Plasma phospholipid transfer protein activity and small,dense LDL in type 2 diabetes mellitus

BACKGROUND: Phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) remodel circulating lipoproteins and play a role in the antiatherogenic reverse cholesterol transport pathway. The present study determined whether abnormalities in the LDL subfraction pattern in type 2 diabetic patients were related to changes in lipid transfer proteins. METHODS: Low-density lipoprotein (LDL) subfractions were measured by density gradient ultracentrifugation and plasma PLTP and CETP activities by radiometric assays in 240 diabetic patients and 136 controls. RESULTS: The diabetic patients had lower LDL-I (P < 0.001) and higher LDL-III concentrations than the controls (P < 0.001). Plasma PLTP activity was increased (P < 0.001) whereas no significant differences were seen in CETP activity. In the diabetic patients, small, dense LDL-III correlated with plasma triglyceride (r = 0.18, P < 0.01), HDL (r = -0.14, P < 0.05), PLTP (r = 0.29, P < 0.001) and CETP activity (r = 0.15, P < 0.05). Linear regression analysis showed that plasma PLTP activity, triglyceride and age were the major determinants of LDL-III concentration (r2 = 28%, P < 0.001). The univariate relationship between CETP and LDL-III was no longer significant after adjusting for PLTP activity. CONCLUSIONS: The increase in plasma PLTP activity was independently associated with small, dense LDL concentrations in type 2 diabetes. Hence, elevated PLTP activity might have both antiatherogenic and pro-atherogenic potential in these patients.     

Type 2 diabetes mellitus is associated with differential effects on plasma cholesteryl ester transfer protein and phospholipid transfer protein activities and concentrations

BACKGROUND: Human plasma contains two lipid transfer proteins, cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), which are crucial in reverse cholesterol transport. METHODS: Plasma CETP and PLTP activity levels and concentrations in 16 type 2 diabetic patients and 16 matched healthy subjects were determined, and these data were correlated to clinical variables, including insulin sensitivity and lipid levels. RESULTS: Plasma triglycerides were higher (p<0.02) and high-density lipoprotein (HDL) cholesterol (p<0.02) was lower in diabetic patients. Plasma CETP activity and concentrations were not significantly different between diabetic and healthy subjects, but CETP specific activity was lower in diabetic patients (p<0.001). Multiple regression analysis showed that plasma CETP activity was positively related to CETP concentration (p=0.0001) and negatively to the diabetic state (p<0.002) or to HbA1c (p<0.02). PLTP activity (p<0.05) and specific activity were higher (p<0.05), whereas there was no difference in PLTP concentration between the two groups. There was no significant bivariate correlation between PLTP concentration and activity, in either healthy or diabetic subjects. Multiple regression analysis did disclose positive relationships of PLTP activity with PLTP concentration (p=0.0001), plasma triglycerides (p=0.0001) and waist/hip ratio (p=0.0001), but not with the diabetic state or HbA1c. CONCLUSIONS: Neither CETP nor PLTP activity was independently associated with insulin sensitivity. Specific CETP activity is decreased in type 2 diabetes mellitus. In contrast, specific PLTP activity is higher in diabetes, as a result of the association of plasma PLTP activity with plasma triglycerides and obesity. Measurement of both plasma lipid transfer protein activity and mass levels may thus provide extra information in diabetes mellitus.     

A low-saturated-fat, low-cholesterol diet decreases plasma CETP activity and pre beta-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.     

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

Abstract. 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 (P7lt;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) It is concluded that the activities of CETP and PLTP are influenced by adiposity and possibly by insulin resistance. Elevated lipid transfer protein activities may provide a mechanism that contributes to alterations in HDL in insulin resistant states.     

Pharmacological modulation of cholesteryl ester transfer protein, a new therapeutic target in atherogenic dyslipidemia

In mediating the transfer of cholesteryl esters (CE) from antiatherogenic high density lipoprotein (HDL) to proatherogenic apolipoprotein (apo)-B-containing lipoprotein particles (including very low density lipoprotein [VLDL], VLDL remnants, intermediate density lipoprotein [IDL], and low density lipoprotein [LDL]), the CE transfer protein (CETP) plays a critical role not only in the reverse cholesterol transport (RCT) pathway but also in the intravascular remodeling and recycling of HDL particles. Dyslipidemic states associated with premature atherosclerotic disease and high cardiovascular risk are characterized by a disequilibrium due to an excess of circulating concentrations of atherogenic lipoproteins relative to those of atheroprotective HDL, thereby favoring arterial cholesterol deposition and enhanced atherogenesis. In such states, CETP activity is elevated and contributes significantly to the cholesterol burden in atherogenic apoB-containing lipoproteins. In reducing the numbers of acceptor particles for HDL-derived CE, both statins (VLDL, VLDL remnants, IDL, and LDL) and fibrates (primarily VLDL and VLDL remnants) act to attenuate potentially proatherogenic CETP activity in dyslipidemic states; simultaneously, CE are preferentially retained in HDL and thereby contribute to elevation in HDL-cholesterol content.Mutations in the CETP gene associated with CETP deficiency are characterized by high HDL-cholesterol levels (>60 mg/dL) and reduced cardiovascular risk. Such findings are consistent with studies of pharmacologically mediated inhibition of CETP in the rabbit, which argue strongly in favor of CETP inhibition as a valid therapeutic approach to delay atherogenesis. Consequently, new organic inhibitors of CETP are under development and present a potent tool for elevation of HDL in dyslipidemias involving low HDL levels and premature coronary artery disease, such as the dyslipidemia of type II diabetes and the metabolic syndrome. The results of clinical trials to evaluate the impact of CETP inhibition on premature atherosclerosis are eagerly awaited.     

Targeted mutation of plasma phospholipid transfer protein gene markedly reduces high-density lipoprotein levels

It has been proposed that the plasma phospholipid transfer protein (PLTP) facilitates the transfer of phospholipids and cholesterol from triglyceride-rich lipoproteins (TRL) into high-density lipoproteins (HDL). To evaluate the in vivo role of PLTP in lipoprotein metabolism, we used homologous recombination in embryonic stem cells and produced mice with no PLTP gene expression. Analysis of plasma of F2 homozygous PLTP-/- mice showed complete loss of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, sphingomyelin, and partial loss of free cholesterol transfer activities. Moreover, the in vivo transfer of [3H]phosphatidylcholine ether from very-low-density proteins (VLDL) to HDL was abolished in PLTP-/- mice. On a chow diet, PLTP-/- mice showed marked decreases in HDL phospholipid (60%), cholesterol (65%), and apo AI (85%), but no significant change in non-HDL lipid or apo B levels, compared with wild-type littermates. On a high-fat diet, HDL levels were similarly decreased, but there was also an increase in VLDL and LDL phospholipids (210%), free cholesterol (60%), and cholesteryl ester (40%) without change in apo B levels, suggesting accumulation of surface components of TRL. Vesicular lipoproteins were shown by negative-stain electron microscopy of the free cholesterol- and phospholipid-enriched IDL/LDL fraction. Thus, PLTP is the major factor facilitating transfer of VLDL phospholipid into HDL. Reduced plasma PLTP activity causes markedly decreased HDL lipid and apoprotein, demonstrating the importance of transfer of surface components of TRL in the maintenance of HDL levels. Vesicular lipoproteins accumulating in PLTP-/- mice on a high-fat diet could influence the development of atherosclerosis.     

Plasma lipid transfer protein as a determinant of the atherogenicity of monkey plasma lipoproteins.

This study was undertaken to determine potential tissue sources of plasma cholesteryl ester transfer protein (CETP), and to assess the influence of CETP on lipoprotein concentrations and atherosclerosis. In a group of 28 cynomolgus monkeys fed high fat, high cholesterol diets, plasma CETP concentration was strongly correlated with the abundance of CETP mRNA in liver and in adipose tissue, and with the output of CETP in liver perfusates. Plasma CETP concentration showed a strong inverse correlation with HDL cholesterol concentrations (r = -0.62, P less than 0.001) and a positive correlation with LDL cholesterol concentration (r = 0.54, P less than 0.005) and molecular weight (r = 0.57, P less than 0.001). The extent of coronary artery atherosclerosis was positively correlated with LDL cholesterol concentration and molecular weight, and with plasma CETP concentration. Thus, in monkeys fed an atherogenic diet, individual variation in CETP mRNA abundance in liver and adipose tissue probably plays a major role in the determination of plasma CETP levels. In plasma, CETP influences the distribution of cholesteryl esters between LDL and HDL, and CETP concentration appears to be a key determinant of the relative atherogenicity of the plasma lipoproteins.     

Multiple abnormalities in the transfer of phospholipids from VLDL and LDL to HDL in non-insulin-dependent diabetes

Transfers or exchanges of cholesterol esters and triglycerides between lipoproteins are mediated by a specialized protein referred to as cholesteryl ester transfer protein (CETP), whereas those of phospholipids (PLs) are facilitated by both CETP and a specific phospholipid transfer protein (PLTP). In the present study, the authors compared phospholipid transfer (PLT) in normal subjects and in patients with non-insulin-dependent diabetes (NIDD), which is associated with an increased risk of atherosclerosis. PLT was measured in different recombination experiments using an isotopic assay in which the transfer of labelled PLs from very low-density lipoprotein (VLDLs) and low-density lipoproteins (LDLs) to high-density lipoproteins (HDLs) was determined. This allowed discrimination between the roles of VLDLs+LDLs, HDLs, and plasma PLT activity (PLTA). VLDL+LDL-dependent PLT, HDL-dependent PLT and PLTA were decreased in NIDD. VLDL+LDL-dependent PLT was found to be negatively correlated with the PL/apolipoprotein B ratio, whereas HDL-dependent PLT was positively correlated with the HDL₂/HDL₃ and PL/apolipoprotein A-I ratios and negatively correlated with the flow activation energy at the HDL surface. The HDL₂/HDL₃ ratio was positively correlated with PLTA but not with CETP, which confirms previous reports suggesting that PLTP might act as an HDL conversion factor. These data show that several abnormalities in PLT occur in NIDD and raise the question as to whether a lowered PLT might be a new characteristic of dis factors associated with an increased risk of atherosclerosis.     

Relationships between changes in plasma lipid transfer proteins and apolipoprotein B-100 kinetics during fenofibrate treatment in the metabolic syndrome

The aim of the present study was to investigate the association between changes in apoB (apolipoprotein B-100) kinetics and plasma PLTP (phospholipid transfer protein) and CETP (cholesteryl ester transfer protein) activities in men with MetS (the metabolic syndrome) treated with fenofibrate. Eleven men with MetS underwent a double-blind cross-over treatment with fenofibrate (200 mg/day) or placebo for 5 weeks. Compared with placebo, fenofibrate significantly increased the FCRs (fractional catabolic rates) of apoB in VLDL (very-low-density lipoprotein), IDL (intermediate-density lipoprotein) and LDL (low-density lipoprotein) (all P<0.01), with no significant reduction (-8%; P=0.131) in VLDL-apoB PR (production rate), but an almost significant increase (+15%, P=0.061) in LDL-apoB PR. Fenofibrate significantly lowered plasma TG [triacylglycerol (triglyceride); P<0.001], the VLDL-TG/apoB ratio (P=0.003) and CETP activity (P=0.004), but increased plasma HDL (high-density lipoprotein)-cholesterol concentration (P<0.001) and PLTP activity (P=0.03). The increase in PLTP activity was positively associated with the increase in both LDL-apoB FCR (r=0.641, P=0.034) and PR (r=0.625, P=0.040), and this was independent of the fall in plasma CETP activity and lathosterol level. The decrease in CETP activity was positively associated with the decrease in VLDL-apoB PR (r=0.615, P=0.044), but this association was not robust and not independent of changes in PLTP activity and lathosterol levels. Hence, in MetS, the effects of fenofibrate on plasma lipid transfer protein activities, especially PLTP activity, may partially explain the associated changes in apoB kinetics.     

Postprandial plasma lipoproteins in normal and hypertriglyceridaemic subjects and their in vitro effect on platelet activity: differences between saturated and polyunsaturated fats

The postprandial plasma lipoprotein pattern was studied in 10 normal and 10 hypertriglyceridaemic subjects after consumption of either a saturated or a polyunsaturated fat-rich meal. Plasma triglycerides increased in both groups 3 h after the meal, and this was followed after 5 h by a dramatic reduction in the normal subjects only; the reduction was less after the saturated fat meal than after the polyunsaturated fat meal. This plasma triglyceride pattern was a consequence of changes in the chylomicron and very-low-density lipoprotein (VLDL) fractions. No significant changes were found in high-density lipoprotein (HDL)- and low-density lipoprotein (LDL)-cholesterol, triglycerides or protein concentration. Plasma cholesterol and apolipoproteins (apo) A-I and B were not significantly altered. The VLDL-apo C-III/apo C-II ratio increased 3 h after the saturated fat-rich meal, but decreased after the polyunsaturated fat-rich meal in normals, but not in the patient group. The effect of these postprandial lipoproteins on platelet function was studied by incubating normal washed platelets with the lipoprotein and then determining aggregation and [14C]serotonin release. All chylomicron fractions decreased platelet activity, whereas postprandial VLDL increased platelet activity. Five hours after the meals, the effect of VLDL on platelet activation was reduced in normal subjects only. The effect of postprandial LDL and HDL on platelet function differed little from that of the fasting lipoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypertension,lipoprotein subclasses and lipid transfer proteins in obese children and adolescents

Background: Obesity-related childhood hypertension is associated with disturbances of serum lipids, but less is known about distribution of lipoprotein subclasses and activities of proteins involved in reverse cholesterol transport in hypertensive obese children. Our objective was to determine low-density lipoprotein (LDL) and high-density lipoprotein (HDL) subclasses distribution and activities of lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) in hypertensive and non-hypertensive obese children.

Methods: A total of 40 hypertensive and 25 non-hypertensive obese children were enrolled. Lipoprotein subclasses were assessed by polyacrylamide gradient gel electrophoresis. LCAT and CETP activities were determined as a rate of formation and a rate of transfer of cholesteryl esters.

Results: Despite of comparable values of serum lipid parameters, a shift toward smaller LDL and HDL subclasses was observed in hypertensive compared to normotensive obese children. Activities of LCAT were similar, but proatherogenic CETP activities were significantly higher in the hypertensive group (p?= 0.036). LCAT/net CETP ratio inversely correlated with relative proportion of small, dense LDL particles (ρ =??0.423; p?= 0.025) in the group with hypertension.

Conclusions: The results of our study demonstrated a tendency toward altered distribution of lipoprotein subclasses in favor of more proatherogenic particles in childhood hypertension. Also, hypertensive obese children had increased proatherogenic CETP activity.     

Lipoprotein composition influences cholesteryl ester transfer in alcohol abusers

Alcohol use is known to increase high-density lipoprotein (HDL) cholesterol, which is at least in part mediated by the alcohol-induced reduction in plasma cholesteryl ester transfer protein (CETP) activity and mass. We have shown that the high plasma HDL concentration reduces the CETP-mediated net mass transfer of cholesteryl esters from HDL to very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL), or even reverses the direction of transfer in plasma incubations. Therefore, we studied the effect of lipoprotein composition on lipid net mass transfers in 14 male alcohol abusers and nine male control subjects by incubating plasma for up to 2 h. The cholesteryl ester net mass transfer in the alcohol abusers was mainly predicted by the VLDL and LDL lipid composition in multiple linear regression, while the HDL composition was the main factor in the controls. The observed difference in the effect of the lipoprotein composition on cholesteryl ester net mass transfer support our previous finding in rabbits that CETP binding to lipoproteins may differ during ethanol oxidation. The results suggest that ethanol oxidation induces alterations which may affect the binding of CETP to lipoproteins.     

Alterations in high-density lipoprotein metabolism and reverse cholesterol transport in insulin resistance and type 2 diabetes mellitus: role of lipolytic enzymes, lecithin:cholesterol acyltransferase and lipid transfer proteins

Insulin resistance and type 2 diabetes mellitus are generally accompanied by low HDL cholesterol and high plasma triglycerides, which are major cardiovascular risk factors. This review describes abnormalities in HDL metabolism and reverse cholesterol transport, i.e. the transport of cholesterol from peripheral cells back to the liver for metabolism and biliary excretion, in insulin resistance and type 2 diabetes mellitus. Several enzymes including lipoprotein lipase (LPL), hepatic lipase (HL) and lecithin: cholesterol acyltransferase (LCAT), as well as cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), participate in HDL metabolism and remodelling. Lipoprotein lipase hydrolyses lipoprotein triglycerides, thus providing lipids for HDL formation. Hepatic lipase reduces HDL particle size by hydrolysing its triglycerides and phospholipids. A decreased postheparin plasma LPL/HL ratio is a determinant of low HDL2 cholesterol in insulin resistance. The esterification of free cholesterol by LCAT increases HDL particle size. Plasma cholesterol esterification is unaltered or increased in type 2 diabetes mellitus, probably depending on the extent of triglyceride elevation. Subsequent CETP action results in transfer of cholesteryl esters from HDL towards triglyceride-rich lipoproteins, and is involved in decreasing HDL size. An increased plasma cholesteryl ester transfer is frequently observed in insulin-resistant conditions, and is considered to be a determinant of low HDL cholesterol. Phospholipid transfer protein generates small pre beta-HDL particles that are initial acceptors of cell-derived cholesterol. Its activity in plasma is elevated in insulin resistance and type 2 diabetes mellitus in association with high plasma triglycerides and obesity. In insulin resistance, the ability of plasma to promote cellular cholesterol efflux may be maintained consequent to increases in PLTP activity and pre beta-HDL. However, cellular cholesterol efflux to diabetic plasma is probably impaired. Besides, cellular abnormalities that are in part related to impaired actions of ATP binding cassette transporter 1 and scavenger receptor class B type I are likely to result in diminished cellular cholesterol efflux in the diabetic state. Whether hepatic metabolism of HDL-derived cholesterol and subsequent hepatobiliary transport is altered in insulin resistance and type 2 diabetes mellitus is unknown. Specific CETP inhibitors have been developed that exert major HDL cholesterol-raising effects in humans and retard atherosclerosis in animals. As an increased CETP-mediated cholesteryl ester transfer represents a plausible metabolic intermediate between high triglycerides and low HDL cholesterol, studies are warranted to evaluate the effects of these agents in insulin resistance- and diabetes-associated dyslipidaemia.     

Reverse cholesterol transport and cholesterol efflux in atherosclerosis

Reverse cholesterol transport (RCT) is a pathway by which accumulated cholesterol is transported from the vessel wall to the liver for excretion, thus preventing atherosclerosis. Major constituents of RCT include acceptors such as high-density lipoprotein (HDL) and apolipoprotein A-I (apoA-I), and enzymes such as lecithin:cholesterol acyltransferase (LCAT), phospholipid transfer protein (PLTP), hepatic lipase (HL) and cholesterol ester transfer protein (CETP). A critical part of RCT is cholesterol efflux, in which accumulated cholesterol is removed from macrophages in the subintima of the vessel wall by ATP-binding membrane cassette transporter A1 (ABCA1) or by other mechanisms, including passive diffusion, scavenger receptor B1 (SR-B1), caveolins and sterol 27-hydroxylase, and collected by HDL and apoA-I. Esterified cholesterol in the HDL is then delivered to the liver for excretion. In patients with mutated ABCA1 genes, RCT and cholesterol efflux are impaired and atherosclerosis is increased. In studies with transgenic mice, disruption of ABCA1 genes can induce atherosclerosis. Levels of HDL are inversely correlated with incidences of cardiovascular disease. Supplementation with HDL or apoA-I can reverse atherosclerosis by accelerating RCT and cholesterol efflux. On the other hand, pro-inflammatory factors such as interferon-gamma (IFN-gamma), endotoxin, tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1beta), can be atherogenic by impairing RCT and cholesterol efflux, according to in vitro studies. RCT and cholesterol efflux play a major role in anti-atherogenesis, and modification of these processes may provide new therapeutic approaches to cardiovascular disease. Further research on new modifying factors for RCT and cholesterol efflux is warranted.     

Role of lipases, lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein in abnormal high density lipoprotein metabolism in insulin resistance and type 2 diabetes mellitus

Dyslipidaemia, hallmarked by low HDL cholesterol and high plasma triglycerides, is a feature of insulin resistance and type 2 diabetes mellitus. These lipoprotein abnormalities represent major cardiovascular risk factors in these conditions. Among other factors, lipoprotein lipase (LPL), hepatic lipase (HL), lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) play an important role in an abnormal HDL metabolism in insulin resistance and type 2 diabetes mellitus. LPL hydrolyses lipoprotein triglycerides, thus providing lipids for HDL formation. In insulin resistant states, a decreased post-heparin plasma LPL activity contributes to a low HDL cholesterol, whereas an increased activity of HL reduces HDL particle size by hydrolysing its triglycerides and phospholipids. High HL activity coincides with low HDL cholesterol. The esterification of free cholesterol by LCAT increases HDL particle size. Subsequent CETP action results in transfer of cholesteryl esters from HDL towards triglyceride-rich lipoproteins. This cholesteryl ester transfer process results in lower HDL cholesterol and indirectly decreases HDL size. Plasma cholesterol esterification is unaltered or increased, whereas cholesteryl ester transfer is enhanced in type 2 diabetes mellitus, abnormalities which are probably related to the degree of hypertriglyceridaemia. It is plausible that a low LPL activity contributes to premature atherosclerosis as observed in insulin resistance and type 2 diabetes mellitus, but the effects of high HL activity and altered plasma cholesterol esterification on atherosclerosis development are uncertain. Since the cholesteryl ester transfer process between lipoproteins provides a metabolic intermediate between low HDL cholesterol and high plasma triglycerides, hypertriglyceridaemia-associated accelerated transfer of cholesteryl ester out of HDL may be pathogenetically involved in the development of cardiovascular disease in insulin resistance and type 2 diabetes mellitus.     

Decreased plasma cholesterol esterification and cholesteryl ester transfer in hypopituitary patients on glucocorticoid replacement therapy

Cardiovascular risk is increased in hypopituitary patients. No data are available with respect to the effect of glucocorticoid replacement therapy on high density lipoproteins (HDL) metabolism in such patients. Plasma lecithin:cholesterol acyl transferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are important determinants of HDL remodelling. The possible influence of conventional glucocorticoid replacement on plasma lipids, plasma LCAT, CETP and PLTP activity levels, as well as on plasma cholesterol esterification (EST) and cholesteryl ester transfer (CET) was evaluated in 24 consecutive hypopituitary patients (12 men and 12 women) with untreated growth hormone deficiency of whom 17 had adrenal insufficiency and were treated with cortisone acetate, 25 to 37.5 mg daily. Twenty-three patients were on stable levothyroxin therapy and 22 patients used sex steroids. Urinary excretion of cortisol and cortisone metabolites was higher (p&lt;0.12) were not significantly different in patients receiving and not receiving glucocorticoids. Fasting blood glucose, plasma insulin and insulin resistance were similar in the groups. Plasma total (p&lt;0.05) and very low+low density lipoprotein cholesterol (p&lt;0.01) were lower in patients receiving glucocorticoids, whereas HDL cholesterol and plasma triglycerides were not different between patients treated and not treated with glucocorticoids. Plasma LCAT activity was 45% lower (p&lt;0.02) and CETP activity was 34% lower (p&lt;0.05) in patients on glucocorticoid treatment. Multiple regression analysis showed that these effects were independent of gender and fat mass. In glucocorticoid-receiving patients, plasma EST and CET were decreased by 80% (p&lt;0.01) and by 58% (p&lt;0.05), respectively. These changes were at least partly attributable to lower LCAT and CETP activity levels. In contrast, plasma PLTP activity was not different between patients with and without glucocorticoid treatment, suggesting that exogenous glucocorticoids exert a different regulatory effect on plasma CETP compared to PLTP. In conclusion, this preliminary study suggests that conventional glucocorticoid replacement in hypopituitary patients is associated with a decrease in plasma cholesterol esterification and cholesteryl ester transfer, indicating that these steps in HDL metabolism are impaired. Such abnormalities in HDL metabolism could be involved in increased cardiovascular risk in glucocorticoid-treated hypopituitary patients, despite a lack of deterioration in plasma lipids.     

The role of phospholipid transfer protein in lipoprotein‐mediated neutralization of the procoagulant effect of anionic liposomes

Summary. Background: Serum has the ability to neutralize the procoagulant properties of anionic liposomes, with transfer of phospholipids (PLs) to both high‐density lipoprotein (HDL) and low‐density lipoprotein (LDL) particles. Phospholipid transfer protein (PLTP) mediates transfer of PLs between HDL and other lipoproteins and conversion of HDL into larger and smaller particles. Objectives: To examine the role of PLTP in the neutralization of procoagulant liposomes. Methods: Procoagulant liposomes were incubated with different lipoproteins in the presence or absence of PLTP, and then tested for their ability to stimulate thrombin formation. Results and Conclusions: In the absence of added PLTP, the lipoprotein‐enriched fraction, total HDL, HDL₃ and very high‐density lipoprotein (VHDL) were all able to neutralize the procoagulant properties of the liposomes. In these samples, endogenous PLTP was present, as judged by Western blotting. In contrast, no PLTP was present in LDL, HDL₂ and lipoprotein‐deficient serum, all of which displayed no ability to neutralize the procoagulant liposomes. The phospholipid (PL) transfer activity was dependent on both enzyme (PLTP) and PL acceptor (lipoproteins). After treatment of the VHDL fraction with antiserum against PLTP, the neutralization of procoagulant activity was reduced, but could be regained by the addition of active PLTP. The neutralizing activity was dependent on a catalytically active form of PLTP, and addition of a low activity form of PLTP had no effect. In conclusion, PLTP was found to mediate transfer of anionic PLs to HDL and LDL, thereby neutralizing the effect of procoagulant liposomes, resulting in a reduction of procoagulant activity.     

Decreased plasma cholesterol esterification and cholesteryl ester transfer in hypopituitary patients on glucocorticoid replacement therapy

Cardiovascular risk is increased in hypopituitary patients. No data are available with respect to the effect of glucocorticoid replacement therapy on high density lipoproteins (HDL) metabolism in such patients. Plasma lecithin:cholesterol acyl transferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are important determinants of HDL remodelling. The possible influence of conventional glucocorticoid replacement on plasma lipids, plasma LCAT, CETP and PLTP activity levels, as well as on plasma cholesterol esterification (EST) and cholesteryl ester transfer (CET) was evaluated in 24 consecutive hypopituitary patients (12 men and 12 women) with untreated growth hormone deficiency of whom 17 had adrenal insufficiency and were treated with cortisone acetate, 25 to 37.5 mg daily. Twenty-three patients were on stable levothyroxin therapy and 22 patients used sex steroids. Urinary excretion of cortisol and cortisone metabolites was higher (p<0.001) in glucocorticoid-treated patients. Body mass index (p<0.08) and fat mass (p<0.12) were not significantly different in patients receiving and not receiving glucocorticoids. Fasting blood glucose, plasma insulin and insulin resistance were similar in the groups. Plasma total (p<0.05) and very low+low density lipoprotein cholesterol (p<0.01) were lower in patients receiving glucocorticoids, whereas HDL cholesterol and plasma triglycerides were not different between patients treated and not treated with glucocorticoids. Plasma LCAT activity was 45% lower (p<0.02) and CETP activity was 34% lower (p<0.05) in patients on glucocorticoid treatment. Multiple regression analysis showed that these effects were independent of gender and fat mass. In glucocorticoid-receiving patients, plasma EST and CET were decreased by 80% (p<0.01) and by 58% (p<0.05), respectively. These changes were at least partly attributable to lower LCAT and CETP activity levels. In contrast, plasma PLTP activity was not different between patients with and without glucocorticoid treatment, suggesting that exogenous glucocorticoids exert a different regulatory effect on plasma CETP compared to PLTP. In conclusion, this preliminary study suggests that conventional glucocorticoid replacement in hypopituitary patients is associated with a decrease in plasma cholesterol esterification and cholesteryl ester transfer, indicating that these steps in HDL metabolism are impaired. Such abnormalities in HDL metabolism could be involved in increased cardiovascular risk in glucocorticoid-treated hypopituitary patients, despite a lack of deterioration in plasma lipids.     

Cholesterol ester transfer protein in children on peritoneal dialysis.

OBJECTIVES: To examine whether cholesterol ester transfer protein (CETP) activity and mass contribute to dyslipidemia in children on peritoneal dialysis (PD), and to determine whether CETP activity or mass is responsible for severer hyperlipidemia in smaller (younger) patients. STUDY DESIGN: 27 patients (18 males, 9 females; mean age 11.8 +/- 6.1 years) were enrolled. Each patient had been receiving PD for more than 6 months. Fasting blood samples were drawn and CETP activity, CETP mass, total cholesterol, triglyceride, beta-lipoprotein profiles, lipoprotein lipid profiles (cholesterol and triglyceride in lipoproteins), apoprotein profile, and serum albumin levels were measured. The results were then compared, using Student's t-test, with those for a control group. In the patient group, the relationships between CETP activity and each factor were examined using simple and multiple regression analyses. RESULTS: Total cholesterol, triglyceride, low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), chylomicron, and ApoB levels were significantly higher in the patient group. Mean CETP activity levels were 106% +/- 24% in the patient group and 111% +/- 21% in the control group. No significant difference in CETP activity was seen between the two groups, but CETP mass was lower in the patient group than in the control group (2.2 +/- 0.6 microL/dL for the patient group vs 2.8 +/- 0.9 microL/dL for the control group, p = 0.01). As a result, specific CETP activity (activity/protein mass ratio) was significantly higher in the patient group (p < 0.0001). CETP activity was positively related to LDL and other atherogenic factors and negatively related to serum albumin level. No relationship between CETP activity and patient body weight was seen. CONCLUSION: Specific CETP activity was higher in the patient group compared with that in the control group, and strong correlations were found between CETP activity and atherogenic factors in the patient group. Therefore, CETP seems to be associated with lipid abnormalities in children on PD but is not responsible for the severer hyperlipidemia seen in smaller children.     

Increased high-density lipoprotein cholesterol concentration in alcoholics is related to low cholesteryl ester transfer protein activity

Cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl esters from HDL to apoB-containing lipoproteins. Since alcoholics have high HDL cholesterol and low LDL cholesterol levels, a defect in cholesteryl ester transfer could be responsible for the alcohol-induced alteration in cholesterol distribution between lipoproteins. To test this hypothesis, we compared CETP activity in plasma from 30 alcoholics without severe liver damage and 16 control subjects. Plasma CETP activity was 28% lower in the alcoholics compared with the controls (P less than 0.001), while the teetotallers among the latter had slightly higher CETP activity than those who consumed alcohol in moderation. CETP activity increased slowly after ethanol withdrawal, but did not reach the control level within the 7-day observation period. A positive correlation was observed between plasma CETP activity and the LDL cholesterol HDL cholesterol ratio (r = 0.480, P less than 0.002), whereas CETP activity showed a negative correlation with HDL cholesterol level (r = -0.467, P less than 0.001). The results indicate that defective transfer of cholesteryl esters from HDL to LDL contributes to the high HDL cholesterol levels in alcoholics.