Accumulation of apolipoprotein E-rich high density lipoproteins in hyperalphalipoproteinemic human subjects with plasma cholesteryl ester transfer protein deficiency.

This study characterized the plasma lipoproteins of familial hyperalphalipoproteinemic patients with or without deficiency of cholesteryl ester transfer protein (CETP) activity. The subjects with CETP deficiency have increased levels of apolipoprotein (apo) E. The increased concentration of apo E in these subjects was correlated to the appearance of apo E-rich high density lipoproteins (HDL). Sodium dodecyl sulfate-polyacrylamide gel analysis revealed that these lipoproteins contained predominantly the apo E (82%) and little amount of apo A-I (18%). These apo E-rich HDL displayed a much higher affinity than human LDL in binding to LDL receptors on human fibroblasts. Furthermore, 3.5 times fewer apo E-rich HDL than LDL were required to saturate the receptors on fibroblasts. These data indicated that the apo E-rich HDL in CETP-deficient human subjects contained multiple copies of apo E and bound to the LDL receptor through multiple interactions. The apo E-rich HDL, with similar properties as cholesterol-induced apo E HDLc, were not detectable in normal human subjects or in hyperalphalipoproteinemic subjects with normal CETP activity. The apo E-containing HDL in the latter subjects were smaller and contained only small amounts of apo E (14%). The difference in apo E-containing HDL in these subjects suggests a correlation between CETP level and the appearance of apo E-rich HDL.     

Variation at the cholesteryl ester transfer protein gene in relation to plasma high density lipoproteins cholesterol levels and carotid intima-media thickness

BACKGROUND: Cholesteryl ester transfer protein (CETP) plays a major role in lipoprotein metabolism. We have screened the CETP gene for mutations and polymorphisms regulating high density lipoproteins cholesterol (HDL-C) levels and the development of atherosclerosis, and found some polymorphisms (I405V and R451Q) to have minor effects. DESIGN: The purpose of this study was to investigate the combined effect of the several polymorphisms of the CETP gene so far found on HDL-C levels and carotid intima-media thickness (IMT), and, in addition, to study whether the recently found functional polymorphism in the promoter region of the CETP gene (C to A, - 629 relative to the first transcribed nucleotide) explains the previous associations due to linkage disequilibrium. The genotypes were determined in a population sample of 481 men and women. RESULTS: There were no significant differences in plasma CETP activity or carotid IMT between the genotypes of the promoter polymorphism. The women with the CC genotype of the promoter polymorphism had the lowest HDL-C levels (P < 0.001), but no such difference was seen in men. Detected polymorphisms of the CETP gene explained about 8% of the variation in HDL-C in women and about 7 and 10% of the variation in carotid IMT in women and men, respectively. The associations of the promoter, I405V and R451Q-A373P polymorphisms with HDL-C and carotid IMT seemed to be independent of each other. The associations with IMT were independent of total HDL-C levels, suggesting that HDL subfractions may have more effect on IMT. CONCLUSION: The CETP gene locus was found to be polymorphic and its polymorphisms explained a reasonable proportion of the variation in the degree of carotid atherosclerosis.     

Particle size analysis of high density lipoproteins in patients with genetic cholesteryl ester transfer protein deficiency

We investigated the detailed distribution of high-density lipoproteins (HDL) particle size in patients with cholesteryl ester transfer protein (CETP) deficiency. Serum samples pre-stained with Sudan black B were electrophoresed using 4-30% polyacrylamide gradient gels, and the Stokes diameter of HDL particles was determined in 23 patients with genetic CETP deficiency, nine patients with hyperalphalipoproteinemia and seven subjects with normal HDL cholesterol concentrations. The mean Stokes diameter of HDL particles in CETP deficient patients (11.2+/-0.6 nm) was significantly greater than hyperalphalipoproteinemia (10.7+/-0.3 nm, P<0.05) and normal subjects (9.5+/-0.4 nm, P<0.01). A significant relationship was found between mean HDL size and serum CETP mass concentrations (P<0.05). When the particle size of all detected HDL bands was investigated, extra-large HDL particles larger than 12 nm were found in 14 of the 23 patients with CETP deficiency, which were not found in any of the hyperalphalipoproteinemia patients or normal subjects. Serum low-density lipoproteins (LDL) cholesterol and total cholesterol concentrations were lower in CETP deficiencies with extra-large HDL particles than those in non-carriers (P<0.01). These results indicate that extra-large HDL may be an index to clarify the relationship between genetic CETP deficiency and atherosclerosis.     

Increased catabolic rate of low density lipoproteins in humans with cholesteryl ester transfer protein deficiency.

The cholesteryl ester transfer protein (CETP) transfers lipids among lipoprotein particles and plays a central role in lipoprotein metabolism. Humans with genetic deficiency of CETP have both elevated HDL cholesterol and apolipoprotein A-I concentrations as well as decreased LDL cholesterol and apolipoprotein B levels. The present study was undertaken to elucidate the metabolic basis for the decreased LDL cholesterol and apo B levels in CETP deficiency. We conducted a series of in vivo apo B kinetic studies in tow unrelated homozygotes with CETP deficiency and in control subjects. A primed constant infusion of stable isotopically labeled phenylalanine was administered to the two CETP deficient subjects and control subjects and apo B kinetic parameters in VLDL, intermediate density lipoproteins, and LDL were obtained by using a multicompartmental model. The fractional catabolic rates (FCR) of LDL apo B were significantly increased in the CETP-deficient subjects (0.56 and 0.75/d) compared with the controls (mean FCR of 0.39/d). Furthermore, the production rates of apo B in VLDL and intermediate density lipoprotein were decreased by 55% and 81%, respectively, in CETP deficiency compared with the controls. In conclusion, CETP-deficient subjects were demonstrated to have substantially increased catabolic rates of LDL apo B as the primary metabolic basis for the low plasma levels of LDL apo B. This result indicates that the LDL receptor pathway may be up-regulated in CETP deficiency.     

Mechanisms of enhanced cholesteryl ester transfer from high density lipoproteins to apolipoprotein B-containing lipoproteins during alimentary lipemia.

In vitro lipoprotein lipase enhances the cholesteryl ester transfer protein (CETP)-mediated transfer of cholesteryl esters from high density lipoproteins (HDL) to very low density lipoproteins as a result of lipolysis-induced alterations in lipoprotein lipids that lead to increased binding of CETP. To determine if there are similar changes during alimentary lipemia, we measured the transfer of cholesteryl esters from HDL to apo B-containing lipoproteins in incubated fasting and postprandial plasma. In seven normolipidemic subjects there was 2-3-fold stimulation of cholesteryl ester transfer in alimentary lipemic plasma. Cholesteryl ester transfer was stimulated when either the d less than 1.063-or d greater than 1.063-g/ml fraction of lipemic plasma was recombined with its complementary fraction of fasting plasma. To determine the distribution of CETP, plasma was fractionated by agarose chromatography and CETP activity was measured in column fractions in a standardized assay. In fasting plasma, most of the CETP was in smaller HDL, and a variable fraction was nonlipoprotein bound. During lipemia there was increased binding of CETP to larger phospholipid-enriched HDL and in two subjects an increase in CETP in apo B-containing lipoproteins. The total CETP activity of fractions of lipemic plasma was increased 1.1-1.7-fold compared with fasting plasma. Lipemic CETP activity was also increased when measured in lipoprotein-free fractions after dissociation of CETP from the lipoproteins. When purified CETP was incubated with phospholipid-enriched HDL isolated from alimentary lipemic or phospholipid vesicle-treated plasma, there was increased binding of CETP to the phospholipid-enriched HDL compared with fasting HDL, with a parallel stimulation in CETP activity. Thus, the pronounced stimulation of cholesteryl ester transfer during alimentary lipemia is due to (a) an increased mass of triglyceride-rich acceptor lipoproteins, (b) a redistribution of CETP, especially increased binding to larger phospholipid-enriched HDL, and (c) an increase in total activity of CETP, perhaps due to an increased CETP mass.     

A delayed-addition enzyme immunoassay for the relative cholesteryl ester transfer protein mass in patients with deficient plasma cholesteryl ester transfer activity

The biochemical basis for the apparent deficiency of cholesteryl ester (CE) transfer activity was investigated in two unrelated subjects with markedly elevated high density lipoprotein-cholesterol (Atherosclerosis 1988; 70:7-12). Essentially no CE or triglyceride transfer activity was detected in the patients' plasma, utilizing four different lipid transfer assays. Using polyclonal antibodies raised against human plasma cholesteryl ester transfer protein (CETP), a delayed-addition enzyme immunoassay was developed to determine plasma CETP mass. CETP could not be detected with this assay in the plasma of the two subjects with transfer activity deficiency, indicating that the CE transfer activity deficiency in these subjects is due to the absence of plasma CETP. In addition, three hyperalphalipoproteinemic subjects with a partial deficiency of CE transfer activity had a reduced level of CETP mass. There was a good correlation between plasma CETP activity and mass levels. The principles of this immunoassay may be applicable to measure the mass levels of other proteins with catalytic activities.     

Accelerated transfer of cholesteryl esters in dyslipidemic plasma. Role of cholesteryl ester transfer protein.

Plasma cholesteryl esters, synthesized in the high density lipoproteins (HDL), may be transferred to other lipoproteins by a cholesteryl ester transfer protein (CETP). We found a twofold increase in mass transfer of cholesteryl ester from HDL to apoB-containing lipoproteins in incubated hypercholesterolemic rabbit plasma compared with control. There was a two- to fourfold increase in the activity of CETP, measured in an isotopic assay in hypercholesterolemic plasma. A CETP-like molecule was isolated in increased amounts from hypercholesterolemic plasma. Incubated plasma from four dysbetalipoproteinemic subjects also showed an increase (threefold) in cholesteryl ester mass transfer, compared with normolipidemic controls. There was a twofold increase in the activity of CETP, assayed in whole or lipoprotein-free plasma. Thus, there is increased transfer of cholesteryl esters from HDL to potentially atherogenic apoB-containing lipoproteins in dyslipidemic rabbit and human plasma. The enhanced transfer results in part from increased activity of CETP, possibly reflecting an increase in CETP mass.     

高HDL-C个体CETP基因15外显子错义突变(442D∶G)的检测及临床意义

目的证实胆固醇酯转移蛋白(CETP)基因15外显子错义突变(442D∶G)是导致高α脂蛋白血症的重要因素之一.方法建立检测CETP基因15外显子错义突变(442D∶G)的聚合酶链反应-限制性内切酶酶切片断长度多态性分析(PCR-RFLP)方法,检测50例高α脂蛋白血症(HDL-C≥1.7 mmol/L)个体CETP基因15外显子442D∶G错义突变的阳性率.结果 50例高α脂蛋白血症患者中,发现杂合子15例,纯合子1例;对照组70例,仅1例杂合子,差异有显著性(u<0.05).结论 CETP基因15外显子错义突变是导致高密度脂蛋白胆固醇(HDL-C)的重要因素之一.     

Contribution of glycaemic control, endogenous lipoproteins and cholesteryl ester transfer protein to accelerated cholesteryl ester transfer in IDDM

Abstract In an earlier study we demonstrated that the transfer of cholesteryl ester (CET) estimated as the net mass of CE lost from HDL to the apoB-containing lipoproteins (VLDL + LDL) during incubation of plasma is accelerated in normolipidaemic patients with insulin-dependent diabetes mellitus (IDDM). Recombination experiments with isolated lipoprotein fractions employing this same mass transfer assay indicated that this disturbance resulted from dysfunction of VLDL and not from changes in the activity of CE transfer protein (CETP). In this study, we sought first to determine whether CET estimated with an isotopic method that measures the transfer of radiolabelled CE from exogenous HDL from non-diabetic controls to endogenous VLDL + LDL was also increased in IDDM and, if so, the extent to which this disturbance was affected by glycaemic control, VLDL and CETP. As observed with the mass transfer assay, the rate of transfer of the HDL-CE label to VLDL + LDL was also significantly accelerated in IDDM plasma (IDDM: k = 0·256±0·07; control: k = 0·092±0·05; mean±SD; P < 0·001). Fasting glucose and fructosamine correlated with both isotopic transfer (k) (r= 0·54, P= 0·009; r= 0·57, P= 0·005, respectively) and the mass of CE transferred at 2 h (r= 0·55, P= 0·006; r= 0·59, P= 0·004, respectively). Recombination experiments revealed that isotopic CET was accelerated when: (a) IDDM VLDL were combined with controls HDL and d > 1·21 fractions; and (b) IDDM d > 1·21 plasma fractions containing CETP were combined with controls VLDL + LDL and HDL. While CETP concentrations in a subset of the study group were higher in the diabetic than in the non-diabetic controls, the difference was not statistically significant (IDDM 2·25±0·97 vs. control 1·58±0·58 μg ml^-1; mean±SD; P<0·1). These findings indicate that dysfunction of VLDL and increased CETP concentrations both contribute to the pathological acceleration of isotopic transfer in IDDM plasma and that the magnitude of this proatherogenic defect correlates closely with glycaemic control.     

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

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

Alcohol intake modulates the effect of a polymorphism of the cholesteryl ester transfer protein gene on plasma high density lipoprotein and the risk of myocardial infarction.

A polymorphism of the CETP gene (CETP/TaqIB) with two alleles B1 (60%) and B2 (40%) has been investigated in relation to lipid variables and the risk of myocardial infarction in a large case-control study (ECTIM) of men aged 25-64. No association was observed between the polymorphism and LDL or VLDL related lipid variables. Conversely, B2 carriers had reduced levels of plasma CETP (P < 0.0001) and increased levels of HDL cholesterol (P < 0.0001) and of other HDL related lipid variables. The effects of the polymorphism on plasma CETP and HDL cholesterol were independent, suggesting the presence of at least two functional variants linked to B2. A search for these variants on the coding sequence of the CETP gene failed to identify them. The effect of B2 on plasma HDL cholesterol was absent in subjects drinking < 25 grams/d of alcohol but increased commensurably, with higher values of alcohol consumption (interaction: P < 0.0001). A similar interaction was not observed for plasma CETP. The odds-ratio for myocardial infarction of B2 homozygotes decreased from 1.0 in nondrinkers to 0.34 in those drinking 75 grams/d or more. These results provide the first demonstration of a gene-environment interaction affecting HDL cholesterol levels and coronary heart disease risk.     

Inhibition of cholesteryl ester transfer protein activity by monoclonal antibody. Effects on cholesteryl ester formation and neutral lipid mass transfer in human plasma.

We have employed a neutralizing monoclonal antibody, prepared against the Mr 74,000 cholesteryl ester transfer protein (CETP), to investigate the regulation of lecithin:cholesterol acyltransferase (LCAT) activity by cholesteryl ester (CE) transfer, and also to determine which lipoproteins are substrates for LCAT in human plasma. The incubation of normolipidemic plasma led to transfer of CE from HDL to VLDL, and of triglycerides from VLDL to LDL and HDL. This net mass transfer of neutral lipids between the lipoproteins was eliminated by the monoclonal antibody. However, CE transfer inhibition had no effect on the rate of plasma cholesterol esterification in plasma incubated from 10 min to 24 h at 37 degrees C. In the absence of CE transfer, HDL and LDL exhibited cholesterol esterification activity, whereas VLDL did not. The rate of CE formation in HDL was three to four times greater than in LDL during the first hour of incubation, but CE formation in HDL decreased after 6-8 h, while that in LDL continued. Thus, (a) the Mr 74,000 CETP is responsible for all neutral lipid mass transfer in incubated human plasma, (b) the rate of CE formation in plasma is not regulated by CE transfer from HDL to other lipoproteins, and (c) HDL is the major initial substrate for LCAT; LDL assumes a more significant role only after prolonged incubation of plasma.     

Sandwich enzyme-linked immunosorbent assay for plasma cholesteryl ester transfer protein concentration.

OBJECTIVES: Cholesteryl ester transfer protein (CETP) mediates the transfer of HDL cholesterol to apoB-containing lipoproteins. Its mass and activity are increased in several pro-atherogenic conditions. The objective of this study is to develop a cost- and time-effective sandwich ELISA for plasma CETP concentration. DESIGN AND METHODS: Monoclonal anti-CETP, TP20, was used as the capture antibody, while the other biotinylated monoclonal anti-CETP, TP2, was used for detection. The results were expressed in an arbitrary unit, ng biotin-TP2 bound per microl plasma. Plasma CETP concentrations, activities and their relationship were assessed in 35 IDDM children. RESULTS: The assay had an intra-assay CV of 8.75% and an inter-assay CV under 10%. Plasma CETP concentration of these subjects ranged from 0.36-1.89 ng biotin-TP2/microL. CETP concentration was significantly correlated with CETP activity (r = 0.51, p < 0.01). CONCLUSION: The sandwich ELISA we have developed carried sufficient sensitivity for assaying plasma CETP concentration in human.     

Increased coronary heart disease in Japanese-American men with mutation in the cholesteryl ester transfer protein gene despite increased HDL levels.

Plasma high density lipoprotein (HDL) levels are strongly genetically determined and show a general inverse relationship with coronary heart disease (CHD). The cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters from HDL to other lipoproteins and is a key participant in the reverse transport of cholesterol from the periphery to the liver. A high prevalence of two different CETP gene mutations (D442G, 5.1%; intron 14G:A, 0.5%), was found in 3,469 men of Japanese ancestry in the Honolulu Heart Program and mutations were associated with decreased CETP (-35%) and increased HDL chol levels (+10% for D442G). However, the overall prevalence of definite CHD was 21% in men with mutations and 16% in men without mutations. The relative risk (RR) of CHD was 1.43 in men with mutations (P < .05); after adjustment for CHD risk factors, the RR was 1.55 (P = .02); after additional adjustment for HDL levels, the RR was 1.68 (P = .008). Similar RR values were obtained for the D442G mutation alone. Increased CHD in men with mutations was primarily observed for HDL chol 41-60 mg/dl; for HDL chol > 60 mg/dl men with and without mutations had low CHD prevalence. Thus, genetic CETP deficiency appears to be an independent risk factor for CHD, primarily due to increased CHD prevalence in men with the D442G mutation and HDL cholesterol between 41 and 60 mg/dl. The findings suggest that both HDL concentration and the dynamics of cholesterol transport through HDL (i.e., reverse cholesterol transport) determine the anti-atherogenicity of the HDL fraction.     

Mechanism of plasma cholesteryl ester transfer in hypertriglyceridemia.

Plasma net cholesteryl ester (CE) transfer and optimum cholesteryl ester transfer protein (CETP) activity were determined in primary hypertriglyceridemic (n = 11) and normolipidemic (n = 15) individuals. The hypertriglyceridemic group demonstrated threefold greater net CE transfer leading to enhanced accumulation of CE in VLDL. This increased net transfer was not accompanied by a change in CETP activity. In normolipidemia, but not in hypertriglyceridemia, net CE transfer correlated with VLDL triglyceride (r = 0.92, P less than 0.001). In contrast, net CE transfer in hypertriglyceridemia, but not in normolipidemia, correlated with CETP activity (r = 0.73, P less than 0.01). Correction of hypertriglyceridemia with bezafibrate reduced net CE transfer towards normal and restored the correlation with VLDL triglyceride (r = 0.90, P less than 0.005) while suppressing the correlation with CETP activity. That net CE transfer depends on VLDL concentration was confirmed by an increase of net CE transfer in normolipidemic plasma supplemented with purified VLDL. Supplementation of purified CETP to normolipidemic plasma did not stimulate net CE transfer. In contrast, net CE transfer was enhanced by addition of CETP to both plasma supplemented with VLDL and hypertriglyceridemic plasma. Thus, in normal subjects, VLDL concentration determines the rate of net CE transfer. CETP becomes rate limiting as VLDL concentration increases, i.e., in hypertriglyceridemia.     

Accelerated cholesteryl ester transfer in plasma of patients with hypercholesterolemia.

To discern the mechanism(s) that underlie abnormal cholesteryl ester transfer (CET) in patients with hypercholesterolemia, we have studied this dysfunctional step in reverse cholesterol transport in 13 subjects with genetically heterogeneous forms of hypercholesterolemia (HC). In all HC patients, the mass of CE transferred in whole plasma from HDL to VLDL and LDL increased rapidly initially and was significantly greater than in controls at 1, 2, and 4 h (P less than 0.005). To further characterize this disturbance, we performed a series of recombination experiments. Combining HC d less than 1.063 containing acceptor VLDL + LDL with the d greater than 1.063 fraction from controls containing donor HDL + CE-transfer protein (CETP) and not the converse combination showed the same characteristics of accelerated CET noted with intact HC plasma, indicating that abnormal transfer was associated with the HC acceptor lipoproteins. When HC VLDL and its subfractions and LDL were isolated separately and then combined with control d greater than 1.063 fractions, accelerated CET was only associated with VLDL1. Consistent with an acceleration of the neutral lipid transfer reaction occurring between HDL and VLDL1 in HC in vivo, we found that the triglyceride/CE ratio was decreased in HC VLDL1 (P less than 0.001), and increased in HDL (P less than 0.25). CETP mass was significantly increased in HC plasma (HC 2.3 +/- 4 micrograms/ml vs. control 1.3 +/- 0.3 micrograms/ml; mean +/- SD; P less than 0.025). This series of observations demonstrate that CET is accelerated in the plasma of HC patients, and this disturbance results from dysfunction of the VLDL1 subfraction rather than an elevation of CETP levels. Since an abnormality of this type in vivo can lead to the accumulation of potentially atherogenic CE-enriched apoB-containing lipoproteins in plasma, it may be an additional previously unrecognized factor that increases cardiovascular risk in HC patients.     

A novel missense LIPA gene mutation, N98S, in a patient with cholesteryl ester storage disease

Lysosomal acid lipase plays an important role in maintaining cellular cholesterol homeostasis. Complete absence of lysosomal acid lipase activity results in Wolman disease and usually death in infancy, whereas partial deficiency of lysosomal acid lipase results in cholesteryl ester storage disease (CESD). We describe a 26 year-old female with CESD who presented with recurrent right upper quadrant abdominal pain. Abnormal liver function tests and a subsequent liver biopsy revealed features consistent with CESD. Sequencing of the LIPA gene revealed that she was a compound heterozygote for the previously reported exon 8 splice junction mutation and a novel missense mutation (N98S) in exon 4. The splice junction mutation allows some (approximately 3%) normal splicing to occur, and therefore gives rise to residual lysosomal acid lipase activity. Asn98 in lysosomal acid lipase is highly conserved among species and mutation of this residue could influence catalytic activity or accessibility to the active site. In summary, we describe a CESD patient compound heterozygous for the LIPA exon 8 splice junction mutation and a novel missense mutation, N98S.     

Delayed catabolism of high density lipoprotein apolipoproteins A-I and A-II in human cholesteryl ester transfer protein deficiency.

Deficiency of the cholesteryl ester transfer protein (CETP) in humans is characterized by markedly elevated plasma concentrations of HDL cholesterol and apoA-I. To assess the metabolism of HDL apolipoproteins in CETP deficiency, in vivo apolipoprotein kinetic studies were performed using endogenous and exogenous labeling techniques in two unrelated homozygotes with CETP deficiency, one heterozygote, and four control subjects. All study subjects were administered 13C6-labeled phenylalanine by primed constant infusion for up to 16 h. The fractional synthetic rates (FSRs) of apoA-I in two homozygotes with CETP deficiency (0.135, 0.134/d) were found to be significantly lower than those in controls (0.196 +/- 0.041/d, P < 0.01). Delayed apoA-I catabolism was confirmed by an exogenous radiotracer study in one CETP-deficient homozygote, in whom the fractional catabolic rate of 125I-apoA-I was 0.139/d (normal 0.216 +/- 0.018/d). The FSRs of apoA-II were also significantly lower in the homozygous CETP-deficient subjects (0.104, 0.112/d) than in the controls (0.170 +/- 0.023/d, P < 0.01). The production rates of apoA-I and apoA-II were normal in both homozygous CETP-deficient subjects. The turnover of apoA-I and apoA-II was substantially slower in both HDL2 and HDL3 in the CETP-deficient homozygotes than in controls. The kinetics of apoA-I and apoA-II in the CETP-deficient heterozygote were not different from those in controls. These data establish that homozygous CETP deficiency causes markedly delayed catabolism of apoA-I and apoA-II without affecting the production rates of these apolipoproteins.     

The activity of cholesteryl ester transfer protein is decreased in hypothyroidism: a possible contribution to alterations in high-density lipoproteins

The activity of cholesteryl ester transfer protein is instrumental in the distribution of cholesteryl ester between lipoproteins in plasma. We measured the activity of cholesteryl ester transfer protein in plasma, designated cholesteryl ester transfer activity, as the rate of cholesteryl ester transfer between exogenous radiolabelled low-density and high-density lipoproteins. The effect of hypothyroidism on cholesteryl ester transfer activity was investigated in 13 athyreotic patients who were studied in the hypothyroid condition and in the euthyroid state, after they had received triiodothyronine supplementation for 33 to 67 days. During hypothyroidism plasma total cholesterol, very-low- plus low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, plasma triacylglycerol, apolipoprotein A1 and B were significantly higher than in the euthyroid state. Cholesteryl ester transfer activity was 15% lower during hypothyroidism (P less than 0.02), and an effect of treatment duration was observed. The changes in high-density lipoprotein total cholesterol (P less than 0.02), free cholesterol (P less than 0.001), triacylglycerol (P less than 0.05) and the free cholesterol/cholesteryl ester molar ratio in high-density lipoproteins (P less than 0.01) were inversely-related to the changes in cholesteryl ester transfer activity. We concluded that thyroid hormone is involved in the regulation of cholesteryl ester transfer protein activity, and that cholesteryl ester transfer protein activity may play a role in the alterations in high-density lipoprotein lipids observed in hypothyroidism.     

Type 2 diabetes mellitus is associated with differential effects on plasma cholesteryl ester transfer protein and phospholipid transfer protein activities and concentrations

BACKGROUND: Human plasma contains two lipid transfer proteins, cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), which are crucial in reverse cholesterol transport. METHODS: Plasma CETP and PLTP activity levels and concentrations in 16 type 2 diabetic patients and 16 matched healthy subjects were determined, and these data were correlated to clinical variables, including insulin sensitivity and lipid levels. RESULTS: Plasma triglycerides were higher (p<0.02) and high-density lipoprotein (HDL) cholesterol (p<0.02) was lower in diabetic patients. Plasma CETP activity and concentrations were not significantly different between diabetic and healthy subjects, but CETP specific activity was lower in diabetic patients (p<0.001). Multiple regression analysis showed that plasma CETP activity was positively related to CETP concentration (p=0.0001) and negatively to the diabetic state (p<0.002) or to HbA1c (p<0.02). PLTP activity (p<0.05) and specific activity were higher (p<0.05), whereas there was no difference in PLTP concentration between the two groups. There was no significant bivariate correlation between PLTP concentration and activity, in either healthy or diabetic subjects. Multiple regression analysis did disclose positive relationships of PLTP activity with PLTP concentration (p=0.0001), plasma triglycerides (p=0.0001) and waist/hip ratio (p=0.0001), but not with the diabetic state or HbA1c. CONCLUSIONS: Neither CETP nor PLTP activity was independently associated with insulin sensitivity. Specific CETP activity is decreased in type 2 diabetes mellitus. In contrast, specific PLTP activity is higher in diabetes, as a result of the association of plasma PLTP activity with plasma triglycerides and obesity. Measurement of both plasma lipid transfer protein activity and mass levels may thus provide extra information in diabetes mellitus.