Plasma lipid transfer proteins

Structural insights on the deformations induced by various mutations on cholesteryl ester transfer protein

Cholesteryl Ester Transfer Protein (CETP) is a plasma glycoprotein that intervenes the reverse cholesterol transport (RCT) by equimolar exchange of Cholesteryl esters (CE) and Triglycerides (TGs) between anti-atherogenic High-Density Lipoproteins (HDLs) and pro-atherogenic Low-Density Lipoproteins (LDLs) resulting in the increased concentration of CEs in LDL. This is a potential cause for the formation of atherosclerotic plaques in blood vessels leading to fatality. Therefore, blocking the function of CETP has emerged as a novel strategy for suppressing atherosclerotic plaques. The crystal structure of CETP revealed two Cholesteryl esters (CEs) in the hydrophobic tunnel and two phospholipids (PLs) plugged on the concave surface. Previous lipid transfer assay experimental studies have shown a substantial reduction in the neutral lipid transfer in [R201S] and [I443W, V198W] mutants. However, the protein conformational arrangements due to the mutations present in the CETP system leading to a decrease in the transfer rate of neutral lipids is not explored. Thus, I explored the reason behind the decreased transfer rate in mutants using molecular dynamics (MD) simulations and free energy calculations. Resulting evidences show that R201S mutant induces unfavorable bending angle to CETP with a decreased binding efficiency between N-terminal phospholipid of CETP with S201. Also, an unfavorable conformation state of TGs is formed which makes them difficult to transfer across CETP. Likewise, [I443W, V198W] mutant induces unfavorable CE, TG, and bending angle conformation to CETP impeding neutral lipid transfer. Thus, my results provide sufficient insights on the causation for a decreased transfer rate as reported earlier. The detailed understanding obtained here could help in developing a new strategy in preventing the function of CETP by blocking the role of potential hot spot residues.

Genetically modified rabbit models for cardiovascular medicine

Genetically modified (GM) rabbits are outstanding animal models for studying human genetic and acquired diseases. As such, GM rabbits that express human genes have been extensively used as models of cardiovascular disease. Rabbits are genetically modified via prokaryotic microinjection. Through this process, genes are randomly integrated into the rabbit genome. Moreover, gene targeting in embryonic stem (ES) cells is a powerful tool for understanding gene function. However, rabbits lack stable ES cell lines. Therefore, ES-dependent gene targeting is not possible in rabbits. Nevertheless, the RNA interference technique is rapidly becoming a useful experimental tool that enables researchers to knock down specific gene expression, which leads to the genetic modification of rabbits. Recently, with the emergence of new genetic technology, such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), clustered regularly interspaced short palindromic repeats (CRISPR), and CRISPR-associated protein 9 (CRISPR/Cas9), major breakthroughs have been made in rabbit gene targeting. Using these novel genetic techniques, researchers have successfully modified knockout (KO) rabbit models. In this paper, we aimed to review the recent advances in GM technology in rabbits and highlight their application as models for cardiovascular medicine.

Metabolism of PLTP, CETP, and LCAT on multiple HDL sizes using the Orbitrap Fusion Lumos

Recent in vivo tracer studies demonstrated that targeted mass spectrometry (MS) on the Q Exactive Orbitrap could determine the metabolism of HDL proteins 100s-fold less abundant than apolipoprotein A1 (APOA1). In this study, we demonstrate that the Orbitrap Lumos can measure tracer in proteins whose abundances are 1000s-fold less than APOA1, specifically the lipid transfer proteins phospholipid transfer protein (PLTP), cholesterol ester transfer protein (CETP), and lecithin-cholesterol acyl transferase (LCAT). Relative to the Q Exactive, the Lumos improved tracer detection by reducing tracer enrichment compression, thereby providing consistent enrichment data across multiple HDL sizes from 6 participants. We determined by compartmental modeling that PLTP is secreted in medium and large HDL (alpha2, alpha1, and alpha0) and is transferred from medium to larger sizes during circulation from where it is catabolized. CETP is secreted mainly in alpha1 and alpha2 and remains in these sizes during circulation. LCAT is secreted mainly in medium and small HDL (alpha2, alpha3, prebeta). Unlike PLTP and CETP, LCAT’s appearance on HDL is markedly delayed, indicating that LCAT may reside for a time outside of systemic circulation before attaching to HDL in plasma. The determination of these lipid transfer proteins’ unique metabolic structures was possible due to advances in MS technologies.

Genome-wide association study of the level of blood components in Pekin ducks

Blood components are considered to reflect nutrient metabolism and immune activity in both humans and animals. In this study, we measured 12 blood components in Pekin ducks and performed genome-wide association analysis to identify the QTLs (quantitative trait locus) using a genotyping-by-sequencing strategy. A total of 54 QTLs were identified for blood components. One genome-wide significant QTL for alkaline phosphatase was identified within the intron-region of the OTOG gene (P = 1.31E-07). Moreover, 21 genome-wide significant SNPs for the level of serum cholinesterase were identified on six different scaffolds. In addition, for serum calcium, one genome-wide significant QTL was identified in the upstream region of gene RAB11B. These results provide new markers for functional studies in Pekin ducks, and several candidate genes were identified, which may provide additional insights into specific mechanisms for blood metabolism in ducks and their potential application for duck breeding programs.

Chronic intake of moderate fat-enriched diet induces fatty liver and low-grade inflammation without obesity in rabbits

Non-Alcoholic Fatty Liver Disease (NAFLD) is the cause of chronic liver disease. Even though NAFLD is strongly associated with obesity and metabolic syndrome, there is a proportion of patients who develop this condition in the absence of obesity and the underlying mechanisms are poorly understood. We investigated early events in the pathogenesis of non-obese NAFLD, analyzing the impact of the chronic intake of a moderate fat-enriched diet on hepatic lipid accumulation and their relationship with inflammation. Rabbits fed with a moderate Fatty-Acid- Enriched Diet 3% palmitic acid (FAED), were evaluated for body weight, biochemical parameters, and liver function. Liver samples were analyzed by histology and RT-qPCR to measure lipid accumulation, the expression of inflammation-related genes IL-1β, IL-6, IL-10, IL-13, IL-18, COX-2, TNF-α, and TLR-4. Chronic consumption by 6-months of FAED did not generate metabolic changes, but it induced fatty liver. We also observed the development of low-grade inflammation characterized by the up regulation of TNF-α, IL-13 and IL-18. The consumption by 12-months of FAED caused the overexpression of IL-6, IL-10, IL-13, COX-2, and TLR-4. We show that hepatic steatosis is an early consequence of fat-enriched diets, and that it is accompanied by an immune response that exerts protective effects that prevent the development of metabolic disorders, such as overweight/obesity and metabolic syndrome. However, the excessive intake of fatty acids renders these mechanisms less efficient for delaying the start of metabolic alterations. Rabbits fed with FAED can be used as a model of NAFLD in non-obese and obese groups, especially at early stages of the disease.

Dissociation of fluorescently labeled lipids from liposomes in biological environments challenges the interpretation of uptake studies

Within nanomedicine, liposomes are investigated for their ability to deliver drug cargoes specifically into subcellular compartments of target cells. Such studies are often based on flow cytometry or microscopy, where researchers rely on fluorescently labeled lipids (FLLs) incorporated into the liposomal membrane to determine the localization of the liposomes within cells. These studies assume that the FLLs stay embedded in the liposomal membrane throughout the duration of the experiment. Here, we used size exclusion chromatography (SEC) to investigate the validity of this assumption by quantitatively determining the propensity of various widely used FLLs to dissociate from liposomes during incubation in human plasma. For certain commonly used off-the-shelf FLLs, up to 75% of the dye dissociated from the liposomes, while others dissociated less than 10%. To investigate the implications of this finding, we measured the peripheral blood leukocyte uptake of liposomes formulated with different FLLs using flow cytometry, and observed a significant difference in uptake correlating with the FLL's dissociation tendencies. Consequently, the choice of FLL can dramatically influence the conclusions drawn from liposome uptake and localization studies due to uptake of dissociated FLLs. The varying dissociation propensities for the FLLs were not reflected when incubating in buffer, showing that non-biological environments are unsuitable to mimic liposomal stability in a drug delivery context. Overall, our findings suggest that it is crucial for researchers to evaluate the stability of their FLL-labeled liposomes in biological environments, and the simplicity of the SEC assay put forward here makes it very applicable for the purpose.

Principles and Applications of Rabbit Models for Atherosclerosis Research

Rabbits are one of the most used experimental animals for biomedical research, particularly as a bioreactor for the production of antibodies. However, many unique features of the rabbit have also made it as an excellent species for examining a number of aspects of human diseases such as atherosclerosis. Rabbits are phylogenetically closer to humans than rodents, in addition to their relatively proper size, tame disposition, and ease of use and maintenance in the laboratory facility. Due to their short life spans, short gestation periods, high numbers of progeny, low cost (compared with other large animals) and availability of genomics and proteomics, rabbits usually serve to bridge the gap between smaller rodents (mice and rats) and larger animals, such as dogs, pigs and monkeys, and play an important role in many translational research activities such as pre-clinical testing of drugs and diagnostic methods for patients. The principle of using rabbits rather than other animals as an experimental model is very simple: rabbits should be used for research, such as translational research, that is difficult to accomplish with other species. Recently, rabbit genome sequencing and transcriptomic profiling of atherosclerosis have been successfully completed, which has paved a new way for researchers to use this model in the future. In this review, we provide an overview of the recent progress using rabbits with specific reference to their usefulness for studying human atherosclerosis.

Clinical and pathophysiological evidence supporting the safety of extremely low LDL levels-The zero-LDL hypothesis

While the impact of very low concentrations of low-density lipoprotein cholesterol (LDL-C) on cardiovascular prevention is very reassuring, it is intriguing to know what effect these extremely low LDL-C concentrations have on lipid homoeostasis. The evidence supporting the safety of extremely low LDL levels comes from genetic studies and clinical drug trials. Individuals with lifelong low LDL levels due to mutations in genes associated with increased LDL-LDL receptor (LDLR) activity reveal no safety issues. Patients achieving extremely low LDL levels in the IMPROVE-IT and FOURIER, and the PROFICIO and ODYSSEY programs seem not to have an increased prevalence of adverse effects. The main concern regarding extremely low LDL-C plasma concentrations is the adequacy of the supply of cholesterol, and other molecules, to peripheral tissues. However, LDL proteomic and kinetic studies reaffirm that LDL is the final product of endogenous lipoprotein metabolism. Four of 5 LDL particles are cleared through the LDL-LDLR pathway in the liver. Given that mammalian cells have no enzymatic systems to degrade cholesterol, the LDL-LDLR pathway is the main mechanism for removal of cholesterol from the body. Our focus, therefore, is to review, from a physiological perspective, why such extremely low LDL-C concentrations do not appear to be detrimental. We suggest that extremely low LDL-C levels due to increased LDLR activity may be a surrogate of adequate LDL-LDLR pathway function.

Preclinical Restenosis Models: Challenges and Successes

Coronary artery disease remains a major problem for Western societies. The advent of percutaneous interventions, including stents has brought clinical care to a new level of efficacy, yet problems remain. Restenosis following stenting in human coronary arteries appears at last to be yielding to therapeutic strategies, especially drug eluting stents. Because therapeutic percutaneous coronary intervention is widely dominated by the intracoronary stent, restenosis therapies must include the stented coronary artery. Animal models and in particular the porcine coronary model seem to represent the human coronary artery reaction to stenting. It mimics several clinical conditions including thrombosis and neointimal formation. A key question in the era of intravascular technologies is how well this and other models can predict clinical events. This paper discusses the models and their application.

Neo High-Density Lipoprotein Produced by the Streptococcal Serum Opacity Factor Activity against Human High-Density Lipoproteins Is Hepatically Removed via Dual Mechanisms

Injection of streptococcal serum opacity factor (SOF) into mice reduces the plasma cholesterol level by ∼40%. In vitro, SOF converts high-density lipoproteins (HDLs) into multiple products, including a small HDL, neo HDL. In vitro, neo HDL accounts for ∼60% of the protein mass of the SOF reaction products; in vivo, the accumulated mass of neo HDL is <1% of that observed in vitro. To identify the underlying cause of this difference, we determined the fate of neo HDL in plasma in vitro and in vivo. Following incubation with HDL, neo HDL-PC rapidly transfers to HDL, giving a small remnant, which fuses with HDL. An increased level of SR-B1 expression in Huh7 hepatoma cells and a reduced level of LDLR expression in CHO cells had little effect on neo HDL-[³H]CE uptake. Thus, the dominant receptors for neo HDL uptake are not LDLR or SR-B1. The in vivo metabolic fates of neo HDL-[³H]CE and HDL-[³H]CE were different. Thirty minutes after the injection of neo HDL-[³H]CE and HDL-[³H]CE into mice, plasma [³H]CE counts were 40 and 53%, respectively, of injected counts, with 10 times more [³H]CE appearing in the livers of neo HDL-[³H]CE-injected than in those of HDL-[³H]CE-injected mice. These data support a model of neo HDL-[³H]CE clearance by two parallel pathways. At early post-neo HDL-[³H]CE injection times, some neo HDL is directly removed by the liver; the remainder transfers its PC to HDL, leaving a remnant that fuses with HDL, which is also hepatically removed more slowly. Given that SR-B1 and SOF both remove CE from HDL, this novel mechanism may also underlie the metabolism of remnants released by hepatocytes following selective SR-B1-mediated uptake of HDL-CE.

Polyhedral 3D structure of human plasma very low density lipoproteins by individual particle cryo-electron tomography1

Human VLDLs assembled in the liver and secreted into the circulation supply energy to peripheral tissues. VLDL lipolysis yields atherogenic LDLs and VLDL remnants that strongly correlate with CVD. Although the composition of VLDL particles has been well-characterized, their 3D structure is elusive because of their variations in size, heterogeneity in composition, structural flexibility, and mobility in solution. Here, we employed cryo-electron microscopy and individual-particle electron tomography to study the 3D structure of individual VLDL particles (without averaging) at both below and above their lipid phase transition temperatures. The 3D reconstructions of VLDL and VLDL bound to antibodies revealed an unexpected polyhedral shape, in contrast to the generally accepted model of a spherical emulsion-like particle. The smaller curvature of surface lipids compared with HDL may also reduce surface hydrophobicity, resulting in lower binding affinity to the hydrophobic distal end of the N-terminal β-barrel domain of cholesteryl ester transfer protein (CETP) compared with HDL. The directional binding of CETP to HDL and VLDL may explain the function of CETP in transferring TGs and cholesteryl esters between these particles. This first visualization of the 3D structure of VLDL could improve our understanding of the role of VLDL in atherogenesis.

Insights into the Tunnel Mechanism of Cholesteryl Ester Transfer Protein through All-atom Molecular Dynamics Simulations

Cholesteryl ester transfer protein (CETP) mediates cholesteryl ester (CE) transfer from the atheroprotective high density lipoprotein (HDL) cholesterol to the atherogenic low density lipoprotein cholesterol. In the past decade, this property has driven the development of CETP inhibitors, which have been evaluated in large scale clinical trials for treating cardiovascular diseases. Despite the pharmacological interest, little is known about the fundamental mechanism of CETP in CE transfer. Recent electron microscopy (EM) experiments have suggested a tunnel mechanism, and molecular dynamics simulations have shown that the flexible N-terminal distal end of CETP penetrates into the HDL surface and takes up a CE molecule through an open pore. However, it is not known whether a CE molecule can completely transfer through an entire CETP molecule. Here, we used all-atom molecular dynamics simulations to evaluate this possibility. The results showed that a hydrophobic tunnel inside CETP is sufficient to allow a CE molecule to completely transfer through the entire CETP within a predicted transfer time and at a rate comparable with those obtained through physiological measurements. Analyses of the detailed interactions revealed several residues that might be critical for CETP function, which may provide important clues for the effective development of CETP inhibitors and treatment of cardiovascular diseases.

Genetics of non-conventional lipoprotein fractions

Lipoprotein subclass measures associate with cardiometabolic disease risk. Currently the information that lipoproteins convey on disease risk over that of traditional demographic and lipid measures is minimal, and so their use is clinics is limited. However, lipoprotein subclass perturbations represent some of the earliest manifestations of metabolic dysfunction, and their etiology is partially distinct from lipids, so information on the genetic etiology of lipoproteins offers promise for improved risk prediction, and unique mechanistic insights into IR and atherosclerosis. Here, I review the genetic variants validated as associating with lipoprotein measures to date, and show that the majority of identified variants have functionality that is best understood as related to lipid measures. Until we focus on the genes as they relate to lipoprotein subclass production, we are limiting our understanding of biological mechanisms underlying cardiometabolic disease.

Rabbit models for the study of human atherosclerosis: from pathophysiological mechanisms to translational medicine

Laboratory animal models play an important role in the study of human diseases. Using appropriate animals is critical not only for basic research but also for the development of therapeutics and diagnostic tools. Rabbits are widely used for the study of human atherosclerosis. Because rabbits have a unique feature of lipoprotein metabolism (like humans but unlike rodents) and are sensitive to a cholesterol diet, rabbit models have not only provided many insights into the pathogenesis and development of human atherosclerosis but also made a great contribution to translational research. In fact, rabbit was the first animal model used for studying human atherosclerosis, more than a century ago. Currently, three types of rabbit model are commonly used for the study of human atherosclerosis and lipid metabolism: (1) cholesterol-fed rabbits, (2) Watanabe heritable hyperlipidemic rabbits, analogous to human familial hypercholesterolemia due to genetic deficiency of LDL receptors, and (3) genetically modified (transgenic and knock-out) rabbits. Despite their importance, compared with the mouse, the most widely used laboratory animal model nowadays, the use of rabbit models is still limited. In this review, we focus on the features of rabbit lipoprotein metabolism and pathology of atherosclerotic lesions that make it the optimal model for human atherosclerotic disease, especially for the translational medicine. For the sake of clarity, the review is not an attempt to be completely inclusive, but instead attempts to summarize substantial information concisely and provide a guideline for experiments using rabbits.

Cholesteryl ester-transfer protein inhibitors stimulate aldosterone biosynthesis in adipocytes through Nox-dependent processes

Hyperaldosteronism and hypertension were unexpected side effects observed in trials of torcetrapib, a cholesteryl ester-transfer protein (CETP) inhibitor that increases high-density lipoprotein. Given that CETP inhibitors are lipid soluble, accumulate in adipose tissue, and have binding sites for proteins involved in adipogenesis, and that adipocytes are a source of aldosterone, we questioned whether CETP inhibitors (torcetrapib, dalcetrapib, and anacetrapib) influence aldosterone production by adipocytes. Studies were performed using human adipocytes (SW872), which express CETP, and mouse adipocytes (3T3-L1), which lack the CETP gene. Torcetrapib, dalcetrapib, and anacetrapib increased expression of CYP11B2, CYP11B1, and steroidogenic acute regulatory protein, enzymes involved in mineralocorticoid and glucocorticoid generation. These effects were associated with increased reactive oxygen species formation. Torcetrapib, dalcetrapib, and anacetrapib upregulated signal transducer and activator of transcription 3 (STAT3) and peroxisome proliferation-activated receptor-γ, important in adipogenesis, but only torcetrapib stimulated production of chemerin, a proinflammatory adipokine. To determine mechanisms whereby CETP inhibitors mediate effects, cells were pretreated with inhibitors of Nox1/Nox4 [GKT137831; 2-(2-chlorophenyl)-4-[3-(dimethylamino)phenyl]-5-methyl-1H-pyrazolo[4,3-c]pyridine-3,6(2H,5H)-dione], Nox1 (ML171 [2-acetylphenothiazine]), mitochondria (rotenone), and STAT3 (S3I-201 [2-hydroxy-4-(((4-methylphenyl)sulfonyloxy)acetyl)amino)-benzoic acid]). In torcetrapib-stimulated cells, Nox inhibitors, rotenone, and S3I-201 downregulated CYP11B2 and steroidogenic acute regulatory protein and reduced aldosterone. Dalcetrapib and anacetrapib effects on aldosterone were variably blocked by GKT137831, ML171, rotenone, and S3I-201. In adipocytes, torcetrapib, dalcetrapib, and anacetrapib inhibit enzymatic pathways responsible for aldosterone production through Nox1/Nox4- and mitochondrial-generated reactive oxygen species and STAT3. CETP inhibitors also influence adipokine production. These processes may be CETP independent. Our findings identify novel adipocyte-related mechanisms whereby CETP inhibitors increase aldosterone production. Such phenomena may contribute to hyperaldosteronism observed in CETP inhibitor clinical trials.

CETP genotype and changes in lipid levels in response to weight-loss diet intervention in the POUNDS LOST and DIRECT randomized trials

Little is known about whether cholesteryl ester transfer protein (CETP) genetic variation may modify the effect of weight-loss diets varying in fat content on changes in lipid levels. We analyzed the interaction between the CETP variant rs3764261 and dietary interventions on changes in lipid levels among 732 overweight/obese adults from a 2 year randomized weight-loss trial [Preventing Overweight Using Novel Dietary Strategies (POUNDS LOST)], and replicated the findings in 171 overweight/obese adults from an independent 2 year weight-loss trial [Dietary Intervention Randomized Controlled Trial (DIRECT)]. In the POUNDS LOST, participants with the CETP rs3764261 CC genotype on the high-fat diet had larger increases in HDL cholesterol (P = 0.001) and decreases in triglycerides (P = 0.007) than those on the low-fat diet at 6 months, while no significant difference between these two diets was observed among participants carrying other genotypes. The gene-diet interactions on changes in HDL-cholesterol and tri-glyc-erides were replicated in the DIRECT (pooled P for interaction ≤ 0.01). Similar results on trajectory of changes in HDL cholesterol and triglycerides over the 2 year intervention were observed in both trials. Our study provides replicable evidence that individuals with the CETP rs3764261 CC genotype might derive greater effects on raising HDL cholesterol and lowering triglycerides by choosing a low-carbohydrate/high-fat weight-loss diet instead of a low-fat diet.

A vaccine targeted at CETP alleviates high fat and high cholesterol diet-induced atherosclerosis and non-alcoholic steatohepatitis in rabbit

Low HDL-C levels are associated with atherosclerosis and non-alcoholic steatohepatitis, and increased levels may reduce the risk of these diseases. Inhibition of cholesteryl ester transfer protein (CETP) activity is considered a promising strategy for increasing HDL-C levels. Since CETP is a self-antigen with low immunogenicity, we developed a novel CETP vaccine (Fc-CETP₆) to overcome the low immunogenicity of CETP and for long-term inhibition of CETP activity. The vaccine consists of a rabbit IgG Fc domain for antigen delivery to antigen-presenting cells fused to a linear array of 6 repeats of a CETP epitope to efficiently activate B cells. Rabbits were fed a high fat/cholesterol (HFC) diet to induce atherosclerosis and NASH, and immunized with Fc-CETP₆ vaccine. The Fc-CETP₆ vaccine successfully elicited anti-CETP antibodies and lowered plasma CETP activity. The levels of plasma HDL-C and ApoA-I were higher, and plasma ox-LDL lower, in the Fc-CETP₆-immunized rabbits as compared to the unimmunized HFC diet-fed rabbits. Pathological analyses revealed less lipid accumulation and inflammation in the aorta and liver of the Fc-CETP₆-immunized rabbits. These results show that the Fc-CETP₆ vaccine efficiently elicited antibodies against CETP and reduced susceptibility to both atherosclerosis and steatohepatitis induced by the HFC diet. Our findings suggest that the Fc-CETP₆ vaccine may improve atherosclerosis and NASH and has high potential for clinical use.

Structural features of cholesteryl ester transfer protein: a molecular dynamics simulation study

Cholesteryl ester transfer protein (CETP) mediates the net transfer of cholesteryl esters (CEs) from atheroprotective high-density lipoproteins (HDLs) to atherogenic low-density lipoproteins (LDLs) or very-low-density lipoproteins (VLDLs). Inhibition of CETP raises HDL cholesterol (good cholesterol) levels and reduces LDL cholesterol (bad cholesterol) levels, making it a promising drug target for the prevention and treatment of coronary heart disease. Although the crystal structure of CETP has been determined, the molecular mechanism mediating CEs transfer is still unknown, even the structural features of CETP in a physiological environment remain elusive. We performed molecular dynamics simulations to explore the structural features of CETP in an aqueous solution. Results show that the distal portion flexibility of N-terminal β-barrel domain is considerably greater in solution than in crystal; conversely, the flexibility of helix X is slightly less. During the simulations the distal end of C-terminal β-barrel domain expanded while the hydrophilic surface increasing more than the hydrophobic surface. In addition, a new surface pore was generated in this domain. This surface pore and all cavities in CETP are stable. These results suggest that the formation of a continuous tunnel within CETP by connecting cavities is permitted in solution.

Dietary cholesterol affects plasma lipid levels, the intravascular processing of lipoproteins and reverse cholesterol transport without increasing the risk for heart disease

The associations between dietary cholesterol and heart disease are highly controversial. While epidemiological studies and clinical interventions have shown the lack of correlation between cholesterol intake and cardiovascular disease (CVD) risk, there is still concern among health practitioners and the general population regarding dietary cholesterol. In this review, several clinical studies utilizing cholesterol challenges are analyzed in terms of changes that occur in lipoprotein metabolism resulting from excess consumption of cholesterol. Dietary cholesterol has been shown to increase both LDL and HDL in those individuals who respond to a cholesterol challenge without altering the LDL cholesterol/HDL cholesterol ratio, a key marker of CVD risk. Further, dietary cholesterol has been shown to increase only HDL with no changes in LDL with average cholesterol consumption and during weight loss interventions. Ingestion of cholesterol has also been shown to increase the size of both LDL and HDL particles with the associated implications of a less atherogenic LDL particle as well as more functional HDL in reverse cholesterol transport. Other changes observed in lipoprotein metabolism are a greater number of large LDL and decreases in small LDL subfractions. All this information put together points to specific roles of dietary cholesterol in substantially altering intravascular processing of lipoproteins as well as reverse cholesterol transport.

Lipoprotein Candidate Genes for Multivariate Factors of the Insulin Resistance Syndrome: A Sib-pair Linkage Analysis in Women Twins

The insulin resistance syndrome (IRS) is characterized by a combination of interrelated coronary heart disease risk factors, including low high-density lipoprotein cholesterol (HDLC) levels, obesity and increases in triglyceride (TG), systolic and diastolic blood pressure (BP), small low-density lipoprotein particles (LDL-size), and fasting and postload plasma insulin and glucose. Using factor analysis, we previously identified multivariate factors based on data from women participating in the Kaiser Permanente Women Twins Study: 1) Weight/Fat, 2) Insulin/Glucose, 3) Lipids, and 4) BP. The purpose of this study is to evaluate evidence for genetic linkage between the multivariate factors and candidate genes. Quantitative sib-pair analysis based on the factor scores with markers for 9 candidate genes was carried out based on data from 126 pairs of dizygotic (DZ) women twins from the second exam of the Kaiser Permanente Women Twins study. Suggestive evidence for linkage was found for the Weight/fat factor and the Apo E gene (p= 0.01), and stronger evidence for linkage with the Lipid factor and the cholesterol ester transfer protein (p= 0.002) gene. Therefore, the CETP gene appears to influence covariation in LDL size, TG, and HDL, and may account for a portion of the well-established statistical and metabolic associations observed between these risk factors.

Effects of nasal immunization of multi-target preventive vaccines on atherosclerosis

Previous investigations have demonstrated that anti-inflammatory or lipid-lowering treatments could be useful for alleviating morbidity and mortality of atherosclerotic cardiovascular diseases. However, whether a vaccine designed to target inflammation and lipid simultaneously is more powerful to control the process of atherosclerosis remain to be unknown. Here, a vaccine was designed to target heat shock protein-65(Hsp65) and cholesteryl ester transfer protein (CETP) simultaneously and the effects of nasal immunization of multi-target vaccine on high-cholesterol-diet-driven rabbit atherosclerosis lesions were evaluated. Sera, nasal lavages and lung washes were used to ELISA assay for the analysis of IgG and IgA against Hsp65 and CETP. Sera were also used to the analysis of the avidity of combination of anti-Hsp65 and anti-CETP IgG antibodies with corresponding antigen, cytokines IL-10 and IFN-γ, and lipoproteins. In addition, aortas were harvested for analysis of atherosclerotic lesions. The results showed that lower and lasting specific anti-Hsp65 IgG and high anti-CETP IgG in sera and protective anti-Hsp65 and anti-CETP IgA in nasal cavity and lung were induced, the avidity of combination of anti-Hsp65 and anti-CETP IgG with antigen were higher, and more protective IL-10 and less adverse IFN-γ were produced. In addition, sera TC, and LDL-C were decreased. As a result, the size of aorta atherosclerotic plaques was significantly reduced. We conclude that multifaceted vaccine combining lipid-regulating with anti-inflammation was a potential remedy, especially for atherosclerosis with complicated etiology.

The liver X receptor: control of cellular lipid homeostasis and beyond Implications for drug design

Liver X receptor (LXR) α and β are nuclear receptors that control cellular metabolism. LXRs modulate the expression of genes involved in cholesterol and lipid metabolism in response to changes in cellular cholesterol status. Because of their involvement in cholesterol homeostasis, LXRs have emerged as promising drug targets for anti-atherosclerotic therapies. In rodents, synthetic LXR agonists promote cellular cholesterol efflux, transport and excretion. As a result, the progression of atherosclerosis is halted. However, pharmacological LXR activation also induces hepatic steatosis and promotes the secretion of atherogenic triacylglycerol-rich VLDL particles by the liver, complicating the clinical application of LXR agonists. The more recently emerged roles of LXRs in fat tissue, pituitary and brain may have implications for treatment of obesity and Alzheimer disease. In addition to the improvements in atherosclerosis, LXR activation exerts beneficial effects on glucose control in mouse models of type 2 diabetes. Future therapeutic strategies aiming to exert beneficial effects on cholesterol and glucose homeostasis, while circumventing the undesired effects on hepatic lipid metabolism, should target specific LXR-mediated processes. Therefore, tissue and/or isotype-specific effects of LXR action need to be established. The consequences of combinatorial drug approaches and the identification of the co-regulatory networks involved in the LXR-mediated control of particular genes may contribute to development of novel LXR agonists. Finally, pathway analyses of LXR actions provide tools to evaluate and optimize the effectiveness of novel therapeutic strategies to prevent and/or treat metabolic diseases.

HIV-1 antiretrovirals induce oxidant injury and increase intima-media thickness in an atherogenic mouse model

A growing body of evidence suggests HIV patients are at a greater risk for developing atherosclerosis. However, clinical investigations have generated conflicting results with regard to whether antiretrovirals are independently involved in the development of HIV-associated atherosclerosis. By administering antiretrovirals in an atherogenic mouse model, we determined whether two commonly prescribed antiretrovirals, the protease inhibitor indinavir and the nucleoside reverse transcriptase inhibitor AZT, can induce premature atherosclerosis. C57BL/6 mice were administered an atherogenic diet+/-AZT, indinavir, or AZT plus indinavir for 20 weeks. Aortic intima-media thickness (IMT) and cross-sectional area (CSA) were determined. Compared to controls, treatment with AZT, indinavir or AZT plus indinavir, significantly increased aortic IMT and CSA. This suggests that antiretrovirals can directly exacerbate atherogenesis, in the absence of interaction with a retroviral infection. To elucidate the role of oxidant injury in the drug-induced initiation of atherosclerosis, a separate group of mice were treated for 2 weeks with an atherogenic diet+/-AZT, indinavir or AZT plus indinavir. Aortic reactive oxygen species (ROS) production and glutathione/glutathione disulfide (GSH/GSSG) ratios, as well as plasma levels of 8-isoprostanes (8-iso-PGF(2alpha)) and lipids were determined. At 2 weeks, aortic ROS was increased and GSH/GSSG ratios were decreased in all antiretroviral treatment groups. Plasma 8-iso-PGF(2alpha) was increased in the AZT and AZT plus indinavir-treated groups. At 20 weeks, increased ROS production was maintained for the AZT and indinavir treatment groups, and increased 8-iso-PGF(2alpha) levels remained elevated in the AZT treatment group. Cholesterol levels were moderately elevated in the AZT and AZT plus indinavir-treated groups at 2 but not 20 weeks. Conversely, indinavir treatment increased plasma cholesterol at 20 but not 2 weeks. Thus, though effects on plasma lipid levels occurred, with effects of the individual antiretrovirals variable across the treatment period, there was consistent evidence of oxidant injury across both early and late time points. Together with the known metabolic abnormalities induced by antiretrovirals, drug-induced oxidant production may contribute to the development of antiretroviral-associated atherosclerosis.

Effect of hypoalbuminemia on the increased serum cholesteryl ester transfer protein concentration in children with idiopathic nephrotic syndrome

OBJECTIVES

To examine the alteration of cholesteryl ester transfer protein (CETP) mass with the regression of albumin level in childhood nephrotic syndrome (NS) in order to clarify the effect of albumin on CETP in NS.

DESIGN AND METHODS

Serum concentrations of CETP, kidney parameters and lipid traits were determined in 110 children with idiopathic NS and 150 control subjects. Of the NS patients, 69 children with an active phase formed group 1, and 41 in remission formed group 2.

RESULTS

Group 1 presented severe hypoalbuminemia and hyperlipidemia, while group 2 exhibited marked recovery in both serum albumin level and lipid/lipoprotein profile. CETP concentration was significantly higher in group 1 (7.36+/-2.43 mg/L, compared with controls 3.38+/-1.83 mg/L, P<0.0001), and declined to within normal range in group 2 (2.91+/-1.77 mg/L). CETP concentration had a strong inverse correlation with serum albumin level (r=-0.688, P<0.0001) in NS patients. Furthermore, when multiple linear regression analysis was performed, in which albumin, proteinuria, lipid traits, and prednisone dose were treated as independent variables, albumin was the only variable showing a significant correlation with CETP in the NS patients (R(2)=0.587, beta=-0.475, P<0.0001).

CONCLUSIONS

The results demonstrate that the decreased serum albumin level might be a main determinant of the increased CETP concentration in pediatric NS.

Effect of postprandial lipaemia and Taq 1B polymorphism of the cholesteryl ester transfer protein (CETP) gene on CETP mass, activity, associated lipoproteins and plasma lipids

A large number of studies in recent years have investigated the effects of hyperlipidaemias and diabetes on cholesteryl ester transfer protein (CETP) on neutral lipid transfer activity and plasma lipids. There has been an ongoing debate as to whether CETP is pro- or anti-atherogenic as it provides a mechanism for the transfer of cholesterol from the cardioprotective HDL subfraction to the potentially atherogenic LDL subfraction. This study was designed to investigate whether there was significant variability of CETP mass and activity in a large normolipidaemic population and whether there is an association between CETP and plasma lipoprotein composition. The presence of a known polymorphism of CETP gene (Taq 1B) was investigated to see if there was any association between this polymorphism and CETP mass and activity, and plasma lipids. There was significant (P < 0·0001) increase in CETP mass and activity in plasma postprandially at 6 h. Using multiple stepwise regression analysis there was significant association with fasting CETP mass and activity (β = 0·055; P = 0·002) and triacylglycerol-rich lipoprotein (β = 0·013; P = 0·005) and postprandial CETP mass (β = 0·254; P = 0·007). Repeated-measures analysis showed a strong association between the absence of Taq 1B polymorphism and low CETP mass and elevated HDL- and HDL2-cholesterol and HDL-phospholipid concentrations than did those who were homozygous or heterozygous for the presence of the restriction site.

Human Cholestryl Ester Transfer Protein (TaqIB) Polymorphism among Filipinos with Cardiovascular Risk Factors

AIM

BACKGROUND

HDL-C has emerged as an important independent predictor of cardiovascular disease. The FNRI-HDL and NNHes Study Group in the Philippines reported that there was a high prevalence of low HDL among Filipinos. Most cases of low HDL-C are associated with secondary causes like Metabolic Syndrome. A primary cause of reduced HDL-C such as increase Cholesteryl Ester Transfer Protein activity has been identified.

OBJECTIVES

1. To determine the phenotype and frequency of Cholesteryl Ester Transfer Protein (TaqIB) polymorphism among Filipinos with cardiovascular risk factors. 2. To determine the association of TaqIB polymorphism with HDL-C levels among Filipinos with cardiovascular risk factors.

DESIGN

Cross-sectional Study.

SETTING

University of the Philippines-Philippine General Hospital.

STATISTICAL ANALYSIS

Descriptive statistics, Chi square test and Fisher's correlation test using Stata version 6.

METHODS

Fifty patients were included in this pilot study and were examined with respect to genotype, lipid profiles, blood sugar and other cardiovascular risk factors. Polymerase Chain Reaction (PCR), Restriction Fragment Length Polymorphism (RFLP) and Agarose Gel Electrophoresis techniques were used to determine the CETP TaqIB Polymorphism.

RESULTS

Out of 50 patients, 66% were females and 34% were males with a mean age of 55 y/o and a BMI of 27 kg/m(2). The following risk factors were identified: hypertension (92%), dyslipidemia (88%), obesity (68%), smoking (50%), diabetes mellitus type 2 (18%) and family history of premature CAD (14%). The genotype frequencies of B1B1; B1B2; B2B2 were 40%; 50% 10% respectively. The B1B1 homozygote was associated with lower HDL-C levels (45.35 +/- 8.82 mg/dL) compared to B1B2 (48.96 +/- 10.10 mg/dL) and B2B2 (48.99 +/- 10.13 mg/dL)).

CONCLUSIONS

Cholesteryl Ester Transfer Protein (TaqIB) Polymorphisms exist among Filipinos with cardiovascular risk factors. The frequency of TaqIB polymorphism among Filipinos with cardiovascular risk factors were B1B1 (40%), B1B2 (50%) and B2B2 (10%). B1B1 polymorphism is more common than B2B2 and associated with low HDL-C.

Favourable impact of low-calorie cranberry juice consumption on plasma HDL-cholesterol concentrations in men

A low HDL-cholesterol concentration is an independent risk factor for CVD. Studies have suggested that flavonoid consumption may be cardioprotective, and a favourable impact on circulating HDL-cholesterol concentrations has been suggested to partially explain this association. The aim of the present study was to determine the effect of consuming increasing daily doses of low-calorie cranberry juice cocktail (CJC) on the plasma lipid profile of abdominally obese men. For that purpose, thirty men (mean age 51 (SD 10) years) consumed increasing doses of CJC during three successive periods of 4 weeks (125 ml/d, 250 ml/d, 500 ml/d). Before the study and after each phase, we measured changes in physical and metabolic variables. We noted a significant increase in plasma HDL-cholesterol concentration after the consumption of 250 ml CJC/d (+8.6+/-14.0% v. 0 ml CJC/d; P<0.01), an effect that plateaued during the last phase of the study (500 ml CJC/d: +8.1+/-10.0% v. 0 ml CJC/d; P<0.0001). Multivariate analyses revealed that changes in plasma apo A-I (R(2)=48%, P<0.0001) and triacylglycerol (R(2)=16%, P<0.005) concentrations were the only variables significantly contributing to the variation in plasma HDL-cholesterol concentration noted in response to the intervention. No variation was observed in total as well as in LDL and VLDL cholesterol. The present results show that daily CJC consumption is associated with an increase in plasma HDL-cholesterol concentrations in abdominally obese men. We hypothesise that polyphenolic compounds from cranberries may be responsible for this effect, supporting the notion that the consumption of flavonoid-rich foods can be cardioprotective.

Phospholipid transfer proteins in perspective

Since their discovery and subsequent purification from mammalian tissues more than 30 years ago an impressive number of studies have been carried out to characterize and elucidate the biological functions of phosphatidylcholine transfer protein (PC-TP), phosphatidylinositol transfer protein (PI-TP) and non-specific lipid transfer protein, more commonly known as sterol carrier protein 2 (SCP-2). Here I will present information to show that these soluble, low-molecular weight proteins constitute domain structures in StArR-related lipid transfer (START) proteins (i.e. PC-TP), in retinal degeneration protein, type B (RdgB)-related PI-TPs (e.g. Dm RdgB, Nir2, Nir3) and in peroxisomal beta-oxidation enzyme-related SCP-2 (i.e. 3-oxoacyl-CoA thiolase, also denoted as SCP-X and the 80-kDa D-bifunctional protein). Further I will summarize the most recent studies pertaining to the physiological function of these soluble phospholipid transfer proteins in metazoa.

Effects of diacylglycerol oil on adiposity in obese children: initial communication

Several studies have shown that diacylglycerol (DAG) oil may suppress accumulation of body fat in adults compared to triacylglycerol (TAG) oil. In this study, we investigated the effect of DAG oil as part of dietetic therapy in obese children. The participants were 11 male and female obese children who were under treatment at the outpatient clinic (four boys, seven girls, age: 7-17 years old). Daily-use cooking oil was changed to DAG oil, and the effects on abdominal fat areas, adipocytokines, and serum lipids were investigated. The total and subcutaneous fat areas significantly decreased in the 5th month after ingestion of DAG oil. Leptin was significantly lower than the initial level after ingestion of DAG oil. The ingestion of DAG oil decreased both the abdominal fat area and leptin in obese children, suggesting that DAG oil prevents obesity in children as well as in adults.

Prescribing Aerobic Exercise for the Regulation of Postprandial Lipid Metabolism

Prolonged presence of elevated plasma triglycerides (TGs) during the postprandial period has been suggested to increase the risk for coronary artery disease. Aerobic exercise attenuates postprandial lipaemia and this has generally been described as a short-term effect of the exercise. Effects of exercise on postprandial lipaemia have mostly been investigated, and documented, with large exercise-induced energy expenditures (i.e. 1000 kcal). The exact mechanisms involved in the attenuation of postprandial lipaemia with exercise are not completely understood, but it appears that at least two mechanisms are involved: a decrease in TG secretion by the liver and an increase in plasma TG clearance by the muscle. Changes in the metabolism of other lipids, such as those in high-density lipoprotein cholesterol, have been documented only when the exercise is performed some hours before the fat meal. Although factors such as the physical fitness and percentage body fat of an individual are likely to also be involved, the most important factors determining the magnitude of the attenuation in postprandial lipaemia appear to be the magnitude of the exercise-induced energy expenditure and the intensity of exercise. To date, the evidence suggests that healthy individuals can generally induce favourable changes in postprandial lipaemia with aerobic exercise that: (i) is completed during the period extending from 16 hours before a meal through 1.5 hours after a meal; (ii) is of moderate intensity; and (iii) results in an energy expenditure of approximately 500 kcal (or more).

Modulation of plasma cholesteryl ester transfer protein activity by unsaturated fatty acids in Tunisian type 2 diabetic women

BACKGROUND AND AIM

Type 2 diabetes mellitus is associated with atherosclerosis, which has been, in part, ascribed to abnormalities in the reverse cholesterol transport system. Among the key actors involved in this pathway is cholesteryl ester transfer protein (CETP) which mediates the transfer of cholesteryl esters (CE) from HDL to apoB-containing lipoproteins.

METHODS AND RESULTS

The purpose of this study was to examine CETP activity in 220 patients with type 2 diabetes mellitus (type 2 DM) treated with diet alone or diet and sulphonylurea drugs and to identify the factors that may regulate it in the diabetic state. We also examined the effect of diet on the activity of plasma CETP in a subgroup of type 2 DM women. CETP activity was assessed by measuring plasma-mediated cholesteryl ester transfer (CET) between pooled exogenous HDL and apoB-containing lipoproteins. In 220 patients with type 2 DM, CET was significantly higher in conjunction with higher plasma triglycerides and lower HDL-cholesterol compared to 100 matched healthy controls. Correlation analysis showed that CETP activity was significantly correlated with the HDL-C to apoA1 ratio (r = -0.205, P = 0.003) and to LDL-C to HDL-C ratio in diabetic women (P = 0.010). Furthermore, CETP activity was correlated marginally with total energy intake (P = 0.052) but to a statistically significant extent with the amount of fat consumed daily (P = 0.008). A significant negative correlation was found between plasma CETP activity and MUFA of plasma phospholipids or free PUFA (P = 0.032), especially with omega3-fatty acids (P = 0.001).

CONCLUSION

Our findings indicate that CET is accelerated in patients with type 2 DM and that this may be regulated by dietary fatty acids in the diabetic state.

Maintenance of the LDL cholesterol:HDL cholesterol ratio in an elderly population given a dietary cholesterol challenge

We previously evaluated the responses to dietary cholesterol in children and young adults. In this study, the effects of dietary cholesterol on plasma lipids and LDL atherogenicity were evaluated in 42 elderly subjects (29 postmenopausal women and 13 men > 60 y old). Our exclusion criteria were diabetes, heart disease, and the use of reductase inhibitors. The study followed a randomized crossover design in which subjects were assigned to consume the equivalent of 3 large eggs (EGG) daily or the same amount of a cholesterol-free, fat-free egg substitute (SUB) for a 1-mo period. After a 3-wk washout period, subjects were assigned to the alternate treatment. The concentration of plasma cholesterol after the EGG period varied among subjects. When all subjects were evaluated, there were significant increases in LDL cholesterol (LDL-C) (P < 0.05) and HDL-C (P < 0.001) for both men and women during the EGG period, resulting in no alterations in the LDL-C:HDL-C or the total cholesterol:HDL-C ratios. In addition, the LDL peak diameter was increased during the EGG period for all subjects. In contrast, the measured parameters of LDL oxidation, conjugated diene formation, and LDL lag time did not differ between the EGG and the SUB periods. We conclude from this study that dietary cholesterol provided by eggs does not increase the risk for heart disease in a healthy elderly population.

Molecular Mechanism of the Blockade of Plasma Cholesteryl Ester Transfer Protein by Its Physiological Inhibitor Apolipoprotein CI

Genetically engineered mice demonstrated that apolipoprotein (apo) CI is a potent, physiological inhibitor of plasma cholesteryl ester transfer protein (CETP) activity. The goal of this study was to determine the molecular mechanism of the apoCI-mediated blockade of CETP activity. Kinetic analyses revealed that the inhibitory property of apoCI is independent of the amount of active CETP, but it is tightly dependent on the amount of high density lipoproteins (HDL) in the incubation mixtures. The electrostatic charge of HDL, i.e. the main carrier of apoCI in human plasma, is gradually modified with increasing amounts of apoCI, and the neutralization of apoCI lysine residues by acetylation produces a marked reduction in its inhibitory potential. The inhibitory property of full-length apoCI is shared by its C-terminal alpha-helix with significant electrostratic properties, whereas its N-terminal alpha-helix with no CETP inhibitory property has no effect on HDL electronegativity. Finally, binding experiments demonstrated that apoCI and to a lower extent its C-terminal alpha-helix are able to disrupt CETP-lipoprotein complexes in a concentration-dependent manner. It was concluded that the inhibition of CETP activity by apoCI is in direct link with its specific electrostatic properties, and the apoCI-mediated reduction in the binding properties of lipoproteins results in weaker CETP-HDL interactions and fewer cholesteryl ester transfers.

2005 Dr. Gary J. Becker Young Investigator Award: Periprocedural Oral Administration of the Leflunomide Analogue FK778 Inhibits Neointima Formation in a Double-injury Rat Model of Restenosis

PURPOSE

To test the efficacy of limited oral administration of the new leflunomide analogue FK778 for suppression of neointima proliferation in a double-injury restenosis model in the rat.

MATERIALS AND METHODS

For induction of aortic lesions, silicon cuffs were placed operatively around the infrarenal aortas of Lewis rats. After 21 days, the aortic cuffs were removed and the lesions were dilated with 2-F Fogarty catheters inserted via the left common carotid artery. The novel immunosuppressant FK778 was administered at a dose of 5 mg/kg body weight (group 1) or 15 mg/kg body weight (group 2) in a total of 38 animals. For both doses, three different periinterventional time periods, each with a 5-day course of oral FK778, were defined as follows: (i) days -2 to 2, (ii) days 1-5, and (iii) days 7-11, with six or seven rats in each group. After 3 weeks, intima/media ratios were assessed morphometrically and immunohistochemistry for quantification of intimal alpha-actin expression was performed.

RESULTS

In both dose groups, there was a trend toward inhibition of neointima formation when the 5-day course of FK778 was started before or 1 day after the intervention. However, in the lower-dose group, inhibition of neointima was not statistically significant regardless of the time frame of treatment (groups 1a-c). With the higher dose, suppression of intimal hyperplasia was significant when FK778 was administered between days 1 and 5 after angioplasty (group 2b; P<.01). Expression of alpha-actin in the intima of FK778-treated rats was significantly reduced when the drug was started 2 days before angioplasty in group 1a (P<.05) or 1 day after angioplasty in both dosage groups (group 1b, P<.01; group 2b, P<.05).

CONCLUSION

In the double-injury rat model presented, balloon-mediated proliferation of smooth muscle cells in the intima with consecutive intimal thickening was influenced by FK778 in a dose-dependent manner. However, long-term studies are needed to exclude a delay of vascular healing in this particular model.

Characterization of a New Double-Injury Restenosis Model in the Rat Aorta

PURPOSE

To characterize a new rat model of restenosis for evaluation of local or systemic drug strategies.

METHODS

Arterial lesions were induced by placement of silicone cuffs around the aorta of Lewis rats. After 21 days, the cuffs were removed, and a subgroup of rat aortas was subjected to secondary balloon injury. Remodeling of wall compartments and cell kinetics were assessed morphometrically at 3, 7, 14, 21, and 28 days after the single and double-injury approaches. Immunohistochemistry was used to assess the distribution of macrophages, smooth muscle cells, and proliferating cells within the layers of the arterial wall in the experimental groups versus sham-operated and untreated controls.

RESULTS

After cuff placement, the adventitia initially undergoes significant enlargement, while the media shows a reduction in relative thickness. Accumulation of cells within the adventitia at 3 and 7 days is followed by a marked decline in cell density at 14 days, with simultaneously increasing cell numbers in the intima. At this time, activated macrophages are detected in the adventitia, indicating chronic inflammation. Following cuff placement, mild intimal hyperplasia develops. In the double-injury model, extensive neointimal hyperplasia forms rapidly, with a peak at 14 days.

CONCLUSIONS

This new double-injury model is technically easy, and multiple experiments can be accrued in short periods of time. It provides an additional platform to identify new targets and strategies for the prophylaxis of postangioplasty restenosis.

A review of CETP and its relation to atherosclerosis

Although the atheroprotective role of HDL cholesterol (HDL-c) is well documented, effective therapeutics to selectively increase plasma HDL-c levels are not yet available. Recent progress in unraveling human HDL metabolism has fuelled the development of strategies to decrease the incidence and progression of coronary artery disease (CAD) by raising HDL-c. In this quest for novel drugs, cholesteryl ester transfer protein (CETP) represents a pivotal target. The role of this plasma protein in HDL metabolism is highlighted by the discovery that genetic CETP deficiency is the main cause of high HDL-c levels in Asian populations. The use of CETP inhibitors to effectively increase HDL-c concentration in humans was recently published and data with regard to the effect on human atherosclerosis are expected shortly. This review discusses the potential of CETP inhibitors to protect against atherosclerosis in the context of the current knowledge of CETP function in both rodents and humans.

Lipoprotein Lipase Gene Polymorphism and Lipid Profile in Coronary Artery Disease

Context.—Lipoprotein lipase (LPL) plays a central role in lipid metabolism, hydrolyzing triglyceride in chylomicrons and very-low-density lipoproteins. The PvuII polymorphic variant of LPL gene is common and might affect risk of coronary artery disease (CAD).

Objective.—Our aim was to determine whether LPL– PvuII polymorphism can be considered to be an independent risk factor or a predictor for CAD in Turkish subjects.

Design.—We used polymerase chain reaction and restriction enzyme digestion to determine the distribution of the previously described C→T transition that causes a PvuII polymorphism in intron 6 among healthy blood donors of Turkish origin and among angiographically confirmed CAD patients with comparable ethnic backgrounds.

Results.—For the PvuII genotypes, within the CAD group (n = 80), the +/− genotype was found in 39 individuals (48.8%), whereas 25 (31.3%) carried the +/+ genotype, and 14 (17.5%) carried the −/− genotype. Within the control group (n = 49), the −/− genotype was found in 19 individuals (38.8%), 16 (32.7%) carried the +/− genotype, and 14 (28.6%) carried the +/+ genotype. The genotype frequency distribution was significantly different (P = .049) in the CAD and control study groups. The most frequent genotype among CAD patients was +/−; this genotype was more frequent in patients than in control subjects. However, the −/− genotype was more prevalent in the control group. Lipoprotein lipase–PvuII polymorphism was found to be associated with fasting total cholesterol and low-density lipoprotein cholesterol levels. The +/+ genotype was found to have higher levels of total cholesterol and low-density lipoprotein cholesterol in both the CAD and control groups.

Conclusion.—There was a difference in the distribution of LPL–PvuII genotypes between the healthy subjects and the patients with CAD. Lipoprotein lipase–PvuII polymorphisms were not detected as independent risk factors for CAD in this study group, but had associations with lipid levels.

Lipid transfer protein transports compounds from lipid nanoparticles to plasma lipoproteins

Nanometer-sized lipid emulsion particles with a diameter of 25-50 nm, called Lipid Nano-Sphere (LNS), are expected as a promising drug carrier to show prolonged plasma half-life of an incorporating drug. In terms of successful drug delivery using LNS, a drug should be incorporated into the lipid particles and remain within the particle, not only in the formulation in vitro but also after administration into the systemic blood circulation. In this study, we showed that phospholipids and some water-insoluble molecules also moved from lipid particles to plasma lipoproteins or albumin in serum and plasma half-lives of these compounds did not reflect that of the drug carriers. It was suggested that phospholipid or its derivative were transferred from LNS particles to plasma lipoproteins by lipid transfer proteins (LTP) in the circulation. These phenomena leaded to unsuccessful delivery of the drug with lipid-particulate drug carriers. On the other hand, lipophilic derivatives with cholesterol pro-moiety tested in this study were not released from LNS particles and showed prolonged plasma half-lives. Lipophilicity is known to be an important parameter for incorporating drugs into lipid particles but substrate specificity for LTP seems to be another key to success promising drug design using lipid emulsion particulate delivery system.

Enlargement of high density lipoprotein in mice via liver X receptor activation requires apolipoprotein E and is abolished by cholesteryl ester transfer protein expression

The factors involved in the generation of larger high density lipoprotein (HDL) particles, HDL1 and HDLc, are still not well understood. Administration of a specific synthetic liver X receptor (LXR) agonist, T0901317, in mice resulted in an increase of not only HDL cholesterol but also HDL particle size (Cao, G., Beyer, T. P., Yang, X. P., Schmidt, R. J., Zhang, Y., Bensch, W. R., Kauffman, R. F., Gao, H., Ryan, T. P., Liang, Y., Eacho, P. I., and Jiang, X. C. (2002) J. Biol. Chem. 277, 39561-39565). We have investigated the roles that apoE and CETP may play in this process. We treated apoE-deficient, cholesterol ester transport protein (CETP) transgenic, and wild type mice with various doses of the LXR agonist and monitored their HDL levels. Fast protein liquid chromatography and apolipoprotein analysis revealed that in apoE knockout mouse plasma, there was neither induction of larger HDL formation nor increase of HDL cholesterol, suggesting that apoE is essential for the LXR agonist effects on HDL metabolism. In CETP transgenic mice, CETP expression completely abolished LXR agonist-mediated HDL enlargement and greatly attenuated HDL cholesterol levels. Analysis of HDL particles by electron microscope and nondenaturing gel electrophoresis revealed similar findings. In apoE-deficient mice, LXR agonist also produced a significant increase in very low density lipoprotein/low density lipoprotein cholesterol and apolipoprotein B content. Our studies provide direct evidence that apoE and CETP are intimately involved in the accumulation of the enlarged HDL (HDL1 or HDLc) particles in mice.