We recorded no serious adverse events or signs of liver or muscle toxic effects. INTERPRETATION: TA-8995, a novel CETP inhibitor, is well tolerated and has beneficial effects on lipids and apolipoproteins in patients with mild dyslipidaemia. A cardiovascular disease outcome trial is needed to translate these effects into a reduction of cardiovascular disease events. FUNDING: Dezima.

Lipoproteins as biomarkers and therapeutic targets in the setting of acute coronary syndrome.

The period following an acute coronary syndrome (ACS) represents a critical time frame with a high risk for recurrent events and death. The pathogenesis of this increase in clinical cardiovascular disease events after ACS is complex, with molecular mechanisms including increased thrombosis and inflammation. Dyslipoproteinemia is common in patients with ACS and predictive of recurrent cardiovascular disease events after presentation with an ACS event. Although randomized clinical trials have provided fairly convincing evidence that high-dose statins reduce the risk of recurrent cardiovascular events after ACS, there remain questions about how aggressively to reduce low-density lipoprotein cholesterol levels in ACS. Furthermore, no other lipid-related interventions have yet been proven to be effective in reducing major cardiovascular events after ACS. Here, we review the relationship of lipoproteins as biomarkers to cardiovascular risk after ACS, the evidence for lipid-targeted interventions, and the potential for novel therapeutic approaches in this arena.

Novel therapies focused on the high-density lipoprotein particle.

Cardiovascular disease (CVD) remains a major burden for morbidity and mortality in the general population, despite current efficacious low-density lipoprotein-cholesterol-lowering therapies. Consequently, novel therapies are required to reduce this residual risk. Prospective epidemiological studies have shown that high-density lipoprotein-cholesterol (HDL-C) levels are inversely correlated with cardiovascular disease risk, and this initiated the quest for HDL-C-increasing therapies. Consequently, several different targets in HDL metabolism have been identified. Initial studies addressing the effect of cholesteryl ester transfer protein inhibition on cardiovascular disease outcome have been discontinued for reasons of futility or increased mortality. As of yet, 2 cholesteryl ester transfer protein inhibitors are still in phase III studies. Other HDL-based interventions, such as apolipoprotein A1-based compounds, ABC-transporter upregulators, selective peroxisome proliferator-activated receptor modulators and lecithin-cholesterol acyltransferase-based therapy, hold great promise for the future. The aim of this review is to provide a comprehensive overview of HDL-targeted pharmaceutical strategies in humans, both in early development as well as in late stage clinical trials.

Assessment of the clinical effects of cholesteryl ester transfer protein inhibition with evacetrapib in patients at high-risk for vascular outcomes: Rationale and design of the ACCELERATE trial.

BACKGROUND: Potent pharmacologic inhibition of cholesteryl ester transferase protein by the investigational agent evacetrapib increases high-density lipoprotein cholesterol by 54% to 129%, reduces low-density lipoprotein cholesterol by 14% to 36%, and enhances cellular cholesterol efflux capacity. The ACCELERATE trial examines whether the addition of evacetrapib to standard medical therapy reduces the risk of cardiovascular (CV) morbidity and mortality in patients with high-risk vascular disease. STUDY DESIGN: ACCELERATE is a phase 3, multicenter, randomized, double-blind, placebo-controlled trial. Patients qualified for enrollment if they have experienced an acute coronary syndrome within the prior 30 to 365 days, cerebrovascular accident, or transient ischemic attack; if they have peripheral vascular disease; or they have diabetes with coronary artery disease. A total of 12,092 patients were randomized to evacetrapib 130 mg or placebo daily in addition to standard medical therapy. The primary efficacy end point is time to first event of CV death, myocardial infarction, stroke, hospitalization for unstable angina, or coronary revascularization. Treatment will continue until 1,670 patients reached the primary end point; at least 700 patients reach the key secondary efficacy end point of CV death, myocardial infarction, and stroke, and the last patient randomized has been followed up for at least 1.5 years. CONCLUSIONS: ACCELERATE will establish whether the cholesteryl ester transfer protein inhibition by evacetrapib improves CV outcomes in patients with high-risk vascular disease.

Intravascular ultrasound analysis to determine the relationship between high-density lipoprotein cholesterol and lesion characteristics in patients with coronary artery disease.

OBJECTIVES: This study utilized grayscale intravascular ultrasound (IVUS) to explore the relationship between high-density lipoprotein cholesterol (HDL-C) levels and culprit lesion characteristics in patients with coronary artery disease. BACKGROUND: Low HDL-C is associated with an increased risk of cardiovascular events. Previous IVUS studies have suggested a significant association between lesion characteristics and cardiovascular events. METHODS: According to HDL-C levels, 120 patients who underwent IVUS for native, de novo coronary lesions before any intervention were divided into a low HDL-C group (<40 mg/dL, n = 60) and a high HDL-C group (≥40 mg/dL, n = 60). Quantitative and qualitative IVUS analyses were performed to compare lesion characteristics. RESULTS: Quantitative IVUS measurements showed no significant differences between the 2 groups. HDL-C level was not significantly correlated with remodeling index (r = 0.03, P = 0.78). However, attenuated plaque was more frequent in the low HDL-C group (48.3% vs. 28.3%, P = 0.02) and a greater percentage of attenuated plaque was found in this group (32.5 ± 21.3% vs. 21.0 ± 11.0%, P = 0.02). Moreover, when categorized into 4 groups according to HDL-C levels, the proportion of attenuated plaque (64.7% in group with <30 mg/dL, 41.9% in group with 30-39 mg/dL, 36.4% in group with 40-59 mg/dL, and 6.3% in group with ≥60 mg/dL; P = 0.001 for trend) was significantly different among groups. On multivariate analysis, only HDL-C and male gender were independently associated with the presence of attenuated plaque at the culprit lesions. CONCLUSIONS: Patients with low levels of HDL-C may be at increased risk of having a higher incidence of attenuated plaques.

High-density lipoprotein infusion therapy: A review.

Increased cholesterol-rich, low-density, non-calcified atheromas as assessed by computer coronary tomography angiography analyses have been shown to predict myocardial infarction significantly better than coronary artery calcium score or the presence of obstructive coronary artery disease (CAD) as evaluated with standard coronary angiography. Low serum high-density lipoprotein (HDL) cholesterol values are an independent risk factor for CAD. Very small, lipid-poor preß-1 HDL particles have been shown to be most effective in promoting cellular cholesterol efflux. HDL infusions have been documented to reduce aortic atherosclerosis in cholesterol-fed animal models. However, human studies using infusions of either the HDL mimetic containing recombinant apolipoprotein (apo) A-I Milano or Cerenis Compound-001 with native recombinant apoA-I have been mainly negative in promoting coronary atherosclerosis progression as assessed by intravascular ultrasound. In contrast, a study using 7 weekly infusions of autologous delipidated HDL in six homozygous familial hypercholesterolemic patients was effective in promoting significant regression of low-density non-calcified coronary atheroma regression as assessed by computed coronary angiography. This therapy has received Food and Drug Administration approval. Commonwealth Serum Laboratories has carried out a large clinical endpoint trial using an HDL complex (native apoA-I with phospholipid), and the results were negative. Our purpose is to review animal and human studies using various forms of HDL infusion therapy to promote regression of atherosclerosis. In our view, differences in results may be due to: 1) the HDL preparations used, 2) the subjects studied, and 3) the methods used to assess coronary atherosclerosis.

ApoA-I induction as a potential cardioprotective strategy: rationale for the SUSTAIN and ASSURE studies.

BACKGROUND: Considerable interest has focused on the development of therapies that target the functionality of high-density lipoproteins (HDL). Upregulation of endogenous synthesis of the major protein on HDL particles, apolipoprotein A-I (apoA-I), represents a novel approach to generation of new HDL particles. The Study of Quantitative Serial Trends in Lipids with Apolipoprotein A-I Stimulation (SUSTAIN, NCT01423188) study aims to evaluate the lipid efficacy, safety and tolerability of an apoA-I inducer (RVX-208). The ApoA-I Synthesis Stimulation and Intravascular Ultrasound for Coronary Atheroma Regression Evaluation (ASSURE, NCT01067820) study aims to evaluate the effect of RVX-208 on plaque burden. METHODS: In SUSTAIN, 172 patients with low levels of HDL-C will be randomized to receive RVX-208 100 mg bid or placebo for 24 weeks. The primary efficacy parameter will be the percentage change in HDL-C levels. In ASSURE, 310 patients with angiographic coronary artery disease and low HDL-C levels will be randomized to receive RVX-208 100 mg bid or placebo for 26 weeks. The primary efficacy parameter will be the nominal change in percent atheroma volume (PAV), determined by analysis of intravascular ultrasound (IVUS) images of matched coronary artery segments acquired at baseline and at 26-week follow-up. The effect of RVX-208 on other lipid and inflammatory markers, safety and tolerability will also be assessed in both studies. CONCLUSION: ApoA-I induction represents a potential novel strategy to reduce cardiovascular risk, by generating nascent HDL particles. These studies will provide early evaluation of the effects of RVX-208 on lipids and atherosclerotic plaque.

HDL measures, particle heterogeneity, proposed nomenclature, and relation to atherosclerotic cardiovascular events.

BACKGROUND: A growing body of evidence from epidemiological data, animal studies, and clinical trials supports HDL as the next target to reduce residual cardiovascular risk in statin-treated, high-risk patients. For more than 3 decades, HDL cholesterol has been employed as the principal clinical measure of HDL and cardiovascular risk associated with low HDL-cholesterol concentrations. The physicochemical and functional heterogeneity of HDL present important challenges to investigators in the cardiovascular field who are seeking to identify more effective laboratory and clinical methods to develop a measurement method to quantify HDL that has predictive value in assessing cardiovascular risk. CONTENT: In this report, we critically evaluate the diverse physical and chemical methods that have been employed to characterize plasma HDL. To facilitate future characterization of HDL subfractions, we propose the development of a new nomenclature based on physical properties for the subfractions of HDL that includes very large HDL particles (VL-HDL), large HDL particles (L-HDL), medium HDL particles (M-HDL), small HDL particles (S-HDL), and very-small HDL particles (VS-HDL). This nomenclature also includes an entry for the pre-ß-1 HDL subclass that participates in macrophage cholesterol efflux. SUMMARY: We anticipate that adoption of a uniform nomenclature system for HDL subfractions that integrates terminology from several methods will enhance our ability not only to compare findings with different approaches for HDL fractionation, but also to assess the clinical effects of different agents that modulate HDL particle structure, metabolism, and function, and in turn, cardiovascular risk prediction within these HDL subfractions.

Effects of the CETP inhibitor evacetrapib administered as monotherapy or in combination with statins on HDL and LDL cholesterol: a randomized controlled trial.

CONTEXT: Interest remains high in cholesteryl ester transfer protein (CETP) inhibitors as cardioprotective agents. Few studies have documented the efficacy and safety of CETP inhibitors in combination with commonly used statins. OBJECTIVE: To examine the biochemical effects, safety, and tolerability of evacetrapib, as monotherapy and in combination with statins, in patients with dyslipidemia. DESIGN, SETTING, AND PARTICIPANTS: Randomized controlled trial conducted among 398 patients with elevated low-density lipoprotein cholesterol (LDL-C) or low high-density lipoprotein cholesterol (HDL-C) levels from April 2010 to January 2011 at community and academic centers in the United States and Europe. INTERVENTIONS: Following dietary lead-in, patients were randomly assigned to receive placebo (n = 38); evacetrapib monotherapy, 30 mg/d (n = 40), 100 mg/d (n = 39), or 500 mg/d (n = 42); or statin therapy (n = 239) (simvastatin, 40 mg/d; atorvastatin, 20 mg/d; or rosuvastatin, 10 mg/d) with or without evacetrapib, 100 mg/d, for 12 weeks. MAIN OUTCOME MEASURES: The co-primary end points were percentage changes from baseline in HDL-C and LDL-C after 12 weeks of treatment. RESULTS: The mean baseline HDL-C level was 55.1 (SD, 15.3) mg/dL and the mean baseline LDL-C level was 144.3 (SD, 26.6) mg/dL. As monotherapy, evacetrapib produced dose-dependent increases in HDL-C of 30.0 to 66.0 mg/dL (53.6% to 128.8%) compared with a decrease with placebo of -0.7 mg/dL (-3.0%; P < .001 for all compared with placebo) and decreases in LDL-C of -20.5 to -51.4 mg/dL (-13.6% to -35.9%) compared with an increase with placebo of 7.2 mg/dL (3.9%; P < .001 for all compared with placebo). In combination with statin therapy, evacetrapib, 100 mg/d, produced increases in HDL-C of 42.1 to 50.5 mg/dL (78.5% to 88.5%; P < .001 for all compared with statin monotherapy) and decreases in LDL-C of -67.1 to -75.8 mg/dL (-11.2% to -13.9%; P < .001 for all compared with statin monotherapy). Compared with evacetrapib monotherapy, the combination of statins and evacetrapib resulted in greater reductions in LDL-C (P <.001) but no greater increase in HDL-C (P =.39). Although the study was underpowered, no adverse effects were observed. CONCLUSIONS: Compared with placebo or statin monotherapy, evacetrapib as monotherapy or in combination with statins increased HDL-C levels and decreased LDL-C levels. The effects on cardiovascular outcomes require further investigation. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01105975.

Effect of ACAT inhibition on the progression of coronary atherosclerosis.

BACKGROUND: The enzyme acyl-coenzyme A:cholesterol acyltransferase (ACAT) esterifies cholesterol in a variety of tissues. In some animal models, ACAT inhibitors have antiatherosclerotic effects. METHODS: We performed intravascular ultrasonography in 408 patients with angiographically documented coronary disease. All patients received usual care for secondary prevention, including statins, if indicated. Patients were randomly assigned to receive the ACAT inhibitor pactimibe (100 mg per day) or matching placebo. Ultrasonography was repeated after 18 months to measure the progression of atherosclerosis. RESULTS: The primary efficacy variable analyzing the progression of atherosclerosis--the change in percent atheroma volume--was similar in the pactimibe and placebo groups (0.69 percent and 0.59 percent, respectively; P=0.77). However, both secondary efficacy variables assessed by means of intravascular ultrasonography showed unfavorable effects of pactimibe treatment. As compared with baseline values, the normalized total atheroma volume showed significant regression in the placebo group (-5.6 mm3, P=0.001) but not in the pactimibe group (-1.3 mm3, P=0.39; P=0.03 for the comparison between groups). The atheroma volume in the most diseased 10-mm subsegment regressed by 3.2 mm3 in the placebo group, as compared with a decrease of 1.3 mm3 in the pactimibe group (P=0.01). The combined incidence of adverse cardiovascular outcomes was similar in the two groups (P=0.53). CONCLUSIONS: For patients with coronary disease, treatment with an ACAT inhibitor did not improve the primary efficacy variable (percent atheroma volume) and adversely affected two major secondary efficacy measures assessed by intravascular ultrasonography. ACAT inhibition is not an effective strategy for limiting atherosclerosis and may promote atherogenesis. (ClinicalTrials.gov number, NCT00268515.).

HDL and atherosclerotic cardiovascular disease: genetic insights into complex biology.

Plasma levels of HDL cholesterol (HDL-C) predict the risk of cardiovascular disease at the epidemiological level, but a direct causal role for HDL in cardiovascular disease remains controversial. Studies in animal models and humans with rare monogenic disorders link only particular HDL-associated mechanisms with causality, including those mechanisms related to particle functionality rather than cholesterol content. Mendelian randomization studies indicate that most genetic variants that affect a range of pathways that increase plasma HDL-C levels are not usually associated with reduced risk of cardiovascular disease, with some exceptions, such as cholesteryl ester transfer protein variants. Furthermore, only a fraction of HDL-C variation has been explained by known loci from genome-wide association studies (GWAS), suggesting the existence of additional pathways and targets. Systems genetics can enhance our understanding of the spectrum of HDL pathways, particularly those pathways that involve new and non-obvious GWAS loci. Bioinformatic approaches can also define new molecular interactions inferred from both large-scale genotypic data and RNA sequencing data to reveal biologically meaningful gene modules and networks governing HDL metabolism with direct relevance to disease end points. Targeting these newly recognized causal networks might inform the development of novel therapeutic strategies to reduce the risk of cardiovascular disease.

Conditional disruption of the peroxisome proliferator-activated receptor gamma gene in mice results in lowered expression of ABCA1, ABCG1, and apoE in macrophages and reduced cholesterol efflux.

Disruption of the peroxisome proliferator-activated receptor gamma (PPAR gamma) gene causes embryonic lethality due to placental dysfunction. To circumvent this, a PPAR gamma conditional gene knockout mouse was produced by using the Cre-loxP system. The targeted allele, containing loxP sites flanking exon 2 of the PPAR gamma gene, was crossed into a transgenic mouse line expressing Cre recombinase under the control of the alpha/beta interferon-inducible (MX) promoter. Induction of the MX promoter by pIpC resulted in nearly complete deletion of the targeted exon, a corresponding loss of full-length PPAR gamma mRNA transcript and protein, and marked reductions in basal and troglitazone-stimulated expression of the genes encoding lipoprotein lipase, CD36, LXR alpha, and ABCG1 in thioglycolate-elicited peritoneal macrophages. Reductions in the basal levels of apolipoprotein E (apoE) mRNA in macrophages and apoE protein in total plasma and high-density lipoprotein (HDL) were also observed in pIpC-treated PPAR gamma-MXCre(+) mice. Basal cholesterol efflux from cholesterol-loaded macrophages to HDL was significantly reduced after disruption of the PPAR gamma gene. Troglitazone selectively inhibited ABCA1 expression (while rosiglitazone, ciglitazone, and pioglitazone had little effect) and cholesterol efflux in both PPAR gamma-deficient and control macrophages, indicating that this drug can exert paradoxical effects on cholesterol homeostasis that are independent of PPAR gamma. Together, these data indicate that PPAR gamma plays a critical role in the regulation of cholesterol homeostasis by controlling the expression of a network of genes that mediate cholesterol efflux from cells and its transport in plasma.

Human lecithin:cholesterol acyltransferase deficiency: in vivo kinetics of low-density lipoprotein and lipoprotein-X.

OBJECTIVE: Lecithin:cholesterol acyltransferase deficiency (LCAT-def) is characterized by low levels of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) and the accumulation of lipoprotein-X (LpX). Despite the low HDL, atherosclerosis is uncommon in LCAT-def. The decreased LDL would be a possible explanation but the underlying mechanism is not clear. In addition, the mechanism(s) for LpX accumulation is not known. The aim of the present study is to elucidate the mechanism(s) responsible for the low LDL and determine the plasma kinetics of LpX in LCAT-def. METHODS AND RESULTS: We conducted a radiotracer study in LCAT-def (n=2) and normal controls (n=10) and a stable isotope study in one patient and other controls (n=7). LCAT-def LDL was catabolized faster than control LDL in the control subjects as well as in LCAT-def patients. Control LDL was catabolized faster in LCAT-def patients than the controls. The production rate of LDL apolipoprotein B-100 was normal in LCAT-def. The increased LDL apoB-100 catabolism was confirmed by a stable isotope study. LpX was catabolized more slowly in LCAT-def. CONCLUSIONS: The decreased LDL in LCAT-def is attributable to an increased catabolism caused by a rapid catabolism of abnormal LDL and an upregulation of LDL receptor pathway. The decreased catabolism of LpX contributes to its accumulation in LCAT-def.