Increasing High-Density Lipoprotein Cholesterol in Dyslipidemia by Cholesteryl Ester Transfer Protein Inhibition
http://www.100md.com
循环学杂志 2005年第4期
the Cardiology Division, Cedars-Sinai Medical Center, Los Angeles, Calif.
Abstract
Reduced HDL cholesterol may be a risk factor comparable in importance to increased LDL cholesterol. Interventions that raise HDL are antiatherosclerotic, presumably through acceleration of reverse cholesterol transport and by antioxidant and antiinflammatory effects. In the hypercholesterolemic rabbit, HDL levels can be increased by >50% by inhibition of cholesteryl ester transfer protein (CETP), a molecule that plays a central role in HDL metabolism. This HDL-raising effect is antiatherosclerotic in moderately severe hyperlipidemia but appears to be ineffective in the presence of severe hypertriglyceridemia. In humans, mutations resulting in CETP inhibition have been associated with both reduced and increased risk of atherosclerosis. Proposed explanations for these apparently disparate observations are that the antiatherosclerotic effect of CETP inhibition varies with either the metabolic milieu or the degree of CETP inhibition. We now have pharmacological inhibitors of CETP that are capable of increasing HDL by as much as 50% to 100% in humans. The importance of this development is that reduced HDL is a risk factor independent of LDL and that these new agents alter HDL by a magnitude comparable to that of statins on LDL. Clinical trials, now beginning, will need to identify the patient subsets in which CETP inhibition may be more or less effective.
Key Words: atherosclerosis ; cholesterol ; lipids ; metabolism ; statins
Introduction
Although lipid-lowering therapies now have the capability of reducing LDL cholesterol to levels recommended by the National Cholesterol Education Program (NCEP) guidelines in as many as 90% of treated patients,1 the rate of cardiovascular events is reduced by only 20% to 35% in large, randomized trials. These data suggest that the LDL target set by NCEP guidelines may be too high.1–5 Indeed, among patients with acute myocardial infarction, 15% have LDL levels <100 mg/dL on presentation.
A complementary hypothesis is that there is a finite limit to the benefit of LDL lowering and that other non-LDL lipid risk factors must be managed for optimal outcomes. Indeed, epidemiological studies suggest that low HDL cholesterol may be a risk factor comparable in importance to high LDL and that the 2 risk factors are independent (Figure 1).6,7 Although the mechanism by which HDL reduces the development of atherosclerosis has not been defined with certainty, acceleration of reverse cholesterol transport, antioxidant activity, and antiinflammatory action are likely to play central roles.8–10
In contrast to the ability of potent statins to reduce the level of LDL by >50%, however, no currently approved therapy increases HDL by a comparable magnitude. The most potent, currently available HDL-raising therapy is nicotinic acid. This therapy also has a multitude of other antiatherosclerotic effects on the levels of LDL and triglycerides, lipid oxidation, and endothelial function.11 Combination therapy with a statin has been reported to increase HDL levels by 30%12 and to decrease cardiac events.13
Recent studies in the animal laboratory have demonstrated that inhibition of cholesteryl ester transfer protein (CETP), a molecule that plays a central role in HDL metabolism, can raise HDL levels by as much as 50%. Initial testing of pharmacological CETP inhibitors in the hypercholesterolemic rabbit model of atherosclerosis has suggested that this effect could substantially alter the course of atherogenesis. In this article, we will critically analyze these data as clinical trials of this potentially important therapeutic strategy for prevention of atherosclerosis begin.
Raising HDL: Three Limitations Not Recognized by Clinical HDL Measurements
Before analyzing the potential of any new HDL-raising therapy, we must recognize that the traditional HDL blood level has at least 3 limitations either as an index of risk or as a criterion for clinical decision making. The serum HDL level does not assess its functional properties. HDL has both proinflammatory and antiinflammatory properties, both in vitro and in vivo.14–16 Ansell et al17 studied 2 groups of patients. The first group included high-risk, normolipidemic patients studied before and after statin therapy. Despite normal HDL cholesterol levels, the HDL of these patients was found to be proinflammatory compared with age- and sex-matched healthy controls who had antiinflammatory HDL. Statin therapy induced a significant improvement in the proinflammatory HDL, although it remained proinflammatory. In a second group of patients with documented coronary heart disease selected for high HDL (average HDL 95 mg/dL), proinflammatory HDL was found, compared with healthy age- and sex-matched controls who had antiinflammatory HDL. Even within a given individual, HDL may become transiently pro-oxidant in the presence of systemic infection. A second limitation is that the HDL blood level does not necessarily reveal the kinetics of HDL metabolism. For example, subjects with the apoA1 Milano mutation have very low HDL cholesterol levels.18 These HDL molecules, however, have very high fractional catabolic rates, which result in the antiatherosclerotic effect of an accelerated return of cholesterol ester to the liver. Conversely, in some CETP mutations with genetically high HDL and low LDL values, the increased HDL is represented by a large, apoE-enriched particle that is a weak promoter of cholesterol efflux, and the LDL particle reacts poorly with the LDL receptor. As a consequence, atherosclerosis is increased despite an apparently "favorable" effect of the mutation on the lipid profile.19 Finally, the subfractions of HDL generated by CETP inhibition20 may have different effects on inhibition of atherogenesis. For instance, HDL2 is typically a potent antiatherosclerotic molecule, whereas the smaller, denser HDL3 subfraction may have less effect. Similarly, the composition of HDL particles may influence their functional properties. Two major apoAI-containing particles exist: LpA-I, which contains only apoA-I, and LpA-I+A-II, which contains both apoA-I and apoA-II. Because apoA-I is antiatherogenic whereas apoA-II can be proatherogenic (based on studies in transgenic mice), LpA-1 particles may be more antiatherogenic than LpA-I+A-II–containing particles. It has been shown that the majority of LpA-I has the same density and charge as HDL2, whereas the majority of LpA-I+A-II has the same density and charge as HDL3. Thus, the apparent benefit that might be inferred from a therapy that increases HDL, eg, CETP inhibition, must be tempered by these potential limitations.
Historical Perspective: The Epidemiology and Biochemistry of CETP
Some years ago, a mutation in the CETP gene was discovered in the Japanese. This mutation was accompanied by a substantial increase in HDL. Because HDL regulates reverse cholesterol transport and has antioxidant, antithrombotic, and antiinflammatory properties and the prevalence of atherosclerotic disease is low in Japanese, epidemiological studies were undertaken to define the prevalence of the mutation. These studies suggested that the mutation occurred in 11% of the Japanese population and that affected individuals were resistant to atherosclerosis.21,22
During the ensuing years, at least 13 different mutations in the coding region of the CETP gene have been identified. These mutations remain particularly prevalent in the Japanese. In some regions of Japan, the incidence is strikingly high. For instance, as many as 27% of people in the northernmost region, in the environs of Akita, have a CETP gene mutation.23 Homozygotes have up to 4-fold increases in HDL, with substantial increases in apoA-I and apoA-II and as much as a 40% reduction in LDL cholesterol and apoB.24
These epidemiological data triggered interest in the biochemical characteristics of CETP. Detailed analysis of CETP metabolism, beyond the scope of this article, is the subject of several excellent recent reviews of reverse cholesterol transport.25,26 In brief, CETP is a plasma glycoprotein manufactured in the liver. It circulates in the blood, bound predominantly to HDL. Two principal actions of CETP have been identified. The primary action of CETP is to mediate the transfer of cholesteryl esters from HDL to VLDL and LDL in exchange for triglyceride (Figure 2). 27–30 CETP also promotes the transformation of HDL2 to HDL 3, an action that could promote reverse cholesterol transport. CETP inhibition, on the other hand, results in an increase in HDL by markedly delaying catabolism of apoA-I and A-II.31 This action also can increase reverse cholesterol transport. This overlap of the potential effects of CETP and CETP inhibition has served to confound an understanding of potential therapeutic mechanisms in atherosclerosis.25,26,32
For more information about the following terms, which are not mentioned in the text of the present article, see von Eckardstein et al,27 Borggreve et al,28 Ma et al,29 and Cilingiroglu and Ballantyne.30 ABC A-1: adenosine triphosphate binding cassette, the initiator of cholesterol efflux from the cell membrane. SR-BI: scavenger receptor class B-1, the receptor responsible for uptake of cholesterol ester from the HDL particle when it arrives in the liver. LCAT: lecithin cholesterol acyl transferase; the enzyme responsible for esterifying cholesterol after it is carried from the cell membrane. HL: hepatic lipase, which hydrolyzes HDL triglyceride and phospholipids remodeling larger HDL particles to smaller HDL particles. The smaller HDL particles are at greater risk of renal catabolism. EL: endothelial lipase, which like HL remodels HDL to smaller particles. LPL: lipoprotein lipase, which contributes to HDL formation by generating phospholipids on apoB-containing lipoproteins that are then transferred to HDL. Secretory phospholipase A2: a lipase that remodels HDL to smaller particles.
The uncertainty about the potential therapeutic value of CETP inhibition was amplified by subsequent epidemiological studies. Although initially CETP mutations were thought to be atheroprotective, this has not proven to be universally true. Reports of both an increased33,34 and a decreased35 or even no36 effect on the prevalence of coronary artery disease in patients with CETP deficiency have appeared in the literature.
Subgroup analyses of the epidemiological studies suggested that the level of HDL and triglyceride might influence the relation between CETP mutations and atherosclerosis. Thus, Moriyama et al37 found that in CETP-deficient individuals with HDL >80 mg/dL, the prevalence of coronary disease was reduced to a level comparable to that of individuals with elevated HDL and no CETP deficiency. This finding is consistent with that of the Honolulu Heart Study,38,39 in which CETP-deficient individuals with HDL >60 mg/dL also had a low prevalence of coronary artery disease. On the other hand, individuals with CETP deficiency and an HDL <60 mg/dL or with triglyceride >165 mg/dL appeared to have an increased incidence of coronary heart disease. This pattern of increased cardiac events in CETP-deficient patients without markedly elevated HDL and/or with high triglyceride also has been noted in hyperlipidemic Finns40 and in patients undergoing renal dialysis.41 Thus, some investigators have speculated that although the CETP-deficient genotype may be atheroprotective in some, it can also confer an increase in coronary risk when associated with minimal to modest increases in HDL or elevated triglyceride levels.
Because both biochemical and epidemiological data suggest that reduced circulating CETP could, in principle, have both proatherogenic and antiatherogenic effects, study in animal models has seemed to be an essential step to understanding the potential therapeutic value of CETP inhibition.
Animal Models: Is CETP Proatherogenic;
Analysis of studies in the animal model, however, is potentially confounded by a different set of biological variables. Animal species exhibit major differences in CETP expression and in the mechanisms used for reverse cholesterol transport. Mice lack CETP, and thus, reverse cholesterol transport in mice does not involve this protein. In contrast, rabbits have high CETP levels. Human CETP activity is intermediate among the animal species.42 Thus, the mouse model has been used to study overexpression of CETP, whereas rabbits have been used in the study of CETP inhibition.
Mice transduced with the human CETP gene exhibit a dose-related decrease in HDL, accompanied by an increase in LDL and VLDL.43 Plump et al44 transduced atherosclerosis-prone, apoE-knockout mice with human CETP and apoA-I transgenes, thereby inducing plasma CETP levels to rise to 5 to 10 times that of healthy normal humans. This increase in CETP was associated with a 76% reduction in HDL cholesterol. In further studies, the atherosclerosis-prone, LDL receptor–knockout mouse was transduced with the human CETP transgene. At 3 months, the mean lesion area was increased by 1.8-fold compared with controls. Other investigators transduced mice with the simian CETP gene in atherosclerosis-prone mice. Similar to the human CETP gene transduction, the formation of fatty streaks increased dramatically.45 Taken together, these transgenic mouse studies suggest a proatherogenic effect of CETP activity when HDL is reduced, LDL clearance is impaired, and cholesteryl esters are redistributed from HDL to VLDL/LDL. The results are consistent with the observation that CETP is expressed by monocyte-derived macrophages and by smooth muscle cells in human atheroma.46
Nonetheless, studies of CETP overexpression in mice are not entirely consistent. In at least 2 transgenic mouse studies, overexpression of CETP decreased atherogenesis. Using apoC-III transgene–induced hypertriglyceridemia, Hayek et al47 reported that the percentage of mice with atherosclerotic lesions fell from 93% to 38% when they were transduced with both CETP and apoA-I. Although this study suggests that CETP overexpression could be atheroprotective in the presence of hypertriglyceridemia, its clinical relevance is uncertain, because no comparable genotype is found in humans. In the second study, CETP-transgenic mice were crossbred with atherosclerosis-prone, lecithin:cholesterol acyltransferase (LCAT)–transgenic mice.48 Although the mean aortic lesion area was reduced by 41%, this result may reflect species differences, because naturally high-CETP rabbits transduced with the LCAT transgene exhibited an increase in HDL with reduced atherosclerosis.49
In summary, the preponderance of mouse data suggests that CETP overexpression is proatherogenic. Like the human epidemiological data, however, they also raise the possibility that CETP could be either proatherogenic or antiatherogenic, depending on the lipid environment.
Is CETP Inhibition Antiatherogenic;
Inhibition of CETP expression has been studied in high-CETP animals, such as the hypercholesterolemic rabbit, a model that more closely models the human condition. Sugano et al50,51 used antisense oligodeoxynucleotides against CETP. Total cholesterol and CETP were significantly decreased at 12 and 16 weeks compared with controls. HDL cholesterol, measured by ultracentrifugation and column chromatography, increased significantly. Aortic cholesterol content and the percentage of surface area with atherosclerosis were significantly reduced. Similar effects on CETP and HDL levels have been obtained with anti-CETP antibodies.52
Rabbits immunized with a peptide containing a region of the CETP molecule required for neutral lipid transfer function developed antibodies against CETP, with a significant reduction in plasma CETP activity and alterations in the lipoprotein profile.53 The fraction of plasma cholesterol in HDL was 42% higher and the fraction of plasma cholesterol in LDL was 24% lower in the immunized group than in controls. The extent of aortic surface covered by atherosclerotic plaque was reduced by 39.6%. The vaccine has entered phase I clinical testing. When the vaccine (AVANT Immunotherapeutics, Inc, Needham, Mass) was tested in 15 volunteers,54 53% of those who received a second injection of the active vaccine developed anti-CETP antibodies, compared with 1 of 8 placebo controls. HDL levels did not increase significantly, however. The vaccine induced no significant clinical or laboratory abnormalities but also did not significantly increase the level of HDL.
In summary, these rabbit studies suggest that CETP inhibition increases plasma HDL and induces redistribution of cholesteryl esters between HDL and VLDL/LDL, with a fall in both plasma total cholesterol and in aortic tissue cholesterol.
Moving Toward Clinical Application: Pharmacological Inhibition of CETP
In principle, pharmacological inhibition of CETP could accelerate cholesterol transport to the liver by HDL (Figure 3). The first pharmacological CETP inhibitor for potential human use was developed in Japan. JTT-705 (Akros Pharma), a thioester that inhibits CETP by forming disulfide bonds, can reduce CETP activity in rabbits by 90%. The concentration of drug necessary to inhibit 50% of the CETP activity (IC50) is similar in rabbits and humans.55 HDL extracted from JTT-705–fed rabbits increases cholesterol efflux from cultured macrophages.56 When given to rabbits with diet-induced atherosclerosis (mean plasma cholesterol 200 mg/dL) for 6 months, JTT-705 inhibited CETP activity by 95%, with a 90% increase in HDL cholesterol and a 40% decrease non-HDL cholesterol. These changes in blood lipids were accompanied by an 80% decrease in aortic atherosclerosis.57 The relative contribution of increased HDL and decreased LDL to the inhibition of atherosclerosis was, however, not defined.
As with the epidemiological and transgenic mouse data, studies with JTT-705 have not been entirely consistent. A subsequent study in severely hypercholesterolemic rabbits with mean plasma cholesterol values >600 mg/dL compared 2 doses of JTT-705, 100 mg/kg (low dose) and 300 mg/kg (high dose). Both doses failed to reduce aortic atherosclerotic area (60% versus 58%, high dose versus controls) despite a 200% increase in HDL cholesterol.58 The higher dose induced hypertriglyceridemia. Moreover, the non-HDL cholesterol level was correlated with atherosclerotic area, whereas CETP activity and HDL level were not. The authors speculated that the antiatherogenic mechanism that functioned successfully in the prior moderately hypercholesterolemic rabbit study was overwhelmed in the presence of very severe hyperlipidemia; ie, that in very severe hyperlipidemia, HDL-elevating therapy may be less important than decreasing non-HDL cholesterol.
Extension to Human Investigation
Given the magnitude of HDL increase and atherosclerosis reduction achieved in the animal studies, there is a consensus that strategies that increase HDL and/or augment reverse cholesterol transport should be tested in clinical trials.25,26,32 Because reverse cholesterol transport is controlled at several discrete steps by different protein regulators and receptors, CETP inhibition is only one of several potential approaches for augmenting reverse cholesterol transport49,59–63 (see the Table).49,53,54,58,62,63–67 In fact, the clinical efficacy of pharmacological CETP inhibition could be substantially influenced by both diet and drugs that alter CETP pharmacokinetics. For instance, body weight influences CETP activity. Obese children have substantially increased levels of CETP,68 and conversely, weight loss can cause as much as a 37% decrease in CETP activity.69 Dietary components also influence CETP. Garlic and red pepper have been reported to inhibit CETP activity.70,71 Alcohol consumption may have secondary effects by poorly defined mechanisms in individuals with CETP polymorphisms. For instance, heavy drinkers who are homozygous for one particular CETP allele have a substantially reduced risk of myocardial infarction.72
Antiatherogenic Effects of Strategies Thought to Augment Reverse Cholesterol Transport
High CETP concentration has been associated with more rapid progression of coronary disease, and statin therapy is more effective in this subgroup, independent of baseline or on-treatment lipid levels, suggesting that the plasma CETP level may be an important determinant of the response to statins.73 Statins reduce plasma CETP activity by 5% to 10% and cholesteryl ester transfer by 35%.70–78 For instance, atorvastatin (10 mg/d for 6 weeks) reduces CETP activity by 7%, and cholesterol transfer from HDL to non-HDL particles is reduced by 37%.77,78 The magnitude of these effects is modified by the CETP genotype.30,79 Because statins alone cause a substantial decrease in triglyceride and a small increase in HDL, one might speculate that the combination of a statin with a CETP inhibitor would be more effective than either therapy alone.
JTT-705 has been tested in an initial 4-week, randomized, dose-response trial at 300, 600, and 900 mg/d in 198 healthy mildly hyperlipidemic patients.80 The highest dose induced a 37% decrease in CETP activity, a 34% increase in HDL, and a 7% decrease in LDL, with no change in triglyceride. An increase in HDL2, HDL3, and apoA-I paralleled the increase in total HDL. No important clinical or laboratory toxicity was noted, and the drug was well tolerated at all doses, although treated patients had significantly more mild gastrointestinal complaints. This small study did not include any surrogate measures of atherosclerotic burden or clinical end points. Phase II studies of JTT-705 in combination with pravastatin are in progress.
A second CETP inhibitor, torcetrapib (Pfizer), has also entered clinical trials. In the first phase I multidose trial, 5 groups of 8 healthy young subjects received 10, 30, 60, and 120 mg daily and 120 torcetrapib mg twice daily for 14 days.81 All doses were well tolerated. CETP inhibition increased with escalating dose, leading to elevations of HDL of 16% to 91%. Total plasma cholesterol did not change significantly, however, reflecting a parallel reduction in non-HDL cholesterol. At the highest dose, LDL was decreased by 42%. In a second trial, 19 subjects with HDL <40 mg/dL received 120 mg torcetrapib, 9 of whom also received 20 mg atorvastatin daily for 4 weeks.82 Plasma HDL cholesterol increased by 61% in the atorvastatin group and by 46% in the non-atorvastatin groups. In an additional group, torcetrapib at 120 mg twice daily increased HDL cholesterol by 106%. Torcetrapib also reduced LDL levels by 17% in the atorvastatin group. In all groups, the mean particle size of HDL and LDL increased. These 2 studies suggest that the effect of pharmacological CETP inhibition resembles that observed in partial CETP deficiency and serve as a prelude to trials in patients with atherosclerosis and low HDL or other dyslipidemias. The initial phase III trials will test 60 mg torcetrapib. In one such trial, intravascular ultrasound is being used to compare atheroma volume at baseline and after 2 years of therapy with either atorvastatin alone or atorvastatin plus torcetrapib. The results of these randomized trials with JTT-705 and with torcetrapib should serve to clarify the potential value of CETP inhibition for atherosclerotic vascular disease in humans.
Conclusion
The most reasonable proposed integration of animal and human data is that the effect of CETP and its inhibition is modified by the genetic and metabolic milieu.25,32 Using human genetic data as a starting point, we may speculate that CETP deficiency may be antiatherogenic when it is associated with a significant increase in HDL (perhaps >60 mg/dL) but that it is not protective in the presence of substantial hypertriglyceridemia, major increases in LDL cholesterol, or lower attained HDL cholesterol levels. Studies in rabbits are consistent with this idea. In moderate hyperlipidemia, CETP inhibition is antiatherogenic, at least partly through progressive reduction in the rate of transfer of cholesteryl esters from HDL to VLDL and LDL. The lack of effect in the profoundly hyperlipidemic rabbit, despite a major increase in serum HDL, suggests that in this particular metabolic milieu, the HDL itself is insufficient to be antiatherogenic. Thus the effect of CETP and its inhibition seems to be to be dependent on the interaction between the level and distribution of lipoprotein components. Although data are currently insufficient to draw any conclusions, an additional reasonable speculation is that the effect of the metabolic milieu on CETP inhibition may involve alteration in HDL function, catabolism, or particle distribution not detected in the measurement of HDL blood levels.
We now have promising pharmacological inhibitors of CETP that are capable of increasing HDL by a magnitude comparable to that of statins on LDL. From the standpoint of clinical trial design, a reasonable hypothesis is that inhibition of CETP is antiatherogenic in the absence of severe hypertriglyceridemia. Nonetheless, despite our wealth of animal, epidemiological, and genetic data, we cannot predict the antiatherogenic effect of CETP inhibition or identify human subsets in whom the intervention might be more or less effective. Consequently, these randomized clinical trials will exemplify equipoise, the ethical principle that serves as the foundation of clinical trials. The investigator describing the trial will be truly uncertain as to which course of therapy that he/she offers is best for that patient.
References
Shah PK. Low-density lipoprotein lowering and atherosclerosis progression: does more mean less; Circulation. 2002; 106: 2039–2040.
Forrester JS, Bairey-Merz CN, Kaul S. The aggressive low density lipoprotein lowering controversy. J Am Coll Cardiol. 2000; 36: 1419–1425.
Nissen SE, Tuzcu EM, Schoenhagen P, Brown BG, Ganz P, Vogel RA, Crowe T, Howard G, Cooper CJ, Brodie B, Grines CL, DeMaria AN; REVERSAL Investigators. Effect of intensive compared with moderate lipid-lowering therapy on progression of coronary atherosclerosis: a randomized controlled trial. JAMA. 2004; 291: 1071–1080.
Cannon CP, Braunwald E, McCabe CH, Rader DJ, Rouleau JL, Belder R, Joyal SV, Hill KA, Pfeffer MA, Skene AM; Pravastatin or Atorvastatin Evaluation and Infection Therapy—Thrombolysis in Myocardial Infarction 22 Investigators. Intensive versus moderate lipid lowering with statins after acute coronary syndromes. N Engl J Med. 2004; 350: 1495–1504.
Grundy SM, Cleeman JI, Bairey-Merz CN, Brewer HB Jr, Clark LT, Hunninghake DB, Pasternak RC, Smith SC Jr, Stone NJ; Coordinating Committee of the National Cholesterol Education Program; National Heart, Lung, and Blood Institute; American College of Cardiology Foundation; American Heart Association. Implications of recent clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines. Arterioscler Thromb Vasc Biol. 2004; 24: e149–e161.
Gordon T, Castelli WP, Hjortland MC, Kannel WB, Dawber TR. High density lipoprotein as a protective factor against coronary heart disease: the Framingham Study. Am J Med. 1977; 62: 707–714.
Kannel WB, Wilson PW. Efficacy of lipid profiles in prediction of coronary disease. Am Heart J. 1992; 124: 768–774.
Shah PK, Kaul S, Nilsson J, Cercek B. Exploiting the vascular protective effects of high-density lipoprotein and its apolipoproteins: an idea whose time for testing is coming, part I. Circulation. 2001; 104: 2376–2383.
Shah PK, Kaul S, Nilsson J, Cercek B. Exploiting the vascular protective effects of high-density lipoprotein and its apolipoproteins: an idea whose time for testing is coming, part II. Circulation. 2001; 104: 2498–2502.
Navab M, Hama SY, Hough GP, Subbanagounder G, Reddy ST, Fogelman AMA. Cell-free assay for detecting HDL that is dysfunctional in preventing the formation of or inactivating oxidized phospholipids. J Lipid Res. 2001; 42: 1308–1317.
Rosenson RS. Antiatherothrombotic effects of nicotinic acid. Atherosclerosis. 2003; 171: 87–96.
Hunninghake DB, McGovern ME, Koren M, Brazg R, Murdock D, Weiss S, Pearson T. A dose-ranging study of a new, once-daily, dual-component drug product containing niacin extended-release and lovastatin. Clin Cardiol. 2003; 26: 112–118.
Brown BG, Zhao XQ, Chait A, Fisher LD, Cheung MC, Morse JS, Dowdy AA, Marino EK, Bolson EL, Alaupovic P, Frohlich J, Albers JJ. Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease. N Engl J Med. 2001; 345: 1583–1592.
Navab M, Anantharamaiah GM, Reddy ST, Van Lenten BJ, Ansell BJ, Fonarow GC, Vahabzadeh K, Hama S, Hough G, Kamranpour N, Berliner JA, Lusis AJ, Fogelman AM. Thematic review series: the pathogenesis of atherosclerosis: the oxidation hypothesis of atherogenesis: the role of oxidized phospholipids and HDL. J Lipid Res. 2004; 45: 993–1007.
Zheng L, Nukuna B, Brennan ML, Sun M, Goormastic M, Settle M, Schmitt D, Fu X, Thomson L, Fox PL, Ischiropoulos H, Smith JD, Kinter M, Hazen SL. Apolipoprotein A-I is a selective target for myeloperoxidase-catalyzed oxidation and functional impairment in subjects with cardiovascular disease. J Clin Invest. 2004; 114: 529–541.
Brewer HB. Increasing HDL cholesterol levels. N Engl J Med. 2004; 350: 1491–1494.
Ansell BJ, Navab M, Hama S, Kamranpour N, Fonarow G, Hough G, Rahmani S, Mottahedeh R, Dave R, Reddy ST, Fogelman M. Inflammatory/anti-inflammatory properties of high-density lipoprotein distinguish patients from control subjects better than high-density lipoprotein cholesterol levels and are favorably affected by simvastatin treatment. Circulation. 2003; 108: 2751–2756.
Perez-Mendez O, Bruckert E, Franceschini G, Duhal N, Lacroix B, Bonte JP, Sirtori C, Fruchart JC, Turpin G, Luc G. Metabolism of apolipoproteins AI and AII in subjects carrying similar apoAI mutations, apoAI Milano and apoAI Paris. Atherosclerosis. 2000; 148: 317–325.
Brewer HB. High-density lipoproteins: a new potential therapeutic target for the prevention of cardiovascular disease. Arterioscler Thromb Vasc Biol. 2004; 24: 387–391.
Zuckerman SH, Evans GF. Cholesteryl ester transfer protein inhibition in hypercholesterolemic hamsters: kinetics of apoprotein changes. Lipids. 1995; 30: 307–311.
Koizumi J, Mabuchi H, Yoshimura A, Michishita I, Takeda M, Itoh H, Sakai Y, Sakai T, Ueda K, Takeda R. Deficiency of serum cholesteryl-ester transfer activity in patients with familial hyperalphalipoproteinemia. Atherosclerosis. 1985; 58: 175–186.
Moriyama Y, Okamura T, Inazu A, Doi M, Iso H, Mouri Y, Ishikawa Y, Suzuki H, Iida M, Koizumi J, Mabuchi H, Komachi Y. A low prevalence of coronary heart disease among subjects with increased high-density lipoprotein cholesterol levels, including those with plasma cholesteryl ester transfer protein deficiency. Prev Med. 1998; 27 (5 pt 1): 659–667.
Hirano K, Yamashita S, Nakajima N, Arai T, Maruyama T, Yoshida Y, Ishigami M, Sakai N, Kameda-Takemura K, Matsuzawa Y. Genetic cholesteryl ester transfer protein deficiency is extremely frequent in the Omagari area of Japan: marked hyperalphalipoproteinemia caused by CETP gene mutation is not associated with longevity. Arterioscler Thromb Vasc Biol. 1997; 17: 1053–1059.
Inazu A, Brown ML, Hesler CB, Agellon LB, Koizumi J, Takata K, Maruhama Y, Mabuchi H, Tall AR. Increased high-density lipoprotein levels caused by a common cholesteryl-ester transfer protein gene mutation. N Engl J Med. 1990; 323: 1234–1238.
Barter PJ, Brewer HB Jr, Chapman MJ, Hennekens CH, Rader DJ, Tall AR. Cholesteryl ester transfer protein: a novel target for raising HDL and inhibiting atherosclerosis. Arterioscler Thromb Vasc Biol. 2003; 23: 160–167.
Inazu I, Koizumi J, Mabuchi H. Cholesteryl ester transfer protein and atherosclerosis. Curr Opin Lipidol. 2000; 11: 389–396.
von Eckardstein A, Crook D, Elbers J, Ragoobir J, Ezeh B, Helmond F, Miller N, Dieplinger H, Bennink HC, Assmann G. Tibolone lowers high density lipoprotein cholesterol by increasing hepatic lipase activity but does not impair cholesterol efflux. Clin Endocrinol. 2003; 58: 49–58.
Borggreve SE, De Vries R, Dullaart RP. Alterations in high-density lipoprotein metabolism and reverse cholesterol transport in insulin resistance and type 2 diabetes mellitus: role of lipolytic enzymes, lecithin:cholesterol acyltransferase and lipid transfer proteins. Eur J Clin Invest. 2003; 33: 1051–1069.
Ma K, Cilingiroglu M, Otvos JD, Ballantyne CM, Marian AJ, Chan L. Endothelial lipase is a major genetic determinant for high-density lipoprotein concentration, structure, and metabolism. Proc Natl Acad Sci U S A. 2003; 100: 2748–2753.
Cilingiroglu M, Ballantyne C. Endothelial lipase and cholesterol metabolism. Curr Atheroscler Rep. 2004; 6: 126–130.
Ikewaki K, Rader DJ, Sakamoto T, Nishiwaki M, Wakimoto N, Schaefer JR, Ishikawa T, Fairwell T, Zech LA, Nakamura H, Nagano M, Brewer HB. Delayed catabolism of high density lipoprotein apolipoprotein A-I and A-II in human cholesteryl ester transfer protein deficiency. J Clin Invest. 1993; 92: 1650–1658.
Watts GF. The yin and yang of cholesteryl ester transfer protein and atherosclerosis. Clin Sci. 2002; 103: 595–597.
Agerholm-Larsen B, Nordestgaard BG, Steffensen R, Jensen G, Tybjaerg-Hansen A. Elevated HDL cholesterol is a risk factor for ischemic heart disease in white women when caused by a common mutation in the cholesteryl ester transfer protein gene. Circulation. 2000; 101: 1907–1912.
Blankenberg S, Rupprecht HJ, Bickel C, Jiang XC, Poirier O, Lackner KJ, Meyer J, Cambien F, Tiret L; AtheroGene Investigators. Common genetic variation of the cholesteryl ester transfer protein gene strongly predicts future cardiovascular death in patients with coronary artery disease. J Am Coll Cardiol. 2003; 41: 1983–1989.
Barzilai N, Atzmon G, Schechter C, Schaefer EJ, Cupples AL, Lipton R, Cheng S, Shuldiner AR. Unique lipoprotein phenotype and genotype associated with exceptional longevity. JAMA. 2003; 290: 2030–2040.
de Grooth GJ, Zerba KE, Huang SP, Tsuchihashi Z, Kirchgessner T, Belder R, Vishnupad P, Hu B, Klerkx AH, Zwinderman AH, Jukema JW, Sacks FM, Kastelein JJ, Kuivenhoven JA. The cholesteryl ester transfer protein (wCETP) TaqIB polymorphism in the cholesterol and recurrent events study: no interaction with the response to pravastatin therapy and no effects on cardiovascular outcome: a prospective analysis of the CETP TaqIB polymorphism on cardiovascular outcome and interaction with cholesterol-lowering therapy. J Am Coll Cardiol. 2004; 43: 854–857.
Moriyama Y, Okamura T, Inazu A, Doi M, Iso H, Mouri Y, Ishikawa Y, Suzuki H, Iida M, Koizumi J, Mabuchi H, Komachi Y. A low prevalence of coronary heart disease among subjects with increased high-density lipoprotein cholesterol levels, including those with plasma cholesteryl ester transfer protein deficiency. Prev Med. 1998; 27: 659–667.
Zhong S, Sharp DS, Grove JS, Bruce C, Yano K, Curb JD, Tall AR. Increased coronary heart disease in Japanese-American men with mutation in the cholesteryl ester transfer protein gene despite increased HDL levels. J Clin Invest. 1996; 97: 2917–2923.
Bruce C, Sharp DS, Tall AR. Relationship of HDL and coronary heart disease to a common amino acid polymorphism in the cholesteryl ester transfer protein in men with and without hypertriglyceridemia. J Lipid Res. 1998; 39: 1071–1078.
Kakko S, Tamminen M, Paivansalo M, Kauma H, Rantala AO, Lilja M, Reunanen A, Kesaniemi YA, Savolainen MJ. Cholesteryl ester transfer protein gene polymorphisms are associated with carotid atherosclerosis in men. Eur J Clin Invest. 2000; 30: 18–25.
Kimura H, Miyazaki R, Suzuki S, Gejyo F, Yoshida H. Cholesteryl ester transfer protein as a protective factor against vascular disease in hemodialysis patients. Am J Kidney Dis. 2001; 38: 70–76.
Cheung MC, Wolfbauer G, Albers JJ. Plasma phospholipid mass transfer rate: relationship to plasma phospholipid and cholesteryl ester transfer activities and lipid parameters. Biochim Biophys Acta. 1996; 1303: 103–110.
Agellon LB, Walsh A, Hayek T, Moulin P, Jiang XC, Shelanski SA, Breslow JL, Tall AR. Reduced high density lipoprotein cholesterol in human cholesteryl ester transfer protein transgenic mice. J Biol Chem. 1991; 266: 10796–10801.
Plump AS, Masucci-Magoulas L, Bruce C, Bisgaier CL, Breslow JL, Tall AR. Increased atherosclerosis in apoE and LDL receptor gene knock-out mice as a result of human cholesteryl ester transfer protein transgene expression. Arterioscler Thromb Vasc Biol. 1999; 19: 1105–1110.
Marotti KR, Castle CK, Boyle TP, Lin AH, Murray RW, Melchior GW. Severe atherosclerosis in transgenic mice expressing simian cholesteryl ester transfer protein. Nature. 1993; 364: 73–75.
Ishikawa Y, Ito K, Akasaka Y, Ishii T, Masuda T, Zhang L, Akishima Y, Kiguchi H, Nakajima K, Hata Y. The distribution and production of cholesteryl ester transfer protein in the human aortic wall. Atherosclerosis. 2001; 156: 29–37.
Hayek T, Masucci-Magoulas L, Jiang X, Walsh A, Rubin E, Breslow JL, Tall AR. Decreased early atherosclerotic lesions in hypertriglyceridemic mice expressing cholesteryl ester transfer protein transgene. J Clin Invest. 1995; 96: 2071–2074.
Foger B, Chase M, Amar MJ, Vaisman BL, Shamburek RD, Paigen B, Fruchart-Najib J, Paiz JA, Koch CA, Hoyt RF, Brewer HB Jr, Santamarina-Fojo S. Cholesteryl ester transfer protein corrects dysfunctional high density lipoproteins and reduces aortic atherosclerosis in lecithin cholesterol acyltransferase transgenic mice. J Biol Chem. 1999; 274: 36912–36920.
Hoeg JM, Santamarina-Fojo S, Berard AM, Cornhill JF, Herderick EE, Feldman SH, Haudenschild CC, Vaisman BL, Hoyt RF Jr, Demosky SJ Jr, Kauffman RD, Hazel CM, Marcovina SM, Brewer HB Jr. Overexpression of lecithin:cholesterol acyltransferase in transgenic rabbits prevents diet-induced atherosclerosis. Proc Natl Acad Sci U S A. 1996; 93: 11448–1153.
Sugano M, Makino N, Sawada S, Otsuka S, Watanabe M, Okamoto H, Kamada M, Mizushima A. Effect of antisense oligonucleotides against cholesteryl ester transfer protein on the development of atherosclerosis in cholesterol-fed rabbits. J Biol Chem. 1998; 273: 5033–5036.
Sugano M, Sawada S, Tsuchida K, Makino N, Kanada M. Low density lipoproteins develop resistance to oxidative modification due to inhibition of cholesteryl ester transfer protein by a monoclonal antibody. J Lipid Res. 2000; 41: 126–133.
Whitlock ME, Swenson TL, Ramakrishnan R, Leonard MT, Marcel YL, Milne RW, Tall AR. Monoclonal antibody inhibition of cholesteryl ester transfer protein activity in the rabbit. J Clin Invest. 1989; 84: 129–137.
Rittershaus CW, Miller DP, Thomas LJ, Picard MD, Honan CM, Emmett CD, Pettey CL, Adari H, Hammond RA, Beattie DT, Callow AD, Marsh HC, Ryan US. Vaccine-induced antibodies inhibit CETP activity in vivo and reduce aortic lesions in a rabbit model of atherosclerosis. Arterioscler Thromb Vasc Biol. 2000; 20: 2106–2112.
Davidson MH, Maki K, Umporowicz D, Wheeler A, Rittershaus C, Ryan U. The safety and immunogenicity of a CETP vaccine in healthy adults. Atherosclerosis. 2003; 169: 113–120.
Okamoto H, Yonemori F, Wakitani K, Minowa T, Maeda K, Shinkai H. A cholesteryl ester transfer protein inhibitor attenuates atherosclerosis in rabbits. Nature. 2000; 406: 203–207.
Kobayashi J, Okamoto H, Otabe M, Bujo H, Saito Y. Effect of HDL, from Japanese white rabbit administered a new cholesteryl ester transfer protein inhibitor JTT-705, on cholesteryl ester accumulation induced by acetylated low density lipoprotein in J774 macrophage. Atherosclerosis. 2002; 162: 131–135.
Okamoto H, Iwamoto Y, Maki M, Sotani Y, Fumihiko Y, Wakitani K. Effect of JTT-705 on cholesteryl ester transfer protein and plasma lipid levels in normolipidemic animals. Eur J Pharmacol. 2003; 466: 147–154.
Huang Z, Inazu A, Nohara A, Higashikata T, Mabuchi H. Cholesteryl ester transfer protein inhibitor (JTT-705) and the development of atherosclerosis in rabbits with severe hypercholesterolaemia. Clin Sci. 2002; 103: 587–594.
Brousseau ME, Schaefer EJ, Wolfe ML, Bloedon LT, Digenio AG, Clark RW, Mancuso JP, Rader DJ. Effects of a potent inhibitor of cholesteryl ester transfer protein on plasma lipoproteins in patients with low HDL cholesterol levels. N Engl J Med. 2004; 350: 1505–1515.
Rader DJ. Regulation of reverse cholesterol transport and clinical implications. Am J Cardiol. 2003; 92: 42J–49J.
Navab M, Hama S, Hough G, Fogelman AM. Oral synthetic phospholipid (DMPC) raises high-density lipoprotein cholesterol levels, improves high-density lipoprotein function, and markedly reduces atherosclerosis in apolipoprotein E-null mice. Circulation. 2003; 108: 1735–1739.
Badimon JJ, Badimon L, Fuster V. Regression of atherosclerotic lesions by high density lipoprotein plasma fraction in the cholesterol-fed rabbit. J Clin Invest. 1990; 85: 1234–1241.
Nissen SE, Tsunoda T, Tuzcu EM, Schoenhagen P, Cooper CJ, Yasin M, Eaton GM, Lauer MA, Sheldon WS, Grines CL, Halpern S, Crowe T, Blankenship JC, Kerensky R. Effect of recombinant ApoA-I Milano on coronary atherosclerosis in patients with acute coronary syndromes: a randomized controlled trial. JAMA. 2003; 290: 2292–2300.
Ameli S, Hultgardh-Nilsson A, Cercek B, Shah PK, Forrester JS, Ageland H, Nilsson J. Recombinant apolipoprotein A-I Milano reduces intimal thickening after balloon injury in hypercholesterolemic rabbits. Circulation. 1994; 90: 1935–1941.
Shah PK, Nilsson J, Kaul S, Fishbein MC, Ageland H, Hamsten A, Johansson J, Karpe F, Cercek B. Effects of recombinant apolipoprotein A-I(Milano) on aortic atherosclerosis in apolipoprotein E-deficient mice. Circulation. 1998; 97: 780–785.
Shah PK, Yano J, Reyes O, Chyu KY, Kaul S, Bisgaier CL, Drake S, Cercek B. High-dose recombinant apolipoprotein A-I(Milano) mobilizes tissue cholesterol and rapidly reduces plaque lipid and macrophage content in apolipoprotein e-deficient mice: potential implications for acute plaque stabilization. Circulation. 2001; 103: 3047–3050.
Chiesa G, Monteggia E, Marchesi M, Lorenzon P, Laucello M, Lorusso V, Di Mario C, Karvouni E, Newton RS, Bisgaier CL, Franceschini G, Sirtori CR. Recombinant apolipoprotein A-I(Milano) infusion into rabbit carotid artery rapidly removes lipid from fatty streaks. Circ Res. 2002; 90: 974–980.
Asayama K, Hayashibe H, Dobashi K, Uchida N, Nakane T, Kodera K, Shirahata A. Increased serum cholesteryl ester transfer protein in obese children. Obes Res. 2002; 10: 439–446.
Ebenbichler CF, Laimer M, Kaser S, Ritsch A, Sandhofer A, Weiss H, Aigner F, Patsch JR. Relationship between cholesteryl ester transfer protein and atherogenic lipoprotein profile in morbidly obese women. Arterioscler Thromb Vasc Biol. 2002; 22: 1465–1469.
Kwon MJ, Song YS, Choi MS, Park SJ, Jeong KS, Song YO. Cholesteryl ester transfer protein activity and atherogenic parameters in rabbits supplemented with cholesterol and garlic powder. Life Sci. 2003; 72: 2953–2964.
Kwon MJ, Song YS, Choi MS, Song YO. Red pepper attenuates cholesteryl ester transfer protein activity and atherosclerosis in cholesterol-fed rabbits. Clin Chim Acta. 2003; 332: 37–44.
Corbex M, Poirier O, Fumeron F, Betoulle D, Evans A, Ruidavets JB, Arveiler D, Luc G, Tiret L, Cambien F. Extensive association analysis between the CETP gene and coronary heart disease phenotypes reveals several putative functional polymorphisms and gene-environment interaction. Genet Epidemiol. 2000; 19: 64–80.
Klerkx AH, de Grooth GJ, Zwinderman AH, Jukema JW, Kuivenhoven JA, Kastelein JJ. Cholesteryl ester transfer protein concentration is associated with progression of atherosclerosis and response to pravastatin in men with coronary artery disease (REGRESS). Eur J Clin Invest. 2004; 34: 21–28.
Guerin M, Dolphin PJ, Talussot C, Gardette J, Berthezene F, Chapman MJ. Pravastatin modulates cholesteryl ester transfer from HDL to apoB-containing lipoproteins and lipoprotein subspecies profile in familial hypercholesterolemia. Arterioscler Thromb Vasc Biol. 1995; 15: 1359–1368.
Contacos C, Barter PJ, Vrga L, Sullivan DR. Cholesteryl ester transfer in hypercholesterolemia: fasting and postprandial studies with and without pravastatin. Atherosclerosis. 1998; 141: 87–98.
Inazu A, Koizumi J, Kajinami K, Kiyohar T, Chichibu K, Mabuchi H. Opposite effects on serum cholesteryl ester transfer protein levels between long-term treatments with pravastatin and probucol in patients with primary hypercholesterolemia and xanthoma. Atherosclerosis. 1999; 145: 405–413.
Guerin M, Lassel TS, Le Goff W, Farnier M, Chapman MJ. Action of atorvastatin in combined hyperlipidemia: preferential reduction of cholesteryl ester transfer from HDL to VLDL1 particles. Arterioscler Thromb Vasc Biol. 2000; 20: 189–197.
Mann CJ, Yen FT, Grant AM, Bihain BE. Mechanism of plasma cholesteryl ester transfer in hypertriglyceridemia. J Clin Invest. 1991; 88: 2059–2066.
Kotake H, Sekikawa A, Tokita Y, Ishigaki Y, Oikawa S. Effect of HMG-CoA reductase inhibitor on plasma cholesteryl ester transfer protein activity in primary hypercholesterolemia: comparison among CETP/TaqIB genotype subgroups. J Atheroscler Thromb. 2002; 9: 207–212.
de Grooth GJ, Kuivenhoven JA, Stalenhoef AF, de Graaf J, Zwinderman AH, Posma JL, van Tol A, Kastelein JJ. Efficacy and safety of a novel cholesteryl ester transfer protein inhibitor, JTT-705, in humans: a randomized phase II dose-response study. Circulation. 105: 2159–2165.
Clark RW, Sutfin TA, Ruggeri RB, Willauer AT, Sugarman ED, Magnus-Aryitey G, Cosgrove PG, Sand TM, Wester RT, Williams JA, Perlman ME, Bamberger MJ. Raising high-density lipoprotein in humans through inhibition of cholesteryl ester transfer protein: an initial multidose study of torcetrapib. Arterioscler Thromb Vasc Biol. 2004; 24: 490–497.
Brousseau ME, Schaefer EJ, Wolfe ML, Bloedon LT, Digenio AG, Clark RW, Mancuso JP, Rader DJ. Effects of an inhibitor of cholesteryl ester transfer protein on HDL cholesterol. N Engl J Med. 2004; 350: 1505–1515.(James S. Forrester, MD; R)
Abstract
Reduced HDL cholesterol may be a risk factor comparable in importance to increased LDL cholesterol. Interventions that raise HDL are antiatherosclerotic, presumably through acceleration of reverse cholesterol transport and by antioxidant and antiinflammatory effects. In the hypercholesterolemic rabbit, HDL levels can be increased by >50% by inhibition of cholesteryl ester transfer protein (CETP), a molecule that plays a central role in HDL metabolism. This HDL-raising effect is antiatherosclerotic in moderately severe hyperlipidemia but appears to be ineffective in the presence of severe hypertriglyceridemia. In humans, mutations resulting in CETP inhibition have been associated with both reduced and increased risk of atherosclerosis. Proposed explanations for these apparently disparate observations are that the antiatherosclerotic effect of CETP inhibition varies with either the metabolic milieu or the degree of CETP inhibition. We now have pharmacological inhibitors of CETP that are capable of increasing HDL by as much as 50% to 100% in humans. The importance of this development is that reduced HDL is a risk factor independent of LDL and that these new agents alter HDL by a magnitude comparable to that of statins on LDL. Clinical trials, now beginning, will need to identify the patient subsets in which CETP inhibition may be more or less effective.
Key Words: atherosclerosis ; cholesterol ; lipids ; metabolism ; statins
Introduction
Although lipid-lowering therapies now have the capability of reducing LDL cholesterol to levels recommended by the National Cholesterol Education Program (NCEP) guidelines in as many as 90% of treated patients,1 the rate of cardiovascular events is reduced by only 20% to 35% in large, randomized trials. These data suggest that the LDL target set by NCEP guidelines may be too high.1–5 Indeed, among patients with acute myocardial infarction, 15% have LDL levels <100 mg/dL on presentation.
A complementary hypothesis is that there is a finite limit to the benefit of LDL lowering and that other non-LDL lipid risk factors must be managed for optimal outcomes. Indeed, epidemiological studies suggest that low HDL cholesterol may be a risk factor comparable in importance to high LDL and that the 2 risk factors are independent (Figure 1).6,7 Although the mechanism by which HDL reduces the development of atherosclerosis has not been defined with certainty, acceleration of reverse cholesterol transport, antioxidant activity, and antiinflammatory action are likely to play central roles.8–10
In contrast to the ability of potent statins to reduce the level of LDL by >50%, however, no currently approved therapy increases HDL by a comparable magnitude. The most potent, currently available HDL-raising therapy is nicotinic acid. This therapy also has a multitude of other antiatherosclerotic effects on the levels of LDL and triglycerides, lipid oxidation, and endothelial function.11 Combination therapy with a statin has been reported to increase HDL levels by 30%12 and to decrease cardiac events.13
Recent studies in the animal laboratory have demonstrated that inhibition of cholesteryl ester transfer protein (CETP), a molecule that plays a central role in HDL metabolism, can raise HDL levels by as much as 50%. Initial testing of pharmacological CETP inhibitors in the hypercholesterolemic rabbit model of atherosclerosis has suggested that this effect could substantially alter the course of atherogenesis. In this article, we will critically analyze these data as clinical trials of this potentially important therapeutic strategy for prevention of atherosclerosis begin.
Raising HDL: Three Limitations Not Recognized by Clinical HDL Measurements
Before analyzing the potential of any new HDL-raising therapy, we must recognize that the traditional HDL blood level has at least 3 limitations either as an index of risk or as a criterion for clinical decision making. The serum HDL level does not assess its functional properties. HDL has both proinflammatory and antiinflammatory properties, both in vitro and in vivo.14–16 Ansell et al17 studied 2 groups of patients. The first group included high-risk, normolipidemic patients studied before and after statin therapy. Despite normal HDL cholesterol levels, the HDL of these patients was found to be proinflammatory compared with age- and sex-matched healthy controls who had antiinflammatory HDL. Statin therapy induced a significant improvement in the proinflammatory HDL, although it remained proinflammatory. In a second group of patients with documented coronary heart disease selected for high HDL (average HDL 95 mg/dL), proinflammatory HDL was found, compared with healthy age- and sex-matched controls who had antiinflammatory HDL. Even within a given individual, HDL may become transiently pro-oxidant in the presence of systemic infection. A second limitation is that the HDL blood level does not necessarily reveal the kinetics of HDL metabolism. For example, subjects with the apoA1 Milano mutation have very low HDL cholesterol levels.18 These HDL molecules, however, have very high fractional catabolic rates, which result in the antiatherosclerotic effect of an accelerated return of cholesterol ester to the liver. Conversely, in some CETP mutations with genetically high HDL and low LDL values, the increased HDL is represented by a large, apoE-enriched particle that is a weak promoter of cholesterol efflux, and the LDL particle reacts poorly with the LDL receptor. As a consequence, atherosclerosis is increased despite an apparently "favorable" effect of the mutation on the lipid profile.19 Finally, the subfractions of HDL generated by CETP inhibition20 may have different effects on inhibition of atherogenesis. For instance, HDL2 is typically a potent antiatherosclerotic molecule, whereas the smaller, denser HDL3 subfraction may have less effect. Similarly, the composition of HDL particles may influence their functional properties. Two major apoAI-containing particles exist: LpA-I, which contains only apoA-I, and LpA-I+A-II, which contains both apoA-I and apoA-II. Because apoA-I is antiatherogenic whereas apoA-II can be proatherogenic (based on studies in transgenic mice), LpA-1 particles may be more antiatherogenic than LpA-I+A-II–containing particles. It has been shown that the majority of LpA-I has the same density and charge as HDL2, whereas the majority of LpA-I+A-II has the same density and charge as HDL3. Thus, the apparent benefit that might be inferred from a therapy that increases HDL, eg, CETP inhibition, must be tempered by these potential limitations.
Historical Perspective: The Epidemiology and Biochemistry of CETP
Some years ago, a mutation in the CETP gene was discovered in the Japanese. This mutation was accompanied by a substantial increase in HDL. Because HDL regulates reverse cholesterol transport and has antioxidant, antithrombotic, and antiinflammatory properties and the prevalence of atherosclerotic disease is low in Japanese, epidemiological studies were undertaken to define the prevalence of the mutation. These studies suggested that the mutation occurred in 11% of the Japanese population and that affected individuals were resistant to atherosclerosis.21,22
During the ensuing years, at least 13 different mutations in the coding region of the CETP gene have been identified. These mutations remain particularly prevalent in the Japanese. In some regions of Japan, the incidence is strikingly high. For instance, as many as 27% of people in the northernmost region, in the environs of Akita, have a CETP gene mutation.23 Homozygotes have up to 4-fold increases in HDL, with substantial increases in apoA-I and apoA-II and as much as a 40% reduction in LDL cholesterol and apoB.24
These epidemiological data triggered interest in the biochemical characteristics of CETP. Detailed analysis of CETP metabolism, beyond the scope of this article, is the subject of several excellent recent reviews of reverse cholesterol transport.25,26 In brief, CETP is a plasma glycoprotein manufactured in the liver. It circulates in the blood, bound predominantly to HDL. Two principal actions of CETP have been identified. The primary action of CETP is to mediate the transfer of cholesteryl esters from HDL to VLDL and LDL in exchange for triglyceride (Figure 2). 27–30 CETP also promotes the transformation of HDL2 to HDL 3, an action that could promote reverse cholesterol transport. CETP inhibition, on the other hand, results in an increase in HDL by markedly delaying catabolism of apoA-I and A-II.31 This action also can increase reverse cholesterol transport. This overlap of the potential effects of CETP and CETP inhibition has served to confound an understanding of potential therapeutic mechanisms in atherosclerosis.25,26,32
For more information about the following terms, which are not mentioned in the text of the present article, see von Eckardstein et al,27 Borggreve et al,28 Ma et al,29 and Cilingiroglu and Ballantyne.30 ABC A-1: adenosine triphosphate binding cassette, the initiator of cholesterol efflux from the cell membrane. SR-BI: scavenger receptor class B-1, the receptor responsible for uptake of cholesterol ester from the HDL particle when it arrives in the liver. LCAT: lecithin cholesterol acyl transferase; the enzyme responsible for esterifying cholesterol after it is carried from the cell membrane. HL: hepatic lipase, which hydrolyzes HDL triglyceride and phospholipids remodeling larger HDL particles to smaller HDL particles. The smaller HDL particles are at greater risk of renal catabolism. EL: endothelial lipase, which like HL remodels HDL to smaller particles. LPL: lipoprotein lipase, which contributes to HDL formation by generating phospholipids on apoB-containing lipoproteins that are then transferred to HDL. Secretory phospholipase A2: a lipase that remodels HDL to smaller particles.
The uncertainty about the potential therapeutic value of CETP inhibition was amplified by subsequent epidemiological studies. Although initially CETP mutations were thought to be atheroprotective, this has not proven to be universally true. Reports of both an increased33,34 and a decreased35 or even no36 effect on the prevalence of coronary artery disease in patients with CETP deficiency have appeared in the literature.
Subgroup analyses of the epidemiological studies suggested that the level of HDL and triglyceride might influence the relation between CETP mutations and atherosclerosis. Thus, Moriyama et al37 found that in CETP-deficient individuals with HDL >80 mg/dL, the prevalence of coronary disease was reduced to a level comparable to that of individuals with elevated HDL and no CETP deficiency. This finding is consistent with that of the Honolulu Heart Study,38,39 in which CETP-deficient individuals with HDL >60 mg/dL also had a low prevalence of coronary artery disease. On the other hand, individuals with CETP deficiency and an HDL <60 mg/dL or with triglyceride >165 mg/dL appeared to have an increased incidence of coronary heart disease. This pattern of increased cardiac events in CETP-deficient patients without markedly elevated HDL and/or with high triglyceride also has been noted in hyperlipidemic Finns40 and in patients undergoing renal dialysis.41 Thus, some investigators have speculated that although the CETP-deficient genotype may be atheroprotective in some, it can also confer an increase in coronary risk when associated with minimal to modest increases in HDL or elevated triglyceride levels.
Because both biochemical and epidemiological data suggest that reduced circulating CETP could, in principle, have both proatherogenic and antiatherogenic effects, study in animal models has seemed to be an essential step to understanding the potential therapeutic value of CETP inhibition.
Animal Models: Is CETP Proatherogenic;
Analysis of studies in the animal model, however, is potentially confounded by a different set of biological variables. Animal species exhibit major differences in CETP expression and in the mechanisms used for reverse cholesterol transport. Mice lack CETP, and thus, reverse cholesterol transport in mice does not involve this protein. In contrast, rabbits have high CETP levels. Human CETP activity is intermediate among the animal species.42 Thus, the mouse model has been used to study overexpression of CETP, whereas rabbits have been used in the study of CETP inhibition.
Mice transduced with the human CETP gene exhibit a dose-related decrease in HDL, accompanied by an increase in LDL and VLDL.43 Plump et al44 transduced atherosclerosis-prone, apoE-knockout mice with human CETP and apoA-I transgenes, thereby inducing plasma CETP levels to rise to 5 to 10 times that of healthy normal humans. This increase in CETP was associated with a 76% reduction in HDL cholesterol. In further studies, the atherosclerosis-prone, LDL receptor–knockout mouse was transduced with the human CETP transgene. At 3 months, the mean lesion area was increased by 1.8-fold compared with controls. Other investigators transduced mice with the simian CETP gene in atherosclerosis-prone mice. Similar to the human CETP gene transduction, the formation of fatty streaks increased dramatically.45 Taken together, these transgenic mouse studies suggest a proatherogenic effect of CETP activity when HDL is reduced, LDL clearance is impaired, and cholesteryl esters are redistributed from HDL to VLDL/LDL. The results are consistent with the observation that CETP is expressed by monocyte-derived macrophages and by smooth muscle cells in human atheroma.46
Nonetheless, studies of CETP overexpression in mice are not entirely consistent. In at least 2 transgenic mouse studies, overexpression of CETP decreased atherogenesis. Using apoC-III transgene–induced hypertriglyceridemia, Hayek et al47 reported that the percentage of mice with atherosclerotic lesions fell from 93% to 38% when they were transduced with both CETP and apoA-I. Although this study suggests that CETP overexpression could be atheroprotective in the presence of hypertriglyceridemia, its clinical relevance is uncertain, because no comparable genotype is found in humans. In the second study, CETP-transgenic mice were crossbred with atherosclerosis-prone, lecithin:cholesterol acyltransferase (LCAT)–transgenic mice.48 Although the mean aortic lesion area was reduced by 41%, this result may reflect species differences, because naturally high-CETP rabbits transduced with the LCAT transgene exhibited an increase in HDL with reduced atherosclerosis.49
In summary, the preponderance of mouse data suggests that CETP overexpression is proatherogenic. Like the human epidemiological data, however, they also raise the possibility that CETP could be either proatherogenic or antiatherogenic, depending on the lipid environment.
Is CETP Inhibition Antiatherogenic;
Inhibition of CETP expression has been studied in high-CETP animals, such as the hypercholesterolemic rabbit, a model that more closely models the human condition. Sugano et al50,51 used antisense oligodeoxynucleotides against CETP. Total cholesterol and CETP were significantly decreased at 12 and 16 weeks compared with controls. HDL cholesterol, measured by ultracentrifugation and column chromatography, increased significantly. Aortic cholesterol content and the percentage of surface area with atherosclerosis were significantly reduced. Similar effects on CETP and HDL levels have been obtained with anti-CETP antibodies.52
Rabbits immunized with a peptide containing a region of the CETP molecule required for neutral lipid transfer function developed antibodies against CETP, with a significant reduction in plasma CETP activity and alterations in the lipoprotein profile.53 The fraction of plasma cholesterol in HDL was 42% higher and the fraction of plasma cholesterol in LDL was 24% lower in the immunized group than in controls. The extent of aortic surface covered by atherosclerotic plaque was reduced by 39.6%. The vaccine has entered phase I clinical testing. When the vaccine (AVANT Immunotherapeutics, Inc, Needham, Mass) was tested in 15 volunteers,54 53% of those who received a second injection of the active vaccine developed anti-CETP antibodies, compared with 1 of 8 placebo controls. HDL levels did not increase significantly, however. The vaccine induced no significant clinical or laboratory abnormalities but also did not significantly increase the level of HDL.
In summary, these rabbit studies suggest that CETP inhibition increases plasma HDL and induces redistribution of cholesteryl esters between HDL and VLDL/LDL, with a fall in both plasma total cholesterol and in aortic tissue cholesterol.
Moving Toward Clinical Application: Pharmacological Inhibition of CETP
In principle, pharmacological inhibition of CETP could accelerate cholesterol transport to the liver by HDL (Figure 3). The first pharmacological CETP inhibitor for potential human use was developed in Japan. JTT-705 (Akros Pharma), a thioester that inhibits CETP by forming disulfide bonds, can reduce CETP activity in rabbits by 90%. The concentration of drug necessary to inhibit 50% of the CETP activity (IC50) is similar in rabbits and humans.55 HDL extracted from JTT-705–fed rabbits increases cholesterol efflux from cultured macrophages.56 When given to rabbits with diet-induced atherosclerosis (mean plasma cholesterol 200 mg/dL) for 6 months, JTT-705 inhibited CETP activity by 95%, with a 90% increase in HDL cholesterol and a 40% decrease non-HDL cholesterol. These changes in blood lipids were accompanied by an 80% decrease in aortic atherosclerosis.57 The relative contribution of increased HDL and decreased LDL to the inhibition of atherosclerosis was, however, not defined.
As with the epidemiological and transgenic mouse data, studies with JTT-705 have not been entirely consistent. A subsequent study in severely hypercholesterolemic rabbits with mean plasma cholesterol values >600 mg/dL compared 2 doses of JTT-705, 100 mg/kg (low dose) and 300 mg/kg (high dose). Both doses failed to reduce aortic atherosclerotic area (60% versus 58%, high dose versus controls) despite a 200% increase in HDL cholesterol.58 The higher dose induced hypertriglyceridemia. Moreover, the non-HDL cholesterol level was correlated with atherosclerotic area, whereas CETP activity and HDL level were not. The authors speculated that the antiatherogenic mechanism that functioned successfully in the prior moderately hypercholesterolemic rabbit study was overwhelmed in the presence of very severe hyperlipidemia; ie, that in very severe hyperlipidemia, HDL-elevating therapy may be less important than decreasing non-HDL cholesterol.
Extension to Human Investigation
Given the magnitude of HDL increase and atherosclerosis reduction achieved in the animal studies, there is a consensus that strategies that increase HDL and/or augment reverse cholesterol transport should be tested in clinical trials.25,26,32 Because reverse cholesterol transport is controlled at several discrete steps by different protein regulators and receptors, CETP inhibition is only one of several potential approaches for augmenting reverse cholesterol transport49,59–63 (see the Table).49,53,54,58,62,63–67 In fact, the clinical efficacy of pharmacological CETP inhibition could be substantially influenced by both diet and drugs that alter CETP pharmacokinetics. For instance, body weight influences CETP activity. Obese children have substantially increased levels of CETP,68 and conversely, weight loss can cause as much as a 37% decrease in CETP activity.69 Dietary components also influence CETP. Garlic and red pepper have been reported to inhibit CETP activity.70,71 Alcohol consumption may have secondary effects by poorly defined mechanisms in individuals with CETP polymorphisms. For instance, heavy drinkers who are homozygous for one particular CETP allele have a substantially reduced risk of myocardial infarction.72
Antiatherogenic Effects of Strategies Thought to Augment Reverse Cholesterol Transport
High CETP concentration has been associated with more rapid progression of coronary disease, and statin therapy is more effective in this subgroup, independent of baseline or on-treatment lipid levels, suggesting that the plasma CETP level may be an important determinant of the response to statins.73 Statins reduce plasma CETP activity by 5% to 10% and cholesteryl ester transfer by 35%.70–78 For instance, atorvastatin (10 mg/d for 6 weeks) reduces CETP activity by 7%, and cholesterol transfer from HDL to non-HDL particles is reduced by 37%.77,78 The magnitude of these effects is modified by the CETP genotype.30,79 Because statins alone cause a substantial decrease in triglyceride and a small increase in HDL, one might speculate that the combination of a statin with a CETP inhibitor would be more effective than either therapy alone.
JTT-705 has been tested in an initial 4-week, randomized, dose-response trial at 300, 600, and 900 mg/d in 198 healthy mildly hyperlipidemic patients.80 The highest dose induced a 37% decrease in CETP activity, a 34% increase in HDL, and a 7% decrease in LDL, with no change in triglyceride. An increase in HDL2, HDL3, and apoA-I paralleled the increase in total HDL. No important clinical or laboratory toxicity was noted, and the drug was well tolerated at all doses, although treated patients had significantly more mild gastrointestinal complaints. This small study did not include any surrogate measures of atherosclerotic burden or clinical end points. Phase II studies of JTT-705 in combination with pravastatin are in progress.
A second CETP inhibitor, torcetrapib (Pfizer), has also entered clinical trials. In the first phase I multidose trial, 5 groups of 8 healthy young subjects received 10, 30, 60, and 120 mg daily and 120 torcetrapib mg twice daily for 14 days.81 All doses were well tolerated. CETP inhibition increased with escalating dose, leading to elevations of HDL of 16% to 91%. Total plasma cholesterol did not change significantly, however, reflecting a parallel reduction in non-HDL cholesterol. At the highest dose, LDL was decreased by 42%. In a second trial, 19 subjects with HDL <40 mg/dL received 120 mg torcetrapib, 9 of whom also received 20 mg atorvastatin daily for 4 weeks.82 Plasma HDL cholesterol increased by 61% in the atorvastatin group and by 46% in the non-atorvastatin groups. In an additional group, torcetrapib at 120 mg twice daily increased HDL cholesterol by 106%. Torcetrapib also reduced LDL levels by 17% in the atorvastatin group. In all groups, the mean particle size of HDL and LDL increased. These 2 studies suggest that the effect of pharmacological CETP inhibition resembles that observed in partial CETP deficiency and serve as a prelude to trials in patients with atherosclerosis and low HDL or other dyslipidemias. The initial phase III trials will test 60 mg torcetrapib. In one such trial, intravascular ultrasound is being used to compare atheroma volume at baseline and after 2 years of therapy with either atorvastatin alone or atorvastatin plus torcetrapib. The results of these randomized trials with JTT-705 and with torcetrapib should serve to clarify the potential value of CETP inhibition for atherosclerotic vascular disease in humans.
Conclusion
The most reasonable proposed integration of animal and human data is that the effect of CETP and its inhibition is modified by the genetic and metabolic milieu.25,32 Using human genetic data as a starting point, we may speculate that CETP deficiency may be antiatherogenic when it is associated with a significant increase in HDL (perhaps >60 mg/dL) but that it is not protective in the presence of substantial hypertriglyceridemia, major increases in LDL cholesterol, or lower attained HDL cholesterol levels. Studies in rabbits are consistent with this idea. In moderate hyperlipidemia, CETP inhibition is antiatherogenic, at least partly through progressive reduction in the rate of transfer of cholesteryl esters from HDL to VLDL and LDL. The lack of effect in the profoundly hyperlipidemic rabbit, despite a major increase in serum HDL, suggests that in this particular metabolic milieu, the HDL itself is insufficient to be antiatherogenic. Thus the effect of CETP and its inhibition seems to be to be dependent on the interaction between the level and distribution of lipoprotein components. Although data are currently insufficient to draw any conclusions, an additional reasonable speculation is that the effect of the metabolic milieu on CETP inhibition may involve alteration in HDL function, catabolism, or particle distribution not detected in the measurement of HDL blood levels.
We now have promising pharmacological inhibitors of CETP that are capable of increasing HDL by a magnitude comparable to that of statins on LDL. From the standpoint of clinical trial design, a reasonable hypothesis is that inhibition of CETP is antiatherogenic in the absence of severe hypertriglyceridemia. Nonetheless, despite our wealth of animal, epidemiological, and genetic data, we cannot predict the antiatherogenic effect of CETP inhibition or identify human subsets in whom the intervention might be more or less effective. Consequently, these randomized clinical trials will exemplify equipoise, the ethical principle that serves as the foundation of clinical trials. The investigator describing the trial will be truly uncertain as to which course of therapy that he/she offers is best for that patient.
References
Shah PK. Low-density lipoprotein lowering and atherosclerosis progression: does more mean less; Circulation. 2002; 106: 2039–2040.
Forrester JS, Bairey-Merz CN, Kaul S. The aggressive low density lipoprotein lowering controversy. J Am Coll Cardiol. 2000; 36: 1419–1425.
Nissen SE, Tuzcu EM, Schoenhagen P, Brown BG, Ganz P, Vogel RA, Crowe T, Howard G, Cooper CJ, Brodie B, Grines CL, DeMaria AN; REVERSAL Investigators. Effect of intensive compared with moderate lipid-lowering therapy on progression of coronary atherosclerosis: a randomized controlled trial. JAMA. 2004; 291: 1071–1080.
Cannon CP, Braunwald E, McCabe CH, Rader DJ, Rouleau JL, Belder R, Joyal SV, Hill KA, Pfeffer MA, Skene AM; Pravastatin or Atorvastatin Evaluation and Infection Therapy—Thrombolysis in Myocardial Infarction 22 Investigators. Intensive versus moderate lipid lowering with statins after acute coronary syndromes. N Engl J Med. 2004; 350: 1495–1504.
Grundy SM, Cleeman JI, Bairey-Merz CN, Brewer HB Jr, Clark LT, Hunninghake DB, Pasternak RC, Smith SC Jr, Stone NJ; Coordinating Committee of the National Cholesterol Education Program; National Heart, Lung, and Blood Institute; American College of Cardiology Foundation; American Heart Association. Implications of recent clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines. Arterioscler Thromb Vasc Biol. 2004; 24: e149–e161.
Gordon T, Castelli WP, Hjortland MC, Kannel WB, Dawber TR. High density lipoprotein as a protective factor against coronary heart disease: the Framingham Study. Am J Med. 1977; 62: 707–714.
Kannel WB, Wilson PW. Efficacy of lipid profiles in prediction of coronary disease. Am Heart J. 1992; 124: 768–774.
Shah PK, Kaul S, Nilsson J, Cercek B. Exploiting the vascular protective effects of high-density lipoprotein and its apolipoproteins: an idea whose time for testing is coming, part I. Circulation. 2001; 104: 2376–2383.
Shah PK, Kaul S, Nilsson J, Cercek B. Exploiting the vascular protective effects of high-density lipoprotein and its apolipoproteins: an idea whose time for testing is coming, part II. Circulation. 2001; 104: 2498–2502.
Navab M, Hama SY, Hough GP, Subbanagounder G, Reddy ST, Fogelman AMA. Cell-free assay for detecting HDL that is dysfunctional in preventing the formation of or inactivating oxidized phospholipids. J Lipid Res. 2001; 42: 1308–1317.
Rosenson RS. Antiatherothrombotic effects of nicotinic acid. Atherosclerosis. 2003; 171: 87–96.
Hunninghake DB, McGovern ME, Koren M, Brazg R, Murdock D, Weiss S, Pearson T. A dose-ranging study of a new, once-daily, dual-component drug product containing niacin extended-release and lovastatin. Clin Cardiol. 2003; 26: 112–118.
Brown BG, Zhao XQ, Chait A, Fisher LD, Cheung MC, Morse JS, Dowdy AA, Marino EK, Bolson EL, Alaupovic P, Frohlich J, Albers JJ. Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease. N Engl J Med. 2001; 345: 1583–1592.
Navab M, Anantharamaiah GM, Reddy ST, Van Lenten BJ, Ansell BJ, Fonarow GC, Vahabzadeh K, Hama S, Hough G, Kamranpour N, Berliner JA, Lusis AJ, Fogelman AM. Thematic review series: the pathogenesis of atherosclerosis: the oxidation hypothesis of atherogenesis: the role of oxidized phospholipids and HDL. J Lipid Res. 2004; 45: 993–1007.
Zheng L, Nukuna B, Brennan ML, Sun M, Goormastic M, Settle M, Schmitt D, Fu X, Thomson L, Fox PL, Ischiropoulos H, Smith JD, Kinter M, Hazen SL. Apolipoprotein A-I is a selective target for myeloperoxidase-catalyzed oxidation and functional impairment in subjects with cardiovascular disease. J Clin Invest. 2004; 114: 529–541.
Brewer HB. Increasing HDL cholesterol levels. N Engl J Med. 2004; 350: 1491–1494.
Ansell BJ, Navab M, Hama S, Kamranpour N, Fonarow G, Hough G, Rahmani S, Mottahedeh R, Dave R, Reddy ST, Fogelman M. Inflammatory/anti-inflammatory properties of high-density lipoprotein distinguish patients from control subjects better than high-density lipoprotein cholesterol levels and are favorably affected by simvastatin treatment. Circulation. 2003; 108: 2751–2756.
Perez-Mendez O, Bruckert E, Franceschini G, Duhal N, Lacroix B, Bonte JP, Sirtori C, Fruchart JC, Turpin G, Luc G. Metabolism of apolipoproteins AI and AII in subjects carrying similar apoAI mutations, apoAI Milano and apoAI Paris. Atherosclerosis. 2000; 148: 317–325.
Brewer HB. High-density lipoproteins: a new potential therapeutic target for the prevention of cardiovascular disease. Arterioscler Thromb Vasc Biol. 2004; 24: 387–391.
Zuckerman SH, Evans GF. Cholesteryl ester transfer protein inhibition in hypercholesterolemic hamsters: kinetics of apoprotein changes. Lipids. 1995; 30: 307–311.
Koizumi J, Mabuchi H, Yoshimura A, Michishita I, Takeda M, Itoh H, Sakai Y, Sakai T, Ueda K, Takeda R. Deficiency of serum cholesteryl-ester transfer activity in patients with familial hyperalphalipoproteinemia. Atherosclerosis. 1985; 58: 175–186.
Moriyama Y, Okamura T, Inazu A, Doi M, Iso H, Mouri Y, Ishikawa Y, Suzuki H, Iida M, Koizumi J, Mabuchi H, Komachi Y. A low prevalence of coronary heart disease among subjects with increased high-density lipoprotein cholesterol levels, including those with plasma cholesteryl ester transfer protein deficiency. Prev Med. 1998; 27 (5 pt 1): 659–667.
Hirano K, Yamashita S, Nakajima N, Arai T, Maruyama T, Yoshida Y, Ishigami M, Sakai N, Kameda-Takemura K, Matsuzawa Y. Genetic cholesteryl ester transfer protein deficiency is extremely frequent in the Omagari area of Japan: marked hyperalphalipoproteinemia caused by CETP gene mutation is not associated with longevity. Arterioscler Thromb Vasc Biol. 1997; 17: 1053–1059.
Inazu A, Brown ML, Hesler CB, Agellon LB, Koizumi J, Takata K, Maruhama Y, Mabuchi H, Tall AR. Increased high-density lipoprotein levels caused by a common cholesteryl-ester transfer protein gene mutation. N Engl J Med. 1990; 323: 1234–1238.
Barter PJ, Brewer HB Jr, Chapman MJ, Hennekens CH, Rader DJ, Tall AR. Cholesteryl ester transfer protein: a novel target for raising HDL and inhibiting atherosclerosis. Arterioscler Thromb Vasc Biol. 2003; 23: 160–167.
Inazu I, Koizumi J, Mabuchi H. Cholesteryl ester transfer protein and atherosclerosis. Curr Opin Lipidol. 2000; 11: 389–396.
von Eckardstein A, Crook D, Elbers J, Ragoobir J, Ezeh B, Helmond F, Miller N, Dieplinger H, Bennink HC, Assmann G. Tibolone lowers high density lipoprotein cholesterol by increasing hepatic lipase activity but does not impair cholesterol efflux. Clin Endocrinol. 2003; 58: 49–58.
Borggreve SE, De Vries R, Dullaart RP. Alterations in high-density lipoprotein metabolism and reverse cholesterol transport in insulin resistance and type 2 diabetes mellitus: role of lipolytic enzymes, lecithin:cholesterol acyltransferase and lipid transfer proteins. Eur J Clin Invest. 2003; 33: 1051–1069.
Ma K, Cilingiroglu M, Otvos JD, Ballantyne CM, Marian AJ, Chan L. Endothelial lipase is a major genetic determinant for high-density lipoprotein concentration, structure, and metabolism. Proc Natl Acad Sci U S A. 2003; 100: 2748–2753.
Cilingiroglu M, Ballantyne C. Endothelial lipase and cholesterol metabolism. Curr Atheroscler Rep. 2004; 6: 126–130.
Ikewaki K, Rader DJ, Sakamoto T, Nishiwaki M, Wakimoto N, Schaefer JR, Ishikawa T, Fairwell T, Zech LA, Nakamura H, Nagano M, Brewer HB. Delayed catabolism of high density lipoprotein apolipoprotein A-I and A-II in human cholesteryl ester transfer protein deficiency. J Clin Invest. 1993; 92: 1650–1658.
Watts GF. The yin and yang of cholesteryl ester transfer protein and atherosclerosis. Clin Sci. 2002; 103: 595–597.
Agerholm-Larsen B, Nordestgaard BG, Steffensen R, Jensen G, Tybjaerg-Hansen A. Elevated HDL cholesterol is a risk factor for ischemic heart disease in white women when caused by a common mutation in the cholesteryl ester transfer protein gene. Circulation. 2000; 101: 1907–1912.
Blankenberg S, Rupprecht HJ, Bickel C, Jiang XC, Poirier O, Lackner KJ, Meyer J, Cambien F, Tiret L; AtheroGene Investigators. Common genetic variation of the cholesteryl ester transfer protein gene strongly predicts future cardiovascular death in patients with coronary artery disease. J Am Coll Cardiol. 2003; 41: 1983–1989.
Barzilai N, Atzmon G, Schechter C, Schaefer EJ, Cupples AL, Lipton R, Cheng S, Shuldiner AR. Unique lipoprotein phenotype and genotype associated with exceptional longevity. JAMA. 2003; 290: 2030–2040.
de Grooth GJ, Zerba KE, Huang SP, Tsuchihashi Z, Kirchgessner T, Belder R, Vishnupad P, Hu B, Klerkx AH, Zwinderman AH, Jukema JW, Sacks FM, Kastelein JJ, Kuivenhoven JA. The cholesteryl ester transfer protein (wCETP) TaqIB polymorphism in the cholesterol and recurrent events study: no interaction with the response to pravastatin therapy and no effects on cardiovascular outcome: a prospective analysis of the CETP TaqIB polymorphism on cardiovascular outcome and interaction with cholesterol-lowering therapy. J Am Coll Cardiol. 2004; 43: 854–857.
Moriyama Y, Okamura T, Inazu A, Doi M, Iso H, Mouri Y, Ishikawa Y, Suzuki H, Iida M, Koizumi J, Mabuchi H, Komachi Y. A low prevalence of coronary heart disease among subjects with increased high-density lipoprotein cholesterol levels, including those with plasma cholesteryl ester transfer protein deficiency. Prev Med. 1998; 27: 659–667.
Zhong S, Sharp DS, Grove JS, Bruce C, Yano K, Curb JD, Tall AR. Increased coronary heart disease in Japanese-American men with mutation in the cholesteryl ester transfer protein gene despite increased HDL levels. J Clin Invest. 1996; 97: 2917–2923.
Bruce C, Sharp DS, Tall AR. Relationship of HDL and coronary heart disease to a common amino acid polymorphism in the cholesteryl ester transfer protein in men with and without hypertriglyceridemia. J Lipid Res. 1998; 39: 1071–1078.
Kakko S, Tamminen M, Paivansalo M, Kauma H, Rantala AO, Lilja M, Reunanen A, Kesaniemi YA, Savolainen MJ. Cholesteryl ester transfer protein gene polymorphisms are associated with carotid atherosclerosis in men. Eur J Clin Invest. 2000; 30: 18–25.
Kimura H, Miyazaki R, Suzuki S, Gejyo F, Yoshida H. Cholesteryl ester transfer protein as a protective factor against vascular disease in hemodialysis patients. Am J Kidney Dis. 2001; 38: 70–76.
Cheung MC, Wolfbauer G, Albers JJ. Plasma phospholipid mass transfer rate: relationship to plasma phospholipid and cholesteryl ester transfer activities and lipid parameters. Biochim Biophys Acta. 1996; 1303: 103–110.
Agellon LB, Walsh A, Hayek T, Moulin P, Jiang XC, Shelanski SA, Breslow JL, Tall AR. Reduced high density lipoprotein cholesterol in human cholesteryl ester transfer protein transgenic mice. J Biol Chem. 1991; 266: 10796–10801.
Plump AS, Masucci-Magoulas L, Bruce C, Bisgaier CL, Breslow JL, Tall AR. Increased atherosclerosis in apoE and LDL receptor gene knock-out mice as a result of human cholesteryl ester transfer protein transgene expression. Arterioscler Thromb Vasc Biol. 1999; 19: 1105–1110.
Marotti KR, Castle CK, Boyle TP, Lin AH, Murray RW, Melchior GW. Severe atherosclerosis in transgenic mice expressing simian cholesteryl ester transfer protein. Nature. 1993; 364: 73–75.
Ishikawa Y, Ito K, Akasaka Y, Ishii T, Masuda T, Zhang L, Akishima Y, Kiguchi H, Nakajima K, Hata Y. The distribution and production of cholesteryl ester transfer protein in the human aortic wall. Atherosclerosis. 2001; 156: 29–37.
Hayek T, Masucci-Magoulas L, Jiang X, Walsh A, Rubin E, Breslow JL, Tall AR. Decreased early atherosclerotic lesions in hypertriglyceridemic mice expressing cholesteryl ester transfer protein transgene. J Clin Invest. 1995; 96: 2071–2074.
Foger B, Chase M, Amar MJ, Vaisman BL, Shamburek RD, Paigen B, Fruchart-Najib J, Paiz JA, Koch CA, Hoyt RF, Brewer HB Jr, Santamarina-Fojo S. Cholesteryl ester transfer protein corrects dysfunctional high density lipoproteins and reduces aortic atherosclerosis in lecithin cholesterol acyltransferase transgenic mice. J Biol Chem. 1999; 274: 36912–36920.
Hoeg JM, Santamarina-Fojo S, Berard AM, Cornhill JF, Herderick EE, Feldman SH, Haudenschild CC, Vaisman BL, Hoyt RF Jr, Demosky SJ Jr, Kauffman RD, Hazel CM, Marcovina SM, Brewer HB Jr. Overexpression of lecithin:cholesterol acyltransferase in transgenic rabbits prevents diet-induced atherosclerosis. Proc Natl Acad Sci U S A. 1996; 93: 11448–1153.
Sugano M, Makino N, Sawada S, Otsuka S, Watanabe M, Okamoto H, Kamada M, Mizushima A. Effect of antisense oligonucleotides against cholesteryl ester transfer protein on the development of atherosclerosis in cholesterol-fed rabbits. J Biol Chem. 1998; 273: 5033–5036.
Sugano M, Sawada S, Tsuchida K, Makino N, Kanada M. Low density lipoproteins develop resistance to oxidative modification due to inhibition of cholesteryl ester transfer protein by a monoclonal antibody. J Lipid Res. 2000; 41: 126–133.
Whitlock ME, Swenson TL, Ramakrishnan R, Leonard MT, Marcel YL, Milne RW, Tall AR. Monoclonal antibody inhibition of cholesteryl ester transfer protein activity in the rabbit. J Clin Invest. 1989; 84: 129–137.
Rittershaus CW, Miller DP, Thomas LJ, Picard MD, Honan CM, Emmett CD, Pettey CL, Adari H, Hammond RA, Beattie DT, Callow AD, Marsh HC, Ryan US. Vaccine-induced antibodies inhibit CETP activity in vivo and reduce aortic lesions in a rabbit model of atherosclerosis. Arterioscler Thromb Vasc Biol. 2000; 20: 2106–2112.
Davidson MH, Maki K, Umporowicz D, Wheeler A, Rittershaus C, Ryan U. The safety and immunogenicity of a CETP vaccine in healthy adults. Atherosclerosis. 2003; 169: 113–120.
Okamoto H, Yonemori F, Wakitani K, Minowa T, Maeda K, Shinkai H. A cholesteryl ester transfer protein inhibitor attenuates atherosclerosis in rabbits. Nature. 2000; 406: 203–207.
Kobayashi J, Okamoto H, Otabe M, Bujo H, Saito Y. Effect of HDL, from Japanese white rabbit administered a new cholesteryl ester transfer protein inhibitor JTT-705, on cholesteryl ester accumulation induced by acetylated low density lipoprotein in J774 macrophage. Atherosclerosis. 2002; 162: 131–135.
Okamoto H, Iwamoto Y, Maki M, Sotani Y, Fumihiko Y, Wakitani K. Effect of JTT-705 on cholesteryl ester transfer protein and plasma lipid levels in normolipidemic animals. Eur J Pharmacol. 2003; 466: 147–154.
Huang Z, Inazu A, Nohara A, Higashikata T, Mabuchi H. Cholesteryl ester transfer protein inhibitor (JTT-705) and the development of atherosclerosis in rabbits with severe hypercholesterolaemia. Clin Sci. 2002; 103: 587–594.
Brousseau ME, Schaefer EJ, Wolfe ML, Bloedon LT, Digenio AG, Clark RW, Mancuso JP, Rader DJ. Effects of a potent inhibitor of cholesteryl ester transfer protein on plasma lipoproteins in patients with low HDL cholesterol levels. N Engl J Med. 2004; 350: 1505–1515.
Rader DJ. Regulation of reverse cholesterol transport and clinical implications. Am J Cardiol. 2003; 92: 42J–49J.
Navab M, Hama S, Hough G, Fogelman AM. Oral synthetic phospholipid (DMPC) raises high-density lipoprotein cholesterol levels, improves high-density lipoprotein function, and markedly reduces atherosclerosis in apolipoprotein E-null mice. Circulation. 2003; 108: 1735–1739.
Badimon JJ, Badimon L, Fuster V. Regression of atherosclerotic lesions by high density lipoprotein plasma fraction in the cholesterol-fed rabbit. J Clin Invest. 1990; 85: 1234–1241.
Nissen SE, Tsunoda T, Tuzcu EM, Schoenhagen P, Cooper CJ, Yasin M, Eaton GM, Lauer MA, Sheldon WS, Grines CL, Halpern S, Crowe T, Blankenship JC, Kerensky R. Effect of recombinant ApoA-I Milano on coronary atherosclerosis in patients with acute coronary syndromes: a randomized controlled trial. JAMA. 2003; 290: 2292–2300.
Ameli S, Hultgardh-Nilsson A, Cercek B, Shah PK, Forrester JS, Ageland H, Nilsson J. Recombinant apolipoprotein A-I Milano reduces intimal thickening after balloon injury in hypercholesterolemic rabbits. Circulation. 1994; 90: 1935–1941.
Shah PK, Nilsson J, Kaul S, Fishbein MC, Ageland H, Hamsten A, Johansson J, Karpe F, Cercek B. Effects of recombinant apolipoprotein A-I(Milano) on aortic atherosclerosis in apolipoprotein E-deficient mice. Circulation. 1998; 97: 780–785.
Shah PK, Yano J, Reyes O, Chyu KY, Kaul S, Bisgaier CL, Drake S, Cercek B. High-dose recombinant apolipoprotein A-I(Milano) mobilizes tissue cholesterol and rapidly reduces plaque lipid and macrophage content in apolipoprotein e-deficient mice: potential implications for acute plaque stabilization. Circulation. 2001; 103: 3047–3050.
Chiesa G, Monteggia E, Marchesi M, Lorenzon P, Laucello M, Lorusso V, Di Mario C, Karvouni E, Newton RS, Bisgaier CL, Franceschini G, Sirtori CR. Recombinant apolipoprotein A-I(Milano) infusion into rabbit carotid artery rapidly removes lipid from fatty streaks. Circ Res. 2002; 90: 974–980.
Asayama K, Hayashibe H, Dobashi K, Uchida N, Nakane T, Kodera K, Shirahata A. Increased serum cholesteryl ester transfer protein in obese children. Obes Res. 2002; 10: 439–446.
Ebenbichler CF, Laimer M, Kaser S, Ritsch A, Sandhofer A, Weiss H, Aigner F, Patsch JR. Relationship between cholesteryl ester transfer protein and atherogenic lipoprotein profile in morbidly obese women. Arterioscler Thromb Vasc Biol. 2002; 22: 1465–1469.
Kwon MJ, Song YS, Choi MS, Park SJ, Jeong KS, Song YO. Cholesteryl ester transfer protein activity and atherogenic parameters in rabbits supplemented with cholesterol and garlic powder. Life Sci. 2003; 72: 2953–2964.
Kwon MJ, Song YS, Choi MS, Song YO. Red pepper attenuates cholesteryl ester transfer protein activity and atherosclerosis in cholesterol-fed rabbits. Clin Chim Acta. 2003; 332: 37–44.
Corbex M, Poirier O, Fumeron F, Betoulle D, Evans A, Ruidavets JB, Arveiler D, Luc G, Tiret L, Cambien F. Extensive association analysis between the CETP gene and coronary heart disease phenotypes reveals several putative functional polymorphisms and gene-environment interaction. Genet Epidemiol. 2000; 19: 64–80.
Klerkx AH, de Grooth GJ, Zwinderman AH, Jukema JW, Kuivenhoven JA, Kastelein JJ. Cholesteryl ester transfer protein concentration is associated with progression of atherosclerosis and response to pravastatin in men with coronary artery disease (REGRESS). Eur J Clin Invest. 2004; 34: 21–28.
Guerin M, Dolphin PJ, Talussot C, Gardette J, Berthezene F, Chapman MJ. Pravastatin modulates cholesteryl ester transfer from HDL to apoB-containing lipoproteins and lipoprotein subspecies profile in familial hypercholesterolemia. Arterioscler Thromb Vasc Biol. 1995; 15: 1359–1368.
Contacos C, Barter PJ, Vrga L, Sullivan DR. Cholesteryl ester transfer in hypercholesterolemia: fasting and postprandial studies with and without pravastatin. Atherosclerosis. 1998; 141: 87–98.
Inazu A, Koizumi J, Kajinami K, Kiyohar T, Chichibu K, Mabuchi H. Opposite effects on serum cholesteryl ester transfer protein levels between long-term treatments with pravastatin and probucol in patients with primary hypercholesterolemia and xanthoma. Atherosclerosis. 1999; 145: 405–413.
Guerin M, Lassel TS, Le Goff W, Farnier M, Chapman MJ. Action of atorvastatin in combined hyperlipidemia: preferential reduction of cholesteryl ester transfer from HDL to VLDL1 particles. Arterioscler Thromb Vasc Biol. 2000; 20: 189–197.
Mann CJ, Yen FT, Grant AM, Bihain BE. Mechanism of plasma cholesteryl ester transfer in hypertriglyceridemia. J Clin Invest. 1991; 88: 2059–2066.
Kotake H, Sekikawa A, Tokita Y, Ishigaki Y, Oikawa S. Effect of HMG-CoA reductase inhibitor on plasma cholesteryl ester transfer protein activity in primary hypercholesterolemia: comparison among CETP/TaqIB genotype subgroups. J Atheroscler Thromb. 2002; 9: 207–212.
de Grooth GJ, Kuivenhoven JA, Stalenhoef AF, de Graaf J, Zwinderman AH, Posma JL, van Tol A, Kastelein JJ. Efficacy and safety of a novel cholesteryl ester transfer protein inhibitor, JTT-705, in humans: a randomized phase II dose-response study. Circulation. 105: 2159–2165.
Clark RW, Sutfin TA, Ruggeri RB, Willauer AT, Sugarman ED, Magnus-Aryitey G, Cosgrove PG, Sand TM, Wester RT, Williams JA, Perlman ME, Bamberger MJ. Raising high-density lipoprotein in humans through inhibition of cholesteryl ester transfer protein: an initial multidose study of torcetrapib. Arterioscler Thromb Vasc Biol. 2004; 24: 490–497.
Brousseau ME, Schaefer EJ, Wolfe ML, Bloedon LT, Digenio AG, Clark RW, Mancuso JP, Rader DJ. Effects of an inhibitor of cholesteryl ester transfer protein on HDL cholesterol. N Engl J Med. 2004; 350: 1505–1515.(James S. Forrester, MD; R)