Accelerated Cholesteryl Ester Transfer Research Articles

Impact of LDL apheresis on atheroprotective reverse cholesterol transport pathway in familial hypercholesterolemia

In familial hypercholesterolemia (FH), low HDL cholesterol (HDL-C) levels are associated with functional alterations of HDL particles that reduce their capacity to mediate the reverse cholesterol transport (RCT) pathway. The objective of this study was to evaluate the consequences of LDL apheresis on the efficacy of the RCT pathway in FH patients. LDL apheresis markedly reduced abnormal accelerated cholesteryl ester transfer protein (CETP)-mediated cholesteryl ester (CE) transfer from HDL to LDL, thus reducing their CE content. Equally, we observed a major decrease (-53%; P < 0.0001) in pre-β1-HDL levels. The capacity of whole plasma to mediate free cholesterol efflux from human macrophages was reduced (-15%; P < 0.02) following LDL apheresis. Such reduction resulted from a marked decrease in the ABCA1-dependent efflux (-71%; P < 0.0001) in the scavenger receptor class B type I-dependent efflux (-21%; P < 0.0001) and in the ABCG1-dependent pathway (-15%; P < 0.04). However, HDL particles isolated from FH patients before and after LDL apheresis displayed a similar capacity to mediate cellular free cholesterol efflux or to deliver CE to hepatic cells. We demonstrate that rapid removal of circulating lipoprotein particles by LDL apheresis transitorily reduces RCT. However, LDL apheresis is without impact on the intrinsic ability of HDL particles to promote either cellular free cholesterol efflux from macrophages or to deliver CE to hepatic cells.

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

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. 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). 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.

Atorvastatin reduces postprandial accumulation and cholesteryl ester transfer protein-mediated remodeling of triglyceride-rich lipoprotein subspecies in type IIb hyperlipidemia.

The effect of atorvastatin, at 10 mg or 40 mg for 6 wk, on lipid and lipoprotein metabolism during the postprandial phase in subjects (n = 11) displaying type IIB hyperlipidemia was evaluated. The postprandial increment in area under the curve above baseline concentrations in type IIB subjects was significantly decreased by atorvastatin for plasma triglyceride (A10: -42% and A40: -55%, P < 0.01), chylomicrons (CMs) (A10: -24% and A40: -40%, P < 0.03) and VLDL-1 (A10: -54% and A40: -52%, P < 0.02). Before atorvastatin therapy, postprandial cholesteryl ester (CE) transfer from high-density lipoprotein (HDL) to CMs (2.5-fold; P < 0.005), very low-density lipoprotein (VLDL)-1 (1.8-fold; P < 0.005), VLDL-2 (1.4-fold; P < 0.05), and intermediate-density lipoproteins (1.4-fold; P < 0.05) were significantly increased 4 h postprandially. Following statin treatment, the postprandial transfer of CE from HDL to triglyceride-rich lipoproteins (TRLs) at the 4-h time point was significantly reduced at 10 mg/d (-26%; P < 0.05) and at 40 mg/d (-24%; P < 0.05), compared with that before treatment. Such postprandial increase in CE transferred from HDLs to TRLs arose exclusively from accelerated CE transfer from HDLs to CMs (2.5-fold; P < 0.005). In conclusion, atorvastatin attenuates the abnormal intravascular remodeling of postprandial TRL particles via marked reduction in CE transfer in type IIB hyperlipidemia and diminishes the postprandial formation and accumulation of CMs and VLDL-1.

Cholesteryl ester transfer in hypercholesterolaemia: fasting and postprandial studies with and without pravastatin

Subjects with hypercholesterolaemia (HC) have increased fasting cholesteryl ester transfer protein (CETP) activity and accelerated cholesteryl ester transfer (CET) from HDL to apo B-containing lipoproteins. The aim of this study was to examine the effects of postprandial lipaemia and pravastatin treatment on plasma triglycerides (TG) and CETP activity and and CET and LDL Stokes’ diameter in primary HC ( n=19, total cholesterol ≥6.5, LDL-cholesterol ≥4.5, TG<4.0 mmol/l). Samples were collected fasting and 6 h after an oral fat load (0.88 g/kg body weight) after 6 weeks therapy with placebo or pravastatin 40 mg nocte according to a double-blind randomized cross-over study. Apart from significant reductions in plasma total cholesterol, LDL-cholesterol apo B and TG, pravastatin significantly reduced CETP activity in both the fasting (mean±SD, 37.9±12.2 to 32.0±10.3 nmol/ml plasma per h) and postprandial state (35.5±11.3 to 31.3±9.5 nmol/ml plasma per h) compared to equivalent placebo phases. CETP activity did not change during postprandial lipaemia despite a significant 45–55% increase in CET to triglyceride-rich lipoproteins (TRL) of d<1.006 g/ml. LDL Stokes’ diameter was unchanged postprandially or by pravastatin. The mass of TRL was the strongest contributor to variation in CET in both fasting and postprandial plasma, accounting for at least 77% of the variance of CET. Postprandial TRL-TG was the strongest contributor to variation in fasting LDL Stokes’ diameter in untreated HC (54%) whilst HDL-cholesterol was the strongest fasting contributor to variation (45%) for placebo- and pravastatin-treated HC. We conclude that pravastatin may reduce the atherogenicity of the lipoprotein profile in HC by reducing CETP activity. Furthermore, CET is strongly influenced by postprandial lipaemia which may have a cumulative effect on LDL size.

Accelerated cholesteryl ester transfer in patients with essential hypertension and the effect of ramipril treatment

Although the transfer of cholesteryl ester (CE) from high-density lipoprotein (HDL) to the apolipoprotein B-containing lipoproteins (very-low-density lipoproteins+low-density lipoproteins) has been shown to be abnormally increased in a number of conditions associated with increased cardiovascular risk, it has not been studied in patients with essential hypertension (EH). To determine whether subjects with EH have increased CE transport, CE transfer (CET) was estimated isotopically and lipoprotein lipid and phospholipid composition determined in a group of 14 untreated normolipidemic (triglycerides 116±46, cholesterol 185±30, HDL 38±10 mg/dl) otherwise healthy ethnically diverse EH subjects. CET was significantly increased in EH subjects compared to a similar group of normotensive controls (EH: k=0.27±0.09 vs. control k=0.11±0.02; P<0.01). Lipoprotein concentration and composition were comparable in the two groups and closely resembled that of an age- and sex-matched reference group. The abnormal increase in CET persisted ( k=0.25±0.12) after 3 months of treatment with the angiotensin converting enzyme (ACE) inhibitor ramipril without a change in either plasma or lipoprotein lipids. Thus, CET is increased in normolipidemic subjects with EH and is not affected by the ACE inhibitor ramipril.

Accelerated cholesteryl ester transfer and altered lipoprotein composition in diabetic cynomolgus monkeys.

To determine whether nonhuman primates demonstrate the same alterations in transport of cholesteryl ester (CE) in plasma observed in diabetic humans, cholesteryl ester transfer (CET) was measured in cynomolgus monkeys with chronic spontaneous diabetes mellitus (glycated hemoglobin: diabetics 10.7 +/- 4.1%; controls 3.8 +/- 0.8%, P < 0.005). Among the plasma lipids, only triglycerides were significantly increased in diabetic monkeys (diabetics 303 +/- 294 mg/dl; controls 85 +/- 34 mg/dl; P < 0.05); total plasma, LDL, HDL2, and HDL3 cholesterol concentrations did not differ significantly from those of control animals. Similar to human beings with insulin-dependent and non-insulin-dependent diabetes mellitus, CET estimated both as the mass of cholesteryl ester transferred from HDL to the apoB-containing lipoproteins (VLDL + LDL) and as the loss of radiolabeled cholesteryl ester from HDL was significantly greater (P < 0.001) in diabetic compared to control monkeys. Glycated hemoglobin levels in the combined control and diabetic groups correlated directly with both the mass of cholesteryl ester transferred at 2 h (r = 0.75; P < 0.001) and the isotopic transfer (k) (r = 0.64; P < 0.005). The mass of cholesteryl ester transfer protein (CETP) tended to be higher in the diabetic animals (diabetic 4.06 +/- 0.73 microgram/ml versus control 3.05 +/- 0.93; P < 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Accelerated cholesteryl ester transfer in baboons with insulin-requiring diabetes mellitus.

Cholesteryl ester transfer (CET), plasma, lipoprotein lipid and phospholipid composition were studied in insulin-treated baboons with chronic streptozotocin-induced diabetes. In these diabetic animals, CET measured both as the mass (p < 0.001) and isotopic transfer (p < 0.05) of CE from HDL to the apo B-containing lipoproteins (VLDL+LDL) were significantly accelerated compared to controls and the response closely resembled that recently reported in diabetic humans. No significant differences were present in plasma triglyceride, cholesterol, or HDL-C or in lipoprotein core or surface lipid composition. Thus, despite the fact that they did not display the same spectrum of abnormalities in lipoprotein composition, these insulin-treated diabetic baboons demonstrated an abnormality in CET identical to that described in humans. These findings suggest that this non-human primate may provide a suitable diabetic animal model in which to better characterize the mechanisms that underlie this potentially atherogenic disturbance in lipoprotein transport.

Abnormal acyltransferase activities and accelerated cholesteryl ester transfer in patients with nephrotic syndrome

To determine the effects of the nephrotic syndrome (NS) on atherogenic risk, we studied the lipoprotein composition and the activities of lecithin-cholesterol acyltransferase (LCAT), lysolecithin acyltransferase (LAT), and cholesteryl ester transfer (CET) in the plasma of 11 NS patients and 10 control subjects. NS plasma had lower ratios of high-density lipoprotein (HDL) to low-density lipoprotein (LDL) and HDL 2 HDL 3 and an elevated free cholesterol (FC) to phosphatidyl choline (PC) ratio (1.09 ± 0.27 in NS and 0.72 ± 0.21 in controls, P < .02), all of which indicate an increased atherogenic potential. LCAT activity was normal in NS plasma when assayed with an exogenous substrate, but was 40% lower than in control plasma when assayed with the endogenous substrates. However, in vitro addition of serum albumin to NS plasma failed to normalize the LCAT activity. The LAT reaction, which is catalyzed by LCAT protein in the presence of LDL, was 60% to 80% higher in NS plasma, and consequently the ratio of LAT LCAT activities was increased twofold. CET activity was significantly increased (+160% of control), and this abnormality was attributable to changes in both the acceptor (very-low-density lipoprotein [VLDL] + LDL) and donor (HDL) lipoproteins and possibly in CET protein. These results suggest that the NS may increase the risk of atherosclerosis not only by adversely affecting the concentrations of lipoproteins, but also by altering their composition and function.

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

In an earlier study we demonstrated that the transfer of cholesteryl ester (CET) estimated as the net mass of CE lost from HDL to the apoB-containing lipoproteins (VLDL + LDL) during incubation of plasma is accelerated in normolipidaemic patients with insulin-dependent diabetes mellitus (IDDM). Recombination experiments with isolated lipoprotein fractions employing this same mass transfer assay indicated that this disturbance resulted from dysfunction of VLDL and not from changes in the activity of CE transfer protein (CETP). In this study, we sought first to determine whether CET estimated with an isotopic method that measures the transfer of radiolabelled CE from exogenous HDL from non-diabetic controls to endogenous VLDL + LDL was also increased in IDDM and, if so, the extent to which this disturbance was affected by glycaemic control, VLDL and CETP. As observed with the mass transfer assay, the rate of transfer of the HDL-CE label to VLDL + LDL was also significantly accelerated in IDDM plasma (IDDM: k = 0.256 +/- 0.07; control: k = 0.092 +/- 0.05; mean +/- SD; P < 0.001). Fasting glucose and fructosamine correlated with both isotopic transfer (k) (r = 0.54, P = 0.009; r = 0.57, P = 0.005, respectively) and the mass of CE transferred at 2 h (r = 0.55, P = 0.006; r = 0.59, P = 0.004, respectively). Recombination experiments revealed that isotopic CET was accelerated when: (a) IDDM VLDL were combined with controls HDL and d > 1.21 fractions; and (b) IDDM d > 1.21 plasma fractions containing CETP were combined with controls VLDL + LDL and HDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Accelerated cholesteryl ester transfer in plasma of patients with hypercholesterolemia.

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

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.