Plasma kinetics of cholesteryl ester transfer protein in the rabbit. Effects of dietary cholesterol

Is hypertriglyceridemia a reliable indicator of cholesterol-depleted Apo B particles?

OBJECTIVES

Because cholesterol-depleted Apo B particles are thought to be a hallmark of hypertriglyceridemia, American, Canadian and European Lipid Guidelines suggest screening for Apo B only in patients with hypertriglyceridemia. Accordingly, this study examines the relationship of triglycerides to the LDL-C/Apo B and non-HDL-C/Apo B ratios.

METHODS

The study cohort consisted of 6272 NHANES subjects adjusted for a weighted sample size of 150 million subjects without previously diagnosed cardiac disease. Data was reported by LDL-C/Apo B tertiles as weighted frequencies and percent. Sensitivity, specificity, negative predictive and positive predictive values were calculated for triglycerides thresholds of >150 mg/dL and >200 mg/dL. The range of values of Apo B for decisional levels of LDL-C and non-HDL-C were also determined RESULTS: Among patients with triglycerides >200 mg/dL, 75.9% were amongst the lowest LDL-C/Apo B tertile. However, this represents only 7.5% of the total population. Of patients with the lowest LDL-C/Apo B ratio, 59.8% had triglycerides <150 mg/dL. Moreover, there was an inverse relationship between non-HDL-C/Apo B such that elevated triglycerides were associated with the highest tertile of non-HDL-C/Apo B. Finally, the range of values of Apo B for decisional levels of LDL-C and non-HDL-C was determined and is so broad- 30.3-40.6 mg/dl Apo B for different levels of LDL-C and 19.5 to 27.6 mg/dl Apo B for different levels of non-HDL-C- that neither is an adequate clinical surrogate for Apo B.

CONCLUSION

Plasma triglycerides should not be used to restrict the measurement of Apo B since cholesterol-depleted Apo B particles may be present at any level of triglyceride.

Human apolipoprotein A-II reduces atherosclerosis in knock-in rabbits

BACKGROUND AND AIMS

Apolipoprotein A-II (apoAII) is the second major apolipoprotein of the high-density lipoprotein (HDL) particle, after apoAI. Unlike apoAI, the biological and physiological functions of apoAII are unclear. We aimed to gain insight into the specific roles of apoAII in lipoprotein metabolism and atherosclerosis using a novel rabbit model.

METHODS

Wild-type (WT) rabbits are naturally deficient in apoAII, thus their HDL contains only apoAI. Using TALEN technology, we replaced the endogenous apoAI in rabbits through knock-in (KI) of human apoAII. The newly generated apoAII KI rabbits were used to study the specific function of apoAII, independent of apoAI.

RESULTS

ApoAII KI rabbits expressed exclusively apoAII without apoAI, as confirmed by RT-PCR and Western blotting. On a standard diet, the KI rabbits exhibited lower plasma triglycerides (TG, 52%, p < 0.01) due to accelerated clearance of TG-rich particles and higher lipoprotein lipase activity than the WT littermates. ApoAII KI rabbits also had higher plasma HDL-C (28%, p < 0.05) and their HDL was rich in apoE, apoAIV, and apoAV. When fed a cholesterol-rich diet for 16 weeks, apoAII KI rabbits were resistant to diet-induced hypertriglyceridemia and developed significantly less aortic atherosclerosis compared to WT rabbits. HDL isolated from rabbits with apoAII KI had similar cholesterol efflux capacity and anti-inflammatory effects as HDL isolated from the WT rabbits.

CONCLUSIONS

ApoAII KI rabbits developed less atherosclerosis than WT rabbits, possibly through increased plasma HDL-C, reduced TG and atherogenic lipoproteins. These results suggest that apoAII may serve as a potential target for the treatment of atherosclerosis.

Dalcetrapib and anacetrapib differently impact HDL structure and function in rabbits and monkeys

Inhibition of cholesteryl ester transfer protein (CETP) increases HDL cholesterol (HDL-C) levels. However, the circulating CETP level varies and the impact of its inhibition in species with high CETP levels on HDL structure and function remains poorly characterized. This study investigated the effects of dalcetrapib and anacetrapib, the two CETP inhibitors (CETPis) currently being tested in large clinical outcome trials, on HDL particle subclass distribution and cholesterol efflux capacity of serum in rabbits and monkeys. New Zealand White rabbits and vervet monkeys received dalcetrapib and anacetrapib. In rabbits, CETPis increased HDL-C, raised small and large α-migrating HDL, and increased ABCA1-induced cholesterol efflux. In vervet monkeys, although anacetrapib produced similar results, dalcetrapib caused opposite effects because the LDL-C level was increased by 42% and HDL-C decreased by 48% (P < 0.01). The levels of α- and preβ-HDL were reduced by 16% (P < 0.001) and 69% (P < 0.01), resulting in a decrease of the serum cholesterol efflux capacity. CETPis modulate the plasma levels of mature and small HDL in vivo and consequently the cholesterol efflux capacity. The opposite effects of dalcetrapib in different species indicate that its impact on HDL metabolism could vary greatly according to the metabolic environment.

CETP genotype and changes in lipid levels in response to weight-loss diet intervention in the POUNDS LOST and DIRECT randomized trials

Little is known about whether cholesteryl ester transfer protein (CETP) genetic variation may modify the effect of weight-loss diets varying in fat content on changes in lipid levels. We analyzed the interaction between the CETP variant rs3764261 and dietary interventions on changes in lipid levels among 732 overweight/obese adults from a 2 year randomized weight-loss trial [Preventing Overweight Using Novel Dietary Strategies (POUNDS LOST)], and replicated the findings in 171 overweight/obese adults from an independent 2 year weight-loss trial [Dietary Intervention Randomized Controlled Trial (DIRECT)]. In the POUNDS LOST, participants with the CETP rs3764261 CC genotype on the high-fat diet had larger increases in HDL cholesterol (P = 0.001) and decreases in triglycerides (P = 0.007) than those on the low-fat diet at 6 months, while no significant difference between these two diets was observed among participants carrying other genotypes. The gene-diet interactions on changes in HDL-cholesterol and tri-glyc-erides were replicated in the DIRECT (pooled P for interaction ≤ 0.01). Similar results on trajectory of changes in HDL cholesterol and triglycerides over the 2 year intervention were observed in both trials. Our study provides replicable evidence that individuals with the CETP rs3764261 CC genotype might derive greater effects on raising HDL cholesterol and lowering triglycerides by choosing a low-carbohydrate/high-fat weight-loss diet instead of a low-fat diet.

Short-term, high-fat diet increases the expression of key intestinal genes involved in lipoprotein metabolism in healthy men

BACKGROUND

The modulation of cholesterol and fatty acid homeostasis by dietary fatty acids is thought to be mediated by changes in the expression of key intestinal genes involved in lipoprotein metabolism. However, the short-term effect of dietary fat intake on the expression of these genes has not been fully investigated in humans.

OBJECTIVE

To test whether short-term changes in dietary fatty acid intake affect the expression of key intestinal genes involved in lipoprotein metabolism, we conducted a randomized, double-blind, crossover study in 12 nonobese, healthy men with normal plasma lipid profiles.

DESIGN

Participants were subjected to the following 2 intensive 3-d dietary interventions under isocaloric conditions: 1) a high-fat diet (37% of energy from fat and 50% of energy from carbohydrates) and 2) a low-fat diet (25% of energy from fat and 62% of energy from carbohydrates). Expressions of key genes involved in lipoprotein metabolism were compared by using real-time polymerase chain reaction quantification on duodenal biopsy specimens obtained in a fasting state after each diet.

RESULTS

After the 3-d high-fat diet, plasma cholesterol, LDL cholesterol, and HDL cholesterol concentrations were significantly higher than concentrations observed after the low-fat diet was consumed. The high-fat diet also resulted in significant increases in the intestinal messenger RNA expression of several key genes involved in lipoprotein metabolism. Plasma triglycerides and apolipoprotein B-48 concentrations were significantly lower after the high-fat diet than after the low-fat diet.

CONCLUSION

These findings suggest that short-term exposure to a high-fat diet upregulates the expression of key genes involved in lipid and lipoprotein metabolism at the enterocyte level. This trial was registered at clinicaltrials.gov as NCT01806441.

Biochemical characterization of cholesteryl ester transfer protein inhibitors

Cholesteryl ester transfer protein (CETP) has been identified as a novel target for increasing HDL cholesterol levels. In this report, we describe the biochemical characterization of anacetrapib, a potent inhibitor of CETP. To better understand the mechanism by which anacetrapib inhibits CETP activity, its biochemical properties were compared with CETP inhibitors from distinct structural classes, including torcetrapib and dalcetrapib. Anacetrapib and torcetrapib inhibited CETP-mediated cholesteryl ester and triglyceride transfer with similar potencies, whereas dalcetrapib was a significantly less potent inhibitor. Inhibition of CETP by both anacetrapib and torcetrapib was not time dependent, whereas the potency of dalcetrapib significantly increased with extended preincubation. Anacetrapib, torcetrapib, and dalcetrapib compete with one another for binding CETP; however anacetrapib binds reversibly and dalcetrapib covalently to CETP. In addition, dalcetrapib was found to covalently label both human and mouse plasma proteins. Each CETP inhibitor induced tight binding of CETP to HDL, indicating that these inhibitors promote the formation of a complex between CETP and HDL, resulting in inhibition of CETP activity.

A low‐saturated‐fat, low‐cholesterol diet decreases plasma CETP activity and pre β‐HDL formation but does not affect cellular cholesterol efflux to plasma from type 1 diabetic patients

The aim of this study was to evaluate the effect of a low-saturated-fat, low-cholesterol diet on plasma lipopoproteins, pre beta-high density lipoprotein (HDL) formation, lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activities, as well as on the ability of plasma to stimulate cellular cholesterol efflux. Twelve male type 1 diabetic patients with plasma cholesterol >5.0 mmol/L were studied while consuming their usual diet and after 6 weeks of a low-fat, low-cholesterol diet. Pre beta-HDL formation was measured using crossed immuno-electrophoresis. Plasma LCAT, CETP and PLTP activities were assayed by exogenous substrate methods. The ability of plasma to promote cellular cholesterol efflux out of Fu5AH rat hepatoma cells and out of human skin fibroblasts was also determined. Saturated fat intake was lowered (p = 0.001) due to replacement with carbohydrates, while mono- and polyunsaturated fat intake remained unchanged. Cholesterol intake decreased as well (p = 0.003). The changes in plasma total cholesterol, very low and low-density lipoprotein (VLDL+LDL) cholesterol, HDL cholesterol, HDL phospholipids, apolipoprotein (apo) A-I, plasma LCAT activity and PLTP activity were not significant. Plasma CETP activity (p = 0.008) and pre beta-HDL formation (p = 0.008) decreased. The ability of plasma to promote cholesterol efflux out of fibroblasts and Fu5AH cells remained unchanged. Reduction in dietary saturated fat and cholesterol intake does not adversely affect cellular cholesterol efflux to plasma from type 1 diabetic patients, despite a drop in pre beta-HDL formation.

Personalized nutrition: nutritional genomics as a potential tool for targeted medical nutrition therapy

An emerging goal of medical nutrition therapy is to tailor dietary advice to an individual's genetic profile. In the United States and elsewhere, "nutrigenetic" services are available over the Internet without the direct involvement of a health care professional. Among the genetic variants most commonly assessed by these companies are those found in genes that influence cardiovascular disease risk. However, the interpretation of DNA-based data is complex. The goal of this paper is to carefully examine nutritional genomics as a potential tool for targeted medical nutrition therapy. The approach is to use heart health susceptibility genes and their common genetic variants as the model.

Inhibition of CETP activity by torcetrapib reduces susceptibility to diet-induced atherosclerosis in New Zealand White rabbits

Cholesteryl ester transfer protein (CETP) inhibitors increase high density lipoprotein-cholesterol (HDL-C) in animals and humans, but whether CETP inhibition will be antiatherogenic is still uncertain. We tested the CETP inhibitor torcetrapib in rabbits fed an atherogenic diet at a dose sufficient to increase HDL-C by at least 3-fold (207 +/- 32 vs. 57 +/- 6 mg/dl in controls at 16 weeks). CETP activity was inhibited by 70-80% throughout the study. Non-HDL-C increased in both groups, but there was no difference apparent by the study's end. At 16 weeks, aortic atherosclerosis was 60% lower in torcetrapib-treated animals (16.4 +/- 3.4% vs. 39.8 +/- 5.4% in controls) and aortic cholesterol content was reduced proportionally. Sera from a separate group of rabbits administered torcetrapib effluxed 48% more cholesterol from Fu5AH cells than did sera from control animals, possibly explaining the reduced aortic cholesterol content. Regression analyses indicated that lesion area in the torcetrapib-treated group was strongly correlated with the ratio of total plasma cholesterol to HDL-C but not with changes in other lipid or lipoprotein levels. CETP inhibition with torcetrapib retards atherosclerosis in rabbits, and the reduced lesion area is associated with increased levels of HDL-C.

HDL from CETP-deficient subjects shows enhanced ability to promote cholesterol efflux from macrophages in an apoE- and ABCG1-dependent pathway

Genetic deficiency or inhibition of cholesteryl ester transfer protein (CETP) leads to a marked increase in plasma levels of large HDL-2 particles. However, there is concern that such particles may be dysfunctional in terms of their ability to promote cholesterol efflux from macrophages. Recently, the ATP-binding cassette transporter ABCG1, a macrophage liver X receptor (LXR) target, has been shown to stimulate cholesterol efflux to HDL. We have assessed the ability of HDL from subjects with homozygous deficiency of CETP (CETP-D) to promote cholesterol efflux from macrophages and have evaluated the role of ABCG1 and other factors in this process. CETP-D HDL-2 caused a 2- to 3-fold stimulation of net cholesterol efflux compared with control HDL-2 in LXR-activated macrophages, due primarily to an increase in lecithin:cholesterol acyltransferase-mediated (LCAT-mediated) cholesteryl ester formation in media. Genetic knockdown or overexpression of ABCG1 showed that increased cholesterol efflux to CETP-D HDL was ABCG1 dependent. LCAT and apoE contents of CETP-D HDL-2 were markedly increased compared with control HDL-2, and increased cholesterol esterification activity resided within the apoE-HDL fraction. Thus, CETP-D HDL has enhanced ability to promote cholesterol efflux from foam cells in an ABCG1-dependent pathway due to an increased content of LCAT and apoE.

Plant sterols combined with exercise for the treatment of hypercholesterolemia: overview of independent and synergistic mechanisms of action

At present, dyslipidemia is most commonly treated with lipid-altering pharmacological therapies. However, safety concerns regarding the use of these agents have prompted the need for safe and efficacious nonpharmacological lipid-altering interventions. One such natural therapy is the combination of plant sterols and endurance training. This combination lifestyle intervention has been shown to decrease total cholesterol, low-density lipoprotein (LDL) cholesterol and triglyceride concentrations while increasing high-density lipoprotein (HDL) cholesterol concentrations. However, the mechanisms that underlie these positive lipid alterations have yet to be clarified. Thus, the purpose of this review is to evaluate individual effects of plant sterols and exercise training on lipid levels while attempting to elucidate the possible independent and synergistic mechanisms of action responsible for these modulations. Results reveal that plant sterols decrease both total and LDL cholesterol levels by reducing exogenous cholesterol absorption by way of cholesterol displacement in the intestinal lumen. Additionally, the intestinal membrane transport proteins, ABCG5, ABCG8, as well as NPC1L1, have also been implicated in plant sterol-mediated cholesterol lowering. Conversely, exercise decreases triglyceride levels by reducing hepatic very low-density lipoprotein secretion and increasing skeletal lipoprotein lipase activity. In addition, endurance training was shown to increase HDL cholesterol levels by way of HDL subfraction alterations, in conjunction with changing reverse cholesterol transport enzyme activities. Moreover, plant sterols and exercise may work synergistically to alter lipid levels by modulating lipoprotein transport, composition, release and metabolism. In sum, the present review lends further insight as to the metabolic benefits of adopting a healthy lifestyle, including plant sterols and endurance training, in the treatment of dyslipidemia.

Modulation of plasma cholesteryl ester transfer protein activity by unsaturated fatty acids in Tunisian type 2 diabetic women

BACKGROUND AND AIM

Type 2 diabetes mellitus is associated with atherosclerosis, which has been, in part, ascribed to abnormalities in the reverse cholesterol transport system. Among the key actors involved in this pathway is cholesteryl ester transfer protein (CETP) which mediates the transfer of cholesteryl esters (CE) from HDL to apoB-containing lipoproteins.

METHODS AND RESULTS

The purpose of this study was to examine CETP activity in 220 patients with type 2 diabetes mellitus (type 2 DM) treated with diet alone or diet and sulphonylurea drugs and to identify the factors that may regulate it in the diabetic state. We also examined the effect of diet on the activity of plasma CETP in a subgroup of type 2 DM women. CETP activity was assessed by measuring plasma-mediated cholesteryl ester transfer (CET) between pooled exogenous HDL and apoB-containing lipoproteins. In 220 patients with type 2 DM, CET was significantly higher in conjunction with higher plasma triglycerides and lower HDL-cholesterol compared to 100 matched healthy controls. Correlation analysis showed that CETP activity was significantly correlated with the HDL-C to apoA1 ratio (r = -0.205, P = 0.003) and to LDL-C to HDL-C ratio in diabetic women (P = 0.010). Furthermore, CETP activity was correlated marginally with total energy intake (P = 0.052) but to a statistically significant extent with the amount of fat consumed daily (P = 0.008). A significant negative correlation was found between plasma CETP activity and MUFA of plasma phospholipids or free PUFA (P = 0.032), especially with omega3-fatty acids (P = 0.001).

CONCLUSION

Our findings indicate that CET is accelerated in patients with type 2 DM and that this may be regulated by dietary fatty acids in the diabetic state.

Lack of stimulation of cholesteryl ester transfer protein by cholesterol in the presence of a high-fat diet

Cholesteryl ester transfer protein (CETP) is a key protein involved in the reverse cholesterol transport pathway. The regulation of CETP by dietary fats is not clearly understood. Transgenic mice expressing human CETP under the control of its natural flanking region were fed low- or high-fat diets enriched in monounsaturated fatty acids (MUFAs) or saturated fatty acids in the presence or absence of cholesterol. Addition of cholesterol to the low-fat MUFA diet increased CETP activity and mRNA expression, whereas addition of cholesterol to the high-fat MUFA diet led to a decrease in CETP activity and mRNA expression. In SW 872 cells, oleic acid and cholesterol stimulated CETP gene expression when given alone. However, addition of fatty acids along with cholesterol interfered with the stimulatory effect of cholesterol on CETP gene regulation. Cholesterol-mediated stimulation of CETP involves the transcription factor liver X receptor alpha (LXRalpha). High-fat MUFA diets inhibited the expression of LXRalpha, and addition of cholesterol to the high-fat MUFA diet did not rescue LXRalpha expression. Therefore, we present evidence for the first time that inhibition of LXRalpha expression by a high-fat MUFA diet leads to inhibition of CETP stimulation by cholesterol.

Plasma lipid transfer proteins, high-density lipoproteins, and reverse cholesterol transport

Cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are members of the lipid transfer/lipopolysaccharide binding protein gene family. Recently, the crystal structure of one of the members of the gene family, bactericidal permeability increasing protein, was solved, providing potential insights into the mechanisms of action of CETP and PLTP. These molecules contain intrinsic lipid binding sites and appear to act as carrier proteins that shuttle between lipoproteins to redistribute lipids. The phenotype of human CETP genetic deficiency states and CETP transgenic mice indicates that CETP plays a major role in the catabolism of high-density lipoprotein (HDL) cholesteryl esters and thereby influences the concentration, apolipoprotein content, and size of HDL particles in plasma. PLTP also appears to have an important role in determining HDL levels and speciation. Recent data indicate that genetic CETP deficiency is associates with an excess of coronary heart disease in humans, despite increased HDL levels. Also, CETP expression is anti-atherogenic in many mouse models, even while lowering HDL. These data tend to support the reverse cholesterol transport hypothesis, i.e., that anti-atherogenic properties of HDL are related to its role in reverse cholesterol transport. Recently, another key molecule involved in this pathway was identified, scavenger receptor BI; this mediates the selective uptake of HDL cholesteryl esters in the liver and thus constitutes a pathway of reverse cholesterol transport parallel to that mediated by CETP. Reflecting its role in reverse cholesterol transport, the CETP gene is up-regulated in peripheral tissues and liver in responses to dietary or endogenous hypercholesterolemia. An analysis of the CETP proximal promoter indicates that it contains sterol regulatory elements highly homologous to those present in 3-hydroxy-3-methylglutaryl-coenzyme A reductase; the CETP gene is transactivated by the binding of SREBP-1 to these elements. A challenge for the future will be the manipulation of components of the reverse cholesterol transport pathway, such as CETP, PLTP, or scavenger receptor BI for therapeutic benefit.

Plasma lipoprotein distribution and lipid transfer activities in patients with type IIb hyperlipidemia treated with simvastatin

The aim of the present study was to search in type IIb hyperlipidemic patients for putative concomitant effects of simvastatin on the physicochemical characteristics of low density lipoproteins (LDL) and high density lipoproteins (HDL), as well as on the activities of the cholesteryl ester transfer protein (CETP) and the phospholipid transfer protein (PLTP) that were determined in both endogenous lipoprotein-dependent and endogenous lipoprotein-independent assays. In a double-blind, randomized trial, patients received either placebo (one tablet/day; n = 12) or simvastatin (20 mg/day; n = 12) for a period of 8 weeks after a 5-week run-in period. Simvastatin, unlike placebo, reduced the lipid and apolipoprotein B contents of the most abundant LDL-1, LDL-2, and LDL-3 subfractions without inducing significant changes in the overall size distribution of LDL and HDL. Whereas simvastatin significantly increased PLTP activity in an endogenous lipoprotein-dependent assay (P < 0.01), no variation was observed in a lipoprotein-independent assay. Simvastatin significantly decreased plasma CETP activity in an endogenous lipoprotein-dependent assay (P < 0.01), and the reduction in plasma cholesteryl ester transfer rates was explained by a 16% drop in CETP mass concentration (P < 0.01). In contrast, the specific activity of CETP was unaffected by the simvastatin treatment reflecting at least in part the lack of significant alteration in plasma triglyceride-rich lipoprotein acceptors. The simvastatin-induced changes in plasma CETP mass levels correlated positively with changes in plasma CETP activity (r = 0.483, P = 0.0561), in total cholesterol levels (r = 0.769; P < 0.01), and in LDL-cholesterol levels (r = 0.736; P < 0.01). Whereas the observations suggest that simvastatin might exert concomitant beneficial effects on plasma CETP and LDL levels, neither plasma cholesteryl ester transfer activity nor plasma phospholipid transfer activity appeared as the main determinants of the LDL and HDL distribution profiles in type IIb hyperlipidemic patients.

Variations in serum cholesteryl ester transfer and phospholipid transfer activities in healthy women and men consuming diets enriched in lauric, palmitic or oleic acids

Cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activities were measured in sera from 32 normolipidemic women and men consuming diets enriched in lauric, palmitic, or oleic acids. Serum CETP activity, measured as the rate of radiolabeled cholesteryl esters transferred from HDL toward serum apo B-containing lipoproteins, was higher with the palmitic acid diet (25.1+/-2.5%) than with the lauric acid (23.7+/-2.4%) and the oleic acid (24.0+/-2.7%) diets (P = 0.0028 and 0.0283, respectively). CETP mass concentrations, as measured with an enzyme-linked immunosorbent assay were increased after the lauric acid diet (2.57+/-0.63 mg/l) and the palmitic acid diet (2.49+/-0.64 mg/l) as compared with the oleic acid diet (2.34+/-0.45 mg/l) (P = 0.0035 and 0.0249, respectively). In contrast with CETP, serum PLTP activity, as measured as the rate of radiolabeled phosphatidylcholine transferred from liposomes toward serum HDL, was significantly higher with the lauric acid diet (23.5+/2.6%) than with the palmitic acid diet (22.5+/-2.5%) (P = 0.0013), while no significant differences were noted when comparing the saturated diets versus the oleic acid diet (23.0+/-2.3%). No significant alterations in the mean apparent diameter of LDL, and in the relative proportions of individual HDL subpopulations were observed from one dietary period to another. Nevertheless, lipid transfer activities correlated significantly with the relative abundance of HDL2b, HDL2a, HDL3b, and HDL3c, with opposite tendencies being observed for cholesteryl ester transfer and phospholipid transfer activities. In general, serum CETP activity correlated negatively with HDL cholesterol, but positively with triglyceride concentrations after the dietary interventions, and the relations with serum lipids were just the opposite for PLTP activity. In addition, CETP and PLTP activities correlated negatively when subjects consumed the standardized diets (P < 0.05 in all cases), but not when subjects consumed their habitual diet. It is concluded that serum lipid transfer activities in normolipidemic subjects can be significantly affected by the fatty acid content of the diet, with differential effects on CETP and PLTP activities.

Role of female sex steroids in regulating cholesteryl ester transfer protein in transgenic mice

The role of sex steroids in the regulation of cholesteryl ester transfer protein (CETP) was examined in the following groups of female transgenic mice carrying the human CETP gene: (1) normal, (2) ovariectomized, (3) ovariectomized and treated with estrogen; (4) ovariectomized and treated with progesterone; (5) ovariectomized and treated with both hormones, and (6) ovariectomized and treated with tamoxifen. CETP activity was measured in the plasma, and in the particulate and the soluble fractions of liver, muscle, and adipose tissue. Human CETP specific activity was determined by taking the difference of cholesterol ester transfer in the presence and absence of an antibody (TP2) against human CETP Ovariectomy reduced hormone levels, but did not completely abolish them from the circulation. Plasma CETP activity was significantly reduced in the tamoxifen group. There were significant reductions in CETP in liver homogenate and the soluble fraction, as well as in the particulate fraction of adipose with ovariectomy. Hormone replacement did not restore CETP activity in either the plasma or the tissues. Tamoxifin treatment resulted in a decrease in CETP activity in both fractions of liver, but had no effect on adipose. In the soluble fraction of adipose tissue and both fractions of muscle, only trace CETP activity was detected. We conclude that (1) minimal amounts of sex steroid hormones may be sufficient to affect CETP expression; (2) the effects of sex steroid hormones vary among tissues; and (3) in addition to the sex steroids, factor(s) from the ovary are needed for the full expression of CETP in this animal model.

Effect of antisense oligonucleotides against cholesteryl ester transfer protein on the development of atherosclerosis in cholesterol-fed rabbits

Cholesteryl ester transfer protein (CETP) is the enzyme that facilitates the transfer of cholesteryl ester from high density lipoprotein (HDL) to apolipoprotein B (apoB)-containing lipoproteins. However, the exact role of CETP in the development of atherosclerosis has not been determined. In the present study, we examined the effect of the suppression of increased plasma CETP by intravenous injection with antisense oligodeoxynucleotides (ODNs) against CETP targeted to the liver on the development of atherosclerosis in rabbits fed a cholesterol diet. The ODNs against rabbit CETP were coupled to asialoglycoprotein (ASOR) carrier molecules, which serve as an important method to regulate liver gene expression. Twenty-two male Japanese White rabbits were used in the experiment. Eighteen animals were fed a standard rabbit chow supplemented with 0.3% cholesterol throughout the experiment for 16 weeks. At 8 weeks, they were divided into three groups (six animals in each group), among which the plasma total and HDL cholesterol concentrations did not significantly change. The control group received nothing, the sense group were injected with the sense ODNs complex, and the antisense group were injected with the antisense ODNs complex, respectively, for subsequent 8 weeks. ASOR. poly(L-lysine) ODNs complex were injected via the ear veins twice a week. Four animals were fed a standard rabbit diet for 16 weeks. The total cholesterol concentrations and the CETP mass in the animals injected with antisense ODNs were all significantly decreased in 12 and 16 weeks compared with those injected with sense ODNs and the control animals. The HDL cholesterol concentrations measured by the precipitation assay did not significantly change among the groups fed a cholesterol diet, and triglyceride concentrations did not significantly change in the four groups. However, at the end of the study, when the HDL cholesterol concentrations were measured after the isolation by ultracentrifugation and a column chromotography, they were significantly higher in the animals injected with antisense ODNs than in the animals injected with sense ODNs and in the control animals. A reduction of CETP mRNA and an increase of LDL receptor mRNA in the liver were observed in the animals injected with antisense ODNs compared with those injected with sense ODNs and the control animals. Aortic cholesterol contents and the aortic percentage lesion to total surface area were significantly lower in the animals injected with antisense ODNs than in the animals injected with sense ODNs and in the control animals. These findings showed for the first time that suppression of increased plasma CETP by the injection with antisense ODNs against CETP coupled to ASOR carrier molecules targeted to the liver could thus inhibit the atherosclerosis possibly by decreasing the plasma LDL + very low density lipoprotein (VLDL) cholesterol in cholesterol-fed rabbits.