Lipoprotein lipase enhances the cholesteryl ester transfer protein-mediated transfer of cholesteryl esters from high density lipoproteins to very low density lipoproteins

These studies were undertaken to examine the effects of lipoprotein lipase (LPL) and cholesteryl ester transfer protein (CETP) on the transfer of cholesteryl esters from high density lipoproteins (HDL) to very low density lipoproteins (VLDL). Human or rat VLDL was incubated with human HDL in the presence of either partially purified CETP, bovine milk LPL or CETP plus LPL. CETP stimulated both isotopic and mass transfer of cholesteryl esters from HDL into VLDL. LPL caused only slight stimulation of cholesteryl ester transfer. However, when CETP and LPL were both present, the transfer of cholesteryl esters from HDL into VLDL remnants was enhanced 2- to 8-fold, compared to the effects of CETP alone. The synergistic effects of CETP and LPL on cholesteryl ester transfer were more pronounced at higher VLDL/HDL ratios and increased with increasing amounts of CETP. In time course studies the stimulation of cholesteryl ester transfer activity occurred during active triglyceride hydrolysis. When lipolysis was inhibited by incubating LPL with either 1 M NaCl or 2 mM diethylparanitrophenyl phosphate, the synergism of CETP and LPL was reduced or abolished, and LPL alone did not stimulate cholesteryl ester transfer. These experiments show that LPL enhances the CETP-mediated transfer of cholesteryl esters from HDL to VLDL. This property of LPL is related to lipolysis.     

ACAT2 stimulates cholesteryl ester secretion in apoB-containing lipoproteins

Previous studies in nonhuman primates revealed a striking positive correlation between liver cholesteryl ester (CE) secretion rate and the development of coronary artery atherosclerosis. CE incorporated into hepatic VLDL is necessarily synthesized by ACAT2, the cholesterol-esterifying enzyme in hepatocytes. We tested the hypothesis that the level of ACAT2 expression, in concert with cellular cholesterol availability, affects the CE content of apolipoprotein B (apoB)-containing lipoproteins. In a model system of lipoprotein secretion using COS cells cotransfected with microsomal triglyceride transfer protein and truncated forms of apoB, ACAT2 expression resulted in a 3-fold increase in microsomal ACAT activity and a 4-fold increase in the radiolabeled CE content of apoB-lipoproteins. After cholesterol-cyclodextrin (Chol-CD) treatment, CE secretion was increased by 27-fold in ACAT2-transfected cells but by only 7-fold in control cells. Chol-CD treatment also caused the percentage of CE in the apoB-lipoproteins to increase from 3% to 33% in control cells and from 16% to 54% in ACAT2-transfected cells. In addition, ACAT2-transfected cells secreted 3-fold more apoB than control cells. These results indicate that under all conditions of cellular cholesterol availability tested, the relative level of ACAT2 expression affects the CE content and, hence, the potential atherogenicity, of nascent apoB-containing lipoproteins.     

Human plasma cholesteryl ester transfer protein enhances the transfer of cholesteryl ester from high density lipoproteins into cultured HepG2 cells

The role of human plasma cholesteryl ester transfer protein (CETP) in the cellular uptake of high density lipoprotein (HDL) cholesteryl ester (CE) was studied in a liver tumor cell line (HepG2). When HepG2 cells were incubated with [3H]cholesteryl ester-labeled HDL3 in the presence of increasing concentrations of CETP there was a progressive increase in cell-associated radioactivity to levels that were 2.8 times control. The CETP-dependent uptake of HDL-CE was found to be saturated by increasing concentrations of both CETP and HDL. The CETP-dependent uptake of CE radioactivity increased continuously during an 18-h incubation. In contrast to the effect on cholesteryl ester, CETP failed to enhance HDL protein cell association or degradation. Enhanced uptake of HDL cholesteryl ester was shown for the d greater than 1.21 g/ml fraction of human plasma, partially purified CETP, and CETP purified to homogeneity, but not for the d greater than 1.21 g/ml fraction of rat plasma which lacks cholesteryl ester transfer activity. HDL cholesteryl ester entering the cell under the influence of CETP was largely degraded to free cholesterol by a process inhibitable by chloroquine. CETP enhanced uptake of HDL [3H]CE in cultured smooth muscle cells and to a lesser extent in fibroblasts but did not significantly influence uptake in endothelial cells or J774 macrophages. These experiments show that, in addition to its known role in enhancing the exchange of CE between lipoproteins, plasma CETP can facilitate the in vitro selective transfer of CE from HDL into certain cells.     

Structural basis of transfer between lipoproteins by cholesteryl ester transfer protein

Human cholesteryl ester transfer protein (CETP) mediates the net transfer of cholesteryl ester mass from atheroprotective high-density lipoproteins to atherogenic low-density lipoproteins by an unknown mechanism. Delineating this mechanism would be an important step toward the rational design of new CETP inhibitors for treating cardiovascular diseases. Using EM, single-particle image processing and molecular dynamics simulation, we discovered that CETP bridges a ternary complex with its N-terminal β-barrel domain penetrating into high-density lipoproteins and its C-terminal domain interacting with low-density lipoprotein or very-low-density lipoprotein. In our mechanistic model, the CETP lipoprotein-interacting regions, which are highly mobile, form pores that connect to a hydrophobic central cavity, thereby forming a tunnel for transfer of neutral lipids from donor to acceptor lipoproteins. These new insights into CETP transfer provide a molecular basis for analyzing mechanisms for CETP inhibition.     

Apparent inhibition of cholesteryl esters exchange by high density lipoproteins

The kinetics of the exchange of Cholesteryl esters between low density lipoproteins (LDL) and high density lipoproteins (HDL) stimulated by lipoprotein depleted plasma has been studied in vitro. The results indicate that the exchange is inhibited with the increase of HDL present in the assay, although the limiting factor is not the absolute concentration of HDL, since in a simultaneous LDL increase, the exchange augments proportionally to the total cholesteryl esters pool. Implications regarding overall metabolism of body cholesterol are discussed.     

Enhanced cholesteryl ester transfer protein activities and abnormalities of high density lipoproteins in familial hypercholesterolemia.

Cholesteryl ester transfer protein may play a role in the cholesteryl ester metabolism between high density lipoproteins (HDL) and apolipoprotein B-containing lipoproteins. To investigate relationship between HDL and cholesteryl ester transfer protein (CETP) activity in the development of atherosclerosis, the present study has focused on CETP activity in the patients with familial hypercholesterolemia (GH). HDL-C and HDL-C/apo A-I mass ratio in heterozygous FH were lower than those in normolipidemic controls. There was a 2-fold increase in total CETP activity in incubated FH serum compared with normolipidemic controls. Assays for CETP activity in the lipoprotein deficient serum (d greater than 1.215 g/ml) were carried out by measuring the transfer of radioactive cholesteryl ester from HDL (1.125 less than d less than 1.21 g/ml) to LDL (1.019 less than d less than 1.060 g/ml). CETP activities in heterozygous FH (79 +/- 4 nmol/ml/h) was significantly higher than those in normolipidemic controls (54 +/- 6 nmol/ml/h). The increased total cholesteryl ester transfer mainly results from increased CETP activity in the d greater than 1.215 g/ml, possibly reflecting an increase in CETP mass in serum. Increased CETP activity in the d greater than 1.215 g/ml was correlated positively with IDL-cholesterol/triglyceride mass ratio (r = 0.496, p less than 0.01), and negatively with HDL-cholesterol/apo A-I mass ratio (r = -0.334, p less than 0.05). These results indicate that the enhanced CETP activities may contribute to increase risk for developing atherosclerosis in FH by changing the distribution of cholesteryl ester in serum lipoproteins.     

Lipid transfer between human serum high density lipoproteins and egg yolk lipoproteins in incubation mixtures

Ultracentrifugally isolated human serum high density lipoproteins of d 1.063-1.21 (HDL) were incubated with egg yolk lipoproteins of d < 1.006 for up to 24 hr at various concentrations. Transfer of HDL cholesterol esters to egg yolk lipoproteins occurred simultaneously with transfer of glycerides from egg yolk lipoproteins to HDL. These observations show that exchange of lipids can take place between lipoproteins in the absence of other serum proteins and enzymes. The mole ratios of HDL cholesterol esters to glycerides approached an integral value of 1 : 1 during the course of the incubation. These results suggest that lipid components form complexes within the HDL structure.     

Cholesteryl ester and apolipoprotein E transfer between human high density lipoproteins and chylomicrons

The transfer of cholesteryl esters and apolipoprotein E has been studied between plasma HDL and chylomicrons isolated either from ascitic fluid or from the plasma of a patient with type V hyperlipoproteinemia. Whereas apolipoprotein E transfer was rapid and occurred at low temperature, cholesteryl ester transfer was suppressed at 4 degrees C. Apolipoprotein E transfer did not depend upon the presence of cholesteryl ester transfer protein and was in fact inhibited by the partially purified preparation of this protein. Apolipoprotein E transfer was not increased by reduction with dithiothreitol. The transfer of cholesteryl esters increased sharply at a chylomicron to HDL ratio of cholesteryl ester above 1/10, a value which may be of physiological significance at the peak of postprandial lipemia. At this ratio, the transfer of apolipoprotein E was minimal and increased only at ratios above 2/1. From these results, it is concluded that there is no connection between apolipoprotein E and cholesteryl ester transfer from HDL to chylomicrons. It is, therefore, proposed that whereas chylomicron apolipoprotein E is acquired rapidly and mostly in the lymphatic system, the concentration of chylomicron cholesteryl esters increases significantly and independently in the circulation.     

Plasma phospholipid transfer protein enhances transfer and exchange of phospholipids between very low density lipoproteins and high density lipoproteins during lipolysis

In order to determine the effects of a plasma phospholipid transfer protein on the transfer of phospholipids from very low density lipoproteins (VLDL) to high density lipoproteins (HDL) during lipolysis, biosynthetically labeled rat 32P-labeled VLDL was incubated with human HDL3 and bovine milk lipoprotein lipase (LPL) in the presence of the plasma d greater than 1.21 g/ml fraction or a partially purified human plasma phospholipid transfer protein (PTP). The addition of either the PTP or the d greater than 1.21 g/ml fraction resulted in a 2- to 3-fold stimulation of the transfer of phospholipid radioactivity from VLDL into HDL during lipolysis. In the absence of LPL, the PTP caused a less marked stimulation of transfer of phospholipid radioactivity. Both the d greater than 1.21 g/ml fraction and the PTP enhanced the transfer of VLDL phospholipid mass into HDL, but the percentage transfer of phospholipid radioactivity was greater than that of phospholipid mass, suggesting stimulation of both transfer and exchange processes. Stimulation of phospholipid exchange was confirmed in experiments where PTP was found to augment transfer of [14C]phosphatidylcholine radioactivity from HDL to VLDL during lipolysis. In experiments performed with human VLDL and human HDL3, both the d greater than 1.21 g/ml fraction and the PTP were found to stimulate phospholipid mass transfer from VLDL into HDL during lipolysis. Analysis of HDL by non-denaturing polyacrylamide gradient gel electrophoresis showed that enhanced lipid transfer was associated with only a slight increase in particle size, suggesting incorporation of lipid by formation of new HDL particles. In conclusion, the plasma d greater than 1.21 g/ml fraction and a plasma PTP enhance the net transfer of VLDL phospholipids into HDL and also exchange of the phospholipids of VLDL and HDL. Both the transfer and exchange activities of PTP are stimulated by lipolysis.     

Lipid exchange mechanism of the cholesteryl ester transfer protein clarified by atomistic and coarse-grained simulations

Cholesteryl ester transfer protein (CETP) transports cholesteryl esters, triglycerides, and phospholipids between different lipoprotein fractions in blood plasma. The inhibition of CETP has been shown to be a sound strategy to prevent and treat the development of coronary heart disease. We employed molecular dynamics simulations to unravel the mechanisms associated with the CETP-mediated lipid exchange. To this end we used both atomistic and coarse-grained models whose results were consistent with each other. We found CETP to bind to the surface of high density lipoprotein (HDL) -like lipid droplets through its charged and tryptophan residues. Upon binding, CETP rapidly (in about 10 ns) induced the formation of a small hydrophobic patch to the phospholipid surface of the droplet, opening a route from the core of the lipid droplet to the binding pocket of CETP. This was followed by a conformational change of helix X of CETP to an open state, in which we found the accessibility of cholesteryl esters to the C-terminal tunnel opening of CETP to increase. Furthermore, in the absence of helix X, cholesteryl esters rapidly diffused into CETP through the C-terminal opening. The results provide compelling evidence that helix X acts as a lid which conducts lipid exchange by alternating the open and closed states. The findings have potential for the design of novel molecular agents to inhibit the activity of CETP.     

In vivo transfer of cholesteryl esters from high density lipoproteins to very low density lipoproteins in man.

The fate of cholesteryl esters in high density lipoprotein (HDL) was studied to determine whether the transfer of esterified cholesterol from HDL to other plasma lipoproteins occurred to a significant extent in man. HDL cholesteryl ester, labelled in vitro with [3H] cholesterol, was injected into human subjects. Labelling of cholesteryl esters in very low density (VLDL) occurred rapidly and by 3 h, the esterified cholesterol in VLDL reached peak specific radioactivity. The removal rate of cholesteryl esters from HDL appeared to be exponential and of the order of 0.2/h; calculation of the apparent flux was about 150 mg/h which approximates reported values for total cholesterol esterification in human plasma in vivo. The rapid rate of labelling of VLDL from HDL suggests that the transfer of HDL cholesteryl esters to VLDL may represent a significant pathway for the disposal of HDL cholesterol.     

cAMP stimulates cholesteryl ester clearance to high density lipoproteins in J7774 macrophages.

The regulation by cAMP of cholesteryl ester hydrolysis and net depletion of cellular cholesteryl ester (cholesteryl ester clearance) in J774 murine macrophages was explored. Using Sandoz 58035 to selectively inhibit acyl CoA:cholesterol acyltransferase, we showed that the absolute rate of cholesteryl ester hydrolysis was stimulated 2-fold in J774 cells by the cAMP analogues 8-(4-chlorophenylthio)adenosine 3':5'-cyclic monophosphate and dibutyryl-cAMP. The rate of hydrolysis was also stimulated by prostaglandin E1, by cholera toxin, and by a mixture of forskolin and isobutylmethylxanthine, but was not affected by epinephrine or dibutyryl-cGMP. These data demonstrate that cholesteryl ester hydrolysis in J774 cells can be stimulated by cAMP-dependent protein kinase. Cholesteryl ester clearance from J774 cells was achieved upon incubation with high density lipoproteins (HDL) plus CPT-cAMP but not with HDL alone. HDL-mediated cholesteryl ester clearance was dependent on the concentration of both HDL and CPT-cAMP. The data suggest that the defect responsible for the lack of HDL-mediated cholesteryl ester clearance in J774 cells involves a failure to modulate cAMP levels.     

Selective uptake of cholesteryl ester from high density lipoproteins by plasma membranes of adipose tissue

The interaction between high density lipoproteins (HDL) and adipose tissue is an important pathway for cholesterol and cholesteryl ester flux. In intact fat cells, a disproportionately greater net uptake of cholesteryl ester occurs subsequent to lipoprotein binding than would have been predicted from a consideration of holoparticle uptake alone. To characterize the early events in this process, cholesteryl hexadecyl ether, a nonmetabolizable, accumulative marker of cholesteryl ester, was incorporated into canine HDL2, and its uptake by omental adipocyte plasma membranes was measured in relation to the binding of HDL2, which in this animal species is enriched in apolipoprotein A-I and free of apolipoprotein E. The dose-response profile for HDL2 binding was consistent with a single lipoprotein binding site at all concentrations of HDL2, whereas uptake of cholesteryl ester from HDL2 was biphasic, suggesting a high affinity site at low HDL2 concentrations and a low affinity site at high lipoprotein concentrations. Pronase treatment stimulated binding twofold and this was accompanied by a parallel twofold stimulation of cholesteryl ester uptake. EDTA, on the other hand, reduced binding and uptake of cholesteryl ester by 20%, indicating partial dependence upon divalent cations. The proportion of HDL2 cholesteryl ester accumulated by plasma membranes relative to HDL2 protein bound was not altered by either pronase or EDTA, despite the fact that these agents had opposite effects upon binding. In dissociation studies, a portion of membrane-associated HDL2 did not equilibrate with exogenous HDL2 and a greater proportion of the cholesteryl ester failed to dissociate. A stepwise mechanism for cholesteryl ester uptake, involving (i) saturable, high affinity HDL2 binding to cell surface sites, (ii) vectoral, HDL2 concentration-dependent delivery of cholesteryl ester to the membrane, and (iii) cholesteryl ester sequestration into a nonexchangeable membrane compartment, appears to be independent of metabolic energy or cell processing.     

Human apolipoprotein C-I accounts for the ability of plasma high density lipoproteins to inhibit the cholesteryl ester transfer protein activity

The aim of the present study was to identify the protein that accounts for the cholesteryl ester transfer protein (CETP)-inhibitory activity that is specifically associated with human plasma high density lipoproteins (HDL). To this end, human HDL apolipoproteins were fractionated by preparative polyacrylamide gradient gel electrophoresis, and 30 distinct protein fractions with molecular masses ranging from 80 down to 2 kDa were tested for their ability to inhibit CETP activity. One single apolipoprotein fraction was able to completely inhibit CETP activity. The N-terminal sequence of the 6-kDa protein inhibitor matched the N-terminal sequence of human apoC-I, the inhibition was completely blocked by specific anti-apolipoprotein C-I antibodies, and mass spectrometry analysis confirmed the identity of the isolated inhibitor with full-length human apoC-I. Pure apoC-I was able to abolish CETP activity in a concentration-dependent manner and with a high efficiency (IC(50) = 100 nmol/liter). The inhibitory potency of total delipidated HDL apolipoproteins completely disappeared after a treatment with anti-apolipoprotein C-I antibodies, and the apoC-I deprivation of native plasma HDL by immunoaffinity chromatography produced a mean 43% rise in cholesteryl ester transfer rates. The main localization of apoC-I in HDL and not in low density lipoprotein in normolipidemic plasma provides further support for the specific property of HDL in inhibiting CETP activity.     

Transfer of cholesteryl ester into high density lipoprotein by cholesteryl ester transfer protein: effect of HDL lipid and apoprotein content

Recombinant high density lipoprotein (rHDL) particles were prepared by cosonication of purified lipids and human apoproteins and incubated with partly purified cholesteryl ester transfer protein (CETP) and low density lipoprotein (LDL) containing [3H]cholesteryl ester. Increasing the triglyceride content relative to cholesteryl ester in rHDL significantly decreased the ability of the particles to accept cholesteryl esters transferred by CETP. Kinetic analysis of the data was performed to numerically define the maximum velocity of lipid transfer, Tmax, and the HDL concentration required for half maximal velocity, KH. Increases in rHDL-triglyceride content were shown to result in a significant reduction in the Tmax without a major change in KH. When the free cholesterol content was increased relative to phospholipid, the ability of the particles to accept cholesteryl esters was also decreased in a similar manner. Conversely, rHDL prepared from purified apoprotein A-I, A-II, or mixtures of both, had significantly elevated Tmax and KH values for their interaction with CETP. The results suggest that increases in triglyceride or free cholesterol content of an rHDL particle decrease the catalytic ability of CETP by noncompetitive inhibition. In addition, some component(s) of HDL apoproteins, other than A-I or A-II, were shown to uncompetitively inhibit the activity of CETP, by modifying both Tmax and the KH for the reaction. This study has shown that altered HDL composition may have marked effects on the transfer and equilibration of cholesteryl esters within the HDL pool.     

Familial cholesteryl ester transfer protein deficiency is associated with triglyceride-rich low density lipoproteins containing cholesteryl esters of probable intracellular origin

The net transfer of core lipids between lipoproteins is facilitated by cholesteryl ester transfer protein (CETP). We have recently documented CETP deficiency in a family with hyperalphalipoproteinemia, due to a CETP gene splicing defect. The purpose of the present study was to characterize the plasma lipoproteins within the low density lipoprotein (LDL) density range and also the cholesteryl ester fatty acid distribution amongst lipoproteins in CETP-deficient subjects. In CETP deficiency, the conventional LDL density range contained both an apoE-rich enlarged high density lipoprotein (HDL) (resembling HDLc), and also apoB-containing lipoproteins. Native gradient gel electrophoresis revealed clear speciation of LDL subclasses, including a distinct population larger in size than normal LDL. Anti-apoB affinity-purified LDL from the CETP-deficient subjects were shown to contain an elevated triglyceride to cholesteryl ester ratio, and also a high ratio of cholesteryl oleate to cholesteryl linoleate, compared to their own HDL or to LDL from normal subjects. Addition of purified CETP to CETP-deficient plasma results in equilibration of very low density lipoprotein (VLDL) cholesteryl esters with those of HDL. These data suggest that, in CETP-deficient humans, the cholesteryl esters of VLDL and its catabolic product, LDL, originate predominantly from intracellular acyl-CoA:cholesterol acyltransferase (ACAT). The CETP plays a role in the normal formation of LDL, removing triglyceride and transferring LCAT-derived cholesteryl esters into LDL precursors.     

Selective uptake of high density lipoproteins cholesteryl ester in the dog, a species lacking in cholesteryl ester transfer protein activity; An in vivo approach using stable isotopes

Amongst the processes involved in the reverse cholesterol transport (RCT) from organs to liver, including high density lipoproteins-apolipoprotein AI (HDL-apoAI) dependent tissue uptake and cholesteryl ester transfer protein (CETP)-mediated transfers, the selective uptake of cholesteryl ester (CE) is of increasing interest through its antiatherogenic role. The purpose of this report is to develop a simple protocol allowing study of this process in an animal model with easier quantification of CE selective uptake. The dog was chosen essentially because this animal has a low CETP activity and an appropriate size to conduce a kinetic study. Tracer kinetics were performed to estimate in vivo the contributions of the pathways involved in HDL-CE turnover in dogs. Stable isotopes, ¹³C-acetate and D₃-leucine as labeled precursors of CE and apoAI, were infused to fasting dogs. Isotopic enrichments were monitored in plasma unesterified cholesterol and in HDL-CE and apoAI by mass spectrometry. Kinetics were analyzed using compartmental modeling. Results concerned the measurement of the activity of cholesterol esterification (0.13±0.032 h⁻¹), rate of HDL-apoAI catabolism (0.024±0.012 h⁻¹), HDL-CE turnover (0.062±0.010 h⁻¹) and CE selective uptake (0.038±0.014 h⁻¹). Our results show that CE in dogs is mainly eliminated by selective uptake of HDL-CE (60% of HDL-CE turnover), unlike in other species studied by similar methods in our laboratory. This study shows that among species used to analyze cholesterol metabolism, the dog appears to be the animal in whom HDL-CE selective uptake represents the largest part of HDL-CE turnover.     

Role of cholesteryl ester transfer protein in selective uptake of high density lipoprotein cholesteryl esters by adipocytes

Previous reports attributed cholesteryl ester transfer protein (CETP)-mediated HDL cholesteryl ester (CE) selective uptake to the CETP-mediated transfer of CE from HDL to newly secreted apolipoprotein B-containing lipoproteins, which are then internalized by the LDL receptor (LDL-R). CETP has also been implicated in the remodeling of HDL, which renders it a better substrate for selective uptake by scavenger receptor class B type I (SR-BI). However, CETP-mediated selective uptake of HDL3-derived CE was not diminished in LDL-R null adipocytes, SR-BI null adipocytes, or in the presence of the receptor-associated protein. We found that monensin treatment or energy depletion of the SW872 liposarcoma cells with 2-deoxyglucose and NaN3 had no effect on CETP-mediated selective uptake, demonstrating that endocytosis is not required. This is supported by data indicating that CETP transfers CE into a compartment from which it can be extracted by unlabeled HDL. CETP could also mediate the selective uptake of HDL3-derived triacylglycerol (TG) and phospholipid (PL). The CETP-specific kinetics for TG and CE uptake were similar, and both reached saturation at approximately 5 microg/ml HDL. In contrast, CETP-specific PL uptake did not attain saturation at 5 microg/ml HDL and was approximately 6-fold greater than the uptake of CE. We propose two possible mechanisms to account for the role of CETP in selective uptake.     

Impaired plasma cholesteryl ester transfer with accumulation of larger high density lipoproteins in some families of baboons (Papio sp.)

Baboons from some families have a higher concentration of plasma high density lipoproteins (HDL) on a chow diet and accumulate large HDL (HDL1) when challenged with a high cholesterol and high saturated fat (HCHF) diet. HDL1 from high HDL1 animals contained more (1.5-fold) cholesteryl ester than HDL (HDL2 + HDL3) from high or low HDL1 animals. HDL from high HDL1 baboons had lower triglyceride content than that from low HDL1 baboons. HDL3 or HDL labeled with [3H]cholesteryl linoleate was incubated with entire lipoprotein fraction (d less than 1.21 g/ml) or very low density lipoprotein + low density lipoprotein (VLDL + LDL) (d less than 1.045 g/ml) and with lipoprotein-deficient serum (LPDS), and the radioactive cholesteryl ester and mass floating at d 1.045 g/ml (VLDL + LDL) after the incubation was measured. The transfer of cholesteryl esters from either HDL or HDL3, prepared from plasma of high HDL1 animals fed chow or the HCHF diet, was slower than the transfer from either HDL or HDL3 of low HDL1 animals, regardless of the source of transfer activity or the ratio of LDL:HDL-protein used in the assay. Addition of HDL from high HDL1 baboons into an assay mixture of plasma components from low HDL1 baboons decreased the transfer of cholesteryl ester radioactivity and mass from HDL to VLDL and LDL. In addition to HDL, a fraction of intermediate density lipoprotein (IDL) and denser HDL were also effective in inhibiting the transfer. These observations suggest that accumulation of HDL1 in high HDL1 baboons fed an HCHF diet is associated with a slower transfer of cholesteryl esters from HDL to LDL.(ABSTRACT TRUNCATED AT 250 WORDS)