Cholesterol Ester Transfer Activity Research Articles

Diphenylpyridylethanamine (DPPE) Derivatives as Cholesteryl Ester Transfer Protein (CETP) Inhibitors

A series of diphenylpyridylethanamine (DPPE) derivatives was identified exhibiting potent CETP inhibition. Replacing the labile ester functionality in the initial lead 7 generated a series of amides and ureas. Further optimization of the DPPE series for potency resulted in the discovery of cyclopentylurea 15d, which demonstrated a reduction in cholesterol ester transfer activity (48% of predose level) in hCETP/apoB-100 dual transgenic mice. The PK profile of 15d was suboptimal, and further optimization of the N-terminus resulted in the discovery of amide 20 with an improved PK profile and robust efficacy in transgenic hCETP/apoB-100 mice and in hamsters. Compound 20 demonstrated no significant changes in either mean arterial blood pressure or heart rate in telemeterized rats despite sustained high exposures.

Effects of fenofibrate on lipid profiles, cholesterol ester transfer activity, and in-stent intimal hyperplasia in patients after elective coronary stenting

BackgroundThe association between modulation of detailed lipoprotein profiles and cholesterol ester transfer (CET) activity by peroxisome proliferator-activated receptor (PPAR)-a agonists in patients with coronary artery disease remains unclear. We assessed lipid profiles, plasma CET activity, and in-stent intimal hyperplasia after fenofibrate treatment in patients who underwent elective coronary stenting.MethodsForty-three consecutive patients who underwent elective coronary stenting were randomized to the fenofibrate group (300 mg/day for 25 weeks, n = 22) or the control group (n = 21). At baseline and follow up, CET activity and lipoprotein profiles were measured, and quantitative coronary angiography was performed.ResultsIn the fenofibrate group, the levels of large very low-density lipoprotein cholesterol, and small low-density lipoprotein (LDL) cholesterol decreased and those of small high-density lipoprotein (HDL) cholesterol increased. Besides, CET activity decreased independent of the effect of fenofibrate on total and LDL cholesterol. The reduction of CET activity significantly correlated with the increase in LDL particle size (r = 0.47, P = 0.03) and the decrease of triglycerides in large HDL subclasses (r = 0.48, P = 0.03). Although there were no significant differences in restenosis parameters between the two groups, low CET activity significantly correlated with the inhibition of neointimal hyperplasia (r = 0.56, P = 0.01).ConclusionsFenofibrate inhibited CET activity and thereby improved atherogenic lipoprotein profiles, and reduced intimal hyperplasia after coronary stenting.

Dietary fat and postprandial lipids.

Impaired clearance of chylomicron remnants is associated with increased risk of atherosclerosis and cardiovascular disease. An intake of 40 to 50 g of fat in a meal results in significant lipemia in healthy adults, with consecutive fat-containing meals enhancing the lipemia. This would suggest that limiting fat intake to approximately 30 g on each eating occasion would minimize postprandial lipemia. Sedentary behavior and obesity independently impair the postprandial metabolism of lipids. Postprandial lipemia causes endothelial dysfunction and results in a transient increase in factor VII activated (FVIIa) concentration. Plasminogen activator inhibitor type-1 activity is associated with fasting plasma triacylglycerol concentration, but is not influenced by postprandial lipemia. Trans-18:1 acid appears to increase cholesterol ester transfer activity acutely compared with oleate. Randomized stearic acid-rich fats result in less postprandial lipemia and a lower postprandial increase in FVIIa, whereas unrandomized cocoa butter results in similar postprandial lipemia and increases in FVIIa compared with oleate. A background diet containing in excess of 3 g/d of long-chain omega-3 fatty acids decreases postprandial lipemia by stimulating lipoprotein lipase expression and decreasing very low-density lipoprotein synthesis, but a diet enriched in alpha-linolenic acid (up to 9.5 g/d) does not show these effects. Future research on diet and postprandial lipids needs to exploit newly gained knowledge on the regulation of adipocyte metabolism by adipokines and nuclear hormone receptors, particularly with regard to fat patterning and reverse cholesterol transport.

Changes in plasma low-density lipoprotein (LDL)- and high-density lipoprotein cholesterol in hypo- and hyperthyroid patients are related to changes in free thyroxine, not to polymorphisms in LDL receptor or cholesterol ester transfer protein genes.

Thyroid function disorders lead to changes in lipoprotein metabolism. Both plasma low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) increase in hypothyroidism and decrease in hyperthyroidism. Changes in LDL-C relate to altered clearance of LDL particles caused by changes in expression of LDL receptors on liver cell surfaces. Changes in cholesterol ester transfer activity partly explain changes in HDL-C. It has been suggested that the magnitude of these changes is related to polymorphisms of involved genes. The aim of the present study is to investigate whether the polymorphic AvaII restriction site in exon 13 of the LDL receptor gene and the polymorphic TaqIB site in intron 1 of the cholesterol ester transfer protein are associated with the magnitude of the changes in plasma LDL-C and HDL-C, respectively, in the transition from the hypo- or hyperthyroid to the euthyroid state. From a consecutive group of 66 untreated hypothyroid and 60 hyperthyroid patients, 47 Caucasians in each group were analyzed. Fasting LDL-C and HDL-C were measured at baseline and 3 months after restoration of the euthyroid state. Genotype was determined by means of PCR techniques. The homozygous presence of a restriction site was designated as +/+, heterozygous as +/-, and absence as -/-. Trend analysis was done with ANOVA. Among hypo- or hyperthyroid patients, subgroups with different genotypes did not differ in thyroid function pre- or post treatment. The mean decrease in LDL-C (mmol/L +/- SD) in hypothyroid patients with different AvaII genotypes did not differ: - 1.07 +/- 1.44 (-/-, N = 15), -1.25 +/- 1.53 (+/-, N = 19), and -1.18 +/- 1.01 (+/+, N = 13) mmol/L [not significant (NS)]; neither did the mean increase in hyperthyroid patients: 1.07 +/- 0.90 (-/-, N = 18), 0.92 +/- 1.00 (+/-, N = 21), and 1.20 +/- 0.45 (+/+, N = 6) (NS). The mean decrease in HDL-C (mmol/L +/- SD) in hypothyroid patients with different TaqIB genotypes did not differ: -0.22 +/- 0.26 (-/-, N = 13), -0.15 +/- 0.23 (+/-, N = 21), and -0.12 +/- 0.22 (+/+, N = 9) (NS); neither did the mean increase in hyperthyroid patients: 0.29 +/- 0.39 (-/-, N = 7), 0.26 +/- 0.23 (+/-, N = 22), and 0.19 +/- 0.31 (+/+, N = 18) (NS). Changes in LDL-C and HDL-C correlated with the logarithm of the change in free T4 (fT4), expressed as the fT4 posttreatment/fT4 pretreatment ratio (r = -0.81, P < 0.001; and r = -0.62, P < 0.001, respectively). In conclusion, in the transition from hypo- or hyperthyroidism to euthyroidism, no association is found between AvaII genotype and changes in plasma LDL-C nor between TaqIB genotype and changes in HDL-C. Changes in LDL-C and HDL-C correlate with changes in fT4.

Cholesteryl ester transfer protein mutations, protein activity and HDL-cholesterol concentration.

We have examined a group of North American subjects, selected to include individuals with a wide variety of HDL-cholesterol concentrations for: 1) mutations in the genes coding for cholesteryl ester transfer protein and hepatic lipase, 2) apolipoprotein E genotype, 3) total cholesterol and triglycerides, 4) HDL-triglycerides. Cholesteryl ester transfer protein activity was also estimated, using a novel technique that does not require separation of substrate and product. Transfer activity was shown to have a monophasic distribution, with a mean activity of 21 pmol substrate transferred/3 h/microl plasma. The cholesterol ester transfer activity of the group with HDL-cholesterol >1.60 mmol/l was significantly less than those with HDL-cholesterol <1.60 mmol/l. The cholesteryl ester transfer protein G1533A mutation was detected at an overall allele frequency of 2.91%. The mutation was more frequent in the group with HDL-cholesterol <1.60 mmol/l than in those >1.60 mmol/l. It was also more frequent in those with protein activity > 30 pmol/ 3h/microl plasma than in those with activity <30. These data suggest that this mutation in cholesteryl ester transfer protein is associated with increased transfer activity and reduced HDL-cholesterol concentrations. The cholesteryl ester transfer protein activity assay described here is simple and convenient. Subject to further evaluation and correlation with the present labour and time intensive assays, this commercially available assay offers the potential of rapid, simple analysis of large numbers of samples.

Effect of dietary vitamin E supplements on cholesteryl ester transfer activity in hamster adipose tissue

Increased concentration of cholesteryl ester transfer protein (CETP) in plasma favours a lipoprotein profile characterized by a reduced high density lipoprotein (HDL) cholesterol. Previous studies have demonstrated that a diet high in cholesterol and saturated fat (HCSF) is associated with elevated plasma CETP and increased release of cholesterol ester transfer activity (CETA) from hamster adipose tissue incubated in vitro. The present study investigated the effects of vitamin E (Vit.E) ingestion on plasma CETP activity and adipose tissue CETA in Syrian Golden hamsters. A regular diet supplemented by the addition of 1% cholesterol and 10% coconut oil (w/w) was associated with a time-dependent increase in plasma CETP activity and increased release of adipose CETA following incubation of fragments of perirenal adipose tissue. Vit.E ingestion (100 mg/kg body weight per day for 8 weeks) suppressed 85% of the increase of CETA released from cultured hamster adipose tissue and 70% of the increase of plasma CETP activity induced by the HCSF diet. Significant decreases in plasma total and LDL cholesterol and an increase in HDL cholesterol were found in hamsters receiving the HCSF diet plus Vit.E compared to the animals on the HCSF diet alone. In the hamsters on regular chow, Vit.E ingestion alone did not significantly alter adipose tissue CETA, plasma CETP activity or plasma lipoproteins. The results indicate that Vit.E prevents the HCSF diet-induced increase in plasma CETP activity, probably via a reduction of CETA secretion from hamster adipose tissue. This suggests that Vit.E supplementation may help to ameliorate the dyslipidemia caused by a HCSF diet through its inhibitory influence on CETP production in adipose tissue.

Cholesterol ester transfer mediated by lipid transfer protein as influenced by changes in the charge characteristics of plasma lipoproteins

The relationship between the cholesterol ester (CE) transfer activity of lipid transfer protein (LTP) and its affinity with lipid and lipoprotein particles was investigated. The study of the effects of chemical modification of low density lipoprotein (LDL) amino groups and carboxyl groups on the CE transfer activity showed that the maximal activity is obtained upon succinylation or acetylation of approximately 7% of LDL amino groups. Further increases in the extent of modification progressively reduced the transfer activity. The treatment of LDL with fatty acids gave results comparable to the chemical modification of LDL amino groups. The addition of low concentrations of fatty acids was stimulatory, while that of high concentrations was inhibitory. Although increases in the positive charges of LDL by the carboxyl group modification did not appreciably influence the CE transfer, the addition of cationic detergents gave a profound effect on the CE transfer. A maximal CE transfer activity was obtained upon addition of very small amounts of the detergents, with the higher concentrations sharply reducing the transfer activity. We also studied the effects of the concentrations of phosphate buffer and various salts on the CE transfer as well as the affinity of LTP for very low density lipoproteins, low density lipoproteins, high density lipoproteins 3, and high density lipoproteins 2. It appeared that the affinity of LTP for various lipoproteins is governed by a delicate balance of electrostatic and hydrophobic interactions. Optimal degrees of the interaction of LTP with both donor and acceptor particles seem to be required for the maximal degree of CE transfer.

The effects of probucol on the levels, structure, composition and metabolism of plasma lipoprotein in rats

The effects of probucol administration on the levels, structure, composition and metabolism of plasma lipoproteins were determined in male rats. Probucol caused a 25% decrease of plasma cholesterol and a 20% decrease of plasma triacylglycerols. The effect was more pronounced on lipoproteins of density less than 1.063 g/ml (− 35%) than on density greater than 1.063 g/ml (− 21%). The density of LDL, HDL-1 and HDL-2 separated by ultracentrifugation on a zonal rotor was shifted towards a higher density. The content of cholesteryl esters increased in VLDL and LDL and decreased in HDL-1 and HDL-2. LDL, HDL-1 and HDL-2 were relatively enriched with proteins. The intravascular metabolism of 125I-labeled apo A-I was identical in control and probucol-treated rats with a circulating half-lifetime of 9.5 h. The circulating half-lifetime of LDL labeled biosynthetically with [ 3H]cholesteryl esters was also identical, 6.5 h. The circulating half-lifetime of [ 3H]cholesteryl esters in HDL-2, in contrast, was 9.5 h in control rats and 7.5 h in probucol-treated animals. Plasma cholesterol ester transfer activity was almost undectectable in either control or probucol treated animals. The investigation demonstrates a pronounced effect of probucol on plasma lipid and lipoprotein levels in rats, on cholesterol ester distribution between lipoproteins and on lipoprotein transport rates in the plasma. These effects may contribute to the anti-atherogenetic action of probucol.

Plasma concentrations of cholesteryl ester transfer protein in hyperlipoproteinemia. Relation to cholesteryl ester transfer protein activity and other lipoprotein variables.

Cholesteryl ester transfer protein (CETP) mediates an important pathway for reverse cholesterol transport. Concentrations of CETP in fasting plasma were measured by radioimmunoassay in two different groups of hyperlipoproteinemic subjects. Plasma CETP concentrations measured by radioimmunoassay correlated closely with cholesterol ester transfer activity in normal plasma (r = 0.86). In the first group of 58 patients, plasma CETP concentrations were significantly increased, as compared with those in 79 normal subjects and in hypercholesterolemic (+26%) and combined hyperlipoproteinemic (+25%) subjects but were not altered in moderately hypertriglyceridemic subjects. Marked elevations in plasma CETP levels were documented in patients with dysbetalipoproteinemia (+68%) and severe chylomicronemia (+85%). Similar results were obtained in a second population of 50 hyperlipoproteinemic subjects. Significant correlations were found between plasma CETP levels and total cholesterol (r = 0.52), very low density lipoprotein (VLDL) cholesterol (r = 0.63), and apolipoprotein E concentration (r = 0.40). Correction of the lipoprotein phenotype by dietary means resulted in significant reductions in plasma CETP concentrations in patients with chylomicronemia and dysbetalipoproteinemia. In these subjects, plasma high density lipoprotein cholesterol concentrations increased as CETP decreased. These studies indicate that CETP levels increase in association with enhanced peripheral cholesterol transport via low density lipoprotein, beta-VLDL, or chylomicron remnants.

Evaluation of pathways for the cellular uptake of high density lipoprotein cholesterol esters in rabbits.

Cholesterol esters (CE) formed in HDL by lecithin:cholesterol acyltransferase are thought to mediate the return of cholesterol from extrahepatic tissues to the liver for excretion or reutilization. Several pathways may be involved in that process. Tracer kinetics were used to estimate the contributions of the various pathways to cellular uptake of HDL CE in rabbits. Tracers of HDL CE, HDL apo A-I, LDL apo B, and VLDL CE were simultaneously injected intravenously. Plasma decays were followed for 24 h in 4 lipoprotein pools: HDL without apo E, HDL with apo E, LDL, and VLDL. Kinetic analysis of the resulting plasma decay curves revealed that the preponderance of plasma CE (greater than 90%) originated in the HDL fraction. About 70% of HDL CE were cleared from plasma after transfer to LDL and VLDL, 20% were cleared directly from the HDL pool without HDL particle uptake ("selective" uptake), and 10% were cleared in HDL particles (including particles containing apo E). Since rabbits have about four times the plasma cholesterol ester transfer activity of man, and since the transfer pathway must compete with the selective uptake pathway, these results make it likely that selective uptake plays a substantial role in humans in the clearance of HDL CE.

An improvement of Barter's method for assaying plasma cholesterol ester transfer activity: experimental and clinical applications

The use of a discontinuous density gradient and of a vertical rotor to separate plasma iipoproteins are modifications of Barter's described method for assaying cholesteryl ester transfer activity (CETA) in plasma. The original feature of our approach is the fast preparation of the labeled substrate by a physiologic-like process, which renders the assay easy and suitable for measurement of this acitivity in both man and animals.