Characterization of plasma lipoproteins in patients heterozygous for human plasma cholesteryl ester transfer protein (CETP) deficiency: plasma CETP regulates high-density lipoprotein concentration and composition

Dalcetrapib and anacetrapib increase apolipoprotein E-containing HDL in rabbits and humans

The large HDL particles generated by administration of cholesteryl ester transfer protein inhibitors (CETPi) remain poorly characterized, despite their potential importance in the routing of cholesterol to the liver for excretion, which is the last step of the reverse cholesterol transport. Thus, the effects of the CETPi dalcetrapib and anacetrapib on HDL particle composition were studied in rabbits and humans. The association of rabbit HDL to the LDL receptor (LDLr) in vitro was also evaluated. New Zealand White rabbits receiving atorvastatin were treated with dalcetrapib or anacetrapib. A subset of patients from the dal-PLAQUE-2 study treated with dalcetrapib or placebo were also studied. In rabbits, dalcetrapib and anacetrapib increased HDL-C by more than 58% (P < 0.01) and in turn raised large apo E-containing HDL by 66% (P < 0.001) and 59% (P < 0.01), respectively. Additionally, HDL from CETPi-treated rabbits competed with human LDL for binding to the LDLr on HepG2 cells more than control HDL (P < 0.01). In humans, dalcetrapib increased concentrations of large HDL particles (+69%, P < 0.001) and apo B-depleted plasma apo E (+24%, P < 0.001), leading to the formation of apo E-containing HDL (+47%, P < 0.001) devoid of apo A-I. Overall, in rabbits and humans, CETPi increased large apo E-containing HDL particle concentration, which can interact with hepatic LDLr. The catabolism of these particles may depend on an adequate level of LDLr to contribute to reverse cholesterol transport.

HDL Receptor in Schistosoma japonicum Mediating Egg Embryonation: Potential Molecular Basis for High Prevalence of Cholesteryl Ester Transfer Protein Deficiency in East Asia

Schistosomiasis is a life-threatening parasitic disease caused by blood flukes, Schistosomes. In its intestinal type, the parasites reside in visceral/portal veins of the human hosts and lay eggs to excrete in feces via intestinal tracts, and some of the aberrant eggs plug into the liver via the portal blood flow. Ectopic growth of these eggs causes fatal granulomatosis and cirrhosis of the liver. The parasites ingest nutrients from the host blood plasma by using nonspecific and specific transport via their body surface and alimentary tracts. It is especially important for the female adults to obtain lipid molecules because they synthesize neither fatty acids nor sterols and yet produce egg yolk. Low-density lipoprotein receptors have been identified in the body of the Schistosomes but their functions in the parasite life cycle have not clearly been characterized. On the other hand, CD36-related protein was identified in the body and the eggs of Asian blood fluke, Schistosoma japonicum, and characterized as a molecule that mediates selective uptake of cholesteryl ester from the host plasma high-density lipoproteins (HDLs). This reaction was shown crucial for their eggs to grow to miracidia. Interestingly, abnormal large HDL generated in lack of cholesteryl ester transfer protein (CETP) is a poor substrate for this reaction, and, therefore, CETP deficiency resists pathogenic ectopic growth of the aberrant parasite eggs in the liver. This genetic mutation is exclusively found in East Asia, overlapping with the current and historic regions of Schistosoma japonicum epidemic, so that this infection could be related to high prevalence of CETP deficiency in East Asia.

Pharmacological Inhibition of CETP (Cholesteryl Ester Transfer Protein) Increases HDL (High-Density Lipoprotein) That Contains ApoC3 and Other HDL Subspecies Associated With Higher Risk of Coronary Heart Disease

Supplemental Digital Content is available in the text.

Plasma total HDL (high-density lipoprotein) is a heterogeneous mix of many protein-based subspecies whose functions and associations with coronary heart disease vary. We hypothesize that increasing HDL by CETP (cholesteryl ester transfer protein) inhibition failed to reduce cardiovascular disease risk, in part, because it increased dysfunctional subspecies associated with higher risk such as HDL that contains apoC3.

Distinct Differences in Lipoprotein Particle Number Evaluation between GP-HPLC and NMR: Analysis in Dyslipidemic Patients Administered a Selective PPARα Modulator, Pemafibrate

AIM

We established a method to evaluate the lipid concentrations, size and particle numbers (PNs) of lipoprotein subclasses by gel permeation chromatography (GP-HPLC). Nuclear magnetic resonance (NMR) is widely used to analyze these parameters of lipoprotein subclasses, but differences of the two methods are unknown. Current study compared the PNs of each lipoprotein subclass measured by GP-HPLC and NMR, and assessed the effect of a selective PPARα modulator, pemafibrate.

METHODS

Lipoprotein profiles of 212 patients with dyslipidemia who participated in the phase 2 clinical trial of a selective PPARα modulator, pemafibrate, were analyzed by two methods, GP-HPLC and NMR, which were performed with LipoSEARCH (Skylight Biotech) and LipoProfile 3 (LabCorp), respectively. GP-HPLC evaluated the PNs of 18 subclasses, consisting of CM, VLDL1-5, LDL1-6, and HDL1-6. NMR evaluated the PNs of 9 subclasses, consisting of large VLDL & CM, medium VLDL, small VLDL, IDL, large LDL, small LDL, large HDL, medium HDL and small HDL.

RESULTS

Three major classes, total CM&VLDL, total LDL and total HDL were obtained by grouping of corresponding subclasses in both methods and PNs of these classes analyzed by GP-HPLC were correlated positively with those by NMR. The correlation coefficients in total CM&VLDL, total LDL and total HDL between GP-HPLC and NMR was 0.658, 0.863 and 0.798 (all p＜0.0001), respectively. The PNs of total CM&VLDL, total LDL and total HDL analyzed by GP-HPLC was 249.5±51.7nM, 1,679±359 nM and 13,273±1,564 nM, respectively, while those by NMR was 124.6±41.8 nM, 1,514±386 nM and 31,161±4,839 nM, respectively. A marked difference in the PNs between the two methods was demonstrated especially in total HDL. The number of apolipoprotein (Apo) B molecule per one ApoB-containing lipoprotein particle, total CM&VLDL plus total LDL, was 1.10±0.05 by GP-HPLC, while 1.32±0.18 by NMR. The number of ApoA-I per one HDL particle was 3.40±0.17 by GP-HPLC, but only 1.46±0.15 by NMR, much less than reported previously.From the phase 2 clinical trial, randomizing 212 patients to pemafibrate 0.025-0.2 mg BID, fenofibrate 100 mg QD, or placebo groups, pemafibrate reduced the PNs of CM, large VLDL1-VLDL3 and medium VLDL4, but not small VLDL5 by GP-HPLC. It significantly decreased the PNs of smaller LDL and larger HDL particles, but increased those of larger LDL and smaller HDL particles. In contrast, NMR showed marked variations in the effect of pemafibrate on lipoprotein PNs, and no significant size-dependent changes.

CONCLUSIONS

GP-HPLC evaluates the lipoprotein PNs more accurately than NMR and can be used for assessing the effects of lipid-lowering drugs on lipoprotein subclasses.

The Association of Passive Smoking and Dyslipidemia Among Adolescence in Japan: Results From A-CHILD Study

CONTEXT

Passive smoking in childhood has been reported to be associated with dyslipidemia in Western countries. However, this association in Asian countries remains unclear. Further, no study has investigated the sex difference of the association.

OBJECTIVE

This study aimed to elucidate the association between passive smoking and dyslipidemia in adolescent boys and girls in Japan.

METHODS

We used a cross-sectional data of junior high school students in the Adachi Child Health Impact of Living Difficulty (A-CHILD) study in Adachi City, Tokyo, Japan in 2016 and 2018. Of the 1431 available students, 1166 students and their parents responded to the survey, including frequency of passive smoking (response rate 81.5%). We assessed dyslipidemia using total cholesterol (TC) levels, low-density lipoprotein cholesterol (LDL-C) levels and high-density lipoprotein cholesterol (HDL-C) levels. The association between passive smoking and dyslipidemia was evaluated by using multivariate regression analyses adjusted for socioeconomic status and lifestyle factors stratified by boys (N = 564) and girls (N = 602).

RESULTS

Among boys, HDL-C levels were significantly lower if exposed to passive smoking frequently, compared with those not exposed (β = -3.19; 95% CI, -5.84 to -0.55). However, this trend does not hold true among girls. Passive smoking was not associated with TC levels and LDL-C levels in either boys or girls.

CONCLUSION

We found that exposure to passive smoking was associated with HDL-C level among boys in Japan, but not in girls. Further longitudinal study is needed to confirm the association between passive smoking and dyslipidemia among boys in Japan.

High level of serum cholesteryl ester transfer protein in active hepatitis C virus infection

AIM: To determine the significance of cholesteryl ester transfer protein (CETP) in lipoprotein abnormalities in chronic hepatitis C virus (HCV) infection.

METHODS: We evaluated the significance of the serum concentration of CETP in 110 Japanese patients with chronic HCV infection. Fifty-five patients had active HCV infection, and HCV eradication had been achieved in 55. The role of CETP in serum lipoprotein abnormalities, specifically, in triglyceride (TG) concentrations in the four major classes of lipoproteins, was investigated using Pearson correlations in conjunction with multiple regression analysis and compared them between those with active HCV infection and those in whom eradication had been achieved.

RESULTS: The serum CETP levels of patients with active HCV infection were significantly higher than those of patients in whom HCV eradication was achieved (mean ± SD, 2.84 ± 0.69 μg/mL vs 2.40 ± 1.00 μg/mL, P = 0.008). In multiple regression analysis, HCV infection status (active or eradicated) was an independent factor significantly associated with the serum CETP level. TG concentrations in low-density lipoprotein (mean ± SD, 36.25 ± 15.28 μg/mL vs 28.14 ± 9.94 μg/mL, P = 0.001) and high-density lipoprotein (HDL) (mean ± SD, 25.9 ± 7.34 μg/mL vs 17.17 ± 4.82 μg/mL, P < 0.001) were significantly higher in patients with active HCV infection than in those in whom HCV eradication was achieved. The CETP level was strongly correlated with HDL-TG in patients with active HCV infection (R = 0.557, P < 0.001), whereas CETP was not correlated with HDL-TG in patients in whom HCV eradication was achieved (R = -0.079, P = 0.56).

CONCLUSION: Our results indicate that CETP plays a role in abnormalities of lipoprotein metabolism in patients with chronic HCV infection.

Prevention of fatal hepatic complication in schistosomiasis by inhibition of CETP

Schistosoma japonicum, once endemic all the East Asia, remains as a serious public health problem in certain regions. Ectopic egg embryonation in the liver causes granulomatosis and eventually fatal cirrhosis, so that prevention of this process is one of the keys to reduce its mortality. The embryonation requires cholesteryl ester from HDL of the host blood for egg yolk formation, and this reaction is impaired from the abnormal large HDL in genetic cholesteryl ester transfer protein (CETP) deficiency. When CETP was expressed in mice that otherwise lack this protein, granulomatosis of the liver was shown increased compared to the wild type upon infection of Schistosoma japonicum. The CETP deficiencies accumulated exclusively in East Asia, from Indochina to Siberia, so that Shistosomiasis can be a screening factor for this accumulation. CD36 related protein (CD36RP) was identified as a protein for this reaction, cloned from the cDNA library of Schistosoma japonicum with 1880-bp encoding 506 amino acids. The antibody against the extracellular loop of CD36RP inhibited cholesteryl ester uptake from HDL and suppressed egg embryonation in culture. Therefore, inhibition of CETP is a potential approach to prevent liver granulomatosis and thereby fatal liver cirrhosis in the infection of Schistosoma japonicum.

Unique features of high-density lipoproteins in the Japanese: in population and in genetic factors

Despite its gradual increase in the past several decades, the prevalence of atherosclerotic vascular disease is low in Japan. This is largely attributed to difference in lifestyle, especially food and dietary habits, and it may be reflected in certain clinical parameters. Plasma high-density lipoprotein (HDL) levels, a strong counter risk for atherosclerosis, are indeed high among the Japanese. Accordingly, lower HDL seems to contribute more to the development of coronary heart disease (CHD) than an increase in non-HDL lipoproteins at a population level in Japan. Interestingly, average HDL levels in Japan have increased further in the past two decades, and are markedly higher than in Western populations. The reasons and consequences for public health of this increase are still unknown. Simulation for the efficacy of raising HDL cholesterol predicts a decrease in CHD of 70% in Japan, greater than the extent by reducing low-density lipoprotein cholesterol predicted by simulation or achieved in a statin trial. On the other hand, a substantial portion of hyperalphalipoproteinemic population in Japan is accounted for by genetic deficiency of cholesteryl ester transfer protein (CETP), which is also commonly unique in East Asian populations. It is still controversial whether CETP mutations are antiatherogenic. Hepatic Schistosomiasis is proposed as a potential screening factor for historic accumulation of CETP deficiency in East Asia.

An in-silico model of lipoprotein metabolism and kinetics for the evaluation of targets and biomarkers in the reverse cholesterol transport pathway

High-density lipoprotein (HDL) is believed to play an important role in lowering cardiovascular disease (CVD) risk by mediating the process of reverse cholesterol transport (RCT). Via RCT, excess cholesterol from peripheral tissues is carried back to the liver and hence should lead to the reduction of atherosclerotic plaques. The recent failures of HDL-cholesterol (HDL-C) raising therapies have initiated a re-examination of the link between CVD risk and the rate of RCT, and have brought into question whether all target modulations that raise HDL-C would be atheroprotective. To help address these issues, a novel in-silico model has been built to incorporate modern concepts of HDL biology, including: the geometric structure of HDL linking the core radius with the number of ApoA-I molecules on it, and the regeneration of lipid-poor ApoA-I from spherical HDL due to remodeling processes. The ODE model has been calibrated using data from the literature and validated by simulating additional experiments not used in the calibration. Using a virtual population, we show that the model provides possible explanations for a number of well-known relationships in cholesterol metabolism, including the epidemiological relationship between HDL-C and CVD risk and the correlations between some HDL-related lipoprotein markers. In particular, the model has been used to explore two HDL-C raising target modulations, Cholesteryl Ester Transfer Protein (CETP) inhibition and ATP-binding cassette transporter member 1 (ABCA1) up-regulation. It predicts that while CETP inhibition would not result in an increased RCT rate, ABCA1 up-regulation should increase both HDL-C and RCT rate. Furthermore, the model predicts the two target modulations result in distinct changes in the lipoprotein measures. Finally, the model also allows for an evaluation of two candidate biomarkers for in-vivo whole-body ABCA1 activity: the absolute concentration and the % lipid-poor ApoA-I. These findings illustrate the potential utility of the model in drug development.

A potential screening factor for accumulation of cholesteyl ester transfer protein deficiency in East Asia: Schistosoma japonicum

Cholesteryl ester transfer protein (CETP)-deficiency manifests a unique plasma lipoprotein profile without other apparent symptoms. It is highly common in East Asia while rather rare anywhere else. A potential environmental screening factor(s) may therefore contribute to this eccentric distribution, such as its selective advantage against a regional illness, most likely an infectious disease, in relation to plasma lipoproteins. Blood flukes use the host plasma lipoproteins as nutrient sources through the lipoprotein receptor-like systems. Its Asian-specific species, Schistosoma (S) japonicum, which has been endemic in East Asia, takes up cholesteryl ester (CE) from high-density lipoprotein (HDL) for the embryonation of their eggs to miracidia, a critical step of the hepatic pathogenesis of this parasite, but poorly from HDL of CETP-deficiency. CD36-related protein (CD36RP) was cloned from the adults and the eggs of S. japonicum, with 1880-bp encoding 506 amino-acid residues exhibiting the CD36 domains and two transmembrane regions. Its extracellular domain selectively bound human HDL but neither LDL nor CETP-deficiency HDL, and the antibody against the extracellular domain suppressed the selective HDL-CE uptake and embryonation of the eggs. When infected with S. japonicum, wild-type mice developed less hepatic granulomatosis than CETP-transgenic mice by the ectopic egg embryonation. CD36RP is thus a candidate receptor of S. japonicum to facilitate uptake of HDL-CE necessary for egg embryonation. Abnormal HDL caused by CETP-deficiency retards this process and thereby protects the patients from development of hepatic lesions. S. japonicum infection is a potential screening factor for high prevalence of CETP deficiency in East Asia.

A comparison of the theoretical relationship between HDL size and the ratio of HDL cholesterol to apolipoprotein A-I with experimental results from the Women's Health Study

BACKGROUND

HDL size and composition vary among individuals and may be associated with cardiovascular disease and diabetes. We investigated the theoretical relationship between HDL size and composition using an updated version of the spherical model of lipoprotein structure proposed by Shen et al. (Proc Natl Acad Sci U S A 1977;74:837-41.) and compared its predictions with experimental data from the Women's Health Study (WHS).

METHODS

The Shen model was updated to predict the relationship between HDL diameter and the ratio of HDL-cholesterol (HDL-C) to apolipoprotein A-I (ApoA-I) plasma concentrations (HDL-C/ApoA-I ratio). In the WHS (n = 26 772), nuclear magnetic resonance spectroscopy (NMR) was used to measure the mean HDL diameter (d(mean,NMR)) and particle concentration (HDL-P); HDL-C and ApoA-I (mg/dL) were measured by standardized assays.

RESULTS

The updated Shen model predicts a quasilinear increase of HDL diameter with the HDL-C/ApoA-I ratio, consistent with the d(mean,NMR) values from WHS, which ranged between 8.0 and 10.8 nm and correlated positively with the HDL-C/ApoA-I ratio (r = 0.608, P < 2.2 × 10(-16)). The WHS data were further described by a linear regression equation: d(WHS) = 4.66 nm + 12.31(HDL-C/Apo-I), where d(WHS) is expressed in nanometers. The validity of this equation for estimating HDL size was assessed with data from cholesteryl ester transfer protein deficiency and pharmacologic inhibition. We also illustrate how HDL-P can be estimated from the HDL size and ApoA-I concentration.

CONCLUSIONS

This study provides a large-scale experimental examination of the updated Shen model. The results offer new insights into HDL structure, composition and remodeling and suggest that the HDL-C/ApoA-I ratio might be a readily available biomarker for estimating HDL size and HDL-P.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Distribution of dolichol in the serum and relationships between serum dolichol levels and various laboratory test values

We examined the correlations between serum dolichol levels and laboratory test parameters in patients affected by disease, as well as the distribution of dolichol in sera from patients with hyperbetalipoproteinemia and hyperalphalipoproteinemia. Serum dolichol was evaluated by a reverse-phase HPLC method. After centrifugation, the serum dolichol found in healthy controls was mainly associated with medium-sized particles of the high-density lipoprotein (HDL) fraction. For patients with hyperbetalipoproteinemia, serum dolichol was also associated with the medium HDL fractions. However, for hyperalphalipoproteinemia patients the levels of large HDL and serum dolichol were increased, and serum dolichol was mainly associated with the large HDL fraction. On laboratory tests of components, the dolichol level was not correlated with the values for markers of the liver and biliary system, with the values of renal function markers, with creatine kinase activity, amylase activity or uric acid concentration, but was correlated with total cholesterol, HDL-cholesterol and apoA-I concentrations, and with lactate dehydrogenase (LDH) activity. These results suggest that serum dolichol exclusively localized in HDL, and in subpopulation, that in normocholesterolemia or hyperbeta-cholesterolemia is associated with HDL(3), which is small sized and high density HDL, however, that in hyperalphacholesterolemia is associated with HDL(2), which is large sized and lower density HDL.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Fenofibrate increases HDL-cholesterol by reducing cholesteryl ester transfer protein expression

In addition to efficiently decreasing VLDL-triglycerides (TGs), fenofibrate increases HDL-cholesterol levels in humans. We investigated whether the fenofibrate-induced increase in HDL-cholesterol is dependent on the expression of the cholesteryl ester transfer protein (CETP). To this end, APOE*3-Leiden (E3L) transgenic mice without and with the human CETP transgene, under the control of its natural regulatory flanking regions, were fed a Western-type diet with or without fenofibrate. Fenofibrate (0.04% in the diet) decreased plasma TG in E3L and E3L.CETP mice (-59% and -60%; P < 0.001), caused by a strong reduction in VLDL. Whereas fenofibrate did not affect HDL-cholesterol in E3L mice, fenofibrate dose-dependently increased HDL-cholesterol in E3L.CETP mice (up to +91%). Fenofibrate did not affect the turnover of HDL-cholesteryl ester (CE), indicating that fenofibrate causes a higher steady-state HDL-cholesterol level without altering the HDL-cholesterol flux through plasma. Analysis of the hepatic gene expression profile showed that fenofibrate did not differentially affect the main players in HDL metabolism in E3L.CETP mice compared with E3L mice. However, in E3L.CETP mice, fenofibrate reduced hepatic CETP mRNA (-72%; P < 0.01) as well as the CE transfer activity in plasma (-73%; P < 0.01). We conclude that fenofibrate increases HDL-cholesterol by reducing the CETP-dependent transfer of cholesterol from HDL to (V)LDL, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool.

Serum cholesteryl ester transfer protein concentrations are associated with serum levels of total cholesterol, beta-lipoprotein and apoproteins in patients with type 2 diabetes mellitus

OBJECTIVE

To investigate the role of serum cholesterol ester transfer protein (CETP) and the metabolism of various lipids including apoproteins in patients with type 2 diabetes.

MATERIALS AND METHODS

The relationships between serum concentrations of CETP and various lipids and apoproteins were investigated in 193 patients with type 2 diabetes mellitus and 68 age-matched healthy subjects. Serum CETP concentrations were measured by an enzyme-linked immunosorbent assay.

RESULTS

Serum CETP values were lower in diabetic patients than in healthy controls (p < 0.01). Female diabetic patients had significantly higher CETP concentrations than male patients. Serum CETP concentrations exhibited a significant positive correlation with serum concentrations of cholesterol (TC) and beta-lipoproteins in diabetic patients (r = 0.485, p = 0.013). Patients with relatively high serum concentrations of high-density lipoprotein cholesterol (HDL-C) tended to have much lower CETP concentrations than patients with lower HDL-C concentrations. Serum CETP concentrations showed significant positive correlations with those of apoproteins B (Apo B; r = 0.384, p = 0.024) and E (Apo E; r = 0.341, p = 0.035).

CONCLUSION

The data indicate that serum CETP is closely involved in the metabolism of TC, beta-lipoprotein, Apo B and Apo E in type 2 diabetic patients.

HDL from CETP-deficient subjects shows enhanced ability to promote cholesterol efflux from macrophages in an apoE- and ABCG1-dependent pathway

Genetic deficiency or inhibition of cholesteryl ester transfer protein (CETP) leads to a marked increase in plasma levels of large HDL-2 particles. However, there is concern that such particles may be dysfunctional in terms of their ability to promote cholesterol efflux from macrophages. Recently, the ATP-binding cassette transporter ABCG1, a macrophage liver X receptor (LXR) target, has been shown to stimulate cholesterol efflux to HDL. We have assessed the ability of HDL from subjects with homozygous deficiency of CETP (CETP-D) to promote cholesterol efflux from macrophages and have evaluated the role of ABCG1 and other factors in this process. CETP-D HDL-2 caused a 2- to 3-fold stimulation of net cholesterol efflux compared with control HDL-2 in LXR-activated macrophages, due primarily to an increase in lecithin:cholesterol acyltransferase-mediated (LCAT-mediated) cholesteryl ester formation in media. Genetic knockdown or overexpression of ABCG1 showed that increased cholesterol efflux to CETP-D HDL was ABCG1 dependent. LCAT and apoE contents of CETP-D HDL-2 were markedly increased compared with control HDL-2, and increased cholesterol esterification activity resided within the apoE-HDL fraction. Thus, CETP-D HDL has enhanced ability to promote cholesterol efflux from foam cells in an ABCG1-dependent pathway due to an increased content of LCAT and apoE.

Estimating the fasting triglyceride concentration from the postprandial HDL-cholesterol and apolipoprotein CIII concentrations

Hypertriglyceridemia is an important risk factor for atherosclerosis. In the fasting state, the triglyceride (TG) concentration is correlated significantly with the high-density lipoprotein-cholesterol (HDL-C) and apolipoprotein CIII (apoCIII) concentrations. A postprandial change is evident in TG, but negligible in HDL-C and apoCIII. We investigated whether the fasting TG concentration could be estimated from the postprandial HDL-C and apoCIII concentrations. We measured the TG, HDL-C, and apoCIII concentrations at seven points a day in 58 inpatients. Multiple regression analysis showed that the actual fasting TG concentration was strongly correlated with the TG concentration estimated from the fasting HDL-C and apoCIII concentrations (ln[TG](fasting)=0.0140[apoCIII](fasting)-0.724[HDL-C](fasting)-0.142, r=0.852, p<0.001). This equation was also fit to the fasting data from 163 outpatients (r=0.883, p<0.001). Although the TG concentration increased by up to 28.2%, the HDL-C and apoCIII concentrations changed little during the day. When we substituted the postprandial HDL-C and apoCIII concentrations for the respective fasting values in this equation, there were still strong positive correlations (r=0.794-0.840) between the actual and estimated fasting TG concentrations throughout the day. In conclusion, the fasting TG concentration can be estimated from the postprandial HDL-C and apoCIII concentrations.

Functional interaction between −629C/A, −971G/A and −1337C/T polymorphisms in the CETP gene is a major determinant of promoter activity and plasma CETP concentration in the REGRESS Study

Cholesteryl ester transfer protein (CETP) plays a key role in the determination of high-density lipoprotein (HDL) levels via its action on intravascular HDL metabolism. The TaqIB polymorphism of the CETP gene is associated with plasma CETP and high-density lipoprotein cholesterol (HDL-C) levels and with premature coronary artery disease. Such associations appear to result from linkage disequilibrium between TaqIB and other functional polymorphisms. To date, only one functional promoter variant, which may explain the effects of TaqIB, has been identified at position -629 in the CETP gene. Here we describe a C/T polymorphism located at position -1337 in the human CETP gene (C allele frequency: 0.684), which is significantly associated with plasma HDL-C and CETP levels (P=0.0001 and P<0.0001, respectively). Transient transfection of a reporter gene construct containing the CETP promoter from -1707/+28 in liver cells (HepG2) revealed that the -1337T allele was expressed to a significantly lower degree (-34%, P<0.0001) than the -1337C allele. In addition, we clearly demonstrated that the -971G/A polymorphism is functional and that its functionality is intimately linked to the presence of the -1337 site. In vitro evaluation of potential interaction between -1337C/T and other functional variants of the CETP gene (-971G/A and -629C/A) demonstrated that these three functional CETP promoter polymorphisms can interact together to determine the overall activity of the CETP gene and thus contribute significantly to variation in plasma CETP mass concentration.

Molecular mechanisms of cholesteryl ester transfer protein deficiency in Japanese

Plasma cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to apolipoprotein B-containing lipoproteins. Since CETP regulates the plasma levels of HDL cholesterol and the size of HDL particles, CETP is considered to be a key protein in reverse cholesterol transport (RCT), a protective system against atherosclerosis. The importance of plasma CETP in lipoprotein metabolism was demonstrated by the discovery of CETP-deficient subjects with marked hyperalphalipoproteinemia (HALP). Genetic CETP deficiency is the most important and common cause of HALP in the Japanese. Ten mutations of the CETP gene have been demonstrated as causes of HALP, including two common mutations: an intron 14 splicing defect (Int14 + 1 G --> A) and an exon 15 missense mutation (D442G). The subjects with CETP deficiency show a variety of abnormalities in the concentration, composition, and function of both HDL and low density lipoprotein (LDL). CETP deficiency is considered a physiological state of impaired RCT, which may possibly lead to the development of atherosclerosis despite high HDL cholesterol levels. However, the pathophysiological significance of CETP in terms of atherosclerosis has been controversial. Epidemiological studies in Japanese-Americans living in Hawaii and Japanese in the Omagari area, where HALP subjects with an intron 14 splicing defect of the CETP gene are markedly frequent, have shown a relatively increased incidence of coronary atherosclerosis in CETP deficiency. On the other hand, the TaqIB polymorphism-B2 allele with low CETP mass and increased HDL cholesterol has been related to a decreased risk for coronary heart disease (CHD) in many studies, including the Framingham Offspring Study. The current review focused on the characterization of the Japanese subjects with CETP deficiency, including our recent findings.

Scavenger receptor type BI potentiates reverse cholesterol transport system by removing cholesterol ester from HDL

High-density lipoprotein (HDL) plays an important role in reverse cholesterol transport by removing accumulated cholesterol from extrahepatic tissues. Subsequently, cholesterol ester (CE) on HDL in humans is transported to apolipoprotein B-containing lipoproteins by cholesteryl ester transfer protein (CETP). CETP deficiency, which is common in the Japanese population, leads to a marked increase in HDL-cholesterol levels due to impaired CE transport from HDL to LDL. It has been reported that the HDL observed in CETP deficiency is an atherogenic lipoprotein, as it contains a large amount of CE. Scavenger receptor class B type I (SR-BI) has been found to be an authentic HDL receptor that mediates the selective uptake of HDL CE and the bi-directional transfer of free cholesterol between HDL and cells. In the present study, the interaction between SR-BI and CE-rich HDL from CETP-deficient patient was studied in order to evaluate the anti-atherosclerotic role of SR-BI in relation to CE uptake and reverse cholesterol transport. When CE-rich HDL was added to the medium of SR-BI-transfected CHO (SR-BI CHO) cells, more CE accumulated in SR-BI CHO cells compared to control HDL. In contrast, the amount of cholesterol efflux from SR-BI CHO cells into HDL was almost the same between the two HDLs. Therefore, when CE-rich HDL was added to the medium of SR-BI CHO cells, the intracellular CE content increased significantly. Moreover, the particle size of HDL in CETP-deficient patient decreased significantly when the HDL was added to the medium of SR-BI CHO cells, and this HDL showed an increment of CE efflux from foam cells. These results indicate that SR-BI reduces the cholesterol content and size of the CE-rich HDL from CETP deficiency, which ultimately activate reverse cholesterol transport system.

Raising High-Density Lipoprotein in Humans Through Inhibition of Cholesteryl Ester Transfer Protein

Objective— The ability of the potent cholesteryl ester transfer protein (CETP) inhibitor torcetrapib (CP-529,414) to raise high-density lipoprotein cholesterol (HDL-C) levels in healthy young subjects was tested in this initial phase 1 multidose study.

Methods and Results— Five groups of 8 subjects each were randomized to placebo (n=2) or torcetrapib (n=6) at 10, 30, 60, and 120 mg daily and 120 mg twice daily for 14 days. Torcetrapib was well tolerated, with all treated subjects completing the study. The correlation of plasma drug levels with inhibition (EC50=43 nM) was as expected based on in vitro potency (IC50 ≈50 nM), and increases in CETP mass were consistent with the proposed mechanism of inhibition. CETP inhibition increased with escalating dose, leading to elevations of HDL-C of 16% to 91%. Total plasma cholesterol did not change significantly because of a reduction in nonHDL-C, including a 21% to 42% lowering of low-density lipoprotein cholesterol at the higher doses. Apolipoprotein A-I and E were elevated 27% and 66%, respectively, and apoB was reduced 26% with 120 mg twice daily. Cholesteryl ester content decreased and triglyceride increased in the nonHDL plasma fraction, with contrasting changes occurring in HDL.

Conclusions— These effects of CETP inhibition resemble those observed in partial CETP deficiency. This work serves as a prelude to further studies in subjects with low HDL, or combinations of dyslipidemia, in assessing the role of CETP in atherosclerosis.

Pharmacological modulation of cholesteryl ester transfer protein, a new therapeutic target in atherogenic dyslipidemia

In mediating the transfer of cholesteryl esters (CE) from antiatherogenic high density lipoprotein (HDL) to proatherogenic apolipoprotein (apo)-B-containing lipoprotein particles (including very low density lipoprotein [VLDL], VLDL remnants, intermediate density lipoprotein [IDL], and low density lipoprotein [LDL]), the CE transfer protein (CETP) plays a critical role not only in the reverse cholesterol transport (RCT) pathway but also in the intravascular remodeling and recycling of HDL particles. Dyslipidemic states associated with premature atherosclerotic disease and high cardiovascular risk are characterized by a disequilibrium due to an excess of circulating concentrations of atherogenic lipoproteins relative to those of atheroprotective HDL, thereby favoring arterial cholesterol deposition and enhanced atherogenesis. In such states, CETP activity is elevated and contributes significantly to the cholesterol burden in atherogenic apoB-containing lipoproteins. In reducing the numbers of acceptor particles for HDL-derived CE, both statins (VLDL, VLDL remnants, IDL, and LDL) and fibrates (primarily VLDL and VLDL remnants) act to attenuate potentially proatherogenic CETP activity in dyslipidemic states; simultaneously, CE are preferentially retained in HDL and thereby contribute to elevation in HDL-cholesterol content. Mutations in the CETP gene associated with CETP deficiency are characterized by high HDL-cholesterol levels (>60 mg/dL) and reduced cardiovascular risk. Such findings are consistent with studies of pharmacologically mediated inhibition of CETP in the rabbit, which argue strongly in favor of CETP inhibition as a valid therapeutic approach to delay atherogenesis. Consequently, new organic inhibitors of CETP are under development and present a potent tool for elevation of HDL in dyslipidemias involving low HDL levels and premature coronary artery disease, such as the dyslipidemia of type II diabetes and the metabolic syndrome. The results of clinical trials to evaluate the impact of CETP inhibition on premature atherosclerosis are eagerly awaited.

Association of cholesteryl ester transfer protein activity and TaqIB polymorphism with lipoprotein variations in Japanese subjects

Cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester from high-density lipoprotein (HDL) to apolipoprotein (apo)B-containing lipoproteins, whereby it potentially regulates steady-state concentrations of HDL-cholesterol (HDL-C), as well as low-density lipoprotein-cholesterol (LDL-C). We performed a multicenter trial to assess the association of CETP activity with plasma lipoprotein levels in 591 Japanese subjects. Women had significantly higher CETP activity (15%) and mass (24%) compared to men. For both genders CETP activity was negatively correlated with HDL-C and HDL(2)-C, but positively correlated with LDL-C. B2 allele frequency in TaqIB polymorphism was 40%, with no gender difference. TaqIB genotypes were significantly associated with CETP activity and HDL-C level (both P <.001). B1B1 had the highest CETP activity and the lowest HDL-C concentrations, whereas B2B2 had the lowest CETP activity and the highest HDL-C concentrations. However, no statistically significant differences in triglycerides (TG) or LDL-C were observed across TaqIB genotypes. Multivariate analysis revealed that determinants of HDL-C were age, gender, body mass index (BMI), smoking, alcohol intake, exercise, CETP activity, and TG, and for LDL-C were BMI, age, and CETP. These data demonstrate that CETP activity is a significant determinant of HDL-C and LDL-C levels and that TaqIB CETP gene polymorphism affects CETP activity and HDL-C level in Japanese population examined.

The human cholesteryl ester transfer protein I405V polymorphism is associated with plasma cholesterol concentration and its reduction by dietary phytosterol esters

We examined the relationships of I405V cholesteryl ester transfer protein (CETP), Taq1B CETP and apolipoprotein (apo)E polymorphisms with the pattern of response to dietary plant sterol ester (PSE) by plasma lipids and CETP concentrations as well as lecithin-cholesterol acyltransferase (LCAT) activity. Subjects with moderate primary hypercholesterolemia (20-60 y old; 50 women; 10 men) consumed margarine (20 g/d) without (placebo) or with PSE (2.8 g/d = 1.68 g/d phytosterols) for 4 wk each period, in a crossover, double-blind study. Plasma CETP concentration was measured by ELISA; endogenous LCAT activity was expressed as the percentage of esterification (30 min incubation) of the subjects' (14)C-unesterified cholesterol HDL. PSE reduced concentrations of plasma total cholesterol (TC) (10%) and LDL cholesterol (LDL-C) (12%). In relation to the I405V CETP polymorphism, the percentage reductions in TC with consumption of PSE for the II, IV and VV phenotypes were 7.2, 4.2 and not significant, respectively, whereas LDL-C significant reductions occurred only for II (9.5%). However, the CETP concentration diminished only in the II phenotype.

Two novel missense mutations in the CETP gene in Japanese hyperalphalipoproteinemic subjects: high-throughput assay by Invader assay

Cholesteryl ester transfer protein (CETP) deficiency is one of the most important and common causes of hyperalphalipoproteinemia (HALP) in the Japanese. CETP deficiency is thought to be a state of impaired reverse cholesterol transport, which may possibly lead to the development of atherosclerotic cardiovascular disease despite high HDL-cholesterol (HDL-C) levels. Thus, it is important to investigate whether HALP is caused by CETP deficiency. In the present study, we identified two novel missense mutations in the CETP gene among 196 subjects with a marked HALP (HDL-C > or = 2.59 mmol/l = 100 mg/dl). The two missense mutations, L151P (CTC-->CCC in exon 5) and R282C (CGC-->TGC in exon 9), were found in compound heterozygous subjects with D442G mutation, whose plasma CETP levels were significantly lower when compared with those in D442G heterozygous subjects. In COS-7 cells expressing the wild type and mutant CETP, these two mutant CETP showed a marked reduction in the secretion of CETP protein into media (0% and 39% of wild type for L151P and R282C, respectively). These results suggested that two novel missense mutations cause the decreased secretion of CETP protein into circulation leading to HALP. By using the Invader assay for seven mutations, including two novel mutations of the CETP gene, we investigated their frequency among 466 unrelated subjects with HALP (HDL-C > or = 2.07 mmol/l = 80 mg/dl). Two novel mutations were rare, but L151P mutation was found in unrelated subjects with a marked HALP. Furthermore, we demonstrated that CETP deficiency contributes to 61.7% and 31.4% of marked HALP and moderate HALP in the Japanese, respectively.

Point mutation (-69 G-->A) in the promoter region of cholesteryl ester transfer protein gene in Japanese hyperalphalipoproteinemic subjects

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester (CE) from HDL to apolipoprotein (apo) B-containing lipoproteins and plays a crucial role in reverse cholesterol transport, which is a major protective system against atherosclerosis. Genetic CETP deficiency is the most common cause of a marked hyperalphalipoproteinemia (HALP) in the Japanese, and various mutations have been identified in the coding region as well as in the exon/intron boundaries in the CETP gene. In the present study, we identified a novel mutation in the promoter region of the CETP gene. This mutation was a G-to-A substitution at the -69 nucleotide of the promoter region (-69 G-->A), corresponding to the second nucleotide of the PEA3/ETS binding site (CGGAA) located upstream of the putative TATA box. Four (2.0%) of 196 unrelated subjects with a marked HALP (HDL cholesterol >/=2.59 mmol/L=100 mg/dL) were revealed to be heterozygous for the -69 G-->A mutation, and the allelic frequency of the mutant was 0.0102 in the subjects with a marked HALP. The subjects with the -69 G-->A mutation had low plasma CETP levels. Reporter gene assay showed that this mutation markedly reduced the transcriptional activities in HepG2 cells (8% of wild type). These results suggested that this mutation would be dominant negative. In conclusion, a novel -69 G-->A mutation in the CETP gene causes the decreased transcriptional activity leading to HALP.

Spontaneous combined hyperlipidemia, coronary heart disease and decreased survival in Dahl salt-sensitive hypertensive rats transgenic for human cholesteryl ester transfer protein

The acceleration of atherosclerosis by polygenic (essential) hypertension is well-characterized in humans; however, the lack of an animal model that simulates human disease hinders the elucidation of pathogenic mechanisms. We report here a transgenic atherosclerosis-polygenic hypertension model in Dahl salt-sensitive hypertensive rats that overexpress the human cholesteryl ester transfer protein (Tg[hCETP]DS). Male Tg[hCETP]DS rats fed regular rat chow showed age-dependent severe combined hyperlipidemia, atherosclerotic lesions, myocardial infarctions and decreased survival. These findings differ from various mouse atherosclerosis models, demonstrating the necessity of complex disease modeling in different species. The data demonstrate that cholesteryl ester transfer protein can be proatherogenic. The interaction of polygenic hypertension and hyperlipidemia in the pathogenesis of atherosclerosis in Tg[hCETP]DS rats substantiates epidemiological observations in humans.

Catabolism of HDL1 cholesteryl ester in the rat. Effect of ethinyl estradiol treatment

The present study was performed in control and ethinyl estradiol-treated rats in order to determine the mechanisms involved in the catabolism of HDL1 cholesteryl ester. Ligand blottings on liver membranes showed that purified HDL1, containing about 70% apolipoprotein E and 10% apolipoprotein AI, bind to the LDL receptor (130 kDa) and not to HB2 (100 kDa) or SR-BI (82 kDa), candidate HDL receptors. Immunoblots showed that the treatment increased the hepatic level of the LDL receptor five- to ten-fold, strongly decreased that of SRBI and did not change that of HB2. An in vivo kinetic study showed that the turnover of HDL1 cholesteryl ester is more rapid in treated than control rats. The liver participation (60%) in this clearance was not modified by the treatment. Therefore, it can be concluded that the catabolism of HDL1 cholesteryl ester, in control as in treated rats, is essentially ensured by the uptake of entire particles in the hepatocytes via LDL receptors.

Cholesteryl ester transfer protein gene effect on CETP activity and plasma high-density lipoprotein in European populations. The EARS Group

BACKGROUND

Variation at the cholesteryl ester transfer protein (CETP) gene locus has been implicated in determining the levels and activity of CETP, apoAI and high-density lipoprotein (HDL) plasma concentration and the risk of developing coronary artery disease.

STUDY DESIGN

The effects of two common polymorphisms of CETP, TaqIB in intron 1 and isoleucine 405 to valine (I405-->V) in exon 14, were examined in a sample of 822 men age 18-28 years from 11 countries in Europe who had participated in a study (the European Atherosclerosis Research Study II) of the offspring of myocardial infarction sufferers before the age of 55 years and age-matched control subjects.

RESULTS

The frequency of the rare TaqIB allele (B2) and the rare V405 allele was 0.44 and 0.28 respectively and was the same in different regions of Europe. There was a moderate linkage disequilibrium between the two polymorphisms in all the regions (D' = +0.31, P < 0.001), explained by the preferential association between the two common alleles, B1 and I405. There was a statistically significant association of the rare alleles for both the polymorphisms with lower activity of CETP (P < 0.001), 11.2% lower for the TaqIB and 7.0% lower for the I405-->V polymorphism. The TaqIB polymorphism explained 9.1% (P < 0.001) and I405-->V explained 3.7% (P < 0.001) of the variance in CETP activity, and in combination these genotypes explained 12.0% of the variance (P < 0.001). Overall, subjects whose fathers had had an early coronary heart disease had 2.4% higher plasma CETP activity than those without such family history, which became statistically significant when adjusted for the effect of the genotypes (P = 0.015), but the significance disappeared after adjustment for the effect of lipids. There was a statistically significant effect of the TaqIB polymorphism on both plasma HDL cholesterol and apoAI level (P < 0.001), with those homozygous for the rare B2 allele having the highest level. Those individuals homozygous for the rare V405 allele had the highest HDL and apoAI levels, although these effects only reached statistical significance for HDL (P < 0.03).

CONCLUSION

These results suggest that the TaqIB and I405-->V polymorphisms represent two independent functional variations in the CETP gene that may affect the activity of CETP and thus plasma levels of HDL.

Hyperalphalipoproteinemia: characterization of a cardioprotective profile associating increased high-density lipoprotein2 levels and decreased hepatic lipase activity

The aim of the present study was to investigate the high-density lipoprotein (HDL) structural characteristics and metabolism in hyperalphalipoproteinemic (HALP) patients (HDL-cholesterol [HDL-C], 92 +/- 14 mg/dL) with combined elevated low-density lipoprotein-cholesterol (LDL-C) levels (LDL-C, 181 +/- 33 mg/dL). Patients were subjected to a complete cardiovascular examination, including ultrasonographic investigation of carotid arteries. Two HALP profiles were identified according to the HDL2/HDL3 ratio. HALP profile A was characterized in 28 patients by increased HDL2/HDL3 ratio, HDL2b, and lipoprotein (Lp)A-I levels compared with normolipidemic subjects, and HALP profile B, including the 12 remaining patients, was characterized by a HDL2/HDL3 ratio within the normal range and by the increase of all HDL subclasses (HDL(2b,2a,3a,3b,3c)), LpA-I, and LpA-I:A-II levels. With regard to the exploration of carotid arteries, in HALP profile A, 20 patients were free from lesions and eight had only intimal wall thickening. In HALP profile B, only one patient was free from lesions, four had intimal wall thickening, and seven displayed plaques, but none had stenosis. Taking into account the number of patients with plaques within each group, HALP profile A was associated with a low prevalence of atherosclerotic lesions, whereas HALP profile B was less cardioprotective (odds ratio, 77.7 [95% confidence interval, 3.7 to 1,569.7]; P < .0001). For both HALP profiles, cholesteryl ester transfer protein (CETP) deficiency was discarded and activities of phospholipid transfer protein (PLTP) and lipoprotein lipase (LPL) were normal. However, hepatic lipase (HL) activity was significantly decreased in HALP profile A, but within the normal range for HALP profile B. In conclusion, an HALP profile A with a low prevalence of atherosclerosis was characterized by an increased HDL2/HDL3 ratio, HDL2b, and LpA-I levels associated with decreased HL activity.

A truncated species of apolipoprotein B (B-38.7) in a patient with homozygous hypobetalipoproteinemia associated with diabetes mellitus

Familial hypobetalipoproteinemia is caused by mutations in the apolipoprotein (apo) B gene. We identified a 57-year-old woman whose plasma total cholesterol and apoB levels were 2.17 mmol/L and 0.03 g/L, respectively. Separation of plasma lipoproteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the absence of apoB-100 and the presence of a faster-migrating form of apoB with an apparent Mr of 195 kDa. Direct sequencing of a polymerase chain reaction-amplified fragment of the patient's apoB gene DNA revealed a single C-->T transition at nucleotide 5472 that converts glutamine 1755 (CAA) to a stop codon (TAA). We predict this novel nonsense mutation of the apoB gene to produce a truncated protein that contains 1754 amino-terminal amino acid residues of apoB-100. We designated this mutant form of apoB apoB-38.7 by following the centile nomenclature of the apoB species. The same mutation was found in both of her children. The proband revealed clinical findings of retinitis pigmentosa, acanthocytosis, and loss of deep tendon reflexes that are characteristic of severe hypobetalipoproteinemia. In addition, the proband had type II diabetes mellitus with nephropathy, anemia, cholelithiasis, hepatic hemangioma, bronchiectasis, and extensive calcification of major arteries including, the celiac, splenic, and renal. In summary, we have found a novel truncated apoB, apoB-38.7, in a patient with an unusual presentation of hypobetalipoproteinemia that includes diabetes mellitus and extensive arterial calcification.

Remodeling of the HDL in NIDDM: a fundamental role for cholesteryl ester transfer protein

When the Ay gene is expressed in KK mice, the yellow offspring (KKAy mice) become obese, insulin resistant, hyperglycemic, and severely hypertriglyceridemic, yet they maintain extraordinarily high plasma high-density lipoprotein (HDL) levels. Mice lack the ability to redistribute neutral lipids among circulating lipoproteins, a process catalyzed in humans by cholesteryl ester transfer protein (CETP). To test the hypothesis that it is the absence of CETP that allows these hypertriglyceridemic mice to maintain high plasma HDL levels, simian CETP was expressed in the KKAy mouse. The KKAy-CETP mice retained the principal characteristics of KKAy mice except that their plasma HDL levels were reduced (from 159 +/- 25 to 25 +/- 6 mg/dl) and their free apolipoprotein A-I concentrations increased (from 7 +/- 3 to 22 +/- 6 mg/dl). These changes appeared to result from a CETP-induced enrichment of the HDL with triglyceride (from 6 +/- 2 to 60 +/- 18 mol of triglyceride/mol of HDL), an alteration that renders HDL susceptible to destruction by lipases. These data support the premise that CETP-mediated remodeling of the HDL is responsible for the low levels of that lipoprotein that accompany hypertriglyceridemic non-insulin-dependent diabetes mellitus.

Characterization of two HDL subfractions and LpA-I, LpA-I:A-II distribution profiles and clinical characteristics of hyperalphalipoproteinemic subjects without cholesterol ester transfer protein deficiency

The aims of the present study were (i) to characterize the HDL2, HDL3 and the LpA-I, LpA-I:A-II distribution, (ii) to investigate the prevalence of atherosclerotic lesions and (iii) to assess the activity of cholesteryl ester transfer protein (CETP) in 29 hyperalphalipoproteinemic (HALP) patients (HDL-C=90+/-11 mg/dl) with combined hypercholesterolemia (LDL-C=180+/-16 mg/dl). According to the HDL2/HDL3 and LpA-I/LpA-I:A-II ratios, two HALP profiles (A and B) were defined: in 22 patients (HALP profile A) these ratios were increased compared to the normolipidemic control subjects (1.19+/-0.11 versus 0.53+/-0.19, P < 0.001 and 1.01+/-0.2 versus 0.51+/-0.25, P < 0.001, respectively) and in seven patients (HALP profile B) these ratios were within the normal range (0.64+/-0.20 and 0.69+/-0.2, respectively). The atherosclerotic lesions were assessed by ultrasonography of the carotid arteries. Amongst patients with HALP profile A, 17 were free from lesions, five had intimal wall thickening and none displayed plaques, whereas for patients within the HALP profile B, only one was free from lesions, two had intimal wall thickening and four displayed plaques. CETP activities (348+/-116 versus 371+/-75%/ml/h) and CETP concentrations (2.4+/-0.5 versus 2.5+/-0.6 microg/ml) were similar in HALP profiles A and B, however these values were both higher than in control subjects (190+/-40%/ml/h, P < 0.001 and 1.8+/-0.3 microg/ml, P < 0.001, respectively). Hence the hyperalphalipoproteinemic profiles (A and B) described here were not related to CETP deficiency. In conclusion, the HALP profile A was characterized by both increased HDL2/HDL3 and LpA-I/LpA-I:A-II ratios and was associated with a low prevalence of atherosclerosis, whereas the HALP profile B, characterized by HDL2/HDL3 and LpA-I/LpA-I:A-II ratios within the normal range, was less cardioprotective.

Increased plasma cholesteryl ester transfer activity in obese children

To determine whether enhanced activity of cholesteryl ester transfer protein (CETP) contributes to the development of atherogenic lipoprotein profiles in obese children, plasma CETP activity was assayed according to a micro-method, by co-incubating lipoprotein-deficient samples with exogenous donor and acceptor lipoproteins. The study subjects were 31 obese children (14 males and 17 females). Serum levels of triglycerides, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), TC:high-density lipoprotein (HDL)-C, LDL-C:HDL-C, apolipoprotein (apo) B, and apo B:apo Al were increased in obese children. Thus they appeared to exhibit an atherogenic lipoprotein profile, with a relative decrease in cholesterol carried by HDL compared with the cholesterol in the other lipoprotein fractions. The mean fasting plasma insulin level was also increased. CETP activity was significantly higher in the obese children than in nonobese control children, and was correlated with LDL-C, TC:HDL-C, LDL-C:HDL-C, and apo B:apo Al. These results suggest that an increase in plasma CETP activity results in atherogenic change in lipoprotein metabolism in obese children. The increase in CETP may be due to the adiposity or insulin resistance. Alternatively, dyslipidemia per se, physical inactivity or excessive fat intake, that are commonly found in obese children, may contribute to the increase in CETP activity.

Relationship of plasma cholesteryl ester transfer protein to HDL cholesterol. Studies in normotriglyceridemia and moderate hypertriglyceridemia

To evaluate the independent effect of cholesteryl ester transfer protein (CETP) on HDL concentrations in humans, we measured lipids, lipoproteins, postprandial lipemia after an oral fat load, CETP mass, and the activities of CETP, lipoprotein lipase (LPL), and hepatic lipase in 16 healthy, normotriglyceridemic men and in 23 men with moderate, primary hypertriglyceridemia on an American Heart Association Step I diet. Fasting triglycerides and postprandial lipemia were increased and HDL cholesterol (HDL-C) was decreased in hypertriglyceridemic men compared with control subjects (P < .001). In the normotriglyceridemic group, CETP mass (P < .001) and activity (P < .005) were directly related to LPL activity After statistical adjustment for this close association, no significant relationship of CETP to HDL-C independent of LPL activity could be demonstrated in the normotriglyceridemic subjects. In contrast, CETP was unrelated to LPL activity in the hypertriglyceridemic subjects, but CETP concentrations showed a close inverse relationship to HDL-C (r = -.504, P = .014). Structural equation modeling of the association structures between HDL and fasting and postprandial triglycerides, endothelial lipases, and CETP in both groups indicated that the overall regression models for the two groups differed (P < .05). Specifically, the associations between CETP mass and activity and HDL-C differed between both groups (both P < .01). We conclude that high-normal CETP levels lower HDL-C in nonsmoking, nonobese men with moderate, primary hypertriglyceridemia on a hypolipidemic diet, but not in healthy, normotriglyceridemic men on an unrestricted diet. Thus, variation in CETP plasma concentrations may contribute to the high-triglyceride, low-HDL phenotype.

Alterations of lipoprotein fluidity by non-esterified fatty acids known to affect cholesteryl ester transfer protein activity. An electron spin resonance study

The aim of the present study was to investigate the effect of saturated, monounsaturated and polyunsaturated non-esterified fatty acids (NEFA) on lipoprotein fluidity by using the electron spin resonance (ESR) method. The fluidity of the lipid phase of lipoproteins was evaluated by calculating from ESR spectra the S parameter of three different positional isomers of spin-labeled stearic acid incorporated into the lipoprotein. In non-enriched lipoproteins, S values were higher in high-density lipoprotein 3 (HDL3) than in low-density lipoprotein (LDL) indicating that the surface of HDL3 was more ordered. Prior incubation of lipoprotein particles with NEFA significantly reduced S values, indicating an increased lipoprotein fluidity as compared with non-supplemented homologous samples. In NEFA-enriched lipoproteins, the modifications in fluidity were shown to be dependent on the structure of the NEFA acyl carbon chains. Medium-chain fatty acids [lauric (12:0) and myristic (14:0) acids] appeared to be better fluidizing molecules as compared with both shorter [octanoic (8:0) and decanoic (10:0) acids] and longer [palmitic (16:0) and stearic (18:0) acids] homologues. In addition, introducing at least one double bond in the acyl carbon chain significantly increased the ability of NEFA to reduce S as compared with saturated homologues. In both LDL and HDL3, the extent of the modifications of the molecular mobility at the lipoprotein surface was dependent on the final NEFA/lipoprotein ratio. In conclusion, these results suggest that the ability of NEFA to modulate the activity of the cholesteryl ester transfer protein might relate in part to alterations in fluidity at the lipoprotein surface.

Sex difference in the regulation of plasma high density lipoprotein cholesterol by genetic and environmental factors

Association between high density lipoprotein (HDL) cholesterol concentration and restriction fragment length polymorphisms at the cholesteryl ester transfer protein (CETP) gene locus was studied in a random population-based cohort of 526 Caucasian subjects (259 men, mean age 50.9 years, and 267 women, mean age 51.8 years). HDL cholesterol concentration was adjusted for age, body mass index, alcohol consumption, smoking and plasma triglyceride and low density lipoprotein cholesterol levels. In females, the HDL cholesterol levels were associated with TaqIB polymorphism (1.46 mmol/l in the B1B1 genotype, 1.56 mmol/l in B1B2 and 1.72 mmol/l in B2B2, P = 0.0001 for the trend). In contrast, this was not observed in men (1.24, 1.20, 1.27 mmol/l, NS). The association was seen even in women who were current smokers (1.41, 1.56, 1.75 mmol/l, n = 72, P = 0.007), but not in male smokers (1.26, 1.19, 1.14 mmol/l, n = 102, NS). In male non-smokers the association was weak (1.22, 1.20, 1.32 mmol/l, n = 157, P = 0.05). In postmenopausal women not receiving hormone replacement therapy (n = 108), the association continued to be present, although weaker (1.50, 1.58, 1.70 mmol/l, P = 0.06). CETP activity (n = 101) tended to be lower in subjects with the B2B2 genotype. In conclusion, a clear-cut sex difference was observed in the genotype effect on plasma HDL cholesterol levels. The slight attenuation of the gene dosage effect after menopause suggests that the gender difference may be, at least in part, due to sex hormones. A genetic subgroup (men with the B2B2 genotype) particularly susceptible to the HDL cholesterol decreasing effect of smoking could be demonstrated.

Increased esterification of cholesterol and transfer of cholesteryl ester to apo B-containing lipoproteins in Type 2 diabetes: relationship to serum lipoproteins A-I and A-II

This study examines the activity of two key enzymes of reverse cholesterol transport, cholesterol ester transfer protein (CETP) and lecithin:cholesterol acyl transferase (LCAT) in 21 patients with non-insulin dependent diabetes mellitus (NIDDM) and 21 control subjects. Serum CETP was assessed by measuring plasma-mediated cholesteryl ester transfer between pooled exogenous lipoprotein with endogenous LCAT inhibited--an estimate of CETP mass. CETP activity was determined as cholesteryl ester transfer in the presence of the patients' lipoproteins and LCAT (endogenous assay). LCAT activity was determined in the same assay. There was no significant difference in CETP mass between the diabetic and non-diabetic subjects and there was no correlation between CETP mass and LCAT activity. Using the endogenous lipoprotein assay, CETP was elevated in serum from diabetic patients compared to control subjects (10.05 +/- 1.89 vs. 5.50 +/- 0.53 nmol/ml/h P < 0.05). LCAT was also increased in the diabetic patients (53.63 +/- 4.70 vs. 41.22 +/- 3.40 nmol/ml/h P < 0.05). Serum free cholesterol from diabetic and control subjects correlated with CETP activity measured using endogenous lipoprotein assay (r = 0.77, P < 0.001 and r = 0.82, P < 0.001), and also with LCAT activity (r = 0.76, P < 0.01 and r = 0.79, P < 0.01). There was a negative correlation between CETP activity with the endogenous lipoprotein assay and serum high density lipoprotein (HDL) cholesterol in the diabetic patients (r = -0.38, P < 0.01), but not in control subjects. In a subgroup of 10 control subjects, there was a positive correlation between LCAT activity and apolipoprotein (apo) A-I (r = 0.49, P < 0.05) and apo A-II (r = 0.51, P < 0.05) and also between CETP activity (endogenous assay) and apo A-I (r = 0.87, P = 0.001) and apo A-II (r = 0.63, P < 0.05). No relationship was observed between CETP activity and apo A-I or apo A-II in the diabetic subjects. Thus, serum CETP mass was normal in Type 2 diabetes but CETP activity (endogenous assay) was increased and was related to free cholesterol levels and LCAT activity in both diabetic and non-diabetic subjects.

Molecular disorders of cholesteryl ester transfer protein

Plasma cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester (CE) from HDL to apolipoprotein B-containing lipoproteins and therefore is a key protein in the reverse cholesterol transport system. The importance of plasma CETP in lipoprotein metabolism has been highlighted by the discovery of CETP-deficient subjects with a marked hyper-HDL-cholesterolemia. The deficiency of CETP causes various abnormalities in the concentration, composition, and functions of high density and low density lipoproteins. The current review will focus on some of the recent knowledge on CETP with special reference to the biochemical and molecular biological aspects of CETP. Furthermore, detailed information will be presented regarding the lipoprotein abnormalities and molecular basis of CETP deficiency.

Plasma HDL cholesterol, triglycerides, and adiposity. A quantitative genetic test of the conjoint trait hypothesis in the San Antonio Family Heart Study

BACKGROUND

The conjoint trait hypothesis proposes that combined low HDL cholesterol (HDL-C) and high triglyceride (TG) levels represent a single, inherited phenotype that adiposity may influence in an unspecified manner. We conducted formal statistical genetic tests of the conjoint trait hypothesis and the relation of the conjoint trait to adiposity using data for 569 subjects in 25 pedigrees from the San Antonio Family Heart Study.

METHODS AND RESULTS

We conducted multivariate genetic analyses to detect the effects of genes and environmental factors on variation in plasma concentrations of HDL-C and TG, fat mass (as percent body weight [FM%], determined by bioelectric impedance), and body mass index (BMI). We used maximum-likelihood methods to simultaneously estimate the phenotypic means and SDs, heritabilities (h2), effects of sex, age-by-sex, eight dietary and medical covariates, and genetic and environmental correlations. Likelihood ratio tests disclosed significant heritabilities (P < .001) for all traits (h2HDL-C = 0.55, h2TG = 0.53, h2FM% = 0.37, h2BMI = 0.44) but significant genetic correlations (P < .001), indicating pleiotropy, between two trait pairs only: HDL-C and TG (PG = -0.52) and fat mass and BMI (PG = 0.86). We obtained significant environmental correlations between all trait pairs except HDL-C and BMI (P > .05).

CONCLUSIONS

Both shared genes (pleiotropy) and shared environmental factors contribute to the commonly observed inverse phenotypic association between plasma levels of HDL-C and TG. Rather than low HDL-C and high TG being a single, genetically transmissible entity, it is the inverse relation between these two phenotypes throughout their normal ranges of variation as well as at the extremes that is influenced by shared genes and shared environments. However, common environmental factors, not shared genes, account for reported associations of plasma HDL-C and TG levels with measures of adiposity.

Evidence that cynomolgus monkey cholesteryl ester transfer protein has two neutral lipid binding sites

Two inhibitors of cynomolgus monkey cholesteryl ester transfer protein were evaluated. One, a monoclonal antibody made against purified cynomolgus monkey cholesteryl ester transfer protein, was capable of severely inhibiting triglyceride transfer, but had a variable effect on cholesteryl ester transfer. At low antibody to antigen ratios, there was what appeared to be a stoichiometric inhibition of cholesteryl ester transfer, but at high antibody to antigen ratios the inhibition of cholesteryl ester transfer was completely relieved, even though triglyceride transfer remained blocked. Fab fragments of the antibody had no effect whatsoever on cholesteryl ester transfer, but were capable of completely blocking triglyceride transfer. The other inhibitor, 6-chloromecuric cholesterol, severely inhibited cholesteryl ester transfer with minimal inhibition of triglyceride transfer. When both inhibitors were added to the assay, both cholesteryl ester and triglyceride transfer were inhibited; an indication that the inhibitors did not compete for the same binding site on cholesteryl ester transfer protein. When the antibody was given subcutaneously to cynomolgus monkeys at a dose which inhibited triglyceride transfer in the plasma by more than 90%, there was no detectable effect on the high density lipoprotein (HDL) cholesterol level, but the HDL triglyceride levels decreased from 13 +/- 2 to 1 +/- 0 mol/mol of HDL (mean +/- S.D.); an indication that the antibody uncoupled cholesteryl ester and triglyceride transfer in vivo. The 6-chloromecuric cholesterol could not be evaluated in vivo because it is a potent lecithin:cholesterol acyltransferase inhibitor. The fact that cholesteryl ester transfer can be inhibited without effect on triglyceride transfer and, conversely, that triglyceride transfer can be inhibited without effect on cholesteryl ester transfer indicates that these two lipids are not transferred by a single, non-discriminatory process.