Cholesterol Ester Transfer Protein Activity Research Articles

In vivo evidence for increased apolipoprotein A-I catabolism in subjects with impaired glucose tolerance.

The in vivo kinetics of the HDL apolipoproteins (apo) A-I and A-II were studied in six subjects with impaired glucose tolerance (IGT) and six control subjects with normal glucose tolerance (NGT), using a stable isotope approach. During a 12-h primed constant infusion of L-[ring-13C6]-phenylalanine, tracer enrichment was determined in apoA-I and apoA-II from ultracentrifugally isolated HDL. The rates of HDL apoA-I and apoA-II production and catabolism were estimated using a one-compartment model-based analysis. Triglycerides were higher in IGT subjects (1.33 +/- 0.21 vs. 0.84 +/- 0.27 mmol/l, P < 0.05), but were within the normal range. HDL cholesterol and apoA-I levels were significantly lower in subjects with IGT (1.07 +/- 0.15 vs. 1.36 +/- 0.14 mmol/l, P < 0.05; 0.94 +/- 0.10 vs. 1.34 +/- 0.07 g/l, P < 0.01). In IGT subjects, HDL composition was significantly altered, characterized by an increase in HDL triglycerides (4.9 +/- 1.9 vs. 3.2 +/- 1.0%, P < 0.05) and HDL phospholipids (34.7 +/- 2.6 vs. 27.5 +/- 5.8%, P < 0.05) and a decrease in HDL cholesteryl esters (10.1 +/- 2.0 vs. 12.7 +/- 2.9%, P < 0.05) and HDL apoA-I (31.5 +/- 4.4 vs. 43.2 +/- 2.4%, P < 0.05). The mean fractional catabolic rate (FCR) of HDL apoA-I was significantly higher in IGT subjects (0.34 +/- 0.05 vs. 0.26 +/- 0.03 day(-1), P < 0.01), while the HDL apoA-I production rate (PR), as well as the PR and FCR of HDL apoA-II, showed no differences between the two groups. There were significant correlations between HDL apoA-I FCR and the following parameters: HDL apoA-I (r = -0.902, P < 0.001), HDL cholesterol (r = -0.797, P = 0.001), plasma triglycerides (r = 0.743, P < 0.01), HDL triglycerides (r = 0.696, P < 0.01), and cholesterol ester transfer protein activity (r = 0.646, P < 0.01). We observed a strong positive association between increased apoA-I catabolism and insulin (r = 0.765, P < 0.01) and proinsulin (r = 0.797, P < 0.01) concentrations. These data support the hypothesis that the decrease in HDL cholesterol and apoA-I levels in IGT is principally the result of an enhanced apoA-I catabolism. The latter seems to be an early metabolic finding in IGT even when other lipid parameters, especially plasma triglycerides, still appear to be not or only weakly affected.

Compositional and functional changes of low-density lipoprotein during hemodialysis in patients with ESRD

This study focused on the effects of hemodialysis on the atherogenic properties of low density lipoprotein (LDL) in patients with end-stage renal disease (ESRD). The impact of cholesterol ester transfer protein (CETP) activity and lipolysis on LDL composition, particularly the changes during hemodialysis, was investigated. Blood was drawn from 15 normotriglyceridemic (NTG) and 15 hypertriglyceridemic patients [HTG; triglycerides (TG) < 2.2 mmol/liter] before hemodialysis, during (1.5 hr after the beginning of anticoagulation) and at the end of treatment. In each sample, lipid values and CETP activity were measured. LDL was prepared and characterized by its components and diameters (2 to 16% PAGGE). To investigate the functional properties of LDL, fractions obtained from NTG and HTG patients were incubated with human skin fibroblasts and a cell line of murine macrophages (P388), and cholesterol ester formation rates were measured. In comparison to LDL from NTG patients at baseline, HTG-LDL were enriched in triglycerides (P < 0.02), depleted in cholesterol proportion (P < 0.01) and small in size (P < 0.001). These LDL induced the cholesterol esterification rates (50 micrograms/mL LDL-protein) in a twofold greater unsaturation in macrophages when compared to LDL from NTG patients (P < 0.04). The rates in fibroblasts were reduced by approximately half (P < 0.05). During hemodialysis, LDL were decreased in size (P < 0.001) and depleted in TG (P < 0.01), particularly in the hypertriglyceridemic state. Although CETP activity increased during hemodialysis (P < 0.001), the cholesterol content remained unchanged. When HTG-LDL obtained during hemodialysis were incubated with cells, esterification rates particularly in macrophages were markedly accelerated in comparison to the unmodified lipoprotein at baseline (P < 0.05). LDL from HTG patients with ESRD was TG-enriched, CH-depleted and smaller in size. As the intracellular esterification rates induced by LDL were related to the cellular uptake, these LDL were a superior substrate for murine macrophages with the tendency of intracellular accumulation, and an inferior substrate for fibroblasts suggesting a decreased uptake by the specific receptor pathway. TG-depletion of LDL during hemodialysis, particularly in HTG patients due to a lipase-mediated TG-hydrolysis, increased these effects in macrophages. We suggest that the alterations of LDL that occur during repeated hemodialysis in vivo could contribute to the high prevalence of premature atherosclerosis found in HTG patients with ESRD.

Effect of 20 days' bed rest on the reverse cholesterol transport system in healthy young subjects.

To study the effects of 20 days of bed rest on HDL cholesterol, lipoprotein lipase, hepatic triglyceride lipase, cholesterol ester transfer protein and lecithin-cholesterol acyltransferase. A 20-day intervention study. Makita general hospital. Five male and five female healthy participants, mean age 20.4 years, range 19-24 years. Twenty days of bed rest. Lipid, lipoprotein, lipoprotein lipase, hepatic triglyceride lipase, cholesterol ester transfer protein and lecithin-cholesterol acyltransferase. Fasting HDL, HDL2 and HDL3 cholesterol levels decreased from 1.748 to 1.404 mmol L(-1) (P < 0.01), from 0.807 to 0.628 mmol L(-1) (P < 0.01) and from 0.939 to 0.784 mmol L(-1) (P < 0.05), respectively, while VLDL triglyceride levels increased from 0.365 to 0.754 mmol L(-1) (P < 0.05). Plasma post-heparin lipoprotein lipase activity decreased from 0.494 to 0.418 micromol mL(-1) h(-1) (P < 0.01), but plasma post-heparin hepatic triglyceride lipase activity and cholesterol ester transfer protein activity did not change during bed rest. Lecithin-cholesterol acyltransferase activity increased from 72.5 to 84.8 nmol mL(-1) h(-1) (P < 0.001). Twenty days of bed rest induced a decline in HDL cholesterol levels and an increase in VLDL triglyceride levels. When considering lipoprotein lipase, hepatic triglyceride lipase, cholesterol ester transfer protein and lecithin-cholesterol acyltransferase as factors in the decreased HDL cholesterol, the contribution of lipoprotein lipase is suggested.

Gene activation, apolipoprotein A-I/high density lipoprotein, atherosclerosis prevention and longevity.

Recent studies in man and human apolipoprotein A-I transgenic animals emphasize the significance of apolipoprotein A-I and high density lipoprotein in antiatherogenesis. Several drugs and other compounds, e.g. phenobarbital, gemfibrozil, fenofibrate, prednisone, estrogen and alcohol, induce apolipoprotein A-I synthesis. They commonly produce serum lipoprotein patterns typical of a low risk of coronary heart disease, and many of them have been found to prevent atherogenesis, reduce coronary heart disease mortality and increase survival. These compounds act against atherosclerosis by using one or several mechanisms that include overexpression of the apolipoprotein A-I gene with an increase in serum apolipoprotein A-I and high density lipoprotein and promotion of reverse cholesterol transport, upregulation of the low density lipoprotein receptor gene with a decrease in serum apolipoprotein B and low density lipoprotein, maintenance of endothelial cell function and protection against thrombosis. They have been found to raise high density lipoprotein cholesterol and apolipoprotein A-I together with a decrease in cholesterol ester transfer protein activity, and to induce hepatic cholesterol 7 alpha-hydroxylase and cholesterol and bile acid elimination from the body. By raising the activities of apolipoprotein A-I/high density lipoprotein-associated paraoxonase and other antioxidative enzymes, the inducers have the capacity to prevent atherogenesis in arterial walls through inhibition of the oxidative modification of low density lipoprotein. Other antiatherogenic vascular actions of high density lipoprotein include interference with low density lipoprotein aggregation and uptake by endothelial cells, and competition with low density lipoprotein for endothelial-localized low density lipoprotein receptors. Apolipoprotein A-I/high density lipoprotein beneficially enhances fibrinolysis, decreases platelet aggregation, increases prostacyclin production and stabilization and prevents atherogenic immune and inflammatory responses. This gene activation or microsomal induction can prevent atherosclerosis and is a basis for tailoring effective new agents and optimal non-invasive therapy against atherosclerotic vascular disease to promote health and enhance longevity.

Inhibition of cholesterol ester transfer protein by CGS 25159 and changes in lipoproteins in hamsters

As a result of screening, several isoflavans were identified to be antagonists of cholesterol ester transfer protein (CETP) activity. The present study evaluates CGS 25159, a synthetic isoflavan, as a putative inhibitor of CETP activity of human and hamster plasma. Determined by [3H]CE transfer from HDL to VLDL+LDL fraction or by fluorescent-CE transfer assay, CGS 25159 inhibited CETP in both human plasma bottom fraction (d=1.21 g/ml) and in plasma from Golden Syrian Hamsters with an IC50<10 μM. The compound also inhibited (IC50≈15 μM) the reciprocal transfer of triglycerides in the incubated whole plasma from normal and hyperlipidemic hamsters. When orally administered to normolipidemic hamsters, CGS 25159 (10 mg/kg, 4 days) reduced plasma transfer activity by 35–60%. Treatment with CGS 25159 (10 and 30 mg/kg, p.o.) resulted in dose dependent and time dependent changes in CETP activity. After two weeks of treatment at 10 mg/kg, the changes in VLDL+LDL cholesterol, total triglycerides and HDL cholesterol were −22±4.6*, −23±7.5 and +10±2.8%, respectively. The corresponding changes at 30 mg/kg were −28±5.5*, −38±6.8* and +29±4.4*%, (*, P, 0.05; mean±S.E.M., n=6). A single spin gradient density ultracentrifugation of plasma lipoproteins from treated animals showed an increase in HDL cholesterol and a redistribution to larger HDL particles. These data support the contention that pharmacological down regulation of CETP activity could result in favorable changes in lipoprotein profile.

Increased esterification of cholesterol and transfer of cholesteryl ester to apo B-containing lipoproteins in Type 2 diabetes: relationship to serum lipoproteins A-I and A-II

This study examines the activity of two key enzymes of reverse cholesterol transport, cholesterol ester transfer protein (CETP) and lecithin:cholesterol acyl transferase (LCAT) in 21 patients with non-insulin dependent diabetes mellitus (NIDDM) and 21 control subjects. Serum CETP was assessed by measuring plasma-mediated cholesteryl ester transfer between pooled exogenous lipoprotein with endogenous LCAT inhibited — an estimate of CETP mass. CETP activity was determined as cholesteryl ester transfer in the presence of the patients' lipoproteins and LCAT (endogenous assay). LCAT activity was determined in the same assay. There was no significant difference in CETP mass between the diabetic and non-diabetic subjects and there was no correlation between CETP mass and LCAT activity. Using the endogenous lipoprotein assay, CETP was elevated in serum from diabetic patients compared to control subjects (10.05 ± 1.89 vs. 5.50 ± 0.53 nmol/ml/h P < 0.05). LCAT was also increased in the diabetic patients (53.63 ± 4.70 vs. 41.22 ± 3.40 nmol/ml/h P < 0.05). Serum free cholesterol from diabetic and control subjects correlated with CETP activity measured using endogenous lipoprotein assay ( r = 0.77, P < 0.001 and r = 0.82, P < 0.001), and also with LCAT activity ( r = 0.76, P < 0.01 and r = 0.79, P < 0.01). There was a negative correlation between CETP activity with the endogenous lipoprotein assay and serum high density lipoprotein (HDL) cholesterol in the diabetic patients ( r = −0.38, P < 0.01), but not in control subjects. In a subgroup of 10 control subjects, there was a positive correlation between LCAT activity and apolipoprotein (apo) A-I ( r = 0.49, P < 0.05) and apo A-II ( r = 0.51, P < 0.05) and also between CETP activity (endogenous assay) and apo A-I ( r = 0.87, P = 0.001) and apo A-II ( r = 0.63, P < 0.05). No relationship was observed between CETP activity and apo A-I or apo A-II in the diabetic subjects. Thus, serum CETP mass was normal in Type 2 diabetes but CETP activity (endogenous assay) was increased and was related to free cholesterol levels and LCAT activity in both diabetic and non-diabetic subjects.

Relation between cholesterol ester transfer protein activities and lipoprotein cholesterol in patients with hypercholesterolemia and combined hyperlipidemia.

Cholesterol ester transfer protein (CETP) promotes the transfer of cholesterol esters among different lipoprotein classes-high-density lipoproteins (HDL), very-low-density lipoproteins, intermediate-density lipoproteins, and low-density lipoproteins (LDL). The current study was carried out to determine whether CETP activities are correlated with lipoprotein cholesterol levels in a large number of patients having elevated LDL cholesterol and normal triglycerides (hypercholesterolemia) and elevated LDL cholesterol and high triglycerides (combined hyperlipidemia). Compared with 50 normolipidemic male patients, 113 hypercholesterolemic patients had a 42% higher mean activity of CETP, and approximately 60% of these patients had CETP activities outside the normal range. A similar elevation of CETP was observed in 47 patients with combined hyperlipidemia. Furthermore, in those with combined hyperlipidemia, CETP activities were highly correlated with LDL cholesterol, non-HDL cholesterol, and non-HDL/HDL ratios. Similar high correlations were obtained by combining normotriglyceridemic patients with and without elevated LDL cholesterol. Since patients with elevated LDL cholesterol had a significantly lower mean level of HDL cholesterol, a high CETP activity also was related to a reduced HDL cholesterol level. Our results are consistent with this concept, although they do not constitute final proof that high CETP activities contribute to elevated cholesterol concentrations and reduced HDL cholesterol levels in patients with hypercholesterolemia and in those with combined hyperlipidemia.

Effect of adiposity on plasma lipid transfer protein activities: a possible link between insulin resistance and high density lipoprotein metabolism.

The mechanisms responsible for the decreased high density lipoprotein (HDL) cholesterol levels associated with obesity and insulin resistance are not well understood. Lecithin: cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein (CETP) are key factors in the esterification of cholesterol in HDL and the subsequent transfer of cholesteryl ester towards apolipoprotein B-containing lipoproteins. Phospholipid transfer protein (PLTP) may be involved in the regulation of HDL particle size. We therefore measured the activities of LCAT, CETP and PLTP using exogenous substrate assays, as well as lipids, lipoproteins, insulin and C-peptide in fasting plasma from eight healthy obese men (body mass index > 27 kg m-2) and 24 non-obese subjects. The obese men had lower levels of HDL cholesterol (P < 0.05) and higher levels of plasma triglycerides (P < 0.05), insulin (P < 0.05) and C-peptide (P < 0.01), as compared to the quartile of subjects with the lowest body mass index (BMI < 22.4 kg m-2). CETP and PLTP activities were elevated in the obese men by 35% (P < 0.01) and by 15% (P < 0.05), respectively. LCAT activity was comparable among the quartiles. Linear regression analysis showed that CETP activity was positively correlated with body mass index (P < 0.02), fasting blood glucose (P < 0.05) and plasma C-peptide (P < 0.05). PLTP activity was positively related to body mass index (P < 0.01), waist to hip circumference ratio (P < 0.001), as well as to fasting blood glucose (P < 0.05) and plasma C-peptide (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)