Function Of Cholesteryl Ester Transfer Protein Research Articles

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.

Novel role of cholesteryl ester transfer protein (CETP): attenuation of adiposity by enhancing lipolysis and brown adipose tissue activity

ObjectiveThe systemic function of CETP has been well characterized. CETP plasma activity reduces HDL cholesterol and thus increases the risk of atherosclerosis. Here, we investigated whether CETP expression modulate adiposity. MethodsBody adiposity and energy metabolism related assays and gene/protein expression were compared in CETP transgenic and non-transgenic mice and in hamsters treated with CETP neutralizing antibody. ResultsWe found that transgenic mice expressing human CETP present less white adipose tissue mass and lower leptinemia than nontransgenic (NTg) littermates. No differences were found in physical activity, food intake, fat fecal excretion, lipogenesis or exogenous lipid accumulation in adipose depots. Nonetheless, adipose lipolysis rates and whole-body energy expenditure were elevated in CETP mice. In accordance, lipolysis-related gene expression and protein content were increased in visceral and brown adipose tissue (BAT). In addition, we verified increased BAT temperature and oxygen consumption. These results were confirmed in two other animal models: 1) hamsters treated with CETP neutralizing antibody and 2) an independent line of transgenic mice expressing simian CETP. ConclusionsThese findings reveal a novel anti-adipogenic role for CETP.

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Cholesteryl ester transfer protein (CETP) exists as full-length (FL) and exon 9 (E9)-deleted isoforms. The function of E9-deleted CETP is poorly understood. Here, we investigated the role of E9-deleted CETP in regulating the secretion of FL-CETP by cells and explored its possible role in intracellular lipid metabolism. CETP overexpression in cells that naturally express CETP confirmed that E9-deleted CETP is not secreted, and showed that cellular FL- and E9-deleted CETP form an isolatable complex. Coexpression of CETP isoforms lowered cellular levels of both proteins and impaired FL-CETP secretion. These effects were due to reduced synthesis of both isoforms; however, the predominate consequence of FL- and E9-deleted CETP coexpression is impaired FL-CETP synthesis. We reported previously that reducing both CETP isoforms or overexpressing FL-CETP impairs cellular triglyceride (TG) storage. To investigate this further, E9-deleted CETP was expressed in SW872 cells that naturally synthesize CETP and in mouse 3T3-L1 cells that do not. E9-deleted CETP overexpression stimulated SW872 triglyceride synthesis and increased stored TG 2-fold. Expression of E9-deleted CETP in mouse 3T3-L1 cells produced a similar lipid phenotype. In vitro, FL-CETP promotes the transfer of TG from ER-enriched membranes to lipid droplets. E9-deleted CETP also promoted this transfer, although less effectively, and it inhibited the transfer driven by FL-CETP. We conclude that FL- and E9-deleted CETP isoforms interact to mutually decrease their intracellular levels and impair FL-CETP secretion by reducing CETP biosynthesis. E9-deleted CETP, like FL-CETP, alters cellular TG metabolism and storage but in a contrary manner.

Role of Bound Phospholipids in Structural Stability and Functionality of Cholesteryl Ester Transfer Protein

Cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters (CEs) and triglycerides (TG) between high density lipoproteins (HDL) and low density lipoproteins (LDL).1 Previous animal model studies have shown that blocking the function of CETP can increase the level of HDL in blood plasma and suppress the risk of cardiovascular disease (CVD). Hence, understanding the mechanism by which CETP transfers the neutral lipids between lipoproteins are of immense importance. In a recent report (Chirasani et al., J. Biol. Chem. 2016), we have shown that the bound CEs intraconvert between bent and linear conformations as a consequence of high degree of conformational flexibility of the protein.2 In this study we explored the importance of bound phospholipids (PLs) in maintaining the structural integrity of CETP and its role in lipid transfer. Results from all atom molecular dynamic simulation show that N-terminal bound PL imparts fluctuations and C-terminal bound PL provides stability to the CETP structure. They are also found to play a crucial role in CE transfer from HDL to LDL. These observations are confirmed by restraining both PLs, which showed conformational rigidity in CE. The detailed insights obtained here on the role of PLs in CETP could help in devising methods to prevent the CETPs function in countering atherosclerosis.

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.

Structural Plasticity of Cholesteryl Ester Transfer Protein Assists the Lipid Transfer Activity

Cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters (CEs) and triglycerides between different lipoproteins. Recent studies have shown that blocking the function of CETP can increase the level of HDL cholesterol in blood plasma and suppress the risk of cardiovascular disease. Hence, understanding the structure, dynamics, and mechanism by which CETP transfers the neutral lipids has received tremendous attention in last decade. Although the recent crystal structure has provided direct evidence of the existence of strongly bound CEs in the CETP core, very little is known about the mechanism of CE/triglyceride transfer by CETP. In this study, we explore the large scale dynamics of CETP by means of multimicrosecond molecular dynamics simulations and normal mode analysis, which provided a wealth of detailed information about the lipid transfer mechanism of CETP. Results show that the bound CEs intraconvert between bent and linear conformations in the CETP core tunnel as a consequence of the high degree of conformational flexibility of the protein. During the conformational switching, there occurred a significant reduction in hydrophobic contacts between the CEs and CETP, and a continuous tunnel traversing across the CETP long axis appeared spontaneously. Thus, our results support the recently proposed "tunnel mechanism" of CETP from cryo-EM studies for the transfer of neutral lipids between different lipoproteins. The detailed understanding obtained here could help in devising methods to prevent CETP function as a cardiovascular disease therapeutic.

Is Cholesteryl Ester Transfer Protein Inhibition an Effective Strategy to Reduce Cardiovascular Risk? CETP Inhibition as a Strategy to Reduce Cardiovascular Risk: The Pro Case.

There is much current interest in the potential of cholesteryl ester transfer protein (CETP) inhibition as a strategy to reduce the risk of developing atherosclerotic cardiovascular disease (ASCVD). There is also great uncertainty. On the one hand, there is a large body of circumstantial evidence suggesting that inhibition of CETP is antiatherogenic and will protect against the development of ASCVD. On the other hand, 2 human clinical outcome trials with CETP inhibitors have failed. However, as outlined below, because of major problems with these 2 human clinical trials, the hypothesis has not been refuted and it remains unknown whether or not CETP inhibition reduces ASCVD risk. This is something we really need to know. The answer will emerge with the results of 2 large ongoing clinical outcome trials designed to test the hypothesis that CETP inhibition reduces ASCVD risk. Response by Hovingh et al on p 432 There is a possibility that the current level of uncertainty about CETP inhibition may impact adversely on the retention of participants in these ongoing clinical trials and thus reduce their power to provide an answer. We believe that everything possible must be done to ensure that the ongoing clinical outcome trials are allowed to proceed to completion with minimal dropout to provide confidence in the result. The purpose of this article is to summarize the large body of evidence showing that CETP inhibition is protective and that continuation of the ongoing trials to completion is essential. To present this evidence, this article addresses a series of fundamental questions. 1. What exactly is the function of CETP? 2. What is the rationale for inhibiting CETP as a strategy to reduce ASCVD risk? 3. What is the relationship between CETP and atherosclerosis in animal studies? 4. What is the relationship between the genetics and activity of CETP and atherosclerosis …

CETP inhibitors and cardiovascular disease: Time to think again

Inhibition of cholesteryl ester transfer protein (CETP) lowers plasma low-density lipoprotein cholesterol concentration and raises high-density lipoprotein (HDL) cholesterol, suggesting it might prevent cardiovascular disease (CVD). From the outset, however, the concept has been controversial owing to uncertainty about its effects on HDL function and reverse cholesterol transport (RCT). Although there has long been good evidence that CETP inhibition reduces atherosclerosis in rabbits, the first information on CETP as a CVD risk factor in a prospectively followed cohort was not published until after the first Phase 3 trial of a CETP inhibitor had begun. The worrying finding that CVD incidence was related inversely to plasma CETP has since been reproduced in each of five further prospective cohort studies. Similar results were obtained in subjects on or off statin therapy, for first and second CVD events, and for mortality as well as CVD morbidity. Additionally, two recent studies have found alleles of the CETP gene that lower hepatic CETP secretion to be associated with an increased risk of myocardial infarction. Meanwhile, CETP gene transfer in mice was found to increase RCT from peripheral macrophages in vivo, and human plasma with high CETP activity was shown to have a greater capacity to remove cholesterol from cultured cells than plasma with low activity. This mounting evidence for a protective function of CETP has been given remarkably little attention, and indeed was not mentioned in several recent reviews. It appears to show that CETP inhibition does not test the HDL hypothesis as originally hoped, and raises a pressing ethical issue regarding two Phase 3 trials of inhibitors, involving more than forty thousand subjects, which are currently in progress. As the weight of evidence now clearly supports an adverse effect of CETP inhibition on CVD, an urgent review is needed to determine if these trials should be discontinued.

CETP inhibitors and cardiovascular disease: Time to think again

Inhibition of cholesteryl ester transfer protein (CETP) lowers plasma low-density lipoprotein cholesterol concentration and raises high-density lipoprotein (HDL) cholesterol, suggesting it might prevent cardiovascular disease (CVD). From the outset, however, the concept has been controversial owing to uncertainty about its effects on HDL function and reverse cholesterol transport (RCT). Although there has long been good evidence that CETP inhibition reduces atherosclerosis in rabbits, the first information on CETP as a CVD risk factor in a prospectively followed cohort was not published until after the first Phase 3 trial of a CETP inhibitor had begun. The worrying finding that CVD incidence was related inversely to plasma CETP has since been reproduced in each of five further prospective cohort studies. Similar results were obtained in subjects on or off statin therapy, for first and second CVD events, and for mortality as well as CVD morbidity. Additionally, two recent studies have found alleles of the CETP gene that lower hepatic CETP secretion to be associated with an increased risk of myocardial infarction. Meanwhile, CETP gene transfer in mice was found to increase RCT from peripheral macrophages in vivo , and human plasma with high CETP activity was shown to have a greater capacity to remove cholesterol from cultured cells than plasma with low activity. This mounting evidence for a protective function of CETP has been given remarkably little attention, and indeed was not mentioned in several recent reviews.  It appears to show that CETP inhibition does not test the HDL hypothesis as originally hoped, and raises a pressing ethical issue regarding two Phase 3 trials of inhibitors, involving more than forty thousand subjects, which are currently in progress. As the weight of evidence now clearly supports an adverse effect of CETP inhibition on CVD, an urgent review is needed to determine if these trials should be discontinued.

CETP inhibitors and cardiovascular disease: Time to think again.

Inhibition of cholesteryl ester transfer protein (CETP) lowers plasma low-density lipoprotein cholesterol concentration and raises high-density lipoprotein (HDL) cholesterol, suggesting it might prevent cardiovascular disease (CVD). From the outset, however, the concept has been controversial owing to uncertainty about its effects on HDL function and reverse cholesterol transport (RCT). Although there has long been good evidence that CETP inhibition reduces atherosclerosis in rabbits, the first information on CETP as a CVD risk factor in a prospectively followed cohort was not published until after the first Phase 3 trial of a CETP inhibitor had begun. The worrying finding that CVD incidence was related inversely to plasma CETP has since been reproduced in each of five further prospective cohort studies. Similar results were obtained in subjects on or off statin therapy, for first and second CVD events, and for mortality as well as CVD morbidity. Additionally, two recent studies have found alleles of the CETP gene that lower hepatic CETP secretion to be associated with an increased risk of myocardial infarction. Meanwhile, CETP gene transfer in mice was found to increase RCT from peripheral macrophages in vivo, and human plasma with high CETP activity was shown to have a greater capacity to remove cholesterol from cultured cells than plasma with low activity. This mounting evidence for a protective function of CETP has been given remarkably little attention, and indeed was not mentioned in several recent reviews. It appears to show that CETP inhibition does not test the HDL hypothesis as originally hoped, and raises a pressing ethical issue regarding two Phase 3 trials of inhibitors, involving more than forty thousand subjects, which are currently in progress. As the weight of evidence now clearly supports an adverse effect of CETP inhibition on CVD, an urgent review is needed to determine if these trials should be discontinued.

Multidimensional profiling of plasma lipoproteins by size exclusion chromatography followed by reverse-phase protein arrays

The composition of lipoproteins and the association of proteins with various particles are of much interest in the context of cardiovascular disease. Here, we describe a technique for the multidimensional analysis of lipoproteins and their associated apolipoproteins. Plasma is separated by size exclusion chromatography (SEC), and fractions are analyzed by reverse-phase arrays. SEC fractions are spotted on nitrocellulose slides and incubated with different antibodies against individual apolipoproteins or antibodies against various apolipoproteins. In this way, tens of analytes can be measured simultaneously in 100 μl of plasma from a single SEC separation. This methodology is particularly suited to simultaneous analysis of multiple proteins that may change their distribution to lipoproteins or alter their conformation, depending on factors that influence circulating lipoprotein size or composition. We observed changes in the distribution of exchangeable apolipoproteins following addition of recombinant apolipoproteins or interaction with exogenous compounds. While the cholesteryl ester transfer protein (CETP)-dependent formation of pre-β-HDL was inhibited by the CETP inhibitors torcetrapib and anacetrapib, it was not reduced by the CETP modulator dalcetrapib. This finding was elucidated using this technique.

Structure and Function of Cholesteryl Ester Transfer Protein in the Tree Shrew

Cholesteryl ester transfer protein (CETP) plays an important role in reverse cholesterol transport (RCT). To study on the structure and function of CETP in the tree shrew, a kind of animal resistant to atherosclerosis, we completed the cloning of the full-length tree-shrew CETP cDNA sequence based on the reported partial sequence. The full-length cDNA of tree shrew CETP was 1,704bp and the deduced protein of the cDNA showed a sequence identity of 81, 80 and 74%, respectively, with the human, monkey and rabbit CETP. The level of CETP mRNA in the liver was much more abundant than that in the other tissues. A mutant protein with a substitution of Asn at position 110 by Gln was found to possess an impaired secretion property compared with the wild-type tree shrew CETP. The mutant proteins, respectively, with a substitution of Pro at position 344 by Ser and a substitution of Gln at position 452 by Arg displayed similar secretion ability, but a decreased cholesteryl ester transfer capability compared with the wild type (48 and 26% lower, respectively). These findings demonstrate that liver is the main tissue synthesizing CETP in the tree shrew. Asn at position 110 plays an important role in the secretion of tree shrew CETP. The residues at position 344 and 452 play essential roles in cholesteryl ester transferring process.

Counterpoint: Cholesteryl Ester Transfer Protein Antagonism by Drugs—A Poor Choice

The recent failure to prevent coronary disease with torcetrapib, a major inhibitor of the cholesteryl ester transfer protein (CETP)2 system, indicated that this therapeutic approach is disputable. Evaluation of prior knowledge confirms that the rationale of CETP inhibition appears to be based on incorrect physiological assumptions and that the interpretation of the torcetrapib trials may be flawed because of overinterpretation or some ancillary findings, as well as a lack of consideration of some potentially very negative clinical observations. In the present report we consider the major genetic and clinical aspects of the CETP system, as well as the reasons why CETP inhibition has not proved to be a winning strategy. Reverse cholesterol transport, a classic function of HDL in humans and higher species, is handled by a transfer/exchange system regulated by CETP, which was first described 30 years ago. The major function of CETP (molecular weight 74 kDa) is the exchange of cholesterol esters with triglycerides present, particularly in VLDLs,leading to a triglyceride-enriched HDL. Triglyceride catabolism in the newly formed HDL then leads back to a “small, cholesterol ester poor HDL” capable of effective cholesterol removal (1). CETP mutations may cause a reduced effectiveness of the transfer/exchange process, eventually leading to large amounts of cholesterol esters in HDL (2). Clinical evaluation of individuals with inactivating mutations and extremely increased HDL cholesterol (HDL-C) concentrations has led to conflicting findings. Major support came from genetic studies of Japanese communities, in which a large number of citizens displayed dramatically increased HDL-C concentrations but an apparently reduced incidence of coronary heart disease (2). A more detailed examination, however, showed a paradoxically enhanced risk in many individuals with the more marked increases (3). In the Western world, epidemiologic data appear to indicate ineffective protection against cardiovascular disease by HDL-C increases due to CETP …

Co-administration of a CpG adjuvant (VaxImmuneTM, CPG 7909) with CETP vaccines increased immunogenicity in rabbits and mice

Cholesteryl ester transfer protein (CETP) is a plasma glycoprotein that facilitates the transfer of neutral lipids and phospholipids between lipoproteins and contributes to the regulation of the plasma concentration of high density lipoprotein cholesterol (HDL-C). Vaccines have been developed that elicit antibodies that bind to and reduce the lipid transfer function of CETP as a way to increase the plasma concentration of HDL-C and prevent or treat atherosclerosis. This study assessed the immunogenicity of two vaccine peptides. The first, CETi-1, is a dimerized synthetic peptide, including residues 461-476 of human CETP and residues 830-843 of tetanus toxoid, TT(830-843). The second, PADRE-CETP, is a monomeric peptide, in which a PADRE T cell epitope (aK-Cha-VAAWTLKAa) replaces the TT(830-843) T cell epitope of CETi-1. Both peptides were formulated with aluminum-containing adjuvants (Alhydrogel®), and tested in mice and rabbits with or without the co-administration of the investigational TLR9 agonist VaxImmuneTM (CPG 7909). In both mice and rabbits, the vaccine peptide utilizing the PADRE T cell epitope elicited stronger anti-CETP antibody responses than the CETi-1 vaccine. Also, co-administration of VaxImmune enhanced the anti-CETP antibody responses to both vaccines. Isotype analysis of the murine anti-CETP antibody response to both vaccines demonstrated a switch from IgG1 to IgG2a upon co-administration of VaxImmune. We conclude that 1) the PADRE T cell epitope is more potent than the TT(830-843) epitope in providing help for the anti-CETP antibody response; and 2) co-administration of VaxImmune with either vaccine increased immunogenicity as measured by antibody response.

Cholesteryl Ester Transfer Protein and Phospholipid Transfer Protein Have Nonoverlapping Functions in Vivo

Plasma phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) are homologous molecules that mediate neutral lipid and phospholipid exchange between plasma lipoproteins. Biochemical experiments suggest that only CETP can transfer neutral lipids but that there could be overlap in the ability of PLTP and CETP to transfer or exchange phospholipids. Recently developed PLTP gene knock-out (PLTP0) mice have complete deficiency of plasma phospholipid transfer activity and markedly reduced high density lipoprotein (HDL) levels. To see whether CETP can compensate for PLTP deficiency in vivo, we bred the CETP transgene (CETPTg) into the PLTP0 background. Using an in vivo assay to measure the transfer of [(3)H]PC from VLDL into HDL or an in vitro assay that determined [(3)H]PC transfer from vesicles into HDL, we could detect no phospholipid transfer activity in either PLTP0 or CETPTg/PLTP0 mice. On a chow diet, HDL-PL, HDL-CE, and HDL-apolipoprotein AI in CETPTg/PLTP0 mice were significantly lower than in PLTP0 mice (45 +/- 7 versus 79 +/- 9 mg/dl; 9 +/- 2 versus 16 +/- 5 mg/dl; and 51 +/- 6 versus 100 +/- 9, arbitrary units, respectively). Similar results were obtained on a high fat, high cholesterol diet. These results indicate 1) that there is no redundancy in function of PLTP and CETP in vivo and 2) that the combination of the CETP transgene with PLTP deficiency results in an additive lowering of HDL levels, suggesting that the phenotype of a human PLTP deficiency state would include reduced HDL levels.

Remodelling of lipoproteins in transgenic mice expressing human cholesteryl ester transfer protein.

Cholesteryl ester transfer protein (CETP) facilitates the transfer of reciprocal exchange of neutral lipids between lipoproteins. To better understand the function of CETP and its role in atherogenic pathways, transgenic mice which express human CETP were generated. The transgene encoding human CETP was under the control of the mouse alpha-fetoprotein enhancer and mouse albumin gene promoter and was expressed exclusively in the liver. The level of human CETP activity in transgenic mouse plasmas was found to be 1- to 5-fold greater than in normolipidemic human plasma. Human CETP induced an approx. 30 and 40% reduction of HDL cholesterol levels in plasma from female and male transgenic mice, respectively, when compared to controls. In addition, multiple alterations in mouse lipoprotein composition were observed in the transgenic mice. Diminished HDL cholesterol levels and disappearance of the apo E-rich HDL1 moiety account for the dramatic reduction in plasma cholesterol. The decrease in HDL cholesterol was accompanied by a marked reduction in HDL particle size and apo A-I content. The cholesterol content and the size of LDL particles increased, but only modestly, in transgenic mouse plasma. In conclusion, human CETP induces a significant remodelling of mouse lipoproteins which results in dramatic reduction in plasma cholesterol levels.

Mammalian adipose tissue and muscle are major sources of lipid transfer protein mRNA

The plasma cholesteryl ester transfer protein (CETP) catalyzes the transfer of cholesteryl esters from high density lipoproteins (HDL) to triglyceride-rich lipoproteins and plays a major role in the catabolism of HDL. Lipoprotein lipase (LPL) is the rate-limiting enzyme for hydrolysis of circulating triglyceride and is involved in HDL formation. We show that tissues containing LPL are major sources of CETP mRNA in several mammalian species, including some with low cholesteryl ester transfer activity in plasma. In hamsters, adipose tissue and heart were found to be the richest sources of both CETP and LPL mRNA; in situ hybridization studies showed that the same cell types (i.e. adipocytes or myocytes) contained CETP and LPL mRNA in these tissues. Isolated adipocytes synthesized active CETP. Dietary studies revealed a complex pattern of response of CETP mRNA levels in different tissues, which showed partial similarity to the changes in LPL mRNA abundance. However, high cholesterol diets resulted in increased CETP mRNA abundance in adipose tissue, heart, and skeletal muscle, without equivalent changes in LPL mRNA. Plasma HDL cholesteryl ester levels showed strong inverse correlations with CETP mRNA abundance in adipose tissue. The results suggest a conserved function of CETP in adipose tissue and heart, such as a co-ordinate action with LPL to enhance HDL turnover. Although there is considerable overlap in the tissue- and cell-specific pattern of CETP and LPL gene expression, dietary studies revealed only limited parallelism in response at the mRNA level. The increase in CETP mRNA in peripheral tissues in response to increased dietary cholesterol suggests that local induction of CETP synthesis may help to recycle cholesterol deposited in these tissues during lipolysis of dietary lipoproteins.

Monoclonal antibody inhibition of cholesteryl ester transfer protein activity in the rabbit. Effects on lipoprotein composition and high density lipoprotein cholesteryl ester metabolism.

Cholesteryl ester transfer protein (CETP) promotes in vitro transfer of cholesteryl ester (CE) and triglyceride (TG) between lipoproteins. We studied the function of CETP in vivo in rabbit lipoprotein metabolism using a neutralizing monoclonal antibody (MAb, TP1) to CETP. Rabbits were injected with TP1 (n = 8), or irrelevant MAb or saline (control, n = 8), resulting in an initial 71% inhibition of CETP, which fell to 45% after 48 h. HDL CE rose in the inhibited animals, reaching levels that doubled initial and control values at 48 h (P less than 0.001). HDL TG fell reciprocally, but HDL protein did not change, suggesting a CE for TG exchange. VLDL CE/TG decreased. Rabbits were also given [3H]cholesteryl ether HDL (a CE analogue). CETP inhibition delayed the initial clearance of radioactivity from HDL (control 6.8 vs. TP1 4.1 pools/d) and plasma (7.8 vs. 5.2 pools/d). We conclude that CETP plays a quantitatively important role in HDL CE catabolism in the rabbit, promoting the exchange of TG for CE and the clearance of CE from plasma.