Tol, A. van

Plasma cholesteryl ester transfer, but not cholesterol esterification, is related to lipoprotein-associated phospholipase A2: Possible contribution to an atherogenic lipoprotein profile (Article)

2011-05-01T00:00:00Z

Context: Plasma lipoprotein-associated phospholipase A2(Lp-PLA2) predicts incident cardiovascular disease and is associated preferentially with negatively charged apolipoprotein B-containing lipoproteins. The plasma cholesteryl ester transfer (CET) process, which contributes to low highdensity lipoprotein cholesterol and small, dense low-density lipoproteins, is affected by the composition and concentration of apolipoprotein B-containing cholesteryl ester acceptor lipoproteins. Objective: We tested relationships of CET with Lp-PLA2in subjects with and without metabolicsyndrome (MetS). Design and Setting: In 68 subjects with MetS and 74 subjects without MetS, plasma Lp-PLA2mass, cholesterol esterification (EST), lecithin:cholesterol acyltransferase (LCAT) activity level, CET, CET protein (CETP) mass, and lipoproteins were measured. Results: EST, LCAT activity, CET (P<0.001 for all), and CETP (P<0.030) were increased, and Lp-PLA2was decreased (P<0.043) in MetS. CET was correlated positively with Lp-PLA2in subjects with and without MetS (P = 0.05 for both). EST and LCAT activity were unrelated to Lp-PLA2, despite a positive correlation between EST and CET (P = 0.001). After controlling for age, sex, and diabetes status, CET was determined by Lp-PLA2in the whole group (β = 0.245; P = 0.001), and in subjects with (β = 0.304; P = 0.001) and without MetS (β = 0.244; P = 0.006) separately, independently of triglycerides and CETP. Conclusions: PlasmaCETis related to Lp-PLA2in subjects withandwithout MetS.Theprocess of CET, but not EST, may be influenced by Lp-PLA2. These findings provide a rationale to evaluate whether maneuvers that inhibit Lp-PLA2will reduce CET, and vice versa to document effects of CETP inhibition on Lp-PLA2. Copyright

Plasma apolipoprotein M responses to statin and fibrate administration in type 2 diabetes mellitus (Article)

2010-11-01T00:00:00Z

Purpose: Plasma apolipoprotein M (apoM) is potentially anti-atherogenic, and has been found to be associated positively with plasma total, LDL and HDL cholesterol in humans. ApoM may, therefore, be intricately related to cholesterol metabolism. Here, we determined whether plasma apoM is affected by statin or fibrate administration in patients with diabetes mellitus. Methods: Fourteen type 2 diabetic patients participated in a placebo-controlled crossover study which included three 8-week treatment periods with simvastatin (40 mg daily), bezafibrate (400 mg daily), and their combination. Results: ApoM was decreased by 7% in response to simvastatin (P< 0.05 from baseline and placebo), and remained unchanged during bezafibrate and combined simvastatin. +. bezafibrate administration. Plasma apoM concentrations correlated positively with apoB-containing lipoprotein measures at baseline and during placebo (P< 0.02 to P< 0.001), but these relationships were lost during all lipid lowering treatment periods. Conclusions: This study suggests that, even though plasma apoM is lowered by statins, apoM metabolism is to a considerable extent independent of statin- and fibrate-affected pathways involved in cholesterol homeostasis.

Effect of increasing doses of Rosuvastatin and Atorvastatin on apolipoproteins, enzymes and lipid transfer proteins involved in lipoprotein metabolism and inflammatory parameters (Article)

2010-10-01T00:00:00Z

This paper contains detailed results of a sub-population of the prospective randomized RADAR (Rosuvastatin and Atorvastatin in different Dosages And Reverse cholesterol transport) study. Objective: Statin treatment results in substantially decreased incidence of cardiovascular events but the exact pathophysiological mechanism of their beneficial effect is yet unclear. We aimed to examine the effects of up-titrated doses of two widely used statins (atorvastatin (ATOR) and rosuvastatin (ROSU)) on parameters involved in lipoprotein metabolism, in patients with low high density lipoprotein cholesterol values (HDL-C). Research design and methods: In this RADAR substudy, 80 patients, aged 4080 years, with known cardiovascular disease and low HDL-C (<1.0mmol/l), were randomized to receive, after an initial 6 week dietary run-in phase, either ATOR 20mg (n41) or ROSU 10mg (n39). The doses were up-titrated (in 6 week intervals) to 80mg of ATOR or 40mg of ROSU at 12 weeks. Serum lipoproteins and lipoprotein metabolism parameters were measured at baseline and at 6 and 18 weeks of follow up. Results: Both statins significantly reduced total cholesterol (TChol) and non-HDL-C values with ROSU being more effective for the doses studied (p<0.05). No statistically significant effect on HDL-C was observed for either statin. Apolipoproteins (apo) B, CI, CIII, AV and E were significantly reduced in both groups (p<0.05), while the ratio of HDL particles containing both apoAI and apoAII (LpAI-AII) over HDL containing apoAI alone (LpAI) was changed for both statins with the decrease of LpAI being more prominent in the ATOR group (p=0.028). Cholesterol ester transfer protein (CETP) mass and activity, phospholipid transfer protein (PLTP) activity and lipoprotein-associated phospholipase A2 (Lp-PLA2) mass and activity were all significantly reduced in both treatment groups over the follow-up period (p<0.001). ATOR displayed a more prominent decrease of PLTP activity compared to ROSU (p=0.043), while ROSU displayed a more prominent decrease of Lp-PLA2 activity compared to ATOR (p=0.04). Both statins effectively reduced, in a dose-dependent way, high sensitivity C-reactive protein values over time, while no effect on the levels of circulating inter cellular adhesion molecule 1 (cICAM-1) was observed. Conclusions: The effects of statin treatment extend further and beyond a mere TChol and LDL cholesterol reduction, as demonstrated by the aforementioned alterations of lipoproteins, enzymes and lipid transfer proteins involved in lipoprotein metabolism and pro-atherogenic and inflammatory molecules. ROSU and ATOR displayed a similar pattern of effect on lipid metabolism with discrete differences in the magnitude of this effect in certain variables. Despite the limitations of small population size and lack of clinical end points, reported data provide an insight for the possible pathophysiological mechanisms implicated in the effect of increasing dosages of different statin treatments.

Genetic variation at the phospholipid transfer protein locus affects its activity and high-density lipoprotein size and is a novel marker of cardiovascular disease susceptibility (Article)

2010-08-03T00:00:00Z

Background-In contrast to clear associations between variants in genes participating in low-density lipoprotein metabolism and cardiovascular disease risk, such associations for high-density lipoprotein (HDL)-related genes are not well supported by recent large studies. We aimed to determine whether genetic variants at the locus encoding phospholipid transfer protein (PLTP), a protein involved in HDL remodeling, underlie altered PLTP activity, HDL particle concentration and size, and cardiovascular disease risk. Methods and Results-We assessed associations between 6 PLTP tagging single nucleotide polymorphisms and PLTP activity in 2 studies (combined n=384) and identified 2 variants that show reproducible associations with altered plasma PLTP activity. A gene score based on these variants is associated with lower hepatic PLTP transcription (P=3.2×10-18) in a third study (n=957) and with an increased number of HDL particles of smaller size (P=3.4×10-17) in a fourth study (n=3375). In a combination of 5 cardiovascular disease case-control studies (n=4658 cases and 11 459 controls), a higher gene score was associated with a lower cardiovascular disease risk (per-allele odds ratio, 0.94; 95% confidence interval, 0.90 to 0.98; P=1.2×10-3; odds ratio for highest versus lowest gene score, 0.69; 95% confidence interval, 0.55 to 0.86; P=1.0×10-3). Conclusions-A gene score based on 2 PLTP single nucleotide polymorphisms is associated with lower PLTP transcription and activity, an increased number of HDL particles, smaller HDL size, and decreased risk of cardiovascular disease. These findings indicate that PLTP is a proatherogenic entity and suggest that modulation of specific elements of HDL metabolism may offer cardiovascular benefit.

Plasma lecithin:cholesterol acyltransferase activity modifies the inverse relationship of C-reactive protein with HDL cholesterol in nondiabetic men (Article)

2010-01-01T00:00:00Z

Lecithin:cholesterol acyltransferase (LCAT) is instrumental in high-density lipoprotein (HDL) maturation, but high LCAT levels do not predict low cardiovascular risk. LCAT may affect antioxidative or anti-inflammatory properties of HDL. We determined the relationship of plasma high-sensitivity C-reactive protein (CRP) with LCAT activity and evaluated whether LCAT activity modifies the decreasing effect of HDL cholesterol (HDL-C) on CRP, as an estimate of its anti-inflammatory properties. Plasma HDL-C, apolipoprotein (apo) A-I and LCAT activity (exogenous substrate method) were measured in 260 nondiabetic men without cardiovascular disease. CRP was correlated inversely with HDL-C and apo A-I, and positively with LCAT activity (P < 0.01 to 0.001). Multivariate regression analysis demonstrated that age- and smoking-adjusted plasma CRP levels were associated negatively with HDL-C (β = - 0.224, P < 0.001) and positively with LCAT activity (β = 0.119, P = 0.034), as well as with the interaction between HDL-C and LCAT activity (β = 0.123, P = 0.026). There was also an interaction between apo A-I and LCAT activity on CRP (β = 0.159, P = 0.005). These relationships remained similar after adjustment for apo B-containing lipoproteins. In conclusion, the inverse relationship of HDL-C with CRP is attenuated by LCAT activity at higher HDL-C levels. It is hypothesized that LCAT could mitigate HDL's anti-inflammatory or antioxidative properties at higher HDL-C concentrations.

Novel roles of hepatic lipase and phospholipid transfer protein in VLDL as well as HDL metabolism (Article)

2009-10-01T00:00:00Z

Objective: Elevated plasma phospholipid transfer protein (PLTP) expression may increase atherosclerosis in mice by reducing plasma HDL and increasing hepatic VLDL secretion. Hepatic lipase (HL) is a lipolytic enzyme involved in several aspects of the same pathways of lipoprotein metabolism. We investigated whether the effects of elevated PLTP activity are compromised by HL deficiency. Methods and results: HL deficient mice were crossbred with PLTP transgenic (PLTPtg) mice and studied in the fasted state. Plasma triglycerides were decreased in HL deficiency, explained by reduced hepatic triglyceride secretion. In PLTPtg mice, a redistribution of HL activity between plasma and tissue was evident and plasma triglycerides were also decreased. HL deficiency mitigated or even abolished the stimulatory effect of elevated PLTP activity on hepatic triglyceride secretion. HL deficiency had a modest incremental effect on plasma HDL, which remained present in PLTP transgenic/HL-/- mice, thereby partially compensating the decrease in HDL caused by elevation of PLTP activity. HDL decay experiments showed that the fractional turnover rate of HDL cholesteryl esters was delayed in HL deficient mice, increased in PLTPtg mice and intermediate in PLTPtg mice in an HL-/- background. Conclusions: HL affects hepatic VLDL. Elevated PLTP activity lowers plasma HDL-cholesterol by stimulating the plasma turnover and hepatic uptake of HDL cholesteryl esters. HL is not required for the increase in hepatic triglyceride secretion or for the lowering of HDL-cholesterol induced by PLTP overexpression.

Plasma pre β-HDL formation is decreased by atorvastatin treatment in type 2 diabetes mellitus: Role of phospholipid transfer protein (Article)

2009-08-01T00:00:00Z

Atorvastatin lowers plasma phospholipid transfer protein (PLTP) activity, which stimulates pre-β-HDL generation in vitro. We determined the effect of atorvastatin on pre-β-HDL formation and its relation with PLTP activity in type 2 diabetes. Methods: Plasma pre-β-HDL formation as well as plasma apo A-I, LpA, LpAI:AII, cholesteryl ester transfer protein (CETP) and PLTP activity were measured before and after 30 weeks treatment in 40 patients randomized to atorvastatin 80 mg daily and 41 placebo receiving patients. Pre-β HDL formation was measured by crossed immunoelectrophoresis under conditions of lecithin:cholesterol acyltransferase (LCAT) inhibition. Results: Plasma pre-β-HDL formation, triglycerides, LDL cholesterol, PLTP activity, and CETP decreased after statin treatment (all P < 0.001 vs placebo), whereas HDL cholesterol increased (P < 0.005). Plasma apo A-I, LpAI and LpAI:AII remained unchanged compared to placebo. In all patients combined, the changes in pre-β-HDL formation were independently related to the decrease in plasma triglycerides (β = 0.31; P = 0.006) and PLTP activity (β = 0.23; P = 0.038), without a contribution of CETP. In the atorvastatin treated patients, the decrease in pre-β-HDL formation tended to be related to the decrease in PLTP activity (β = 0.30, P = 0.061) after controlling for decreases in triglycerides (β = 0.22, P = 0.22). Conclusion: High dose atorvastatin decreases the capacity of plasma to generate pre-β-HDL particles in type 2 diabetic patients, probably via lowering of plasma PLTP activity and triglycerides. This could contribute to an improvement in the atherogenic lipoprotein profile.

Reduction of HDL levels lowers plasma PLTP and affects its distribution among lipoproteins in mice (Article)

2009-08-01T00:00:00Z

Phospholipid transfer protein (PLTP) is associated with HDL particles in plasma, where it transfers phospholipids between lipoproteins and remodels HDL particles. Tangier disease patients, with a mutated ABCA1 transporter, have extremely low plasma HDL concentration and reduced PLTP activity levels, a phenotype that is also observed in mice lacking ABCA1. We investigated whether low HDL levels and low PLTP activity are mechanistically related. Firstly, we studied PLTP expression and distribution among lipoproteins in mice lacking ABCA1 (ABCA1-/-). Parallel to the strong reduction in PLTP activity in plasma of ABCA1-/-mice, decreased PLTP protein levels were observed. Neither PLTP synthesis in liver or macrophages nor the ability of the macrophages to secrete PLTP were impaired in ABCA1-/-mice. However, the PLTP activity level in the medium of cultured macrophages was determined by HDL levels in the medium. PLTP was associated with HDL particles in wild type mice, whereas in ABCA1-/-mice, PLTP was associated with VLDL and LDL particles. Secondly, we treated different mouse models with varying plasma HDL and PLTP levels (wild type, ABCA1-/-, apoE-/-and PLTPtg mice, overexpressing human PLTP) with a synthetic LXR ligand, and investigated the relationship between LXR-mediated PLTP induction and HDL levels in plasma. Plasma PLTP activity in wild type mice was induced 5.6-fold after LXR activation, whereas in ABCA1-/-, apoE-/-and PLTPtg mice, all having reduced HDL levels, induction of PLTP activity was 2.4-, 3.2- and 2.0-fold, respectively. The less pronounced PLTP induction in these mice compared to wild type mice was not caused by a decreased PLTP gene expression in the liver or macrophages. Our findings indicate that the extent of LXR-mediated PLTP induction depends on plasma HDL levels. In conclusion, we demonstrate that ABCA1 deficiency in mice affects plasma PLTP level and distribution through an indirect effect on HDL metabolism. In addition, we show that the extent of LXR-mediated PLTP induction is HDL-dependent. These findings indicate that plasma HDL level is an important regulator of plasma PLTP and might play a role in the stabilization of PLTP in plasma.

Elevation of systemic PLTP, but not macrophage-PLTP, impairs macrophage reverse cholesterol transport in transgenic mice (Article)

2009-06-01T00:00:00Z

Phospholipid transfer protein (PLTP) is a multifunctional protein synthesized by various cell types and secreted into the plasma. Plasma PLTP is able to transfer phospholipids between lipoproteins and modulate HDL particles. Mice with overexpression of human PLTP have an increased ability to generate preβ-HDL, reduced total HDL levels and an increased susceptibility to atherosclerosis. As the macrophage is a key component of the atherosclerotic lesion and an important site of PLTP expression, we investigated the role of systemic and peripheral PLTP in macrophage cholesterol efflux and reverse cholesterol transport (RCT) in vivo. We used an assay in which3H-labelled cholesterol-loaded macrophages were injected intraperitoneally into recipient mice, and radioactivity was quantified in plasma, liver and faeces. Firstly, wild type macrophages were injected into wild type, PLTP transgenic (PLTPtg) and apoAI transgenic (apoAItg) mice. While plasma3H-tracer levels in apoAItg mice were increased compared with wild type mice, they were reduced in PLTPtg mice. Moreover, overexpression of PLTP significantly decreased faecal3H-tracer levels compared with wild type and apoAItg mice. Secondly, wild type mice were injected with peritoneal macrophages derived from PLTPtg or wild type mice. No significant difference in the amount of3H-tracer in plasma, liver or faeces was found between the two groups of mice. Our findings demonstrate that macrophage cholesterol efflux and RCT to faeces is impaired in PLTP transgenic mice, and that elevation of macrophage-PLTP does not affect RCT, indicating that higher systemic PLTP levels may promote atherosclerosis development by decreasing the rate of macrophage RCT.

Serum paraoxonase-I activity is unaffected by short-term administration of simvastatin, bezafibrate, and their combination in type 2 diabetes mellitus (Article)

2009-03-01T00:00:00Z

Background: The high-density lipoprotein (HDL)-associated anti-oxidative and anti-inflammatory enzyme, paraoxonase-I, has been found previously to be lower in type 2 diabetes mellitus. We studied whether statin and fibrate treatment, alone and in combination, affect serum paraoxonase-I activity in conjunction with changes in HDL cholesterol in diabetic patients. Subjects and methods: A placebo-controlled crossover study was carried out in 14 type 2 diabetic patients to test the effect of 8 weeks of active treatment with simvastatin (40 mg daily), bezafibrate (400 mg daily), and their combination on serum paraoxonase-I activity, measured as its activity towards arylesterase and paraoxon. Serum paraoxonase-I activity was also compared between these diabetic patients and 49 non-diabetic control subjects. Results: Serum arylesterase activity was lower in type 2 diabetic patients compared to control subjects (P < 0·001), but the difference in paraoxonase activity was not significant (P = 0·22). Neither arylesterase (P = 0·24) nor paraoxonase activity (P = 0·37) was increased in response to treatment, despite higher HDL cholesterol and apolipoprotein A-I during combination therapy (P < 0·05 for both). Conclusion: Short-term administration of simvastatin and bezafibrate, even when combined, is ineffective in raising serum paraoxonase-I activity in type 2 diabetes.

Role of plasma adiponectin on the HDL-cholesterol raising effect of atorvastatin in patients with type 2 diabetes. (Article)

2009-01-01T00:00:00Z

OBJECTIVE: Adiponectin, secreted by adipose tissue, plays an important role in lipoprotein metabolism and also affects carbohydrate and insulin pathways. We studied the effects of atorvastatin treatment on plasma adiponectin and high density cholesterol (HDL) levels in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: In the 'Diabetes Atorvastatin Lipid Intervention' (DALI) study, a randomized placebo-controlled study on the effects of atorvastatin treatment in 194 patients with type 2 diabetes and mildly elevated plasma triglycerides, adiponectin levels, lipoproteins, cholesteryl ester transfer protein (CETP) mass, as well as postheparin lipoprotein lipase (LPL) and hepatic lipase (HL) activities were assessed at baseline and after 6 months of treatment (placebo, 10 mg or 80 mg atorvastatin). RESULTS: At baseline, plasma adiponectin levels were positively associated with HDL cholesterol (r = 0.40, p < 0.001), and apoA-I (r = 0.38, p < 0.001) in both males and females. Adiponectin was negatively associated with triglycerides (r = -0.26, p < 0.001) in males as well as in females. Atorvastatin treatment had no effect on plasma adiponectin levels. However, adiponectin levels at baseline significantly predicted the effect of atorvastatin treatment on HDL-cholesterol (p = 0.007), i.e. patients with the highest baseline plasma adiponectin concentration (tertile 3) displayed the largest increase in plasma HDL cholesterol during treatment (8-10%), while the HDL-cholesterol increase in tertile 1 was almost negligible (1-3%). CONCLUSION: In this study, high baseline plasma adiponectin levels significantly affect the HDL-cholesterol response to atorvastatin treatment in patients with type 2 diabetes and therefore may play a role in defining future treatment strategy.

Plasma lecithin: Cholesterol acyltransferase activity is elevated in metabolic syndrome and is an independent marker of increased carotid artery intima media thickness (Article)

2008-12-01T00:00:00Z

Context: Lecithin:cholesterol acyltransferase (LCAT), which esterifies free cholesterol to cholesteryl esters, is required for normal plasma lipoprotein structure and is instrumental in high density lipoprotein (HDL) remodeling, but the relationship of variation in plasma LCAT activity with subclinical atherosclerosis is unclear. Objectives: The aim of the study was to determine the effect of the metabolic syndrome (MetS) on plasma LCAT activity and its relationship with carotid artery intima media thickness (IMT). Setting: The study was conducted at the vascular laboratory of a university medical center. Methods: In 74 subjects with MetS and 90 subjects without MetS (National Cholesterol Education Program Adult Treatment Panel III criteria), mean carotid artery IMT, plasma lipids, LCAT activity (exogenous substrate method), high-sensitive C-reactive protein, and homeostasis model assessment insulin resistance (HOMAir) were documented. Results: IMT was greater (P = 0.01) and plasma LCAT activity was higher (P < 0.001) in subjects with MetS compared to subjects without MetS. Similar increases in IMT and LCAT were found in MetS subjects without type 2 diabetes mellitus. Multiple linear regression analysis demonstrated that plasma LCAT activity was independently and positively related to HOMAir, plasma triglycerides, non-HDL cholesterol, and HDL cholesterol (all P < 0.001). After adjustment for age and sex, IMT was positively associated with LCAT activity (P < 0.01), independently of the presence of MetS (or alternatively of plasma lipids), HOMAir, and high-sensitive C-reactive protein. Conclusions: Plasma LCAT activity is elevated in MetS and may be a marker of subclinical atherosclerosis. Our findings do not support the contention that strategies to elevate LCAT are necessarily beneficial for cardioprotection. Copyright

Plasma phospholipid transfer activity is essential for increased atherogenesis in PLTP transgenic mice: A mutation-inactivation study (Article)

2008-12-01T00:00:00Z

Plasma phospholipid transfer protein (PLTP) interacts with HDL particles and facilitates the transfer of phospholipids from triglyceride (TG)-rich lipoproteins to HDL. Overexpressing human PLTP in mice increases the susceptibility to atherosclerosis. In human plasma, high-active and low-active forms of PLTP exist. To elucidate the contribution of phospholipid transfer activity to changes in lipoprotein metabolism and atherogenesis, we developed mice expressing mutant PLTP, still able to associate with HDL but lacking phospholipid transfer activity. In mice heterozygous for the LDL receptor, effects of the mutant and normal human PLTP transgene (mutPLTP tg and PLTP tg, respectively) were compared. In PLTP tg mice, plasma PLTP activity was increased 2.9-fold, resulting in markedly reduced HDL lipid levels. In contrast, in mutPLTP tg mice, lipid levels were not different from controls. Furthermore, hepatic VLDL-TG secretion was stimulated in PLTP tg mice, but not in mutPLTP tg mice. When mice were fed a cholesterol-enriched diet, atherosclerotic lesion size in PLTP tg mice was increased more than 2-fold compared with control mice, whereas in mutPLTP tg mice, there was no change. Our findings demonstrate that PLTP transfer activity is essential for the development of atherosclerosis in PLTP transgenic mice, identifying PLTP activity as a possible target to prevent atherogenesis, independent of plasma PLTP concentration. Copyright

Acute elevation of plasma PLTP activity strongly increases pre-existing atherosclerosis (Article)

2008-07-01T00:00:00Z

Objective - A transgenic mouse model was generated that allows conditional expression of human PLTP, based on the tetracycline-responsive gene system, to study the effects of an acute increase in plasma PLTP activity as may occur in inflammation. Methods and Results - The effects of an acute elevation of plasma PLTP activity on the metabolism of apolipoprotein B-containing lipoproteins and on diet-induced pre-existing atherosclerosis were determined in mice displaying a humanized lipoprotein profile (low-density lipoprotein receptor knockout background). Induced expression of PLTP strongly increases plasma VLDL levels in LDL receptor knockout mice, whereas VLDL secretion is not affected. The elevation in plasma triglyceride levels is explained by a PLTP-dependent inhibition of VLDL catabolism, which is caused, at least partly, by a decreased lipoprotein lipase activity. Together with the decreased plasma HDL levels, the acutely increased PLTP expression results in a highly atherogenic lipoprotein profile. Induction of PLTP expression leads to a further increase in size of pre-existing atherosclerotic lesions, even on a chow diet. In addition, the lesions contain more macrophages and less collagen relative to controls, suggesting a less stable lesion phenotype. Conclusion - In conclusion, acute elevation of PLTP activity destabilizes atherosclerotic lesions and aggravates pre-existing atherosclerosis.

Elevated expression of phospholipid transfer protein in bone marrow derived cells causes atherosclerosis (Article)

2008-05-28T00:00:00Z

Background: Phospholipid transfer protein (PLTP) is expressed by various cell types. In plasma, it is associated with high density lipoproteins (HDL). Elevated levels of PLTP in transgenic mice result in decreased HDL and increased atherosclerosis. PLTP is present in human atherosclerosis lesions, where it seems to be macrophage derived. The aim of the present study is to evaluate the atherogenic potential of macrophage derived PLTP. Methods and Findings: Here we show that macrophages from human PLTP transgenic mice secrete active PLTP. Subsequently, we performed bone marrow transplantations using either wild type mice (PLTPwt/wt), hemizygous PLTP transgenic mice (huPLTPtg/wt) or homozygous PLTP transgenic mice (huPLTPtg/tg) as donors and low density lipoprotein receptor deficient mice (LDLR-/-) as acceptors, in order to establish the role of PLTP expressed by bone marrow derived cells in diet-induced atherogenesis. Atherosclerosis was increased in the huPLTPtg/wt → LDLR-/ - mice (2.3-fold) and even further in the huPLTPtg/tg→LDLR-/ - mice (4.5-fold) compared with the control PLTPwt/wt→LDLR-/- mice (both P<0.001). Plasma PLTP activity levels and non-HDL cholesterol were increased and HDL cholesterol decreased compared with controls (all P<0.01). PLTP was present in atherosclerotic plaques in the mice as demonstrated by immunohistochemistry and appears to co-localize with macrophages. Isolated macrophages from PLTP transgenic mice do not show differences in cholesterol efflux or in cytokine production. Lipopolysaccharide activation of macrophages results in increased production of PLTP. This effect was strongly amplified in PLTP transgenic macrophages. Conclusions: We conclude that PLTP expression by bone marrow derived cells results in atherogenic effects on plasma lipids, increased PLTP activity, high local PLTP protein levels in the atherosclerotic lesions and increased atherosclerotic lesion size.

Phospholipid transfer protein activity is determined by type 2 diabetes mellitus and metabolic syndrome, and is positively associated with serum transaminases (Article)

2008-03-01T00:00:00Z

Background: The extent to which plasma phospholipid transfer protein (PLTP) activity is affected by type 2 diabetes mellitus (DM) and metabolic syndrome (MetS) is still unknown. PLTP is synthesized in the liver, and elevated serum transaminases are considered to predict nonalcoholic fatty liver disease (NAFLD). In this study, we examined the relationship between plasma PLTP activity and liver enzymes in subjects with and without DM and MetS. Design: Plasma PLTP activity, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured in 71 subjects without DM or MetS, 21 without DM but with MetS, 26 with DM but without MetS and 55 with DM and MetS (WHO and NCEP-ATP III criteria). Results: After controlling for age, sex and alcohol intake, PLTP activity was positively related to both MetS (P < 0.001) and DM (P = 0.001). Serum ALT (P = 0.006) and AST (P = 0.04) were both associated with MetS, but only ALT was associated with DM (P < 0.001). In multiple linear regression models, serum ALT and AST were positively and independently associated with PLTP activity (P < 0.01 for all), even when the presence of MetS and DM was taken into account, as well as after controlling for glycated haemoglobin (HbA1c), insulin resistance, triglycerides, free fatty acids (FFA), C-reactive protein (CRP), leptin and adiponectin. Conclusions: Plasma PLTP activity is determined by MetS and by diabetes per se. Serum transaminases are independently associated with PLTP activity. We suggest that this lipid transfer protein may be a marker for NAFLD.

Increased cholesterol efflux from cultured fibroblasts to plasma from hypertriglyceridemic type 2 diabetic patients: Roles of pre β-HDL, phospholipid transfer protein and cholesterol esterification (Article)

2008-02-01T00:00:00Z

We tested whether hypertriglyceridemia associated with type 2 diabetes mellitus is accompanied by alterations in pre β-HDL, which are considered to be initial acceptors of cell-derived cholesterol, and by changes in the ability of plasma to promote cellular cholesterol efflux. In 28 hypertriglyceridemic and 56 normotriglyceridemic type 2 diabetic patients, and in 56 control subjects, we determined plasma lipids, HDL cholesterol and phospholipids, plasma pre β-HDL and pre β-HDL formation, phospholipid transfer protein (PLTP) activity, plasma cholesterol esterification (EST) and cholesteryl ester transfer (CET) and the ability of plasma to stimulate cholesterol efflux out of cultured human fibroblasts. HDL cholesterol and HDL phospholipids were lower, whereas plasma PLTP activity, EST and CET were higher in hypertriglyceridemic diabetic patients than in the other groups. Pre β-HDL levels and pre β-HDL formation were unaltered, although the relative amount of pre β-HDL (expressed as % of total plasma apo A-I) was increased in hypertriglyeridemic diabetic patients. Cellular cholesterol efflux to plasma from hypertriglyceridemic diabetic patients was increased compared to efflux to normotriglyceridemic diabetic and control plasma, but efflux to normotriglyceridemic diabetic and control plasma did not differ. Multiple linear regression analysis demonstrated that cellular cholesterol efflux to plasma was positively and independently related to pre β-HDL formation, PLTP activity and EST (multiple r = 0.48), but not to the diabetic state. In conclusion, cholesterol efflux from fibroblasts to normotriglyceridemic diabetic plasma is unchanged. Efflux to hypertriglyceridemic diabetic plasma is enhanced, in association with increased plasma PLTP activity and cholesterol esterification. Unaltered pre β-HDL formation in diabetic hypertriglyceridemia, despite low apo A-I, could contribute to maintenance of cholesterol efflux.

Fibroblast cholesterol efflux to plasma from metabolic syndrome subjects is not defective despite low high-density lipoprotein cholesterol (Article)

2008-01-01T00:00:00Z

Objective: We tested whether in metabolic syndrome (MetS) subjects the ability of plasma to stimulate cellular cholesterol efflux, an early step in the anti-atherogenic reverse cholesterol transport pathway, is maintained despite low high-density lipoprotein (HDL) cholesterol. Design: In 76 subjects with and 94 subjects without MetS based on the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) criteria, we determined plasma (apo)lipoproteins, pre-β-HDL formation, phospholipid transfer protein (PLTP) activity, cholesterol esterification (EST), cholesteryl ester transfer (CET), adiponectin, and the ability of plasma from each subject to stimulate cholesterol efflux out of cultured fibroblasts obtained from a single donor. Results: Apo E, PUP activity EST, and CET were higher (P = 0.04 to < 0.001), whereas adiponectin was lower in MetS subjects (P < 0.01). Pre-β-HDL and pre-β-HDL formation were not different between subjects with and without MetS. Cellular cholesterol efflux to plasma from MetS subjects was slightly higher versus plasma from subjects without MetS (8.8 ± 1.0 vs 8.5 ± 0.9%, P=0.05), but the difference was not significant after age, sex, and diabetes adjustment. Cellular cholesterol efflux was positively related to pre-β-HDL formation, EST, PLTP activity, and apo E (P < 0.05 for all by multiple linear regression analysis), without an independent association with MetS and diabetes status. Conclusions: The ability of plasma from MetS subjects to promote fibroblast cholesterol efflux is not defective, although HDL cholesterol is decreased. Higher cholesterol esterification, PLTP activity, and apo E levels may contribute to the maintenance of cholesterol efflux in MetS.

The ability of plasma to stimulate fibroblast cholesterol efflux is associated with the - 629C→A cholesteryl ester transfer protein promoter polymorphism: Role of lecithin:cholesterol acyltransferase activity (Article)

2008-01-01T00:00:00Z

A recent population-based study showed that cholesteryl ester transfer protein (CETP) gene variations, which relate to lower plasma CETP, may predict increased cardiovascular risk, in spite of higher HDL cholesterol. Among other functions, CETP activity contributes to cellular cholesterol efflux, an early step in the anti-atherogenic reverse cholesterol transport (RCT) process. We hypothesized that cellular cholesterol efflux stimulating capacity of plasma could be associated with CETP gene variation. In this study, we tested the extent to which the ability of plasma to promote cholesterol efflux from cultured human fibroblasts is associated with CETP gene variation. In 223 men, the - 629C→A CETP promoter polymorphism, plasma lipids, CETP mass, cholesteryl ester transfer (CET), lecithin:cholesterol acyltransferase (LCAT) activity and the ability of plasma to promote cholesterol efflux from human skin fibroblasts, obtained from a single normolipidemic donor, were determined. In - 629CC homozygotes (n = 52), cholesterol efflux, plasma CETP mass, CET and LCAT activity were higher, whereas HDL cholesterol was lower compared to - 629 AA homozygotes (n = 62) and - 629CA + AA carriers (n = 171) (P < 0.05 to P < 0.001). Univariate correlation analysis showed that cellular cholesterol efflux was related to CETP genotype (P = 0.04), plasma CET (P<0.05), LCAT activity (P < 0.001) and apo A-I (P < 0.05). Multiple linear regression analysis confirmed the independent association of cellular cholesterol efflux to plasma with CETP genotype. In conclusion, an association of cellular cholesterol efflux with the - 629C→A CETP polymorphism, possibly also involving LCAT activity, could provide a mechanism explaining why CETP gene variation, which relates to lower plasma CETP, does not confer diminished cardiovascular risk.

Large variations in absolute wall shear stress levels within one species and between species (Article)

2007-12-01T00:00:00Z

Wall shear stress (WSS), the frictional force between blood and endothelium, is an important determinant of vascular function. It is generally assumed that WSS remains constant at a reference value of 15 dyn/cm2. In a study of small rodents, we realized that this assumption could not be valid. This review presents an overview of recent studies in large and small animals where shear stress was measured, derived from velocity measurements or otherwise, in large vessels. The data show that large variations exist within a single species (human: variation of 2-16 N/m2). Moreover, when we compared different species at the same location within the arterial tree, an inverse relationship between animal size and wall shear stress was noted. When we related WSS to diameter, a unique relationship was derived for all species studied. This relationship could not be described by the well-known r3law of Murray, but by the r2law introduced by Zamir et al. in 1972. In summary, by comparing data from the literature, we have shown that: (i) the assumption of a physiological WSS level of ∼15 dyn/cm2for all straight vessels in the arterial tree is incorrect; (ii) WSS is not constant throughout the vascular tree; (iii) WSS varies between species; (iv) WSS is inversely related to the vessel diameter. These data support an "r2law" rather than Murray's r3law for the larger vessels in the arterial tree.

Atherogenic, enlarged, and dysfunctional HDL in human PLTP/apoA-I double transgenic mice (Article)

2007-12-01T00:00:00Z

In low density lipoprotein receptor (LDLR)-deficient mice, overexpression of human plasma phospholipid transfer protein (PLTP) results in increased atherosclerosis. PLTP strongly decreases HDL levels and might alter the antiatherogenic properties of HDL particles. To study the potential interaction between human PLTP and apolipoprotein A-I (apoA-I), double transgenic animals (hPLTPtg/hApoAItg) were compared with hApoAItg mice. PLTP activity was increased 4.5-fold. Plasma total cholesterol and phospholipid were decreased. Average HDL size (analyzed by gel filtration) increased strongly, hPLTPtg/hApoAItg mice having very large, LDL-sized, HDL particles. Also, after density gradient ultracentrifugation, a substantial part of the apoA-I-containing lipoproteins in hPLTPtg/hApoAItg mice was found in the LDL density range. In cholesterol efflux studies from macrophages, HDL isolated from hPLTPtg/hApoAItg mice was less efficient than HDL isolated from hApoAItg mice. Furthermore, it was found that the largest subfraction of the HDL particles present in hPLTPtg/hApoAItg mice was markedly inferior as a cholesterol acceptor, as no labeled cholesterol was transferred to this fraction. In an LDLR-deficient background, the human PLTP-expressing mouse line showed a 2.2-fold increased atherosclerotic lesion area. These data demonstrate that the action of human PLTP in the presence of human apoA-I results in the formation of a dysfunctional HDL subfraction, which is less efficient in the uptake of cholesterol from cholesterol-laden macrophages. Copyright

Appraisal of hepatic lipase and lipoprotein lipase activities in mice (Article)

2007-12-01T00:00:00Z

A variety of methods are currently used to analyze HL and LPL activities in mice. In search of a simple methodology, we analyzed mouse preheparin and postheparin plasma LPL and HL activities using specific polyclonal antibodies raised in rabbit against rat HL (anti-HL) and in goat against rat LPL (anti-LPL). As an alternative, we analyzed HL activity in the presence of 1 M NaCl, a condition known to inhibit LPL activity in humans. The assays were validated using plasma samples from wild-type and HL-deficient C57BL/6 mice. We now show that the use of 1 M NaCl for the inhibition of plasma LPL activity in mice may generate incorrect measurements of both LPL and HL activities. Our data indicate that HL can be measured directly, without heparin injection, in preheparin plasma, because virtually all HL is present in an unbound form circulating in plasma. In contrast, measurable LPL activity is present only in postheparin plasma. Both HL and LPL can be measured using the same assay conditions (low salt and the presence of apolipoprotein C-II as an LPL activator). Total lipase activity in postheparin plasma minus preheparin HL activity reflects LPL activity. Specific antibodies are not required. Copyright

Alterations in lipoprotein homeostasis during human experimental endotoxemia and clinical sepsis (Article)

2007-12-01T00:00:00Z

Cell wall constituents of bacteria are potent endotoxins initiating inflammatory responses which may cause dramatic changes in lipid metabolism during the acute phase response. In this study, the sequential changes in lipoprotein composition and lipid transfer and binding proteins during clinical sepsis and during low-dose experimental endotoxemia were followed. In addition, the effect on (phospho)lipid homeostasis by administration of reconstituted HDL (rHDL) prior to low-dose LPS administration was investigated. Changes in (apo)lipoprotein concentrations typical of the acute phase response were observed during clinical sepsis and experimental endotoxemia with and without the rHDL intervention. During clinical sepsis negative correlations between the acute phase marker C-reactive protein (CRP) and lecithin:cholesterol acyltransferase (LCAT) and cholesterylester transfer protein (CETP) activities were seen, whereas positive correlations between plasma phospholipid transfer protein (PLTP) activity and acute phase markers such as CRP and LPS binding protein were observed. Plasma lipid changes upon rHDL/LPS infusion were comparable with the control group (low-dose LPS only). PLTP activity decreased upon LPS infusion and transiently increased during rHDL infusion, whereas LCAT activity slightly decreased upon both LPS infusion and LPS/rHDL infusion. However, long-lasting increases of circulating HDL cholesterol, apo A-I and a high initial processing of both phosphatidylcholine (PC) and lyso-PC, were indicative for extensive rHDL and LDL remodelling. Both sepsis and experimental endotoxemia lead to a disbalance of lipid homeostasis. Depending on the magnitude of the inflammatory stimulus, LCAT and PLTP activities reacted in divergent ways. rHDL infusion did not prevent the lipid alterations seen during the acute phase response. However profound changes in both HDL and LDL phospholipid composition occurred upon rHDL infusion. This may be explained, at least in part, by the fact that PLTP as a positive acute phase protein, can accelerate the alterations in (phospho)lipid homeostasis thereby playing a role in the attenuation of the acute phase response.

Effect of rosuvastatin versus atorvastatin treatment on paraoxonase-1 activity in men with established cardiovascular disease and a low HDL-cholesterol (Article)

2007-09-01T00:00:00Z

Objective: Paraoxonase-1 (PON-1) is a high-density lipoprotein (HDL) associated enzyme involved in the protective mechanisms of HDL. Our aim was to compare the effect of treatment with rosuvastatin and atorvastatin on serum PON-1 activity. Methods: We performed a prespecified prospective study in 68 patients, part of a larger, multicentre randomized study - RADAR (Rosuvastatin and Atorvastatin in different Dosages And Reverse cholesterol transport). Patients aged 40-80 years, all men, with established cardiovascular disease and high-density lipoprotein cholesterol (HDL-C) < 1.0 mmol/L (< 40 mg/dL) entered a 6-week dietary run-in period before receiving treatment with rosuvastatin 10 mg or atorvastatin 20 mg daily for 6 weeks. Doses were increased after 6 weeks to rosuvastatin 20 mg or atorvastatin 40 mg and after 12 weeks to rosuvastatin 40 mg or atorvastatin 80 mg daily. Serum PON-1 activity and lipid profile were determined at baseline, 6 and 18 weeks. Results: After 18 weeks, the rosuvastatin arm showed a significant increase of PON-1 activity (6.39 U/L, p = 0.02) whereas this was not observed in the atorvastatin arm (1.84 U/L, p = 0.77). The difference between groups did not reach significance (p = 0.11). Both rosuvastatin and atorvastatin resulted in significant (p = 0.0001) and similar increases in HDL-C after 6 weeks [0.06 mmol/L (2.32 mg/dL) vs. 0.05 mmol/L (1.93 mg/dL)] and after 18 weeks [0.10 mmol/L (3.87 mg/dL) vs. 0.10 mmol/L (3.87 mg/dL)]. Conclusions: Rosuvastatin treatment resulted in a significant increment of serum PON-1 activity with increasing dose while this was not observed with atorvastatin.

Plasma phospholipid transfer protein activity, a determinant of HDL kinetics in vivo [1] (Article)

2007-08-01T00:00:00Z

Inducible expression of phospholipid transfer protein (PLTP) in transgenic mice: Acute effects of PLTP on lipoprotein metabolism (Article)

2007-08-01T00:00:00Z

One main determinant in high-density lipoprotein (HDL) metabolism is phospholipid transfer protein (PLTP), a plasma protein that is associated with HDL. In transgenic mice overexpressing human PLTP we found that elevated plasma PLTP levels dose-dependently increased the susceptibility to diet-induced atherosclerosis. This could be mainly due to the fact that most functions of PLTP are potentially atherogenic, such as decreasing plasma HDL levels. To further elucidate the role of PLTP in lipoprotein metabolism and atherosclerosis we generated a novel transgenic mouse model that allows conditional expression of human PLTP. In this mouse model a human PLTP encoding sequence is controlled by a Tet-On system. Upon induction of PLTP expression, our mouse model showed a strongly increased PLTP activity (from 3.0 ± 0.6 to 11.4 ± 2.8 AU, p < 0.001). The increase in PLTP activity resulted in an acute decrease in plasma cholesterol of 33% and a comparable decrease in phospholipids. The decrease in total plasma cholesterol and phospholipids was caused by a 35% decrease in HDL-cholesterol level and a 41% decrease in HDL-phospholipid level. These results demonstrate the feasibility of our mouse model to induce an acute elevation of PLTP activity, which is easily reversible. As a direct consequence of an increase in PLTP activity, HDL-cholesterol and HDL-phospholipid levels strongly decrease. Using this mouse model, it will be possible to study the effects of acute elevation of PLTP activity on lipoprotein metabolism and pre-existing atherosclerosis.

Plasma apoAV levels are markedly elevated in severe hypertriglyceridemia and positively correlated with the APOA5 S19W polymorphism (Article)

2007-07-01T00:00:00Z

Objective: The recently discovered apoAV is hypothesized to affect triglyceride metabolism by stimulating the lipolysis of triglycerides in VLDL and chylomicrons. We set out to determine the association between increased serum TG levels, plasma apoAV levels, and polymorphism of the APOA5 gene, with specific emphasis on the APOA5 S19W variation. This mutation alters the endoplasmic reticulum signal peptide and is hypothesized to impair apoAV secretion into the circulation. Methods and results: Two haplotype-tagging APOA5 polymorphisms, APOA5 S19W and APOA5 -1131T > C and plasma apoAV levels were determined in a population of patients with severe hypertriglyceridemia (HTG). As compared to a random control population, the allele frequencies of the APOA5 S19W and -1131T > C rare variants were significantly increased in HTG patients. Furthermore, the HTG population exhibited markedly elevated plasma apoAV levels that were positively correlated with serum TG levels. Plasma apoAV levels were positively correlated with occurrence of the APOA5 S19W rare variant. Conclusions: The increased allele frequencies of the APOA5 S19W and -1131T > C rare variants in the HTG population are in agreement with previous reports. Our data show a positive correlation between apoAV and TG levels. Moreover the finding of a positive association between apoAV levels and the APOA5 S19W rare variant is in disagreement with the hypothesis that this variant is poorly secreted.

Concerted actions of cholesteryl ester transfer protein and phospholipid transfer protein in type 2 diabetes: Effects of apolipoproteins (Article)

2007-06-01T00:00:00Z

PURPOSE OF REVIEW: Type 2 diabetes frequently coincides with dyslipidemia, characterized by elevated plasma triglycerides, low high-density lipoprotein cholesterol levels and the presence of small dense low-density lipoprotein particles. Plasma lipid transfer proteins play an essential role in lipoprotein metabolism. It is thus vital to understand their pathophysiology and determine which factors influence their functioning in type 2 diabetes. RECENT FINDINGS: Cholesteryl ester transfer protein-mediated transfer is increased in diabetic patients and contributes to low plasma high-density lipoprotein cholesterol levels. Apolipoproteins A-I, A-II and E are components of the donor lipoprotein particles that participate in the transfer of cholesteryl esters from high-density lipoprotein to apolipoprotein B-containing lipoproteins. Current evidence for functional roles of apolipoproteins C-I, F and A-IV as modulators of cholesteryl ester transfer is discussed. Phospholipid transfer protein activity is increased in diabetic patients and may contribute to hepatic very low-density lipoprotein synthesis and secretion and vitamin E transfer. Apolipoprotein E could stimulate the phospholipid transfer protein-mediated transfer of surface fragments of triglyceride-rich lipoproteins to high-density lipoprotein, and promote high-density lipoprotein remodelling. SUMMARY: Both phospholipid and cholesteryl ester transfer proteins are important in very low and high-density lipoprotein metabolism and display concerted actions in patients with type 2 diabetes.

High plasma cholesteryl ester transfer protein levels may favour reduced incidence of cardiovascular events in men with low triglycerides (Article)

2007-04-01T00:00:00Z

Aims: High cholesteryl ester transfer protein (CETP) concentrations are associated with increased risk of cardiovascular disease (CVD) in subjects with high triglycerides. We determined the relationship of plasma CETP with incident CVD in a population with relatively low triglycerides. Methods and results: A nested case-control study was performed in men participating in the prospective PREVEND study, after exclusion of CVD, diabetes mellitus, and lipid-lowering drugs use at baseline. Plasma CETP was measured in 111 men who developed a cardiovascular event (cases) during follow-up and in 116 controls who remained free of CVD. Fasting total cholesterol (P < 0.001) and triglycerides (P < 0.001) were higher, HDL cholesterol was lower (P = 0.001), but CETP was similar in cases and controls (P = 0.39). Cox proportional hazards regression analysis showed that CVD risk tended to be lower with higher plasma CETP after adjustment for age and lipids (hazard ratio 0.84; 95% CI 0.69-1.03, P = 0.10). Plasma CETP was lower in cases than in controls (P = 0.05) with triglycerides ≤ 1.38 mmol/L (median), but not with higher triglycerides. The age-adjusted hazard ratio for CVD was 0.46 (95% CI 0.24-0.90) in men with triglycerides ≤ 1.38 mmol/L and CETP > 2.26 mg/L (median) compared with men with similarly low triglycerides and CETP ≤ 2.26 mg/L. With higher triglycerides, the hazard ratio for CVD was similar in both CETP categories. Conclusion: Relatively high plasma CETP may favour reduced CVD risk in the context of low triglycerides.

Corrigendum to "Plasma cholesteryl ester transfer protein mass and phospholipid transfer protein activity are associated with leptin in type 2 diabetes mellitus" [Biochim. Biophys. Acta 1771 (2007) 113-118] (DOI:10.1016/j.bbalip.2006.11.003) (Article)

2007-04-01T00:00:00Z

Cholesteryl ester transfer protein and hyperalphalipoproteinemia in Caucasians (Article)

2007-03-01T00:00:00Z

It is unclear whether cholesteryl ester transfer protein (CETP) contributes to high density lipoprotein cholesterol (HDL-C) levels in hyperalphalipoproteinemia (HALP) in Caucasians. Moreover, even less is known about the effects of hereditary CETP deficiency in non-Japanese. We studied 95 unrelated Caucasian individuals with HALP. No correlations between CETP concentration or activity and HDL-C were identified. Screening for CETP gene defects led to the identification of heterozygosity for a novel splice site mutation in one individual. Twenty-five heterozygotes for this mutation showed reduced CETP concentration (-40%) and activity (-50%) and a 35% increase of HDL-C compared with family controls. The heterozygotes presented with an isolated high HDL-C, whereas the remaining subjects exhibited a typical high HDL-C/low-triglyceride phenotype. The increase of HDL-C in the CETP-deficient heterozygotes was primarily attributable to increased high density lipoprotein containing apolipoprotein A-I and A-II (LpAI:AII) levels, contrasting with an increase in both high density lipoprotein containing apolipoprotein A-I only and LpAI:AII in the other group. This study suggests the absence of a relationship between CETP and HDL-C levels in Caucasians with HALP. The data furthermore indicate that genetic CETP deficiency is rare among Caucasians and that this disorder presents with a phenotype that is different from that of subjects with HALP who have no mutation in the CETP gene. Copyright

CETP inhibition in cardiovascular risk management: A critical appraisal (Article)

2007-02-01T00:00:00Z

In view of the cardioprotective effect of high-density lipoproteins (HDL) and the limited effects of statin and fibrate therapy on HDL cholesterol, it is clinically relevant to test whether pharmacological treatment aimed at raising HDL lowers cardiovascular risk. Cholesteryl ester transfer protein (CETP) is a new therapeutic target, because the cholesteryl ester transfer process lowers HDL cholesterol and contributes to an atherogenic lipoprotein profile, particularly when plasma triglycerides are high. Clinical evidence suggests that coronary artery calcification as well as intima media thickness is positively related to plasma cholesteryl ester transfer, and that high plasma CETP concentration is associated with increased cardiovascular risk in hypertriglyceridaemia. However, CETP could also have anti-atherogenic potential, since it provides a potentially beneficial route for delivery of HDL-derived cholesteryl esters to the liver. In addition, CETP could also favourably stimulate peripheral cell cholesterol removal and enhance hepatic cholesterol uptake. Recent evidence suggests that a high CETP level may confer lower cardiovascular risk in the context of low triglycerides. At maximal doses, the CETP inhibitors JTT-705 and torcetrapib elicit a marked rise in HDL cholesterol of up to 34% and 91-106%, respectively. The effectiveness of these drugs on (intermediate) clinical outcome measures is currently being tested in large-scale phase III clinical trials, with torcetrapib being only evaluated in combination therapy with atorvastatin. When and how to use CETP inhibitors, e.g. in combination with a statin or a fibrate, is a major challenge. We propose that low HDL cholesterol in the context of high triglycerides, such as found in type 2 diabetes mellitus, could become an important indication area for this new class of drugs.

Plasma cholesteryl ester transfer protein mass and phospholipid transfer protein activity are associated with leptin in type 2 diabetes mellitus (Article)

2007-01-01T00:00:00Z

Adipose tissue contributes to plasma levels of lipid transfer proteins and is also the major source of plasma adipokines. We hypothesized that plasma cholesteryl ester transfer protein (CETP) mass, phospholipid transfer protein (PLTP) activity and cholesteryl ester transfer (CET, a measure of CETP action) are determined by adipokine levels. In this study, relationships of plasma CETP mass, PLTP activity and CET with leptin, resistin and adiponectin were analyzed in type 2 diabetic patients and control subjects. Plasma PLTP activity (P < 0.001), CET (P < 0.001), leptin (P = 0.003), resistin (P < 0.001), high sensitive C-reactive protein (P = 0.005), and insulin resistance (HOMAir) (P < 0.001) were higher, whereas HDL cholesterol (P < 0.001) and plasma adiponectin (P < 0.001) were lower in 83 type 2 diabetic patients (32 females) than in 83 sex-matched control subjects. Multiple linear regression analysis demonstrated that in diabetic patients plasma leptin levels were related to plasma CETP mass (P = 0.018) and PLTP activity (P < 0.001), but not to the other adipokines measured. Plasma CET was inversely correlated with adiponectin in univariate analysis, but this association disappeared in multivariate models that included plasma lipids and CETP. In conclusion, both plasma CETP mass and PLTP activity are associated with plasma leptin in type 2 diabetes. The elevated CET in these patients is not independently related to any of the measured plasma adipokines.

Elevation of plasma phospholipid transfer protein increases the risk of atherosclerosis despite lower apolipoprotein B-containing lipoproteins. (Article)

2004-05-01T00:00:00Z

Plasma phospholipid transfer protein (PLTP) transfers phospholipids between lipoproteins and mediates HDL conversion. PLTP-overexpressing mice have increased atherosclerosis. However, mice do not express cholesteryl ester transfer protein (CETP), which is involved in the same metabolic pathways as PLTP. Therefore, we studied atherosclerosis in heterozygous LDL receptor-deficient (LDLR(+/-)) mice expressing both human CETP and human PLTP. We used two transgenic lines with moderately and highly elevated plasma PLTP activity. In LDLR(+/-)/huCETPtg mice, cholesterol is present in both LDL and HDL. Both are decreased in LDLR(+/-)/huCETPtg/huPLTPtg mice (>50%). An atherogenic diet resulted in high levels of VLDL+LDL cholesterol. PLTP expression caused a strong PLTP dose-dependent decrease in VLDL and LDL cholesterol (-26% and -69%) and a decrease in HDL cholesterol (-70%). Surprisingly, atherosclerosis was increased in the two transgenic lines with moderately and highly elevated plasma PLTP activity (1.9-fold and 4.4-fold, respectively), indicating that the adverse effect of the reduction in plasma HDL outweighs the beneficial effect of the reduction in apolipoprotein B (apoB)-containing lipoproteins. The activities of the antiatherogenic enzymes paraoxonase and platelet-activating factor acetyl hydrolase were both PLTP dose-dependently reduced ( approximately -33% and -65%, respectively). We conclude that expression of PLTP in this animal model results in increased atherosclerosis in spite of reduced apoB-containing lipoproteins, by reduction of HDL and of HDL-associated antioxidant enzyme activities.

Increased risk of atherosclerosis by elevated plasma levels of phospholipid transfer protein. (Article)

2002-12-13T00:00:00Z

Plasma phospholipid transfer protein (PLTP) is thought to be involved in the remodeling of high density lipoproteins (HDL), which are atheroprotective. It is also involved in the metabolism of very low density lipoproteins (VLDL). Hence, PLTP is thought to be an important factor in lipoprotein metabolism and the development of atherosclerosis. We have overexpressed PLTP in mice heterozygous for the low density lipoprotein (LDL) receptor, a model for atherosclerosis. We show that increased PLTP activity results in a dose-dependent decrease in HDL, and a moderate stimulation of VLDL secretion (

Elevation of plasma phospholipid transfer protein in transgenic mice increases VLDL secretion (Article)

2002-01-01T00:00:00Z

Two lipid transfer proteins are active in human plasma, cholesteryl ester transfer protein (CETP), and phospholipid transfer protein (PLTP). Mice by nature do not express CETP. Additional inactivation of the PLTP gene resulted in reduced secretion of VLDL and subsequently in decreased susceptibility to diet-induced atherosclerosis. The aim of this study is to assess possible effects of differences in PLTP expression on VLDL secretion in mice that are proficient in CETP and PLTP. We compared human CETP transgenic (huCETPtg) mice with mice expressing both human lipid transfer proteins (huCETPtg/huPLTPtg). Plasma cholesterol in huCETPtg mice was 1.5-fold higher compared with huCETPtg/huPLTPtg mice (P < 0.001). This difference was mostly due to a lower HDL level in the huCETPtg/huPLTPtg mice, which subsequently could lead to the somewhat decreased CETP activity and concentration that was found in huCETPtg/huPLTPtg mice (P < 0.05). PLTP activity was 2.8-fold increased in these animals (P < 0.001). The human PLTP concentration was 5 microg/ml. Moderate overexpression of PLTP resulted in a 1.5-fold higher VLDL secretion compared with huCETPtg mice (P < 0.05). The composition of nascent VLDL was similar in both strains. These results indicate that elevated PLTP activity in huCETPtg mice results in an increase in VLDL secretion. In addition, PLTP overexpression decreases plasma HDL cholesterol as well as CETP.

Evaluation of phospholipid transfer protein and cholesteryl ester transfer protein as contributors to the generation of pre beta-high-density lipoproteins (Article)

2001-01-01T00:00:00Z

High-density lipoproteins (HDLs) are considered anti-atherogenic because they mediate peripheral cell cholesterol transport to the liver for excretion and degradation. An important step in this reverse cholesterol-transport pathway is the uptake of cellular cholesterol by a specific subclass of small, lipid-poor apolipoprotein A-I particles designated pre beta-HDL. The two lipid-transfer proteins present in human plasma, cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), have both been implicated in the formation of pre beta-HDL. In order to investigate the relative contribution of each of these proteins, we used transgenic mouse models. Comparisons were made between human CETP transgenic mice (huCETPtg), human PLTP transgenic mice (huPLTPtg) and mice transgenic for both lipid-transfer proteins (huCETPtg/huPLTPtg). These animals showed elevated plasma levels of CETP activity, PLTP activity or both activities, respectively. We evaluated the generation of pre beta-HDL in mouse plasma by immunoblotting and crossed immuno-electrophoresis. Generation of pre beta-HDL was equal in huCETPtg and wild-type mice. In contrast, in huPLTPtg and huCETPtg/huPLTPtg mice, pre beta-HDL generation was 3-fold higher than in plasma from either wild-type or huCETPtg mice. Our findings demonstrate that, of the two plasma lipid-transfer proteins, PLTP rather than CETP is responsible for the generation of pre beta-HDL. These data support the hypothesis of a role for PLTP in the initial stage of reverse cholesterol transport.

Human plasma phospholipid transfer protein increases the antiatherogenic potential of high density lipoproteins in transgenic mice (Article)

2000-01-01T00:00:00Z

Plasma phospholipid transfer protein (PLTP) transfers phospholipids between lipoprotein particles and alters high density lipoprotein (HDL) subfraction patterns in vitro, but its physiological function is poorly understood. Transgenic mice that overexpress human PLTP were generated. Compared with wild-type mice, these mice show a 2.5- to 4.5-fold increase in PLTP activity in plasma. This results in a 30% to 40% decrease of plasma levels of HDL cholesterol. Incubation of plasma from transgenic animals at 37 degrees C reveals a 2- to 3-fold increase in the formation of pre-beta-HDL compared with plasma from wild-type mice. Although pre-beta-HDL is normally a minor subfraction of HDL, it is known to be a very efficient acceptor of peripheral cell cholesterol and a key mediator in reverse cholesterol transport. Further experiments show that plasma from transgenic animals is much more efficient in preventing the accumulation of intracellular cholesterol in macrophages than plasma from wild-type mice, despite lower total HDL concentrations. It is concluded that PLTP can act as an antiatherogenic factor preventing cellular cholesterol overload by generation of pre-beta-HDL.

Effect of growth hormone replacement therapy on plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities in growth hormone-deficient adults (Article)

2000-01-01T00:00:00Z

The effects of growth hormone (GH) replacement on plasma lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP), and phospholipid transfer protein (PLTP), factors involved in high density lipoprotein (HDL) metabolism, are unknown. We carried out a 6 months study in 24 GH-deficient adults who were randomized to placebo (n = 8), low dose GH (1 U daily, n = 8), and high dose GH (2 U daily, n = 8), followed by a 6 months open extension study with high dose GH (1 drop-out). No significant changes in plasma lipoproteins, LCAT, CETP, and PLTP activities, cholesterol esterification (EST) and cholesteryl ester transfer (CET) were observed after placebo. After 6 months of GH (combined data, n = 24), very low + low density lipoprotein (VLDL + LDL) cholesterol (P < 0.05) and apolipoprotein B (P < 0.05) decreased, whereas HDL cholesterol and HDL cholesteryl ester increased (P < 0. 05). Prolonged treatment showed comparable effects. Plasma apolipoprotein A-I and Lp[a] remained unchanged. Plasma LCAT (P < 0. 01) and CETP activities (P < 0.01), as well as EST (P < 0.01) and CET decreased (P < 0.01) after 12 months of GH (n = 15), but PLTP activity did not significantly change. Changes in EST and CET after 12 months of treatment were independently related to changes in plasma LCAT (P = 0.001 and CETP activity (P = 0.01). In conclusion, GH replacement therapy improves the lipoprotein profile in GH-deficient adults. Chronic GH replacement lowers plasma LCAT and CETP activities, contributing to a decrease in cholesterol esterification and cholesteryl ester transfer. These effects may have consequences for HDL metabolism and reverse cholesterol transport.

Influence of insulin sensitivity and the TaqIB cholesteryl ester transfer protein gene polymorphism on plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities and their response to hyperinsulinemia in non-diabetic men (Article)

1999-01-01T00:00:00Z

Lecithin:cholesteryl acyl transferase (LCAT), cholesteryl ester transfer protein (CETP), phospholipid transfer protein (PLTP), and lipoprotein lipases are involved in high density lipoprotein (HDL) metabolism. We evaluated the influence of insulin sensitivity and of the TaqIB CETP gene polymorphism (B1B2) on plasma LCAT, CETP, and PLTP activities (measured with exogenous substrates) and their responses to hyperinsulinemia. Thirty-two non-diabetic men without hyperlipidemia were divided in quartiles of high (Q(1)) to low (Q(4)) insulin sensitivity. Plasma total cholesterol, very low + low density lipoprotein cholesterol, triglycerides, and apolipoprotein (apo) B were higher in Q(4) compared to Q(1) (P < 0.05 for all), whereas HDL cholesterol and apoA-I were lowest in Q(4) (P < 0.05 for both). Plasma LCAT activity was higher in Q(4) than in Q(1) (P < 0. 05) and PLTP activity was higher in Q(4) than in Q(2) (P < 0.05). Insulin sensitivity did not influence plasma CETP activity. Postheparin plasma lipoprotein lipase activity was highest and hepatic lipase activity was lowest in Q(1). Insulin infusion decreased PLTP activity (P < 0.05), irrespective of the degree of insulin sensitivity. The CETP genotype exerted no consistent effects on baseline plasma lipoproteins and LCAT, CETP, and PLTP activities. The decrease in plasma PLTP activity after insulin was larger in B1B1 than in B2B2 homozygotes (P < 0.05). These data suggest that insulin sensitivity influences plasma LCAT, PLTP, lipoprotein lipase, and hepatic lipase activities in men. As PLTP, LCAT, and hepatic lipase may enhance reverse cholesterol transport, it is tempting to speculate that high levels of these factors in association with insulin resistance could be involved in an antiatherogenic mechanism. A possible relationship between the CETP genotype and PLTP lowering by insulin warrants further study.

Induction of adrenal scavenger receptor BI and increased high density lipoprotein-cholesteryl ether uptake by in vivo inhibition of hepatic lipase (Article)

1998-01-01T00:00:00Z

Hepatic lipase (HL) and scavenger receptor type B class I (SR-BI) have both been implicated in high density lipoprotein (HDL)-cholesteryl ester uptake in cholesterol-utilizing tissues. Inactivation of HL by gene-directed targeting in mice results in up-regulation of SR-BI expression in adrenal gland (Wang, N., Weng, W., Breslow, J. L., and Tall, A. R. (1996) J. Biol. Chem. 271, 21001-21004). The net effect on HDL-cholesteryl ester uptake is not known. We determined the impact of acute in vivo inhibition of rat adrenal HL activity by antibodies on SR-BI expression and on human and rat HDL-[3H]cholesteryl ether (CEth) uptake in the adrenal gland. Rat HDL was isolated from rats in which HL activity had been inhibited for 1 h. The rats were studied under basal conditions (not ACTH-treated) and after previous treatment with ACTH for 6 days (ACTH-treated). Intravenous injection of anti-HL resulted in 70% lowering of adrenal HL activity in both conditions which were maintained for at least 8 h. In not ACTH-treated rats, inhibition of adrenal HL increased adrenal SR-BI mRNA (5.2-fold) and mass (1. 6-fold) within 4 h. HL inhibition resulted in 41% and 14% more adrenal accumulation of human HDL-[3H]CEth during 4 and 24 h, respectively. The adrenal uptake of rat HDL-[3H]CEth increased by 68%, 4 h after the antibody injection. ACTH treatment increased total adrenal HL activity from 3.7 +/- 0.5 milliunits to 34.0 +/- 17. 2 milliunits, as well as adrenal SR-BI mRNA from 2.9 +/- 0.7 arbitrary units (A.U.) to 86.8 +/- 41.1 A.U. and SR-BI mass from 7.7 +/- 1.8 A.U. to 63.16 +/- 46.7 A.U. The human HDL-[3H]CEth uptake by adrenals was also significantly increased from 0.58 +/- 0.11% of injected dose to 7.24 +/- 1.58% of injected dose. Inhibition of adrenal HL activity did not result in further induction of SR-BI expression and did not affect human HDL-[3H]CEth uptake. These findings indicate that SR-BI expression may be influenced by changes in HL activity. HL activity is not needed for the SR-BI-mediated HDL-cholesteryl ester uptake by rat adrenal glands.

Hepatic fatty acid oxidation : activity, localization and function of some enzymes involved (Doctoral Thesis)

1971-02-24T00:00:00Z

Fatty acid oxidation is an important pathway for energy production in mammals and birds. In animal tissues the enzymes of fatty acid oxidation are located in the mitochondrion. Recent reports suggest that this is not the case in Castor bean endosperm. In this tissue the enzymes of B-oxidation are localized in a very fragile cell organelle, called the glyoxysomes . Fatty acids are transported in the blood complexed to albumin, or in esterified form as triglycerides and phospholipids, complexed to protein (lipoproteins). Lipoproteins are synthesized in the liverand in the intestinal epithelium (chylomicrons). Before entering the cell these triglycerides are generally hydrolyzed by lipoprotein lipase, an enzyme activated by heparin and probably present in the endothelial cells of the capillary wall. From the foregoing it is evident that fatty acid presented to the cell for further metabolism is in the form of "free" fatty acid. Fatty acids cannot participate in any reaction of intermediary metabolism, before they have been "activated" to their thioester with CoA. This reaction is necessary for triglyceride and phospholipid biosynthesis, for acyl interchange between complex lipids, for chain-elongation reactions and also for oxidative degradation of fatty acids.