Reverse cholesterol transport in mice expressing simian cholesteryl ester transfer protein

The role of cholesteryl ester transfer protein (CETP) in atherogenesis remains ambiguous, as both pro and antiatherogenic effects have been described. Expression of CETP increases HDL-cholesteryl ester turnover, but there is no direct evidence whether CETP mobilizes cholesterol in vivo. The rate of cholesterol removal injected into a leg muscle as cationized low density lipoprotein (cat-LDL) was compared in CETP transgenic and control mice. Four days after injection the exogenous cholesterol mass retained in muscle was 65% in CETP transgenic and 70% of injected dose in controls; it decreased to 52-54% by day 8 and negligible amounts remained on day 28. The cat-LDL was labeled with either 3H-cholesterol oleate (3H-CE) or 3H-cholesteryl oleoyl ether (3H-COE), a nonhydrolyzable analog of 3H-CE. After injection of 3H-CE cat-LDL, clearance of 3H-cholesterol had a t(1/2) of 4 days between day 4 and 8 but there was little loss of 3H-COE between day 4 and 51. Liver radioactivity on day 4 was 1.7% in controls and 3.4% in CETP transgenics; it was 2.8 and 4.6%, respectively, on day 8. 3H-COE in liver accounted for 60% of label in CETP transgenics. In conclusion, high levels of plasma CETP in mice do not enhance reverse cholesterol transport in vivo but may act on extracellularly located cholesteryl ester.     

Expression of cholesteryl ester transfer protein in human atherosclerotic lesions and its implication in reverse cholesterol transport.

Reverse cholesterol transport (RCT) is the major protective system against atherosclerosis. In this system, cholesteryl ester transfer protein (CETP) is known to facilitate the transfer of neutral lipids between lipoproteins in plasma. We reported the pathophysiological significance of CETP by clinical studies with genetic CETP deficiency, showing that this protein plays a crucial role in the RCT system. However, information about the expression of this protein in the initial step of RCT, macrophages (Mphi) in the blood vessels, is still very limited. In the present study, we have performed immunohistochemical analyses on the expression of CETP in human atherosclerotic lesions. The immunoreactive mass of CETP was abundantly detected in foam cells in human aortic and coronary atherosclerotic lesions, but not in the normal arterial wall. A double immunostaining showed that the majority of CETP-positive foam cells were derived from Mphi and a minor population appeared to derive from smooth muscle cells. Transient transfection of CETP cDNA into COS-7 cells showed that high density lipoprotein (HDL)-mediated efflux of free cholesterol from the cells expressing CETP was much higher than that from mock-transfected cells, while uptake of HDL-lipids was not affected in cells transfected with CETP cDNA. Efflux of free cholesterol from the Mphi obtained from CETP deficiency was significantly decreased compared with that from normal subjects. These data indicate that CETP is expressed in Mphi in the atherosclerotic lesions and may possess an anti-atherogenic function to remove cholesterol from the cells, suggesting another role of CETP at the initial step of RCT.     

Epistatic effect of cholesteryl ester transfer protein and hepatic lipase on serum high-density lipoprotein cholesterol levels

OBJECTIVES: Polymorphisms in the hepatic lipase (LIPC -514C > T) and cholesteryl ester transfer protein (CETP I405V) genes affect high-density lipoprotein cholesterol (HDL-c) levels, but their relationship with cardiovascular disease and their combined effect is unclear. The objectives of the current study were to characterize the effect of the hepatic lipase variant, and its interaction with the CETP variant, in terms of cholesterol levels, atherosclerosis, and risk of myocardial infarction (MI). DESIGN: The study was conducted in the Rotterdam Study, a large single-center prospective cohort study in people aged 55 yr and older. Lipid levels were analyzed using linear regression models, and risk of MI was assessed with Cox proportional hazards models. RESULTS: The hepatic lipase variant was associated with an increase in serum HDL-c levels of 0.11 mmol/liter in both genders, whereas an increased risk of MI was observed only in men [hazard ratio, 1.32 (95% confidence interval, 1.05-1.66) for CT vs. CC and 1.75 (95% confidence interval, 1.39-2.20) for TT vs. CC]. This effect was independent of serum HDL-c. LIPC -514C > T interacted with CETP I405V with respect to serum HDL-c concentrations. Those homozygous for both mutations saw a marked elevation in HDL-c levels (0.29 mmol/liter, P(interaction) = 0.05). These increased HDL-c levels, however, were not inversely associated with atherosclerosis or MI risk. CONCLUSIONS: LIPC genotype affects HDL-c levels and risk of MI in males. The interaction of this variant with CETP on HDL-c levels helps elucidate the underlying mechanisms and suggests that the beneficial effects of CETP inhibition may vary in particular subgroups.     

Increasing high-density lipoprotein cholesterol in dyslipidemia by cholesteryl ester transfer protein inhibition: an update for clinicians

Reduced HDL cholesterol may be a risk factor comparable in importance to increased LDL cholesterol. Interventions that raise HDL are antiatherosclerotic, presumably through acceleration of reverse cholesterol transport and by antioxidant and antiinflammatory effects. In the hypercholesterolemic rabbit, HDL levels can be increased by >50% by inhibition of cholesteryl ester transfer protein (CETP), a molecule that plays a central role in HDL metabolism. This HDL-raising effect is antiatherosclerotic in moderately severe hyperlipidemia but appears to be ineffective in the presence of severe hypertriglyceridemia. In humans, mutations resulting in CETP inhibition have been associated with both reduced and increased risk of atherosclerosis. Proposed explanations for these apparently disparate observations are that the antiatherosclerotic effect of CETP inhibition varies with either the metabolic milieu or the degree of CETP inhibition. We now have pharmacological inhibitors of CETP that are capable of increasing HDL by as much as 50% to 100% in humans. The importance of this development is that reduced HDL is a risk factor independent of LDL and that these new agents alter HDL by a magnitude comparable to that of statins on LDL. Clinical trials, now beginning, will need to identify the patient subsets in which CETP inhibition may be more or less effective.     

Contribution of cholesteryl ester transfer protein and lecithin:cholesterol acyltransferase to HDL size distribution

High-density lipoproteins (HDL) includes a heterogeneous class of lipoproteins grouped into various subclasses that seem to have different antiatherogenic function. Cholesteryl ester transfer protein (CETP) and lecithin cholesterol acyltransferase (LCAT) play an active role in HDL remodeling. This study was designed to define the role of CETP and LCAT activities on HDL-cholesterol (HDL-C) plasma levels and HDL size distribution, as determined by nondenaturating polyacrylamide gradient gel electrophoresis in 47 clinically healthy Mexican individuals without personal and family history of coronary heart disease. Surprisingly, plasma activities of CETP (29+/-4.1% of transfer) and LCAT (4.8+/-2.2% of esterification) did not correlate either with HDL-C plasma levels or with any other lipid parameter, indicating the poor contribution of these proteins to the lipid profile. The CETP activity showed a negative correlation with small HDL3b (r = -0476, P < 0.05), whereas LCAT was positively associated with this HDL subclass (r = 0.466, P < 0.05). The LCAT showed a negative correlation with large HDL2a (r = - 0.674, P < 0.005). Nevertheless, when the LCAT/CETP ratio was calculated, we observed that the higher the ratio, the greater the relative proportion of small HDL3b (r = 0.551, P < 0.05) and HDL3c (r = 0.477, P < 0.05). These results suggest that the balance of LCAT and CETP activities have a great impact in the plasma HDL size distribution.     

The effect of cholesteryl ester transfer protein -629C->A promoter polymorphism on high-density lipoprotein cholesterol is dependent on serum triglycerides

CONTEXT: The -629C-->A cholesteryl ester transfer protein (CETP) promoter polymorphism is a determinant of HDL cholesterol (HDL-C). The effect of the closely linked CETP TaqIB polymorphism on HDL-C has been suggested to be modified by obesity and hyperinsulinemia. OBJECTIVE: Because the CETP-mediated cholesteryl ester transfer out of HDL is stimulated by high triglycerides, we hypothesized that triglycerides modify the effect of the CETP -629C-->A promoter polymorphism on HDL-C. DESIGN: In 7083 nondiabetic subjects of the PREVEND population, the -629C-->A promoter polymorphism, HDL-C, serum triglycerides, waist circumference, and insulin resistance (HOMA(ir)) were determined. Serum apolipoprotein A-I was available in 6948 subjects. The TaqIB polymorphism was also assessed. SETTING: The study is set in the general community. RESULTS: HDL-C and serum apolipoprotein A-I were on average 0.14 mmol/liter and 0.05 g/liter higher in -629AA (22.9%) compared to -629CC (26.8%) homozygotes (P < 0.001 for both). This genotype effect on HDL-C was on average 0.15 mmol/liter in the lowest triglyceride tertile but only 0.08 mmol/liter in the highest tertile (P < 0.01). Multiple regression analysis showed that HDL-C was determined by the CETP promoter variant (P < 0.001), gender (P < 0.001), triglycerides (P < 0.001), and interactions between triglycerides and genotype (P < 0.05), between triglycerides and gender (P < 0.05), and between genotype and gender (P < 0.05), independently from waist, HOMA(ir), alcohol use, age, and use of lipid-lowering drugs. The TaqIB polymorphism also interacted with triglycerides on HDL-C. The -629C-->A promoter polymorphism did not interact with obesity and HOMA(ir) on HDL-C. CONCLUSIONS: The HDL-C-raising effect of the CETP -629A allele is diminished with higher triglycerides, which may be explained by a predominant effect of triglyceride-rich lipoproteins over circulating CETP itself on cholesteryl ester transfer out of HDL with rising triglycerides.     

The effect of physical exercise on reverse cholesterol transport

High-density lipoproteins (HDL) are recognized for their role in coronary artery disease (CAD) risk reduction. Plasma HDL plays a pivotal role in the reverse cholesterol transport (RCT) process. Physical exercise is well recognized as a modality that affects HDL metabolism. The purpose of this discussion is to describe the effects of physical exercise on RCT.     

Lipoprotein profile and cholesteryl ester transfer protein in neonates

Undernourishment in utero appears to be associated with persisting changes in the metabolic, endocrine, and immune functions. In this study, we determined the influence of birth weight on the lipoprotein profile and cholesteryl ester transfer protein (CETP), which promotes a proatherogenic lipoprotein profile in plasma by determining the chemical, physical, and biologic properties of the respective lipoprotein particles. Triglyceride (TG) concentrations were highest and high-density lipoprotein (HDL)(2)-cholesterol levels were lowest in small for gestational age (SGA) neonates. CETP-mass was determined by enzyme-linked immunosorbent assay (ELISA) and CETP-activity by using exogenous lipoproteins. Cholesteryl ester transfer was determined as transfer of radiolabeled cholesteryl esters (CE) from HDL to apolipoprotein B-containing lipoproteins. CETP mass was lowest and cholesteryl ester transfer was highest in SGA neonates. CETP-activity did not differ among the neonates. Our results suggest that increased and decreased nourishment in utero affects the lipoprotein profile and CETP in neonates. High TG and low HDL(2) levels in SGA neonates might result from increased cholesteryl ester transfer and, may in part, explain the increased risk of coronary heart disease (CHD) of small for gestational age neonates in later life.     

胆固醇酯转运蛋白与血脂、血糖的关系

目的　研究胆固醇酯转运蛋白 (CETP)与各种类型的血脂异常和血糖异常的关系。方法　 1999年 9月至 10月 ,在北京市自然人群中采用分层随机抽样方法进行危险因素的横断面调查。分析了 719名 4 5～ 6 4岁的男女两性的血浆CETP浓度与血脂、血糖的关系。结果　 (1)在正常甘油三酯 (TG)组 ,CETP低于第 2 5百分位数与高于第 75百分位数时低高密并脂蛋白胆固醇 (HDL C)的患病率分别为 7 4 %和 5 3%。在高TG组 ,CETP低于第 2 5百分位数时低HDL C的患病率也仅为3 6 % ,与正常TG组相似 ;但CETP大于第 75百分位数时低HDL C的患病率为 35 7% ,是CETP低于第 2 5百分位数组的 10倍 ,且高低密度脂蛋白胆固醇 (LDL C)和高极低密度脂蛋白胆固醇 (VLDL C)的患病率也最高。 (2 )高TG合并低HDL C组 ,CETP高于第 75百分位数者占 5 0 0 % ,明显高于其他各组(P <0 0 5 )。 (3)采用Logistic回归模型调整了年龄、性别、吸烟、饮酒、肥胖、血糖和总胆固醇后 ,CETP大于第 75百分位数组与小于第 2 5百分位数组相比患高TG低HDL C型血脂异常的危险显著增加 ,OR =10 94 ,P =0 0 2 5。 (4 )高TG和 (或 )低HDL C者合并高血糖的患病率亦较高 (P <0 0 0 1) ,但仅在CETP较高者中 ,高血糖患病率增加有显著性 (P <0 0 0 1)。结论　CETP     

Different locations of cholesteryl ester transfer protein and phospholipid transfer protein activities in plasma

Activities of cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) were measured in plasma of four vertebrate species: man, rabbit, pig, and rat. The activities were measured in the absence and presence of antibodies raised against purified human CETP. PLTP activities were present in all four species with highest values in pig (11.7 ± 1.2 U/ml) and human plasma (9.2 ± 1.6 U/ml). Considerable lower activities were found in rabbit (3.5 ± 0.6 U/ml) and rat plasma (1.6 ± 0.7 U/ml). These activities were not affected significantly by antibody against human CETP. CETP activities could be measured in human (0.23 ± 0.05 U/ml) and in rabbit plasma (0.19 ± 0.03 U/ml). CETP activity in human plasma was inhibited over 97% by antibody against human CETP. Plasma was chromatographed on a Superose 6 gel filtration column. Average HDL particle sizes in the four species differed notably and decreased in the order: rat HDL > rabbit HDL > human HDL > pig HDL. A separation of the two lipid transfer activities was evident after gel filtration chromatography. The peak of the PLTP activity coeluted with a fraction of HDL particles with the size of human HDL₂ (particle weights 300–375 kDa). CETP activity in human and rabbit plasma coeluted largely with relatively small HDL particles (particle weights 140–180 kDa). These results show that CETP and PLTP activities are located in different macromolecular complexes.     

Postprandial variations in the cholesteryl ester transfer protein activity,phospholipid transfer protein activity and plasma cholesterol efflux capacity in normolipidemic men

BACKGROUND AND AIM: Plasma cholesterol efflux capacity is stimulated during postprandial (PP) hypertriglycerdemia. Plasma cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are the key proteins in lipoprotein metabolism and remodelling, but their role during the PP cholesterol efflux process remains indeterminate. The aim of this study was to determine the effect of a fatty meal intake on plasma CETP and PLTP activities, and the capacity of plasma to promote cholesterol efflux, as well as to evaluate the relationship between these three key mechanisms of the reverse cholesterol transport process. METHODS AND RESULTS: CETP and PLTP activities and the cholesterol efflux capacity of plasma were measured over eight hours following a fatty meal (1000 kcal, 62% fat) in 13 normolipidemic men. CETP activity and the cholesterol efflux capacity of plasma from Fu5AH cells increased after the meal, reaching a maximum after eight hours (respectively 32%, p = 0.06, and 6.5%, p = 0.045), whereas PLTP activity remained unchanged. CETP and PLTP activities did not correlate with plasma cholesterol efflux capacity in the fasting or PP state. Plasma CETP activity in the fasting state positively correlated with the plasma non-esterified fatty acid (NEFA) levels, but no correlation was found with any lipid or apolipoprotein postprandially. The cholesterol efflux capacity of plasma correlated positively with high-density lipoprotein (HDL) components, the best correlation being with the HDL phospholipid fraction in both the fasting and PP states. CONCLUSIONS: These findings suggest that plasma CETP and PLTP activities in healthy normolipidemic subjects are differently regulated in the PP state, and are not correlated with the increased cholesterol efflux capacity of PP plasma. HDL-phospholipid remains the key factor in the regulation of the capacity of plasma to promote Fu5AH cell cholesterol efflux.