Effect of the composition of very low and low density lipoproteins on the rate of cholesterylester transfer from high density lipoproteins in man, studied in vitro

Increased large VLDL particles confer elevated cholesteryl ester transfer in diabetes

BACKGROUND

Plasma cholesteryl ester transfer (CET), reflecting transfer of cholesteryl esters from high density lipoproteins (HDL) towards apolipoprotein B-containing lipoproteins, may promote atherosclerosis development, and is elevated in Type 2 diabetes mellitus (T2DM). We determined the extent to which the relationship of plasma CET with very low density lipoprotein (VLDL) and low density lipoprotein (LDL) subfractions is modified in T2DM.

MATERIALS AND METHODS

Plasma CET, cholesteryl ester transfer protein (CETP) mass, as well as VLDL and LDL subfractions (nuclear magnetic resonance spectroscopy) were determined in 62 patients with T2DM and 53 nondiabetic subjects.

RESULTS

Plasma CET and CETP mass were increased in T2DM, coinciding higher triglycerides and large VLDL particles (all P < 0·02). Plasma CET was positively related to the VLDL and the LDL particle concentration in age-, sex- and diabetes status-adjusted analysis (both P < 0·001). Multivariable linear regression analysis demonstrated an independent positive interaction between the presence of T2DM and the VLDL concentration on plasma CET (β = 0·238, P = 0·033). The relationship of plasma CET with the VLDL concentration was also positively modified by plasma glucose (β = 0·211, P = 0·004) and glycated haemoglobin (β = 0·190, P = 0·012). Of the individual VLDL subfractions, a positive interaction of diabetes status with large VLDL on plasma CET was observed (β = 0·280, P = 0·003). Neither the relationship of the LDL particle concentration nor of CETP mass with plasma CET was modified by the presence of T2DM (P > 0·15).

CONCLUSION

Abnormalities in the concentration and composition of large VLDL particles are likely to contribute to elevated plasma CET in T2DM.

CETP-mediated cholesteryl ester enrichment of apoB subclasses in type 1 diabetes

OBJECTIVE

  Accelerated cholesteryl ester transfer (CET) in patients with types 1 (T1D) and 2 diabetes enhances the atherogenicity of the apoB-containing CE acceptor lipoproteins. The study of lipoprotein density fractions cannot identify which of the five immunologically distinct apoB subclasses function as CE acceptors because they are heterogeneous and present in very low-, intermediate- and low density lipoproteins (VLDL, IDL and LDL, respectively). In order to design lipid-modifying therapies that specifically target these CE-enriched lipoprotein particles, it is necessary to first characterize their CE acceptor function.

METHODS AND RESULTS

  To identify the CE acceptors, we estimated CE net mass transfer to the apoB subclasses LpB:C, LpB:E + LpB:C:E, LpB and LpAII:B:C:D:E from changes in neutral lipids measured by gas chromatography following their separation by sequential immunoaffinity chromatography in the plasma of 12 patients with T1D and six control subjects. In both groups, CE was distributed equally to LpB:E + LpB:C:E and LpB:C. In the T1D CE acceptors, however, both the magnitude of the increase (18% vs. 10%; P < 0·01) and the per particle mass of CE transferred were significantly greater than in controls (T1D: 2·29 μmol ± 2·1 vs. control 0·43 ± 0·43/mg apoB; P < 0·047).

CONCLUSION

  While LpB:E + LpB:C:E and LpB:C functioned as CE acceptors in both groups, these subclasses increased their CE content to a greater degree and accrued more CE per particle in the patients with T1D. As this disturbance in lipoprotein remodelling may increase the cholesterol burden and potential atherogenicity of these apoB subclasses, it may be a previously unrecognized factor that increases cardiovascular risk in patients with T1D.

Plasma cholesteryl ester transfer, but not cholesterol esterification, is related to lipoprotein-associated phospholipase A2: possible contribution to an atherogenic lipoprotein profile

CONTEXT

Plasma lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) predicts incident cardiovascular disease and is associated preferentially with negatively charged apolipoprotein B-containing lipoproteins. The plasma cholesteryl ester transfer (CET) process, which contributes to low high-density lipoprotein cholesterol and small, dense low-density lipoproteins, is affected by the composition and concentration of apolipoprotein B-containing cholesteryl ester acceptor lipoproteins.

OBJECTIVE

We tested relationships of CET with Lp-PLA(2) in subjects with and without metabolic syndrome (MetS).

DESIGN AND SETTING

In 68 subjects with MetS and 74 subjects without MetS, plasma Lp-PLA(2) mass, cholesterol esterification (EST), lecithin:cholesterol acyltransferase (LCAT) activity level, CET, CET protein (CETP) mass, and lipoproteins were measured.

RESULTS

EST, LCAT activity, CET (P < 0.001 for all), and CETP (P = 0.030) were increased, and Lp-PLA(2) was decreased (P = 0.043) in MetS. CET was correlated positively with Lp-PLA(2) in subjects with and without MetS (P < 0.05 for both). EST and LCAT activity were unrelated to Lp-PLA(2), despite a positive correlation between EST and CET (P < 0.001). After controlling for age, sex, and diabetes status, CET was determined by Lp-PLA(2) in the whole group (β = 0.245; P < 0.001), and in subjects with (β = 0.304; P = 0.001) and without MetS (β = 0.244; P = 0.006) separately, independently of triglycerides and CETP.

CONCLUSIONS

Plasma CET is related to Lp-PLA(2) in subjects with and without MetS. The process of CET, but not EST, may be influenced by Lp-PLA(2). These findings provide a rationale to evaluate whether maneuvers that inhibit Lp-PLA(2) will reduce CET, and vice versa to document effects of CETP inhibition on Lp-PLA(2).

Apolipoprotein-B subclasses as acceptors of cholesteryl esters transferred by CETP

BACKGROUND

Five apolipoprotein (apo)-defined apoB-containing lipoprotein (Lp) subclasses designated LpB, LpB:C, LpB:E, LpB:C:E and LpA-II:B:C:D:E are present in human plasma. This study was to determine whether these subclasses functioned equally as acceptors of cholesteryl esters (CE) transferred from high-density lipoproteins (HDL) by CE transfer protein in healthy subjects with normal and mildly increased plasma triglyceride (TG) levels.

MATERIALS AND METHODS

After 4 h incubation of plasma from 14 subjects at 37 degrees C, apoB-containing lipoproteins were separated from HDL by heparin-Mn++ precipitation and fractionated by immunochemical methods into these five subclasses. The neutral lipid (NL) composition for each subclass was measured by gas chromatography (GC) and compared between 0 h and 4 h. A subclass was considered to be a CE acceptor if its CE content increased more than 5% at 4 h and a non-acceptor if no change was observed.

RESULTS

Employing the above definition, TG-rich LpB:C and LpB:E + LpB:C:E functioned as CE acceptors and TG-poor LpB and LpA-II:B:C:D:E as non-acceptors. Both LpB:C and LpB:E + LpB:C:E could only actively accept CE as long as they retained their TG-rich character and displayed neutral lipid profiles similar to those of very low-density lipoproteins (VLDL) and intermediate density lipoproteins (IDL). When, as a result of lipolysis their TG content dropped below 25%, they ceased to function as CE acceptors. In subjects with elevated plasma TG, LpB:C was the dominant CE acceptor, a condition that may have pro-atherogenic consequences.

CONCLUSIONS

Among the apoB-containing particles, LpB:C and LpB:C:E + LpB:E functioned as CE acceptors while LpB and LpA-II:B:C:D:E did not.

Differential impact of plasma triglycerides on HDL-cholesterol and HDL-apo A-I in a large cohort

OBJECTIVES

To examine the relationship between plasma triglycerides (TG) to HDL-cholesterol (HDL-C) or HDL apo A-I.

DESIGN AND METHODS

Bivariate and multiple linear regression analyses in a large cohort of 1886 subjects.

RESULTS

Higher plasma TG levels were associated with lower concentrations of both HDL-C and HDL-apo A-I. However, the HDL-C/HDL-apo A-I ratio was inversely correlated with plasma TG indicating that the overall composition of the HDL changed as plasma TG changed. Plasma TG levels contributed to 15.9% of the variance of the HDL-C/HDL-apo A-I ratio, whereas gender, HDL-TG, LDL-TG, body mass index and plasma apo B levels represented between 0.15% and 2.21% of this variance.

CONCLUSIONS

These results indicate that increasing levels of plasma TG result in greater reduction in HDL-C levels than in HDL-apo A-I and this might explain, at least in part, the differences that have been observed in the magnitude of the association of HDL-C versus HDL-apo A-I with the risk of cardiovascular disease.

Age-related effects of genetic variation on lipid levels: The Columbia University BioMarkers Study

OBJECTIVES

To examine the genotype:phenotype association in children compared with their parents.

METHODS

Variations at 4 key gene loci, namely lipoprotein lipase (LPL S447X), hepatic lipase (HL -480C>T), cholesteryl ester transfer protein (CETP TaqIB), and apolipoprotein CIII (APOC3 -455T>C and -482C>T), were examined in children (n = 495) and their parents (n = 353) in the Columbia University BioMarkers Study, 1994 to 1998.

RESULTS

The frequencies of the rare alleles of the HL -480C>T and APOC3 -455T>C and -482C>T (but not LPL S447X or CETP TaqIB) were significantly lower in non-Hispanic white participants compared with Hispanics. Overall, genotype effects seen in the adults were weaker in the children, although similar trends were seen. In an examination of the effect of body fat on the genotypic effects in the children, there was significant HL -480C>T:sum of skinfold interaction.

CONCLUSIONS

All genotypes were associated with clear relationships to plasma lipid levels in adults, but the effects were weaker in their children, unless stressed by body fat. atherosclerosis, cardiovascular disease, child, lipids, genetics.

Lipid transfer protein activities in type 1 diabetic patients without renal failure and nondiabetic control subjects and their association with coronary artery calcification

This study examined the role of cholesteryl ester transfer (CET), cholesteryl ester transfer protein (CETP) activity, and phospholipid transfer protein (PLTP) activity in the increased prevalence of coronary artery calcification (CAC) in diabetic subjects compared with nondiabetic subjects and in the loss of the sex difference in CAC in diabetes. CETP activity, PLTP activity, and CET were measured in 195 type 1 diabetic subjects without renal failure and 194 nondiabetic control subjects of similar age (30-55 years) and sex distribution (50% female). CAC was quantified with electron beam computed tomography. CETP activity was higher in diabetic subjects (mean 84 arbitrary units [AU]) than in nondiabetic subjects (80 AU, P = 0.028). PLTP activity was also higher in diabetic subjects (96 AU) than in nondiabetic subjects (81 AU, P < 0.001). However, CET was lower in diabetic men (geometric mean 32 nmol. ml(-1).h(-1)) than nondiabetic men (37 nmol.ml(-1).h(-1), P = 0.004) and did not differ between diabetic (30 nmol. ml(-1).h(-1)) and nondiabetic (32 nmol.ml(-1).h(-1), P = 0.3) women. CETP and PLTP activities were not associated with CAC. CET was positively associated with CAC in both diabetic and nondiabetic subjects (odds ratio per 10 nmol.ml(-1).h(-1) increase in CET in all subjects = 1.4, P = 0.001). The prevalence of CAC was similar in diabetic (51%) and nondiabetic (54%, P = 0.7) men but was much higher in diabetic (47%) than nondiabetic (21%, odds ratio 3.6, P < 0.001) women so that there was no sex difference in CAC in diabetic subjects. The odds of CAC in diabetic women compared with nondiabetic women was altered little by adjustment for CETP activity, PLTP activity, or CET (odds ratio on adjustment 3.7, P < 0.001). The greater effect of diabetes on CAC in women than in men, i.e., the loss of the sex difference in CAC, was independent of CETP and PLTP activity and CET. In conclusion, among both diabetic and nondiabetic subjects, higher cholesteryl ester transfer is a risk factor for CAC. However, abnormalities in cholesteryl ester transfer or lipid transfer protein activities do not underlie the increased CAC risk in diabetic women compared with nondiabetic women or the loss of the sex difference in CAC in diabetes.

Study of vitamin E net mass transfer between alpha-tocopherol-enriched HDL and erythrocytes: application to asymptomatic hypercholesterolemic men

We previously showed that hypercholesterolemic asymptomatic men had lower erythrocyte vitamin E content, despite normal plasma concentrations compared to normocholesterolemic men. We hypothesized that the reduced erythrocyte vitamin E concentration could be due to an impairment of transfer of vitamin E from plasma lipoproteins. We first developed a model for testing the ability of erythrocytes to accept vitamin E from high-density lipoproteins (HDL) pre-enriched in vitamin E, which allows to measure a net mass transfer of vitamin E from HDL to erythrocytes. Vitamin E-enriched HDL were obtained in controlled conditions of concentration and incubation time with a good reproducibility (CV </= 10%). The kinetic study of the net mass transfer of vitamin E to erythrocytes of healthy volunteers shows small inter- and intraindividual variations. The application of this model to erythrocytes of hyper- and normocholesterolemic men demonstrates that the reduced erythrocyte vitamin E content observed in hypercholesterolemic men was not due to a reduced ability of these cells to accept vitamin E from HDL. It might rather be due to an impairment of lipoproteins in the delivery of vitamin E to tissues, or to an oxidative stress which consumes antioxidants.

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.

Lipoprotein composition influences cholesteryl ester transfer in alcohol abusers

Alcohol use is known to increase high-density lipoprotein (HDL) cholesterol, which is at least in part mediated by the alcohol-induced reduction in plasma cholesteryl ester transfer protein (CETP) activity and mass. We have shown that the high plasma HDL concentration reduces the CETP-mediated net mass transfer of cholesteryl esters from HDL to very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL), or even reverses the direction of transfer in plasma incubations. Therefore, we studied the effect of lipoprotein composition on lipid net mass transfers in 14 male alcohol abusers and nine male control subjects by incubating plasma for up to 2 h. The cholesteryl ester net mass transfer in the alcohol abusers was mainly predicted by the VLDL and LDL lipid composition in multiple linear regression, while the HDL composition was the main factor in the controls. The observed difference in the effect of the lipoprotein composition on cholesteryl ester net mass transfer support our previous finding in rabbits that CETP binding to lipoproteins may differ during ethanol oxidation. The results suggest that ethanol oxidation induces alterations which may affect the binding of CETP to lipoproteins.

Assessment of cholesteryl ester transfer protein function in lipoprotein mixtures by 1H NMR spectroscopy

Studies of cholesteryl ester transfer protein (CETP) function in lipoprotein mixtures pose many difficulties by conventional biochemical methods. For instance, studies on the effects of CETP on the composition of apolipoprotein B containing lipoproteins (very low and low density lipoproteins) in lipoprotein mixtures are tedious due to repeated ultracentrifugational isolations and have thus rarely been performed. Here we present a new 1H NMR spectroscopy technique to assess the CETP function in lipoprotein mixtures. This technique does not require repeated physical isolations of the lipoprotein particles but uses mathematical separation of the fractions on the basis of biochemical prior knowledge based lineshape fitting analysis of specific lipid resonances in the 1H NMR spectra. The lipoproteins are separated according to their size related chemical shift which allows for distinct quantification between very low and low density lipoproteins, the two major apolipoprotein B containing fractions. The methodological basis of the technique is discussed here together with a demonstration that this kind of approach allows dynamic follow up of the lipid transfer reactions in complex lipoprotein and CETP mixtures. The results revealed a consistent behaviour which corroborated the recent findings suggesting that the neutral lipid mass transfer among lipoproteins is not an equimolar heteroexchange.

Lack of effect of vitamin E on cholesteryl ester transfer and lipoprotein composition in cholesterol-fed rabbits

The concentration and activity of cholesteryl ester transfer protein (CETP) is increased in plasma in hypercholesterolemic humans and in experimental animals fed cholesterol. While the concentration of lipo-proteins appears to be the major determinant of CETP activity, we have found previously that dietary measures and pharmacologic agents that alter their lipid composition reduce the activity of CETP in plasma (CET). Since vitamin E is lipophilic and is incorporated into lipoproteins, we have examined the question of whether it too attenuates CET in cholesterol-fed New Zealand White rabbits prior to and 14 weeks after treatment with differing doses (5, 15, 30, 45 mg/kg) of vitamin E. Plasma triglycerides (TG), cholesterol (TC) and phospholipids (Lys, Sph, Lec, PI, PE) all increased significantly to a comparable degree in the rabbits fed cholesterol compared to those fed chow (p < 0.05; p < 0.01); the levels achieved were similar in the vitamin E-treated and untreated groups. As was observed with plasma lipids, cholesteryl ester transfer (CET) was accelerated to the same degree in each of the cholesterol-fed groups independent of whether they received vitamin E compared to chow-fed controls (p < 0.01) and the distribution of cholesterol in apo-B containing lipoproteins (VLDL, IDL, and LDL) was similar in the vitamin E-treated and untreated groups. These findings indicate that vitamin E has no discernible effect on CET when cholesterol levels are markedly elevated.

Interaction of the cholesteryl ester transfer protein I405V polymorphism with alcohol consumption in smoking and non-smoking healthy men, and the effect on plasma HDL cholesterol and apoAI concentration

Three hundred and sixteen healthy Icelandic men and women were examined for the effect of the cholesteryl ester transfer protein (CETP) I405V polymorphism on plasma triglycerides, HDL cholesterol (HDLC) and apoAI concentration. Genotyping was performed using an allele specific oligomelting assay and the frequency of the V allele was 0.31 (95 CI for men 0.23-0.33 and for women 0.29-0.39). In women no significant difference was associated with the V405 genotype for any plasma lipid trait. However, men who were homozygous for the V405 allele had 9% higher apoAI and 14% higher HDLC levels (p < 0.05) than those homozygous for the common I405 allele. The genotype effect was seen only in the non-smokers (p = 0.07 and < 0.05, respectively), and in those consuming alcohol (p < 0.05 for both). Analysis of interaction between the environmental, life-style factors and genotype in men for the traits of HDLC and apoAI showed statistically significant interaction of the genotype only with alcohol consumption. The non-smoking men who reported alcohol consumption and who were homozygous for the CETP V405 allele had 16% higher plasma apoAI concentration than those who carried the I405 allele, and up to 20% higher apoAI level than smokers. On the basis of prospective studies carried out on the Icelandic population, non-smoking, alcohol-consuming men who are homozygous for the V405 allele could have from 32% to 40% lower risk of having a heart attack.

Determinants of plasma HDL-cholesterol in hypertriglyceridemic patients. Role of cholesterol-ester transfer protein and lecithin cholesteryl acyl transferase

Hypertriglyceridemic patients commonly have low levels of HDL cholesterol. Elevated triglycerides per se may be one cause of low HDL levels, but other factors also may be involved. The current study was designed to define the role of cholesterol-ester transfer protein (CETP) in causation of a low HDL cholesterol in hypertriglyceridemic patients; in addition other factors-lecithin cholesterol acyl transferase (LCAT), hepatic triglyceride lipase (HTGL), and lipoprotein lipase (LPL)-were examined. Plasma activities of CETP and LCAT were measured in 137 male patients with moderate hypertriglyceridemia (plasma triglycerides [TGs] 200 to 500 mg/dL and LDL cholesterol < 160 mg/dL). Results were compared with those from 50 normolipidemic men of similar age and body habitus. In addition, lipase activities in postheparin plasma were measured in 118 of the subjects with hypertriglyceridemia. The activities of CETP and LCAT were 17% (P < .01) and 7% (P < .05), respectively, higher in the hypertriglyceridemic group than in control subjects. By stepwise regression analysis CETP appeared to contribute 15.2% and LCAT 9.8% to variation in HDL-cholesterol levels. Activities of LPL and HTGL together contributed an additional 14.1% to HDL-cholesterol variation. In contrast, levels of plasma TG accounted for only 5.4% of the variation. There were no differences in relative contributions of these parameters in patients with and those without coronary heart disease. This study indicates that several factors contribute to the variation in HDL-cholesterol levels in hypertriglyceridemic patients, and five factors-CETP, LCAT, HTGL, LPL, and triglyceride levels-account for almost half of this variation.

Alterations in composition and concentration of lipoproteins and elevated cholesteryl ester transfer in non-insulin-dependent diabetes mellitus (NIDDM)

Cholesteryl esters (CE) exchange between lipoproteins through the action of cholesteryl ester transfer protein (CETP). Situations at high risk for atherosclerosis are often accompanied by an accelerated net mass CE transfer (CET) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL). However, the question as to whether the net mass CET is increased or decreased in non-insulin-dependent diabetes mellitus (NIDDM) has led to controversial data. To clarify this point, we have undertaken a detailed study of CET in 105 NIDDM patients by comparison with 17 control subjects. Net mass CET was approximately doubled in NIDDM. Plasma CETP activity and unidirectional CET from HDL to VLDL + LDL (CETHDL-->VLDL + LDL) or from VLDL + LDL to HDL (CETVLDL + LDL-->HDL) were measured under controlled lipoprotein concentrations using radioisotopic assays. No difference was observed in plasma CETP activity between NIDDM and controls. In NIDDM, CETHDL-->VLDL + LDL and CETVLDL + LDL-->HDL were decreased by 25% and 20%, respectively, as a consequence of alterations in lipoprotein compositions. Net mass CET was highly correlated with plasma triglyceride (TG) concentration (r = 0.66, P < 0.001) but not with that of LDL-cholesterol (r = 0.06, P > 0.6). When TG levels were decreased following dietetic recommendations or insulinotherapy, the net mass CET was lowered accordingly. We conclude that net mass CET is accelerated in NIDDM in spite of a decreased unidirectional CETHDL-->VLDL + LDL. This results from a lowered CETVLDL + LDL-->HDL and from elevated TG concentration, and the latter probably reflects a concentration effect of VLDL.

'In vitro' cholesteryl ester bidirectional flow between high-density lipoproteins and triglyceride-rich emulsions: effects of particle concentration and composition, cholesteryl ester transfer activity and oleic acid

The cholesteryl ester flow between high-density lipoproteins (HDL) and triglyceride-rich lipoproteins was investigated utilizing HDL fractions and synthetic lipid emulsion particles (EM). HDL was labeled in vitro with [1,2-3H(n)]cholesteryl ester or with [1,2,6,7-3H(n)]cholesteryl oleate, whereas EM were made with [4-14C]cholesteryl oleate (CO) or [carboxyl-14C]triolein (TO). The cholesteryl ester (CE) transfer rate between HDL and EM was spontaneous to some extent (because it occurred in saline medium), saturable, enhanced in a dose-dependent manner by the plasma fraction at D > 1.21 g/ml ascribed to its CETP activity, and greater for HDL3 than for HDL2. Unesterified fatty acids in the medium elicited two opposing effects: (1) enhanced the spontaneous cholesteryl oleate shift to EM and inhibited the reverse flow from EM to HDL3 but not to HDL2; (2) partially impaired the plasma D > 1.21 g/ml-induced bidirectional cholesteryl oleate flow. Approx. 2 mol TO from EM exchange for 1 mol CO from HDL3. Net cholesteryl ester balance was dependent on the concentration of HDL-cholesteryl ester, and independent from EM-cholesteryl oleate, possibly due to the much smaller concentration of the latter. These in vitro experiments shed light on the complex physical chemistry of transport of cholesteryl ester and triolein between HDL and TG-rich lipoproteins which occurs during the metabolism of chylomicrons in plasma.

Induction of net mass lipid transfer reactions in plasma by wine consumption with dinner

Moderate alcohol consumption is associated with a reduced risk of coronary heart disease. Alcohol may exert protection through its effects on the metabolism of plasma lipoproteins. In the present study we investigated the effects of moderate wine consumption with an evening dinner on lipoprotein composition and parameters of reverse cholesterol transport (plasma lipid transfer reactions and cholesterol esterification) in eight healthy middle-aged men. Wine consumption, if compared with mineral water, resulted in increased postprandial plasma levels of triglyceride-(TG)-rich lipoproteins (P < 0.005 or < 0.002 at two different time points) and in increased net mass transfer of cholesterylesters (CE) from high-density lipoprotein (HDL) to apolipoprotein B-containing lipoproteins during in vitro incubation of plasma (P < 0.001). Net mass transfer of TG (in the opposite direction) was also significantly increased by wine (P = 0.014). The concentrations of total plasma cholesterol, HDL-cholesterol and apolipoproteins A-I, A-II and B did not change postprandially and were not affected significantly by wine, but the CE TG-1 in HDL was affected postprandially and decreased by wine consumption. It is concluded that moderate wine consumption with evening dinner induces transfer reactions of CE and TG between HDL and TG-rich lipoproteins. Due to the fact that wine raises plasma TG, it also causes changes in plasma cholesterol metabolism and lipoprotein composition, without major effects on total plasma cholesterol concentration.

Bimodal distribution of cholesteryl ester transfer protein activities in normotriglyceridemic men with low HDL cholesterol concentrations

Increased plasma activities of cholesteryl ester transfer protein (CETP) theoretically could lower HDL cholesterol levels due to enhanced transfer of cholesteryl esters from HDL to apo B-containing lipoproteins. To determine whether high CETP activities are associated with isolated hypoalphalipoproteinemia, CETP activities were measured in 109 adult men with HDL cholesterol < 35 mg/dL, plasma triglycerides < 200 mg/dL, and LDL cholesterol < 160 mg/dL; the results were compared with those of 50 normolipidemic (HDL cholesterol > 40 mg/dL) male subjects. CETP activities were assayed in vitro and expressed as the percent of [3H]cholesteryl ester transferred from HDL3 to LDL during a 16-hour incubation. In addition, postheparin plasma activities of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) were determined in 71 patients with a low HDL cholesterol level. Distributions of CETP activities were unimodal in control subjects (mean +/- SD, 23.1 +/- 5.0%), but they were bimodal in the low-HDL patients. Among the latter, 27 patients had elevated CETP activities (40.8 +/- 4.6%), whereas 82 patients had CETP activities that overlapped the normal range (26.14 +/- 7.6%). Low-HDL patients with normal CETP activities had 20% lower LPL activities (P = .01), 25% higher HTGL activities (P = .03), and 63% lower LPL/HTGL ratios (P < .001) than those of low-HDL patients with increased CETP activity. Furthermore, mean LPL and HTGL activities in the low-HDL patients with elevated CETP activities were in the normal range. Another important distinction between the two subgroups with low HDL was that the subgroup with high CETP activity had only a 30% prevalence of coronary heart disease compared with a 70% prevalence in the subgroup with normal CETP activity (P < .01). These findings suggest that elevated CETP activity may be a significant factor in causing low HDL cholesterol levels in a distinct subgroup of normolipidemic patients with low HDL cholesterol levels.

Effect of unesterified cholesterol on the activity of cholesteryl ester transfer protein

Cholesteryl ester transfer protein (CETP) catalyses the transfer of cholesteryl ester from high-density lipoprotein to triacylglycerol-rich lipoproteins and the transfer of triacylglycerols in the reverse direction. The activity of CETP has been studied using a continuous fluorescence assay which measures the excimer fluorescence of cholesteryl 1-pyrene decanoate in a synthetic donor microemulsion as the indicator of cholesteryl ester transfer. Emulsions were composed of cholesteryl oleate and egg phosphatidylcholine and had an average particle size of 14 +/- 1 nm as calculated from the molar volume of the components. The effect of changing the physical state of the emulsion surface was examined by including unesterified cholesterol in the donor and acceptor particles. The rate of CETP-induced transfer of the fluorescent cholesteryl ester between microemulsion particles increased when unesterified cholesterol was present at concentrations up to 17 mol% relative to phospholipid. The presence of cholesterol also changed the exchange kinetics from an apparent single-exponential to a double-exponential phenomenon. Binding of CETP to the emulsion surface was accompanied by an enhancement of fluorescence which was used to measure the binding equilibria. The enhancement of exchange due to the presence of cholesterol did not correlate with any increased binding of CETP to the emulsion surface. The presence of unesterified cholesterol in the donor did not affect the rate of transfer of the fluorescent cholesteryl ester when unlabelled emulsion was replaced by high-density lipoprotein as the acceptor. The studies demonstrate the use of microemulsions of defined size and composition for the study of the mechanism of action of CETP.

Cholesteryl ester transfer protein: its role in plasma lipid transport

1. The cholesteryl ester transfer protein (CETP) is a hydrophobic glycoprotein which acts in plasma to redistribute cholesteryl esters and triglyceride between plasma lipoproteins. 2. CETP also plays an important role in determining the composition and particle size distribution of high density lipoproteins (HDL). 3. Activity of CETP may be regulated in four ways: By factors which influence the concentration of CETP in plasma; by the activity of CETP inhibitor proteins; by variations in the concentrations and compositions of donor and acceptor lipoproteins and by factors which influence the interaction of CETP with plasma lipoproteins. 4. The mechanism of action of CETP is uncertain. Two models have been proposed: (i) a shuttle model in which CETP physically transports lipids between lipoprotein particles and (ii) a ternary complex model in which CETP forms a bridge between two lipoprotein particles, enabling them to exchange lipids. 5. Evidence is accumulating that CETP may be a pro-atherogenic factor.

Preferential cholesteryl ester acceptors among the LDL subspecies of subjects with familial hypercholesterolemia

Elevated cholesteryl ester transfer protein-mediated transfer of cholesteryl ester (CE) from high-density lipoprotein (HDL) to low-density lipoprotein (LDL) may contribute to the atherogenicity of LDL in subjects with familial hypercholesterolemia (FH). To identify the major CE acceptors among LDL subspecies, we investigated the qualitative and quantitative features of CE transfer and exchange to LDL on incubation of plasma under physiological conditions. LDL subspecies were fractionated by density-gradient ultra-centrifugation. Both mass transfer and exchange of HDL CE to and with very-low-density lipoprotein plus intermediate-density lipoprotein and LDL were linear for the first 6 hours of incubation. Thereafter mass transfer ceased, but exchange continued at a comparable rate. The rate of CE mass transfer to apolipoprotein B-containing lipoproteins was significantly enhanced in heterozygous FH subjects compared with normolipidemic individuals (91.6 +/- 28.2 versus 52.9 +/- 19.6 micrograms CE/h per milliliter plasma, FH versus normal subjects, P < .02). In FH subjects the predominant LDL subspecies (LDL 3 and 4, d = 1.029 to 1.050 g/mL) accounted for 59.7 +/- 9.2% of the total CE transferred to LDL from HDL. By contrast, expression of CE mass transfer relative to the mass of each lipoprotein acceptor showed the triglyceride (TG)-rich (10.7% to 17.3%), light LDL subspecies (LDL 1 and 2, d = 1.019 to 1.029 g/mL) to represent the preferential CE acceptors (LDL 1 and 2, 94.8 to 136.5 micrograms CE/mg LDL mass; LDL 3 through 5 [d = 1.029 to 1.063 g/mL], 47.1 to 64.1 micrograms CE/mg LDL mass).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of adiposity on plasma lipid transfer protein activities: a possible link between insulin resistance and high density lipoprotein metabolism

The mechanisms responsible for the decreased high density lipoprotein (HDL) cholesterol levels associated with obesity and insulin resistance are not well understood. Lecithin: cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein (CETP) are key factors in the esterification of cholesterol in HDL and the subsequent transfer of cholesteryl ester towards apolipoprotein B-containing lipoproteins. Phospholipid transfer protein (PLTP) may be involved in the regulation of HDL particle size. We therefore measured the activities of LCAT, CETP and PLTP using exogenous substrate assays, as well as lipids, lipoproteins, insulin and C-peptide in fasting plasma from eight healthy obese men (body mass index > 27 kg m-2) and 24 non-obese subjects. The obese men had lower levels of HDL cholesterol (P < 0.05) and higher levels of plasma triglycerides (P < 0.05), insulin (P < 0.05) and C-peptide (P < 0.01), as compared to the quartile of subjects with the lowest body mass index (BMI < 22.4 kg m-2). CETP and PLTP activities were elevated in the obese men by 35% (P < 0.01) and by 15% (P < 0.05), respectively. LCAT activity was comparable among the quartiles. Linear regression analysis showed that CETP activity was positively correlated with body mass index (P < 0.02), fasting blood glucose (P < 0.05) and plasma C-peptide (P < 0.05). PLTP activity was positively related to body mass index (P < 0.01), waist to hip circumference ratio (P < 0.001), as well as to fasting blood glucose (P < 0.05) and plasma C-peptide (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A new in vitro method for the simultaneous evaluation of cholesteryl ester exchange and mass transfer between HDL and apoB-containing lipoprotein subspecies. Identification of preferential cholesteryl ester acceptors in human plasma

To date, several methods have been developed to determine the activity of plasma lipid transfer proteins. These methods have largely involved the addition of the transfer protein in question to labeled substrates, followed by prolonged incubation (4 to 18 hours) and subsequent evaluation of the radioactivity transferred to precipitated low-density lipoprotein (LDL). While adequate for determining the activity of cholesteryl ester transfer protein (CETP), these methods generally do not take into account the composition or levels of lipoproteins present within a given individual plasma because pools of high-density lipoprotein (HDL) are labeled and used for the transfer experiments. Both the direction and the extent of lipid transfer are dependent on the composition and relative abundance of both donor and acceptor particles as well as the activity of the lipid transfer protein(s). Here we describe a new method for the determination of the capacity of plasma samples to facilitate cholesteryl ester transfer from HDL to LDL and very-low-density lipoprotein (VLDL), a method that has several advantages. First, the subject's HDL is labeled and used for transfer. Second, the labeled HDL, in a quantity equivalent to 1% of the plasma HDL mass, is added to the subject's plasma, and therefore the relative abundance of both donor and acceptor particles is preserved at their physiological levels. Third, both cholesteryl ester mass and radioactivity are determined, allowing the net mass transfer of cholesteryl ester and cholesteryl ester exchange to be quantified separately.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug control of reverse cholesterol transport

Reverse cholesterol transport identifies a series of metabolic events resulting in the transport of excess cholesterol from peripheral tissues to the liver. High-density lipoproteins (HDL) are the vehicle of cholesterol in this reverse transport, a function believed to explain the inverse correlation between plasma HDL levels and atherosclerosis. An attempt to stimulate, by the use of drugs, this transport process may hold promise in the prevention and treatment of arterial disease. Among the agents affecting lipoprotein metabolism, only probucol exerts significant effects on reverse cholesterol transport, by stimulating the activity of the cholesteryl ester transfer protein and, consequently, altering HDL subfraction composition/distribution. Another approach to the stimulation of reverse cholesterol transport consists of raising plasma HDL levels; studies in animals, either by exogenous supplementation or by endogenous overexpression, have shown a consistent benefit in terms of atherosclerosis regression and/or non-progression. Thus, it is time to consider different future treatments of atherosclerosis, combining the classical lipid-lowering treatments with innovative methods to promote cholesterol removal from the arterial wall.

Decreased ability of high density lipoproteins to transfer cholesterol esters in non-insulin-dependent diabetes mellitus

Esterified cholesterol transfer (ECT) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL) may be abnormal in situations at high risk for atherosclerosis. It has been shown to increase in insulin-dependent diabetes and to decrease in non-insulin-dependent diabetes (NIDD). Since the net transfer of esterified cholesterol (EC) results from a bidirectional exchange between HDL and VLDL/LDL, we developed a transfer assay specifically designed to measure the unidirectional transfer of EC from HDL to lipid emulsions according to first-order kinetics. Our results show that in NIDD the rate constant of HDL-dependent ECT is decreased by 30% by comparison with control subjects. Analysis of HDL composition revealed that, in both groups, HDL-dependent ECT was positively correlated with the free cholesterol/phospholipid ratio (r = 0.94; P < 0.001) and negatively correlated with the triglyceride/EC ratio (r = -0.85; P < 0.001). It is concluded that, besides the known defect of acceptor lipoproteins, the abnormality of ECT in NIDD is also caused by a decreased ability of HDL to act as an EC donor, presumably because of a change in composition. In addition, our work shows that the amount of EC lost by HDL during the reaction transfer is counterbalanced by a reciprocal equimolar transfer of triglycerides.

Low density lipoprotein for cytotoxic drug targeting: improved activity of elliptinium derivative against B16 melanoma in mice

Significant low density lipoprotein (LDL) uptake by tumour cells led to the use of LDL as a discriminatory vehicle for the delivery of cytotoxic drugs. In the current study, the lipophilic elliptinium derivative, elliptinium-oleate (OL-NME), was incorporated into LDL to reach an incorporation level of 400 molecules per LDL particle. The OL-NME-LDL complex showed cytotoxic effects on normal human fibroblasts while the cytotoxicity was not observed on receptor-defective human fibroblasts, indicating the ability of the complex to be preferentially metabolised by the LDL receptor. In vivo metabolism of the complex was related to the LDL receptor pathway. The metabolic clearance was the same for native LDL (17.1 ml h-1) and OL-NME-LDL complex (16.2 ml h-1). LDL incorporated OL-NME enhanced the anti-tumour activity against murine B16 melanoma model; this resulted from increased efficacy for OL-NME-LDL at doses equal to free 9-OH-NME (157 vs 76 of Increase Life Span (ILS) (%) values after intraperitoneal (i.p.) drug injection on i.p. implanted tumour model and 45 vs -2 ILS (%) values after intravenous drug injection on subcutaneous implanted tumour model). These data suggest that LDL improves the potency of lipophilic cytotoxic drugs against tumours that express LDL receptor activity.

Lipid transfer protein-mediated distribution of HDL-derived cholesteryl esters among plasma apo B-containing lipoprotein subpopulations

The substrate specificity of lipid transfer protein has been examined in whole plasma in vitro by following the redistribution of high density lipoprotein (HDL)-derived [3H]cholesteryl ester (CE) into apolipoprotein (apo) B-containing lipoproteins using density gradient ultracentrifugation. HDL-derived [3H]CEs were incubated with plasma or isolated lipoprotein classes (very low density lipoprotein, intermediate density lipoprotein, and low density lipoprotein [LDL] subpopulations from the HDL donor) with and without lipoprotein lipase for 0.5-6 hours at 37 degrees C. After incubation, lipoproteins were separated into 38 fractions after density gradient ultracentrifugation, and radioactivity, protein, and cholesterol were monitored across the profiles. These studies indicate that 1) lipid transfer protein activity varied among the individuals as well as within an individual; 2) the majority of the [3H]CE was associated with LDL; 3) in most individuals (71%), more HDL-derived [3H]CE distributed within the buoyant LDL density region; and 4) the distribution of HDL-derived [3H]CE was similar to the distribution of lipoprotein lipase-derived "remnant" particles within buoyant LDL. These in vitro studies support the hypothesis that HDL-derived [3H]CEs vary in their distribution among apo B-containing particles and that more HDL-derived [3H]CEs are transferred to lipoproteins within the buoyant LDL density range. Additional studies suggest that lipoprotein heterogeneity within this density range, such as the presence of remnant-like lipoproteins, may contribute to the selective distribution of HDL-derived [3H]CE into buoyant LDL.

Simvastatin-induced decrease in the transfer of cholesterol esters from high density lipoproteins to very low and low density lipoproteins in normolipidemic subjects

Hyperlipidemic patients often have an accelerated esterified cholesterol transfer (ECT) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL). We investigated the effect of simvastatin on ECT in twelve normolipidemic subjects. After 6 weeks of simvastatin administration, ECT was decreased by 23%. To determine the mechanism of action of simvastatin, we measured ECT in different recombination experiments, using an isotopic assay in which the transfer of labelled EC from HDL to VLDL/LDL was determined. When HDL of the treated subjects were incubated with VLDL/LDL and CETP fractions isolated from control plasma, no effect of simvastatin was observed, indicating that the drug did not alter the HDL-dependent ECT. This might be expected since simvastatin induced only minor modifications of HDL structure. When HDL and VLDL/LDL of control plasma were incubated with CETP fractions of the treated subjects, a clear reduction of ECT occurred after simvastatin administration. The decrease of plasma transfer activity was correlated to that of CETP concentration and accounted for the simvastatin-induced lowering of ECT. The diminution of plasma CETP was correlated to that of the apo B-containing lipoproteins concentration. This finding confirms previous reports suggesting a relationship between LDL level and CETP activity. In conclusion, our work shows that simvastatin administration results in a decrease of ECT and that this effect occurs through a lowering of plasma CETP activity.

HDLs and alimentary lipemia. Studies in men with previous myocardial infarction at a young age

The plasma concentration, particle size, and chemical composition of high density lipoproteins (HDLs) are associated with the metabolism of triglyceride-rich lipoproteins (TGRLs). During alimentary lipemia there is active exchange of lipids and apolipoproteins between HDL and apolipoprotein B-containing lipoproteins. Whereas HDL has been assigned a protective role against the development of atherosclerosis, alimentary lipemia has been proposed to represent a potentially atherogenic state. We examined plasma HDL concentration, particle size, and composition and their relations to postprandial TGRLs in 32 postinfarction patients and 10 healthy control subjects after intake of a standardized oral fat load of a mixed-meal type. All patients had undergone coronary angiographies in connection with the myocardial infarction and around 5 years thereafter. The plasma HDL cholesterol concentration decreased significantly in response to the oral fat load, particularly in hypertriglyceridemic patients, with a concomitant increase of HDL triglycerides. A limited and reversible yet consistent increase of HDL particle size (1-2%) was seen 6 hours after intake of the oral fat load on nondenaturing gradient gel electrophoresis (GGE) in both patients and control subjects. Virtually no changes in the plasma concentration of HDL GGE subclasses, lipoproteins containing apolipoprotein A-I but no apolipoprotein A-II (LpA-I), or lipoproteins containing both apolipoproteins A-I and A-II (LpA-I:A-II) were induced in the postprandial state despite massive increases of large very low density lipoprotein (VLDL) and large chylomicron remnant levels (determined as apolipoproteins B-100 and B-48 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Strong inverse correlations with fasting plasma HDL cholesterol and the larger HDL GGE subspecies were found for large postprandial VLDL and large chylomicron remnants, whereas the corresponding relations for small VLDL and small chylomicron remnants were weaker. The relations of both large and small VLDL and chylomicron remnants to HDL cholesterol were confined to subjects in the lower fasting plasma HDL cholesterol range (< 1.2 mmol/l). None of the HDL parameters measured, either in the fasting or in the postprandial state (HDL cholesterol, HDL triglycerides, HDL GGE subclasses, LpA-I, and LpA-I:A-II), were related to the development of coronary atherosclerosis, whereas the postprandial plasma levels of small chylomicron remnants, which showed weak negative correlations with HDL, related positively to the progression of coronary atherosclerosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Dietary fatty acids, lipoproteins, and cardiovascular disease

Dietary fat quality and quantity significantly affect the metabolism of all the plasma lipoproteins and probably constitute the most significant dietary determinants of plasma lipoprotein levels. Since the major role of the plasma lipoproteins is the transport of exogenous and endogenous fat, this would be expected of a highly regulated, metabolically homeostatic system. The data clearly show that dietary fat saturation affects all aspects of lipoprotein metabolism, from synthesis to intravascular remodeling and exchanges to receptor-mediated and nonspecific catabolism. The experimental data regarding dietary fatty acid effects on lipoprotein metabolism are complicated and at times contradictory due to the large degree of metabolic heterogeneity in the population, which, when coupled with the known abnormalities of lipoprotein metabolism associated with certain types of hyperlipoproteinemia, can present responses from A to Z. It is clear that the same dietary pattern has different effects in different individuals and that complicating factors of individuality raise some concerns regarding generalized dietary recommendations. As new knowledge of the role of dietary factors and CVD risk develops, and our abilities to characterize the individual patient's response to dietary interventions become more refined, it may be possible to specify dietary fat intervention from a patient-oriented concept rather than a single all-purpose diet approach. Thus it would be possible to design dietary interventions to match patient needs and gain both efficacy and compliance. With the spectrum of approaches possible--low fat, moderate fat with MUFA, n-3 PUFA, etc.--we should be able to approach dietary interventions to reduce CVD risk at both a population-based level and a patient-specific level. There remains much to learn regarding the effects of dietary fatty acids on the synthesis, intravascular modifications, and eventual catabolism of the plasma lipoproteins. The area of lipoprotein metabolism in health and disease, of its modifications by diets and drugs, and of the contributions of genetic heterogeneity to these processes is one of notable advances over the past two decades and continues to be an area of intense investigation.

Probucol increases cholesteryl ester transfer protein activity in hypercholesterolaemic patients

Probucol, a widely used lipid lowering drug, reduces both low- and high-density (LDL and HDL) lipoprotein levels and can induce a regression of tissue lipid deposits in both animals and man. The suggested mechanism(s) involve the prevention of LDL oxidative modifications and, possibly, an improvement in the reverse cholesteryl ester transport system. Probucol administration to 10 hypercholesterolaemic patients increased the activity of the cholesteryl ester transfer protein (CETP) by 50%. The rise of CETP activity was significantly related with the plasma steady-state drug levels (r = 0.51, P less than 0.005), thus suggesting that probucol may directly stimulate CEPT synthesis and/or release. Furthermore, CETP activity was inversely related with HDL-cholesterol levels, both in the whole series of 10 patients (r = -0.56, P less than 0.001) and, more so, in the single individuals (r between -0.77 and -0.97), thus suggesting that the reduction of plasma HDL-cholesterol levels is a direct consequence of CETP stimulation. These findings support the hypothesis that an improvement in the reverse cholesteryl ester transport is a major mechanism of probucol and that this may explain the drug induced plasma lipoprotein changes.

Reverse cholesterol transport: physiology and pharmacology

Reverse cholesterol transport identifies a series of metabolic events resulting in the transport of cholesterol from peripheral tissues to the liver and plays a major role in maintaining cholesterol homeostasis in the body. High density lipoproteins (HDL) are the vehicle of cholesterol in this reverse transport, a function believed to explain the inverse correlation between plasma HDL levels and atherosclerosis. An attempt to stimulate, by the use of drugs, this transport process seems to be of great promise in the prevention and treatment of arterial disease. Only few drugs are now known that can modify the activity of the various factors involved in the process. Clofibrate reduces cholesterol esterification, but the newer fibric acids are generally ineffective as anion-exchange resins. Probucol directly increases the activity and mass of cholesteryl ester transfer protein, thus possibly improving the physiological process of cholesterol removal from tissues. The few available data on the effects of drugs on reverse cholesterol transport should stimulate the search for new agents specifically stimulating this antiatherogenic process.

Increase in plasma cholesteryl ester transfer protein during probucol treatment. Relation to changes in high density lipoprotein composition

Probucol is a hypolipidemic agent that causes a marked decrease in high density lipoprotein (HDL) cholesterol. To investigate the mechanism of this effect, two studies were performed in hypercholesterolemic patients who had been stabilized previously on diet and were not receiving other lipid-lowering medication. Plasma cholesteryl ester transfer protein (CETP) concentrations were measured in fasting plasma samples before and after 10 weeks of probucol therapy using a sensitive and specific radioimmunoassay. Plasma total and low density lipoprotein cholesterol concentrations decreased, whereas apolipoprotein (apo) B was unchanged. Plasma apo E concentrations increased markedly. HDL cholesterol and apo A-I decreased in all subjects. These effects of probucol were accompanied by even more striking changes in plasma CETP concentrations, which increased by a mean of 64%. In a second study of six hypercholesterolemic subjects, the time-course effects of probucol on CETP and HDL subspecies were studied. Significant increases in plasma apo E and in CETP occurred after 4 weeks, and CETP, but not apo E, increased further after 16 weeks of treatment. Concomitant and opposite changes occurred in HDL composition, with decreases in HDL cholesterol and lipoprotein containing apo A-I. The increase in plasma CETP concentrations, the decrease in HDL cholesterol, and the increase in plasma apo E concentrations observed during probucol treatment are changes consistent with a postulated increase in reverse cholesterol transport via the remnant pathway.

Accelerated cholesteryl ester transfer in patients with insulin-dependent diabetes mellitus

Abnormalities in cholesteryl ester transfer (CET) may play a role in the development of diabetic arterial vascular complications. To assess this important step systematically in reverse cholesterol transport, we have studied 20 treated, clinically stable, normolipidaemic patients. Contrary to the impairment in CET described previously in NIDDM, the mass of CE transferred from HDL to VLDL + LDL was significantly greater in IDDM patients than in controls at 1,2, and 4 h (P less than 0.001). When the d less than 1.063 plasma fractions from IDDM subjects were combined with controls d less than 1.063 fractions, an accelerated CET response was observed which was identical to that found in intact IDDM plasma. This finding, which indicates that this disturbance in CET was associated with the acceptor lipoproteins, was confirmed when we found that it was reproduced by the addition of IDDM VLDL and not LDL to control d greater than 1.063 fractions. Changes observed in lipoprotein core lipid composition were consistent with accelerated CET occurring in IDDM in vivo: the TG/CE core lipid ratio was decreased in VLDL from six subjects (diabetic 9.5 +/- 0.8 vs control 12.9 +/- 3.4; P less than 0.1) and increased in their HDL (diabetic 0.55 +/- 0.11 vs control 0.42 +/- 0.04; P less than 0.025). No correlation was demonstrable between estimates of diabetic control (glycoalbumin, fasting glucose) and CET. These data indicate that CET may be abnormally increased in normolipidaemic IDDM patients. A defect of this type may be atherogenic because it increases the number of lipoprotein particles in plasma which resemble cholesteryl ester-enriched chylomicron and VLDL remnants but whose normal receptor-mediated catabolism may be altered.

Net mass transfer of cholesteryl esters from low density lipoproteins to high density lipoproteins in plasma from normolipidemic subjects

Net mass transfer of lipids was measured in plasma from fasted, normolipidemic subjects. The plasma was incubated, and lipoproteins were subsequently separated by polyanion precipitation or density gradient ultracentrifugation. Total cholesterol, unesterified cholesterol, and triglycerides were measured in the isolated lipoprotein fractions. The rate of cholesterol esterification was measured simultaneously. All plasma samples showed an increase in high density lipoprotein (HDL) cholesteryl esters during 1-hour incubations. In most cases, this increase was higher than the cholesteryl ester formation in total plasma due to cholesterol esterification. Therefore, we concluded that a net mass transfer of cholesteryl esters occurred from the very low plus low density lipoprotein (VLDL + LDL) fractions to HDL in plasma from most of the subjects studied. Transfer of triglycerides occurred from VLDL + LDL to HDL in plasma from all subjects. The cholesteryl ester transfer (measured after 1 hour) is not related to the activity of cholesteryl ester transfer protein. Inhibition of cholesterol esterification did not change the direction of cholesteryl ester or triglyceride transfer. Ultracentrifugal separation of plasma lipoproteins revealed that both HDL and VLDL are acceptors of cholesteryl esters and that VLDL donates triglycerides to both LDL and HDL. Removal of VLDL from plasma by ultracentrifugation did not affect the cholesteryl ester transfer from LDL to HDL. We conclude that LDL may act as a donor of cholesteryl esters during incubation of normolipidemic plasma.

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.

Normalisation of the composition of very low density lipoprotein in hypertriglyceridemia by nicotinic acid

Large (Sf greater than 100) and small (Sf 100-20) very low density lipoprotein (VLDL) particles were isolated by density gradient ultracentrifugation and characterized chemically in 8 patients with primary hypertriglyceridemia before and after 6 weeks treatment with 4 grammes daily of nicotinic acid (NA). Concomitant changes in high density lipoprotein (HDL) subclass distribution were determined by gradient gel electrophoresis. Small VLDL was subjected to lipolysis in vitro by incubation with bovine lipoprotein lipase before and after NA, and the change in the lipolytic end-product isolated in the low density lipoprotein (LDL) fraction was investigated. Reductions were achieved in the plasma levels of triglycerides, free and esterified cholesterol, phospholipids and proteins in the two VLDL subfractions. In all, the composition of both large and small VLDL particles changed towards potentially less atherogenic particles that were poorer in cholesteryl esters. The HDL cholesterol concentration increased and the HDL protein distribution on gradient gel electrophoresis changed towards larger particles. The mechanism behind the change in cholesterol distribution between VLDL and HDL after NA treatment is unclear, but it could possibly relate to decreased lipid transfer activity. NA reduced the content of apolipoprotein B in both VLDL subclasses and did not decrease the calculated particle size or the number of triglyceride molecules per particle, indicating a reduction of VLDL particle number rather than of particle size. The LDL density fraction isolated after lipolysis in vitro of small VLDL contained less total cholesterol and phospholipids and had a density profile more similar to native LDL after the patients had been treated with NA.

Probucol treatment in hypercholesterolemic patients: effects on lipoprotein composition, HDL particle size, and cholesteryl ester transfer

Despite probucol's capacity to induce regression of tendinous xanthomata and reduce whole plasma and LDL cholesterol (LDL-C) in patients with hypercholesterolemia, its therapeutic use in the United States has been limited because of concern about its HDL-lowering effects. To assess the possibility that probucol might facilitate mobilization of tissue cholesterol in the presence of low HDL levels as a consequence of favorable changes in lipoprotein composition and function, we have analyzed lipoproteins and studied cholesteryl ester transfer (CET) in hypercholesterolemic patients before and after treatment. Prior to treatment, the free cholesterol (FC)/lecithin (L) ratio in plasma, a new index of cardiovascular risk, and the mass of cholesteryl ester transferred from HDL to the apo B-containing lipoproteins (CET) both were significantly increased (P less than 0.001). As previously shown, plasma cholesterol, LDL-C, HDL-C, HDL2, and apolipoproteins A-I, A-II, and B all fell significantly following probucol treatment. The FC/L ratio in plasma (P less than 0.01) and HDL2 (P less than 0.01) both fell significantly also, as did the sphingomyelin/lecithin ratio in VLDL + LDL (P less than 0.001) which is typically increased in untreated patients with hypercholesterolemia. Nondenaturing gradient gel electrophoresis in 6 patients revealed that the quantitative changes in HDL were associated with a redistribution of particles characterized by a decrease in the prevalence of the largest (HDL2b) and a relative increase in the number of the smallest (HDL3b) particles. Moreover, CET following probucol therapy returned to levels which were indistinguishable from those of normolipidemic controls. These results indicate that untreated patients with hypercholesterolemia have abnormalities in (1) lipoprotein composition which have been shown to retard the movement of cholesterol from tissues to HDL, and in (2) CET which is accelerated and can potentially lead to the formation in plasma of atherogenic CE-enriched apo B-containing lipoproteins. Probucol's capacity to reverse these specific alterations suggests that it may have beneficial effects on cholesterol transport in patients with hypercholesterolemia.

Genetic variation in the cholesteryl ester transfer protein and apolipoprotein A-I genes and its relation to coronary heart disease in a Sri Lankan population

The influence of variation in the genes for cholesteryl ester transfer protein and apolipoprotein A-I was investigated in 95 patients with coronary heart disease and 95 matched control subjects of South East Asian extraction. Restriction fragment length polymorphisms (RFLPs) linked to the cholesteryl ester transfer protein gene TaqIA and TaqIB, and to the apolipoprotein A-I gene SstI, were examined to investigate the extent of genetic variation at these loci. None of the alleles defined by these RFLPs were associated with increased coronary risk. Analysis of the data by division of high density lipoprotein-cholesterol levels into tertiles showed a trend of a higher frequency of B1 allele (presence of the TaqIB site) with reduced high density lipoprotein levels. The B1 allele was more frequent in control subjects, with low high density lipoprotein levels (P less than 0.02), but not in coronary heart disease patients. The differences became significant for both groups (P less than 0.05) when the data of non-smokers were analysed separately.

Investigation of lipid transfer in human serum leading to the development of an isotopic method for the determination of endogenous cholesterol esterification and transfer

The rate at which radioactivity appeared in cholesteryl esters (CE) in whole serum and in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) when radioactively labelled free cholesterol (FC) was incubated with serum was investigated. At 4 degrees C equilibration of radioactive FC with native FC occurred, but there was no conversion to CE. At 37 degrees C CE mass increased in parallel with radioactivity in CE both in whole serum and VLDL/LDL. Incubation at 37 degrees C with an inhibitor of lecithin cholesterol acyl transferase (LCAT) abolished the increase in the total CE radioactivity and mass in serum. Transfer of CE from high density lipoprotein (HDL) to VLDL/LDL, however, continued to occur. An assay for LCAT and for cholesteryl ester transfer protein (CETP) was developed, which employed the increases in radioactive CE in whole serum and VLDL/LDL during a single incubation as indices of LCAT and CETP activity, respectively. Determination of the initial serum FC concentration allowed the expression of these activities in nmol/ml per h. References ranges were established in 62 fasting normolipidaemic men and women and increases in both LCAT and CETP were found following a fatty meal. The experiments thus provided further information about the carrier-mediated transfer of CE from its site of esterification on HDL to VLDL/LDL and formed the basis of a relatively simple assay, which has advantages over previously published methods and which may be used in clinical and epidemiological studies to elucidate the role of CETP and LCAT in atherosclerosis.

Enhanced net mass transfer of HDL cholesteryl esters to Apo B-containing lipoproteins in patients with peripheral vascular disease

In vitro net mass transfer of HDL cholesteryl ester to apolipoprotein (Apo) B-containing lipoproteins (HDL-CET) was found to be nearly twofold higher in plasma from 35 male patients with peripheral vascular disease compared to the values of 27 age- and sex-matched healthy controls (P less than 0.001). Differences in HDL-CET were predominantly observed between normolipidemic patients and controls, and were also demonstrable in pairs of patients and controls with similar HDL cholesterol, VLDL + LDL cholesterol, and triglyceride concentrations. Within the control group, higher HDL-CET was found in individuals with enhanced triglyceride or VLDL + LDL cholesterol levels. This dependence was not observed in the patient group. Consequently, enhanced HDL-CET in the patients seems to be independent of plasma lipid levels.

Alimentary lipemia-induced redistribution of cholesteryl ester between lipoproteins. Studies in normolipidemic, combined hyperlipidemic, and hypercholesterolemic men

Alimentary lipemia stimulates the transfer of cholesteryl ester between lipoproteins in vitro and may alter lipoprotein cholesteryl ester distribution in vivo. The effect of a single, large oral fat load on lipoprotein cholesteryl ester redistribution and the activity of cholesteryl ester transfer protein was investigated in six normolipidemic men (Group A), six combined hyperlipidemic men (Group B), and six hypercholesterolemic men (Group C). Fasting triglyceride-rich lipoprotein cholesteryl ester was high in Group B, low in Group A, and intermediate in Group C (A less than C less than B, p less than 0.05). After an oral fat load, total plasma cholesteryl ester was unchanged in all groups. In Group A, cholesteryl ester increased in smaller triglyceride-rich lipoproteins and remained so at 24 hours. Conversely, low density and high density lipoprotein cholesteryl ester decreased and returned to fasting values at 24 hours. In Group B, cholesteryl ester increased in large triglyceride-rich lipoproteins. Low density and high density lipoprotein cholesteryl ester (expressed as percentage of plasma cholesteryl ester) decreased. By contrast, in Group C, triglyceride-rich lipoprotein and low density lipoprotein cholesteryl ester remained unaltered, and only high density lipoprotein cholesteryl ester decreased. The activity of cholesteryl ester transfer protein increased in all groups and returned to fasting values at 24 hours. No differences in response were observed among the three groups. It is concluded that an oral fat load can induce a shift in lipoprotein cholesteryl ester distribution from high and low density lipoproteins to triglyceride-rich lipoproteins without affecting total plasma cholesteryl ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of steroid hormone association with human plasma lipoproteins

Partition coefficient analysis, equilibrium dialysis, and computer simulation were used to evaluate associations of twelve steroid hormones (androstanediol, androstenediol, androstenedione, androsterone, dehydroepiandrosterone, dihydrotestosterone, estradiol, estriol, estrone, hydroxyprogesterone, progesterone, and testosterone) with human plasma high density lipoproteins (HDL), low density lipoproteins (LDL), and very low density lipoproteins (VLDL). It was determined that partitioning of steroid hormones (SH) between the aqueous medium and the surfaces of lipoproteins (LP) was the initial (first order) SH-LP interaction. For some SH, especially dehydroepiandrosterone, significant second order interactions, which may involve chemical conversions, were detected. The first order binding values of the twelve SH with three LP were combined with the corresponding binding values of SH with sex hormone-binding globulin, corticosteroid-binding globulin, and albumin in a 6 X 12 matrix. The computer program TRANSPORT was used to analyze the matrix and determine the distribution of each SH among six different binding agents in the "normal" male. It was concluded that LP are important vehicles for SH conveyance in plasma and may also be important for SH entry into cells.

In vivo evidence for cholesterol ester and triglyceride exchange between high density lipoprotein and infused triglyceride rich particles in abetalipoproteinemia

Abetalipoproteinemia is characterized by the absence of chylomicrons, very low density and low density lipoproteins from the plasma. To study neutral lipid exchange between lipoproteins in vivo a chylomicron model, Intralipid R, was infused in an abetalipoproteinemic patient. During a three hour infusion of 250 mg/kg/hr after a priming dose of 100 mg/kg triglyceride, 8% of the triglyceride mass of Intralipid was replaced by cholesterolester, while 8% of the cholesterylester mass was replaced by triglyceride in high density lipoproteins. Thus, the exchange of cholesterylester and triglyceride between high density lipoprotein and triglyceride rich particles in vivo was directly demonstrated in the absence of apolipoprotein B.