Opposite effects of cholesteryl ester transfer protein and phospholipid transfer protein on the size distribution of plasma high density lipoproteins. Physiological relevance in alcoholic patients

New therapeutic horizons for plasma phospholipid transfer protein (PLTP): Targeting endotoxemia, infection and sepsis

Phospholipid Transfer Protein (PLTP) transfers amphiphilic lipids between circulating lipoproteins and between lipoproteins, cells and tissues. Indeed, PLTP is a major determinant of the plasma levels, turnover and functionality of the main lipoprotein classes: very low-density lipoproteins (VLDL), low-density lipoproteins (LDL) and high-density lipoproteins (HDL). To date, most attention has been focused on the role of PLTP in the context of cardiometabolic diseases, with additional insights in neurodegenerative diseases and immunity. Importantly, beyond its influence on plasma triglyceride and cholesterol transport, PLTP plays a key role in the modulation of the immune response, with immediate relevance to a wide range of inflammatory diseases including bacterial infection and sepsis. Indeed, emerging evidence supports the role of PLTP, in the context of its association with lipoproteins, in the neutralization and clearance of bacterial lipopolysaccharides (LPS) or endotoxins. LPS are amphipathic molecules originating from Gram-negative bacteria which harbor major pathogen-associated patterns, triggering an innate immune response in the host. Although the early inflammatory reaction constitutes a key step in the anti-microbial defense of the organism, it can lead to a dysregulated inflammatory response and to hemodynamic disorders, organ failure and eventually death. Moreover, and in addition to endotoxemia and acute inflammation, small amounts of LPS in the circulation can induce chronic, low-grade inflammation with long-term consequences in several metabolic disorders such as atherosclerosis, obesity and diabetes. After an updated overview of the role of PLTP in lipid transfer, lipoprotein metabolism and related diseases, current knowledge of its impact on inflammation, infection and sepsis is critically appraised. Finally, the relevance of PLTP as a new player and novel therapeutic target in the fight against inflammatory diseases is considered.

Healthy adiposity and extended lifespan in obese mice fed a diet supplemented with a polyphenol-rich plant extract

Obesity may not be consistently associated with metabolic disorders and mortality later in life, prompting exploration of the challenging concept of healthy obesity. Here, the consumption of a high-fat/high-sucrose (HF/HS) diet produces hyperglycaemia and hypercholesterolaemia, increases oxidative stress, increases endotoxaemia, expands adipose tissue (with enlarged adipocytes, enhanced macrophage infiltration and the accumulation of cholesterol and oxysterols), and reduces the median lifespan of obese mice. Despite the persistence of obesity, supplementation with a polyphenol-rich plant extract (PRPE) improves plasma lipid levels and endotoxaemia, prevents macrophage recruitment to adipose tissues, reduces adipose accumulation of cholesterol and cholesterol oxides, and extends the median lifespan. PRPE drives the normalization of the HF/HS-mediated functional enrichment of genes associated with immunity and inflammation (in particular the response to lipopolysaccharides). The long-term limitation of immune cell infiltration in adipose tissue by PRPE increases the lifespan through a mechanism independent of body weight and fat storage and constitutes the hallmark of a healthy adiposity trait.

Reconstituted HDL: Drug Delivery Platform for Overcoming Biological Barriers to Cancer Therapy

Drug delivery to malignant tumors is limited by several factors, including off-target toxicities and suboptimal benefits to cancer patient. Major research efforts have been directed toward developing novel technologies involving nanoparticles (NPs) to overcome these challenges. Major obstacles, however, including, opsonization, transport across cancer cell membranes, multidrug-resistant proteins, and endosomal sequestration of the therapeutic agent continue to limit the efficiency of cancer chemotherapy. Lipoprotein-based drug delivery technology, "nature's drug delivery system," while exhibits highly desirable characteristics, it still needs substantial investment from private/government stakeholders to promote its eventual advance to the bedside. Consequently, this review focuses specifically on the synthetic (reconstituted) high-density lipoprotein rHDL NPs, evaluating their potential to overcome specific biological barriers and the challenges of translation toward clinical utilization and commercialization. This highly robust drug transport system provides site-specific, tumor-selective delivery of anti-cancer agents while reducing harmful off-target effects. Utilizing rHDL NPs for anti-cancer therapeutics and tumor imaging revolutionizes the future strategy for the management of a broad range of cancers and other diseases.

The causal effects of alcohol on lipoprotein subfraction and triglyceride levels using a Mendelian randomization analysis: The Nagahama study

BACKGROUND

Light-to-moderate alcohol consumption may increase circulating high-density lipoprotein cholesterol (HDL-C) levels and decrease low-density lipoprotein cholesterol (LDL-C) levels. However, the effect of alcohol on biologically important lipoprotein subfractions remains largely unknown. Here we aimed to clarify the effects of alcohol on lipoprotein subfractions using a Mendelian randomization analysis.

METHODS

The study subjects consisted of 8364 general Japanese individuals. The rs671 polymorphism in aldehyde dehydrogenase 2 gene, a rate-controlling enzyme of alcohol metabolism, was used as an instrumental variable. Lipoprotein subfractions were measured by a homogeneous assay.

RESULTS

The biologically active *1 allele of the ALDH2 genotype was strongly associated with alcohol consumption in men (p < 0.001). In a regression analysis adjusted for possible covariates, the *1 allele was positively associated with HDL-C even in a sub-analysis for HDL subfractions (HDL2-C: β = 0.082, p < 0.001; HDL3-C: β = 0.195, p < 0.001). In contrast, the *1 allele was inversely associated with total LDL-C levels (β = -0.049, p = 0.008), while its association with large-buoyant LDL-C (β = -0.124, p < 0.001) and small-dense LDL-C (β = 0.069, p < 0.001) was opposite. Therefore, the ratio of small-dense LDL to large-buoyant LDL exhibited a linear increase with the number of *1 alleles carried (β = 0.127, p < 0.001). Furthermore, the *1 allele was inversely associated with triglyceride levels in an analysis adjusted for LDL subfractions (β = -0.097, p < 0.001), but not for the total LDL (β = 0.014, p = 0.410).

CONCLUSIONS

Alcohol may increase HDL-C levels irrespective of the particle size. Moreover, alcohol may decrease the total LDL-C, although the proportion of atherogenic small-dense LDL-C increased partially due to a potential inter-relationship with decreased triglyceride levels.

Elevated CETP Activity Improves Plasma Cholesterol Efflux Capacity From Human Macrophages in Women

Objective—

We aim to identify the impact of endogenous cholesteryl ester transfer protein (CETP) activity on plasma capacity to mediate free cholesterol efflux from human macrophages.

Methods and Results—

Endogenous plasma CETP activity was measured in a population of 348 women. We defined a low CETP group corresponding to subjects displaying an endogenous plasma CETP activity within the first tertile and a high CETP group corresponding to subjects with an endogenous plasma CETP activity within the third tertile. Subjects from the high CETP activity group displayed a significant increase in the capacity of their plasma (+8.2%; P =0.001) to mediate cholesterol efflux from human acute monocytic leukemia cell line human macrophages and from ATP-binding cassette transporter A1-dependent pathway (+23.4%; P =0.0001) as compared with those from the low CETP activity group. Multivariate analyses revealed that the impact of CETP activity was independent of plasma lipids levels. Pre–β1-high-density lipoprotein concentrations were significantly elevated (+29.6%; P =0.01) in the high CETP activity group as compared with the low CETP activity group. A positive correlation between pre–β1-high-density lipoprotein levels and plasma efflux efficiency from human acute monocytic leukemia cell line human macrophages was observed ( r =0.29, P =0.02).

Conclusion—

CETP leading to the improvement of plasma efflux capacity, as a result of efficient pre–β-high-density lipoprotein formation and ATP-binding cassette transporter A1 efflux, should be preserved to prevent lipid accumulation in human macrophages.

Common variation in cholesteryl ester transfer protein: relationship of first major adverse cardiovascular events with the apolipoprotein B/apolipoprotein A-I ratio and the total cholesterol/high-density lipoprotein cholesterol ratio

BACKGROUND

The preference of the apolipoprotein (apo) B/apoA-I ratio over the total cholesterol/HDL cholesterol (TC/HDL-C) ratio in cardiovascular risk prediction is disputed. Cholesteryl ester transfer protein (CETP) is instrumental in lipoprotein remodelling and affects the cholesterol content in pro- and antiatherogenic lipoproteins relative to their major apolipoproteins. We tested the influence of common CETP variations on the strength of associations of a first major adverse cardiovascular event (MACE) with the apoB/apoA-I ratio compared with the TC/HDL-C ratio.

METHODS

A prospective case-cohort study was performed (PREVEND cohort; no previous cardiovascular disease and no use of lipid-lowering drugs initially). Fasting serum TC/HDL-C, apoB/apoA-I, triglycerides, and common CETP variations (TaqIB [rs708272] and -629C>A [rs1800775] polymorphisms) were measured at baseline. The composite end point was incident MACE.

RESULTS

A total of 532 of 6780 subjects experienced a first MACE during 10.8 years follow-up. The age- and sex-adjusted hazard ratio was 1.31 (95 % confidence interval 1.23-1.41) for the apoB/apoA-I ratio and 1.22 (95% confidence interval 1.26-1.39) for the TC/HDL-C ratio (both P < .001). These relationships were essentially similar within each TaqIB and -629C>A CETP genotype group. No interactions of the apoB/apoA-I ratio and the TC/HDL-C ratio with the TaqIB and the -629C>A CETP variations on incident MACE were observed (P > .20 for all).

CONCLUSION

The relationship of first MACE with the TC/HDL-C and the apoB/apoA-I ratio is not to an important extent dependent on common CETP variations. CETP variations are unlikely to affect the strength of the relationship of first MACE with the apoB/apoA-I ratio compared with the TC/HDL-C ratio.

Plasma PLTP (phospholipid-transfer protein): an emerging role in 'reverse lipopolysaccharide transport' and innate immunity

Plasma PLTP (phospholipid-transfer protein) is a member of the lipid transfer/LBP [LPS (lipopolysaccharide)-binding protein] family, which constitutes a superfamily of genes together with the short and long PLUNC (palate, lung and nasal epithelium clone) proteins. Although PLTP was studied initially for its involvement in the metabolism of HDL (high-density lipoproteins) and reverse cholesterol transport (i.e. the metabolic pathway through which cholesterol excess can be transported from peripheral tissues back to the liver for excretion in the bile), it displays a number of additional biological properties. In particular, PLTP can modulate the lipoprotein association and metabolism of LPS that are major components of Gram-negative bacteria. The delayed association of LPS with lipoproteins in PLTP-deficient mice results in a prolonged residence time, in a higher toxicity of LPS aggregates and in a significant increase in LPS-induced mortality as compared with wild-type mice. It suggests that PLTP may play a pivotal role in inflammation and innate immunity through its ability to accelerate the 'reverse LPS transport' pathway.

Worsening of diet-induced atherosclerosis in a new model of transgenic rabbit expressing the human plasma phospholipid transfer protein

OBJECTIVE

Plasma phospholipid transfer protein (PLTP) is involved in intravascular lipoprotein metabolism. PLTP is known to act through 2 main mechanisms: by remodeling high-density lipoproteins (HDL) and by increasing apolipoprotein (apo) B-containing lipoproteins. The aim of this study was to generate a new model of human PLTP transgenic (HuPLTPTg) rabbit and to determine whether PLTP expression modulates atherosclerosis in this species that, unlike humans and mice, displays naturally very low PLTP activity.

METHODS AND RESULTS

In HuPLTPTg rabbits, the human PLTP cDNA was placed under the control of the human eF1-α gene promoter, resulting in a widespread tissue expression pattern and in increased plasma PLTP. The HuPLTPTg rabbits showed a significant increase in the cholesterol content of the plasma apoB-containing lipoprotein fractions, with a more severe trait when animals were fed a cholesterol-rich diet. In contrast, HDL cholesterol level was not modified in HuPLTPTg rabbits. Formation of aortic fatty streaks was increased in hypercholesterolemic HuPLTPTg animals as compared with nontransgenic littermates.

CONCLUSIONS

Human PLTP expression in HuPLTPTg rabbit worsens atherosclerosis as a result of increased levels of atherogenic apoB-containing lipoproteins but not of alterations in their antioxidative protection or in cholesterol content of plasma HDL.

Molecular profiles of drinking alcohol to intoxication in C57BL/6J mice

BACKGROUND

Alcohol addiction develops through a series of stages, and mechanistic studies are needed to understand the transition from initial drug use to sustained controlled alcohol consumption followed by abuse and physical dependence. The focus of this study was to examine the effects of voluntary alcohol consumption on brain gene expression profiles using a mouse model of binge drinking. The main goal was to identify alcohol-responsive genes and functional categories after a single episode of drinking to intoxication.

METHODS

We used a modification of a "Drinking In the Dark" (DID) procedure (Rhodes et al., 2005) that allows mice to experience physiologically relevant amounts of alcohol in a non-stressful environment and also allows for detection of alcohol-sensitive molecular changes in a dose-dependent manner. C57BL/6J male mice were exposed to either 20% ethanol solution or water (single bottle) starting 3 hours after lights off for 4 hours and brains were harvested immediately after the drinking session. cDNA microarrays were used to assess the effects of voluntary drinking on global gene expression in 6 brain regions. We employed three statistical approaches to analyze microarray data.

RESULTS

A commonly used approach that applies a strict statistical threshold identified the eight top statistically significant genes whose expression was significantly correlated with blood ethanol concentration (BEC) in one of the brain regions. We then used a systems network approach to examine brain region-specific transcriptomes and identify modules of co-expressed (correlated) genes. In each brain region, we identified alcohol-responsive modules, i.e., modules significantly enriched for genes whose expression was correlated with BEC. A functional over-representation analysis was then applied to examine the organizing principles of alcohol-responsive modules. Genes were clustered into modules according to their roles in different physiological processes, functional groups, and cell types, including blood circulation, signal transduction, cell-cell communication, and striatal neurons. Finally, a meta-analysis across all brain regions suggested a global role of increasing alcohol dose in coordination of brain blood circulation and reaction of astrocytes.

CONCLUSIONS

This study showed that acute drinking resulted in small but consistent changes in brain gene expression which occurred in a dose-dependent manner. We identified both general and region-specific changes, some of which represent adaptive changes in response to increasing alcohol dose, which may play a role in alcohol-related behaviours, such as tolerance and consumption. Our systems approach allowed us to estimate the functional values of individual genes in the context of their genetic networks and formulate new refined hypotheses. An integrative analysis including other alcohol studies suggested several top candidates for functional validation, including Mt2, Gstm1, Scn4b, Prkcz, and Park7.

Homocysteine is a determinant of ApoA-I and both are associated with ankle brachial index, in an ambulatory elderly population

OBJECTIVE

The ankle brachial index (ABI) is an indicator of lower extremity peripheral arterial disease (PAD) and a predictor of atherothrombosis. ApoA-I and HDL are associated with PAD, in humans. Homocysteine influences the liver expression of ApoA-I and decreases its blood level and HDL in genetic mice models. We aimed therefore to evaluate whether homocysteine and its nutritional determinants, folate and vitamin B12 are associated with ABI by influencing HDL metabolism, in an ambulatory elderly population.

METHODS

667 elderly volunteers from rural Sicily were assessed for ABI, homocysteine and its determinants, lipid markers and other predictors of PAD. HDL size was assessed in 15 sera in upper and lower quartiles of Hcy distribution.

RESULTS

In multivariate analysis, ApoA-I and homocysteine were two predictors of ABI (β-coefficient = 2.86, P<0.004 and β-coefficient = -3.41, P<0.001, respectively). Homocysteine correlated negatively with ApoA-I (R = -0.147, P<0.001) and with HDL-Cholesterol (R = -0.113, P = 0.003). The associations of homocysteine, vitamin B12 and methylmalonic acid with ApoA-I and HDL2a particles and that of homocysteine with increased small size HDL3c suggested mechanisms related with impaired synthesis of ApoA-I and HDL and abnormal maturation of HDL particles.

CONCLUSION

The influence of homocysteine on ApoA-I and HDL metabolism provides new insights on its role on vascular diseases, at a cross-point between atherosclerosis and atherothrombosis.

Increased apolipoprotein AI production rate and redistribution of high-density lipoprotein size induced by estrogen plus progestin as oral contraceptive

CONTEXT

The impact of estrogen plus progestin as an oral contraceptive on high density lipoprotein (HDL) apolipoprotein (apo) AI metabolism in humans is poorly understood.

OBJECTIVES

This study was designed to measure the in vivo effect of Moneva (30 microg ethinylestradiol, 75 microg gestodene) on HDL apoAI production rate and fractional catabolic rate.

DESIGN

Using (13)C-leucine, we performed two kinetic studies in the fed state in 10 normolipidemic young women, before and 3 months after beginning Moneva.

RESULTS

On Moneva, serum triglycerides increased by 12% (P = 0.03) in the fed state, whereas low-density lipoprotein and HDL cholesterol remained unchanged. HDL apoAI pool size and production rate were increased by 9.2% (67.3 +/- 7.1 vs. 61.6 +/- 6.7 mg x kg(-1); P = 0.05) and 26.5% (14.3 +/- 2.7 vs. 11.3 +/- 2.2 mg x kg(-1) x d(-1); P = 0.02), respectively. HDL apoAI fractional catabolic rate was not significantly modified. Three-month treatment by Moneva induced a shift of HDL size distribution from HDL2 toward HDL3 (HDL3 = 51.5 +/- 8.1 vs. 46.5 +/- 9.2% of total HDL; P = 0.02) and an increase in the proportion of apoAI among HDL components (38.8 +/- 4.3 vs. 34.4 +/- 2.8%; P = 0.01).

CONCLUSION

Oral contraception by estrogen plus progestin induces changes in HDL apoAI metabolism characterized by an increase in production rate and pool size, with a higher proportion of HDL3 particles. Whether or not these changes are beneficial to prevent atherosclerosis has to be explored further.

Atorvastatin effect on the distribution of high-density lipoprotein subfractions and human paraoxonase activity

Human serum paraoxonase-1 (PON1) protects lipoproteins against oxidation by hydrolyzing lipid peroxides in oxidized low-density lipoprotein (LDL); therefore, it may protect against atherosclerosis. Changes in the ratio of high-density lipoprotein (HDL) subfractions may alter the stability and the antioxidant capacity of PON1. The aim of the study was to examine the effect of atorvastatin treatment on the distribution of HDL subfractions, LDL size, cholesteryl ester transfer protein (CETP), lecithin-cholesterol acyltransferase (LCAT), and PON1 activity. In all, 33 patients with type IIa and IIb hypercholesterolemia were involved in the study. LDL sizes and HDL subfractions were determined by gradient gel electrophoresis. CETP, LCAT, and PON1 activities were measured spectrophotometrically. Three months of treatment with atorvastatin 20 mg daily significantly increased the HDL3 (+8.13%) and decreased the HDL2a and HDL2b subfractions (-1.57% and -6.55%, respectively). The mean LDL size was significantly increased (+3.29%). The level of oxidized LDL was significantly decreased (-46.0%). The PON1 activity was augmented by the atorvastatin treatment (+5.0%). The CETP activity positively correlated with the HDL2b level and negatively correlated with the HDL3 and HDL2a levels. Atorvastatin alters the HDL subfractions, which may improve its antiatherogenic effect via enhancement of the PON1 activity.

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

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.

HDL particles from type 1 diabetic patients are unable to reverse the inhibitory effect of oxidised LDL on endothelium-dependent vasorelaxation

AIMS/HYPOTHESIS

In healthy individuals, HDL can counteract the inhibition of vasorelaxation induced by oxidised LDL. Several abnormalities such as increased size, glycation and decreased paraoxonase activity have been reported for HDL from type 1 diabetic patients. Thus, we hypothesised that the ability of HDL to protect vessels against impairments of vasorelaxation would be decreased in these patients.

METHODS

We compared the ability of HDL from 18 type 1 diabetic patients and 12 control participants to counteract the inhibition of endothelium-dependent relaxation induced by oxidised LDL on rabbit aorta rings.

RESULTS

Serum triacylglycerol and total cholesterol, LDL- and HDL-cholesterol were similar in type 1 diabetic and control participants. Fasting glycaemia and the HDL-fructosamine level were higher in diabetic patients than in controls (9.06 +/- 3.55 vs 5.27 +/- 0.23 mmol/l, p < 0.005; and 10.2 +/- 3.2 vs 7.7 +/- 2.5 micromol/g protein, p < 0.05, respectively). HDL composition, size and paraoxonase activity were similar in both groups. HDL from controls reduced the inhibitory effect of oxidised LDL on maximal relaxation (E (max); 79.3 +/- 11.8 vs 66.4 +/- 11.7%, p < 0.05), whereas HDL from type 1 diabetic patients had no effect (E (max) = 70.6 +/- 17.4 vs 63.9 +/- 17.2%, NS). In type 1 diabetic patients, E (max) was not correlated with glycaemia or the HDL-fructosamine level.

CONCLUSIONS/INTERPRETATION

HDL particles from type 1 diabetic patients do not protect against inhibition of endothelium-dependent vasorelaxation induced by oxidised LDL, in contrast to HDL particles from healthy individuals. This defect cannot be explained by abnormalities in HDL composition, size or paraoxonase activity, and may contribute to the early development of atherosclerotic lesions in type 1 diabetic patients.

Beyond HDL-cholesterol increase: phospholipid enrichment and shift from HDL3 to HDL2 in alcohol consumers

The reduction of cardiovascular mortality associated with moderate alcohol consumption is chiefly thought to be mediated by an increase of high density lipoprotein cholesterol (HDL-CH). This study highlights additional qualitative changes of HDL that might augment this antiatherogenic effect. In 279 healthy men, alcohol and nutrient consumption were evaluated. Groups 1 (n=62), 2 (n=172), and 3 (n=45) comprised subjects with alcohol consumption of 0-5.0, 5.1-30.0, and 30.1-75 g/day, respectively. Lipid analysis was performed in nonfractionated and fractionated plasma, including subfractions HDL(2a), HDL(2b), and HDL(3). No difference in LDL-cholesterol was observed. Compared with group 1, groups 2 and 3 exhibited significant increases of HDL-CH (group 1, 44 +/- 10 mg/dl; group 2, 51 +/- 11 mg/dl; group 3, 55 +/- 11 mg/dl; mean +/- SD, P<0.0005), accompanied by enhanced lipidation of HDL (increase of the HDL(2)-CH/HDL(3)-CH ratio). Moreover, phospholipid enrichment of HDL occurred in alcohol consumers, whereas the ratios between other HDL components remained constant. Multivariate analysis revealed alcohol to have the foremost statistical influence on changes of the HDL fraction, followed by body mass index and physical activity level. The increased lipidation of HDL found in alcohol consumers might augment the antiatherogenic effect of HDL-CH increase. In addition, the phospholipid enrichment of HDL might reduce the inflammatory response of atherogenesis.

Early decreases in plasma lipid transfer proteins during weight reduction

OBJECTIVE

To determine the effect of short-term weight loss in obese women on concentrations of plasma cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), two new risk factors for cardiovascular disease.

RESEARCH METHODS AND PROCEDURES

Plasma CETP and PLTP mass concentrations were measured in 38 obese, non-diabetic women before and after a moderate, 4% weight loss that was obtained by a 1250 kcal/d diet for 4 weeks. Anthropometric and biological parameters were measured before and after weight loss.

RESULTS

Plasma CETP concentration decreased substantially after weight loss (2.76 +/- 0.79 before and 2.31 +/- 0.69 mg/L after; p = 0.000), and the same was true for plasma PLTP concentration (9.01 +/- 2.44 mg/L before vs. 8.34 +/- 2.57 after; p = 0.043). The HDL profile shifted toward the small-sized range, with significant decreases in the relative abundance of HDL(2b) and HDL(2a) at the expense of HDL(3b) after weight loss. A significant, positive correlation between CETP and PLTP mass concentrations is reported for the first time in obese patients (r = 0.43, p = 0.004), and weight reduction was accompanied by early, concomitant, and parallel decreases in plasma CETP and PLTP levels (r = 0.47, p = 0.003). The significant relationship between CETP and PLTP levels was lost after the dietary intervention (r = 0.27; p = 0.11).

DISCUSSION

CETP and PLTP correlate positively and significantly in obese patients. The hypocaloric dietary manipulation constitutes a relevant intervention to reduce rapidly and simultaneously plasma levels of CETP and PLTP. The impact of reduced PLTP activity on HDL size appeared to be more prominent than the impact of concomitant reduction in CETP activity.

Effects of ethanol on lipids and atherosclerosis

Moderate alcohol consumption is associated with an increase in plasma high density lipoprotein (HDL) cholesterol concentration and a decrease in low density lipoprotein (LDL) cholesterol concentration. Changes in the concentration and composition of lipoproteins are estimated to account for more than half of alcohol's protective effect for coronary heart disease. Alcohol intake also affects plasma proteins involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, and phospholipases. In addition, alcohol intake may result in acetaldehyde modification of apolipoproteins. Furthermore, "abnormal" lipids, phosphatidylethanol and fatty acid ethyl esters are formed in the presence of ethanol and are associated with lipoproteins in plasma. Ethanol and ethanol-induced modifications of lipids may modulate the effects of lipoproteins on the cells in the arterial wall. The molecular mechanisms involved in these processes are complex, requiring further study to better understand the specific effects of ethanol in the pathogenesis of atherosclerosis. This review discusses the effects of ethanol on lipoproteins and lipoprotein metabolism, as well as the novel effects of lipoproteins on vascular wall cells.

Apolipoprotein CI overexpression is not a relevant strategy to block cholesteryl ester transfer protein (CETP) activity in CETP transgenic mice

ApoCI (apolipoprotein CI) is a potent inhibitor of plasma CETP [CE (cholesteryl ester) transfer protein]. The relevance of apoCI overexpression as a method for CETP blockade in vivo was addressed in the present study in CETPTg/apoCITg mice (mice expressing both human CETP and apoCI). Despite a significant reduction in specific CETP activity in CETPTg/apoCITg mice compared with CETPTg mice [transgenic mouse to human CETP; 46.8+/-11.1 versus 101.8+/-25.7 pmol x h(-1).(mug of plasma CETP)(-1) respectively; P<0.05], apoCI overexpression increased both the CETP mass concentration (3-fold increase; P<0.05) and the hepatic CETP mRNA level (4-fold increase, P<0.005), leading to an increase in total plasma CE transfer activity (by 39%, P<0.05). The ratio of apoB-containing lipoprotein to HDL (high-density lipoprotein) CE was 10-fold higher in CETPTg/apoCITg mice than in apoCITg mice (P<0.0005). It is proposed that the increased CETP expression in CETPTg/apoCITg mice is a direct consequence of liver X receptor activation in response to the accumulation of cholesterol-rich apoB-containing lipoproteins. In support of the latter view, hepatic mRNA levels of other liver X receptor-responsive genes [ABCG5 (ATP-binding cassette transporter GS) and SREBP-1c (sterol-regulatory-binding protein-1c)] were higher in CETPTg/apoCITg mice compared with CETPTg mice. In conclusion, overexpression of apoCI, while producing a significant inhibitory effect on specific CETP activity, does not represent a suitable method for decreasing total CE transfer activity in CETPTg/apoCITg mice, owing to an hyperlipidaemia-mediated effect on CETP gene expression.

Human plasma phospholipid transfer protein activity is decreased by acute hyperglycaemia: studies without and with hyperinsulinaemia in Type 1 diabetes mellitus

AIMS

Little is known about the regulation of phospholipid transfer protein (PLTP), that plays a key role in lipoprotein metabolism. PLTP secretion may be up-regulated by glucose in vitro, whereas plasma PLTP activity is decreased by exogenous hyperinsulinaemia and glucose-induced hyperinsulinaemia in vivo. In the present study, we evaluated the separate effects of hyperglycaemia and hyperinsulinaemia in C-peptide-negative Type 1 diabetic patients.

METHODS

The protocol was carried out in 16 patients (eight females). In each individual, plasma PLTP mass and activity (measured by enzyme-linked immuno-sorbent assay and liposome-high density lipoprotein system, respectively) as well as plasma cholesteryl ester transfer protein (CETP) activity, lipids and apolipoprotein levels were determined at the end of four different glucose clamps, each lasting 210 min: standard insulin (30 mU/kg/h) and standard glucose (glucose 5.0 mmol/l) (SI-SG), standard insulin and high glucose (glucose 12 mmol/l) (SI-HG), high insulin (150 mU/kg/h) and standard glucose (HI-SG), and high insulin and high glucose (HI-HG).

RESULTS

Plasma lipids and (apo)lipoproteins, measured at the end of the SI-HG, HI-SG and HI-HG clamps, were not significantly different compared with the levels obtained at the end of the SI-SG clamp. Median plasma PLTP mass and activity at the end of the SI-SG clamp were 12.8 mg/l and 13.2 micromol/ml/h, respectively. Median plasma PLTP mass decreased by 9.1% at the end of the HI-HG clamp (P < 0.01), whereas the changes at the end of the SI-HG and HI-SG clamps were not significant. Median plasma PLTP activity decreased by 5.7, 4.6 and 8.6% at the end of the SI-HG, HI-SG and HI-HG clamps, respectively (all P < 0.05). Median plasma CETP activity was 177 nmol/ml/h at the end of the SI-SG clamp, and decreased by 4.9% (P < 0.05) and by 8.3% (P < 0.05) at the end of the HI-SG and the HI-HG clamps, respectively. Plasma CETP activity did not change significantly at the end of the SI-HG clamp.

CONCLUSIONS

The present study demonstrates that plasma PLTP activity is independently decreased by acute hyperglycaemia and hyperinsulinaemia in humans in vivo. These data do not support a direct role of short-term hyperglycaemia in up-regulating plasma PLTP levels.

Transfer of Phosphatidylethanol Between Lipoproteins

BACKGROUND

Phosphatidylethanol (PEth) is an abnormal phospholipid formed only in the presence of ethanol. It has been recently shown that lipoprotein-associated PEth may mediate the effects of ethanol on endothelial cells, and this may explain, at least in part, the beneficial effect of ethanol on atherosclerosis. This study was performed to investigate the transfer of PEth between lipoproteins and the effects of PEth on cholesteryl ester transfer protein (CETP) activity in plasma.

METHODS

Lipoproteins were isolated from the plasma of healthy male volunteers (n = 16) and male alcoholics (n = 13). The transfer of cholesteryl esters and PEth was determined between labeled low-density lipoprotein (LDL) and unlabeled high-density lipoprotein particles in vitro. The electrophoretic mobility of PEth-modified LDL particles was determined by agarose gel electrophoresis.

RESULTS

PEth was transferred from PEth-modified LDL to high-density lipoprotein at an initial rate of 25.9 nmol/ml/hr. Monoclonal antibody (TP2) against the putative lipid-binding domain of CETP inhibited the transfer rate of PEth by approximately 64%, whereas the cholesteryl ester transfer was inhibited by 86%. This indicates that most of PEth was transferred by transfer proteins other than CETP.

CONCLUSIONS

The transfer of PEth between lipoproteins enables the redistribution of PEth from lipoprotein fractions with a slow turnover to those with a rapid clearance. Moreover, the PEth-induced change in the electrical charge of lipoproteins may affect the binding of lipoproteins to their receptors and binding proteins. This in turn may alter the metabolism of lipoproteins and lipid-mediated signaling pathways in the cells delineating the vascular wall.

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.

PLTP activity decreases with weight loss: changes in PLTP are associated with changes in subcutaneous fat and FFA but not IAF or insulin sensitivity

Phospholipid transfer protein (PLTP) activity is elevated in obese and diabetic subjects. No prospective studies have examined the effect of weight loss on PLTP activity and assessed whether the resultant changes in activity are related to changes in body weight, insulin resistance, or both. PLTP activity was measured at baseline in 46 subjects (body mass index = 19-64 kg/m2) and after diet-induced weight loss in 19 of the obese subjects. Total body fat mass (FM) by dual-energy X-ray absorptiometry, intraabdominal fat (IAF), and abdominal subcutaneous fat (SQF) by CT scan, insulin sensitivity (SI) by frequently sampled intravenous glucose tolerance test, leptin, and lipids were determined. At baseline, PLTP activity correlated with FM (r = 0.36, P = 0.02) and SQF (r = 0.31, P = 0.045), but not with IAF (r = 0.16, P = 0.32) or SI (r = 0.10, P = 0.52). With diet-induced weight loss (16 +/- 7.3 kg), PLTP activity significantly decreased 9.1% (P = 0.002). The change in PLTP activity correlated with the change in SQF (r = 0.55, P = 0.014) (33.6% decrease), but not with IAF (r = 0.09, P = 0.73) or SI (r = 0.18, P = 0.44), and was highly correlated with the change in nonesterified fatty acid (NEFA) (r = 0.71, P < 0.001). In conclusion, elevated PLTP activity in obese subjects is likely a result of increased body fat, reflected by SQF, and is influenced by NEFAs but is not directly related to insulin resistance.

Low cholesteryl ester transfer protein (CETP) concentration but normal CETP activity in serum from patients with short-term hypothyroidism Lack of relationship to lipoprotein abnormalities

OBJECTIVES

Hypothyroidism is associated with a number of abnormalities in lipoprotein metabolism. Although alterations in neutral lipid exchanges among plasma lipoproteins might be one characteristic feature of hypothyroidism, a few human studies of cholesteryl ester transfer protein (CETP) activity have led to heterogeneous and fragmentary observations. The aim of the present study was to analyse the influence of short-term hypothyroidism on CETP activity, as well as on the structure and composition of lipoproteins. PATIENTS, DESIGN AND MEASUREMENTS: Sixty-six thyroidectomized patients were withdrawn from L-thyroxine (L-T4) treatment for 5 weeks. Subsequently, L-T4 therapy was reinstated for 2 months and patients were compared to 61 matched normolipidaemic controls. Serum CETP activity and mass concentration, serum lipids, apolipoproteins and lipoprotein size distribution were determined in the three groups.

RESULTS

Serum CETP mass concentration was significantly decreased in short-term hypothyroid patients, as compared to control subjects (3.22 +/- 0.98 vs. 3.79 +/- 1.2 mg/l, respectively; P < 0.001), and the values were normalized during L-T4 therapy. The ability of endogenous serum lipoproteins to interact with CETP was normal in short-term hypothyroid patients. Concordant observations were made regardless of whether neutral lipid transfers were measured from high-density lipoproteins (HDL) toward apo B-containing lipoproteins or from liposomes toward HDL. The size distribution of HDL was significantly different in short-term hypothyroid patients, compared to either the control or treated subgroups, with significant higher proportions of large-sized HDL2b and HDL2a (HDL2b: 13.6 +/- 6.5% before vs. 8.5 +/- 4.2% during L-T4 therapy, P < 0.05; HDL2a, 33.0 +/- 7.0% before vs. 29.3 +/- 6.9% during L-T4 therapy, P < 0.05). Although serum CETP mass concentration correlated negatively with the HDL2 to HDL3 ratio in control subjects (r = -0.588; P < 0.0001), no significant correlations were observed in hypothyroid patients, regardless of whether they were treated or not. Similarly, whereas the previously recognized positive correlation of CETP mass concentration with serum LDL cholesterol levels was found in control subjects (r = 0.264; P < 0.05), no significant correlations appeared in treated and untreated patients.

CONCLUSIONS

Short-term hypothyroidism may constitute an unique situation in which concomitant alterations in serum cholesteryl ester transfer protein concentration and lipoprotein parameters are disconnected.

Plasma concentrations of LPL and LCAT are in putative association with females and alcohol use which are independent negative risk factors for coronary atherosclerosis among Japanese

BACKGROUND

Coronary heart disease (CHD) prevalence appears low among Japanese. Analysis of their negative risk factors is therefore important for public health strategy.

METHODS

We analyzed the impact on coronary atherosclerosis of sex, alcohol intake, plasma lipoproteins and enzymes to regulate cholesterol transport, lipoprotein lipase (LPL) and lecithin:cholesterol acyltransferase (LCAT) for the 110 patients who underwent coronary angiography, consecutively enrolled by excluding those >70 years or under hypolipidemic-drug treatment. Subgroup combinations compared were males vs. females in non-drinkers, and drinkers vs. non-drinkers in males.

RESULTS

Coronary stenosis was less in females and in drinkers, accompanied by high-density lipoprotein (HDL) in the respective comparison. LPL associated with sex (females>males) and LCAT with alcohol intake (drinkers>non-drinkers) although neither enzyme demonstrated direct correlation with coronary stenosis. LPL positively associated only with HDL in most of subgroups and LCAT correlated with low-density lipoprotein (LDL) in all subgroups but with HDL only in males.

CONCLUSIONS

Among non-drinkers, females are at lower risk for coronary atherosclerosis than males mainly due to higher HDL in potential association with high LPL, and that drinkers are protected among males also by high HDL that is in apparent association with LCAT.

Relationship of phospholipid transfer protein activity to HDL and apolipoprotein B-containing lipoproteins in subjects with and without type 1 diabetes

Patients with type 1 diabetes have greatly increased phospholipid transfer protein (PLTP) activity and have an altered HDL subclass distribution. In 195 patients with type 1 diabetes and in 194 men and women aged 30-55 years, we examined the relationship of PLTP activity to HDL and examined whether PLTP activity contributes to differences in HDL found in type 1 diabetes. PLTP activity was measured using an exogenous substrate assay. Average HDL particle size and HDL subclasses were measured using nuclear magnetic resonance spectroscopy. Apolipoprotein AI (apoAI) and apoAII were measured by immunoturbidimetry. The amount of apoAI present in LpAI was measured using a differential electroimmunoassay, and the amount of apoAI in LpAIAII was inferred from the apoAI and LpAI data. Higher PLTP activity was associated with more large HDL (P < 0.001) and less small HDL (P < 0.01), more apoAI and apoAII (both at P < 0.001), and more apoAI in both LpAI and LpAIAII (P = 0.02 and P < 0.001, respectively). These associations were independent of other lipids and enzyme activities. Adjusting for PLTP activity halved the difference between subjects with and without diabetes in apoA1 (from 10.1 mg/dl higher in subjects with diabetes to 4.6 mg/dl higher) and large HDL (2.4 micro mol/l higher to 1.2 micro mol/l higher) and reduced the difference in HDL size (from 0.31 nm higher to 0.26 nm higher). PLTP activity was also positively associated with apoB, total VLDL and LDL particle number, and IDL level in subjects with diabetes. These data support the idea that PLTP is a major factor in HDL conversion and remodeling in humans and that higher PLTP activity makes an important contribution to the higher apoAI levels and altered HDL subclass distribution in type 1 diabetes. They also support a role for PLTP in the metabolism of apoB-containing lipoproteins.

Apolipoprotein CI deficiency markedly augments plasma lipoprotein changes mediated by human cholesteryl ester transfer protein (CETP) in CETP transgenic/ApoCI-knocked out mice

Transgenic mice expressing human cholesteryl ester transfer protein (HuCETPTg mice) were crossed with apolipoprotein CI-knocked out (apoCI-KO) mice. Although total cholesterol levels tended to be reduced as the result of CETP expression in HuCETPTg heterozygotes compared with C57BL6 control mice (-13%, not significant), a more pronounced decrease (-28%, p < 0.05) was observed when human CETP was expressed in an apoCI-deficient background (HuCETPTg/apoCI-KO mice). Gel permeation chromatography analysis revealed a significant, 6.1-fold rise (p < 0.05) in the cholesteryl ester content of very low density lipoproteins in HuCETPTg/apoCI-KO mice compared with control mice, whereas the 2.7-fold increase in HuCETPTg mice did not reach the significance level in these experiments. Approximately 50% decreases in the cholesteryl ester content and cholesteryl ester to triglyceride ratio of high density lipoproteins (HDL) were observed in HuCETPTg/apoCI-KO mice compared with controls (p < 0.05 in both cases), with intermediate -20% changes in HuCETPTg mice. The cholesteryl ester depletion of HDL was accompanied with a significant reduction in their mean apparent diameter (8.68 +/- 0.04 nm in HuCETPTg/apoCI-KO mice versus 8.83 +/- 0.02 nm in control mice; p < 0.05), again with intermediate values in HuCETPTg mice (8.77 +/- 0.04 nm). In vitro purified apoCI was able to inhibit cholesteryl ester exchange when added to either total plasma or reconstituted HDL-free mixtures, and coincidently, the specific activity of CETP was significantly increased in the apoCI-deficient state (173 +/- 75 pmol/microg/h in HuCETPTg/apoCI-KO mice versus 72 +/- 19 pmol/microg/h in HuCETPTg, p < 0.05). Finally, HDL from apoCI-KO mice were shown to interact more readily with purified CETP than control HDL that differ only by their apoCI content. Overall, the present observations provide direct support for a potent specific inhibition of CETP by plasma apoCI in vivo.

Effect of alcohol on lipids and lipoproteins in relation to atherosclerosis

Several studies indicate that light-to-moderate alcohol consumption is associated with a low prevalence of coronary heart disease. An increase in high-density lipoprotein (HDL) cholesterol is associated with alcohol intake and appears to account for approximately half of alcohol's cardioprotective effect. In addition to changes in the concentration and composition of lipoproteins, alcohol consumption may alter the activities of plasma proteins and enzymes involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, paraoxonase-1 and phospholipases. Alcohol intake also results in modifications of lipoprotein particles: low sialic acid content in apolipoprotein components of lipoprotein particles (e.g., HDL apo E and apo J) and acetaldehyde modification of apolipoproteins. In addition, "abnormal" lipids, phosphatidylethanol, and fatty acid ethyl esters formed in the presence of ethanol are associated with lipoproteins in plasma. The effects of lipoproteins on the vascular wall cells (endothelial cells, smooth muscle cells, and monocyte/macrophages) may be modulated by ethanol and the alterations further enhanced by modified lipids. The present review discusses the effects of alcohol on lipoproteins in cholesterol transport, as well as the novel effects of lipoproteins on vascular wall cells.

The impact of phospholipid transfer protein (PLTP) on HDL metabolism

High-density lipoproteins (HDL) play a major protective role against the development of coronary artery disease. Phospholipid transfer protein (PLTP) is a main factor regulating the size and composition of HDL in the circulation and plays an important role in controlling plasma HDL levels. This is achieved via both the phospholipid transfer activity of PLTP and its capability to cause HDL conversion. The present review focuses on the impact of PLTP on HDL metabolism. The basic characteristics and structure of the PLTP protein are described. The two main functions of PLTP, PLTP-mediated phospholipid transfer and HDL conversion are reviewed, and the mechanisms and control, as well as the physiological significance of these processes are discussed. The relationship between PLTP and the related cholesteryl ester transfer protein (CETP) is reviewed. Thereafter other functions of PLTP are recapitulated: the ability of PLTP to transfer cholesterol, alpha-tocopherol and lipopolysaccharide (LPS), and the suggested involvement of PLTP in cellular cholesterol traffic. The discussion on PLTP activity and mass in (patho)physiological settings includes new data on the presence of two forms of PLTP in the circulation, one catalytically active and the other inactive. Finally, future directions for PLTP research are outlined.

Particle size analysis of high density lipoproteins in patients with genetic cholesteryl ester transfer protein deficiency

We investigated the detailed distribution of high-density lipoproteins (HDL) particle size in patients with cholesteryl ester transfer protein (CETP) deficiency. Serum samples pre-stained with Sudan black B were electrophoresed using 4-30% polyacrylamide gradient gels, and the Stokes diameter of HDL particles was determined in 23 patients with genetic CETP deficiency, nine patients with hyperalphalipoproteinemia and seven subjects with normal HDL cholesterol concentrations. The mean Stokes diameter of HDL particles in CETP deficient patients (11.2+/-0.6 nm) was significantly greater than hyperalphalipoproteinemia (10.7+/-0.3 nm, P<0.05) and normal subjects (9.5+/-0.4 nm, P<0.01). A significant relationship was found between mean HDL size and serum CETP mass concentrations (P<0.05). When the particle size of all detected HDL bands was investigated, extra-large HDL particles larger than 12 nm were found in 14 of the 23 patients with CETP deficiency, which were not found in any of the hyperalphalipoproteinemia patients or normal subjects. Serum low-density lipoproteins (LDL) cholesterol and total cholesterol concentrations were lower in CETP deficiencies with extra-large HDL particles than those in non-carriers (P<0.01). These results indicate that extra-large HDL may be an index to clarify the relationship between genetic CETP deficiency and atherosclerosis.

The relationship between apolipoprotein AI-containing lipoprotein fractions and environmental factors: the prospective epidemiological study of myocardial infarction (PRIME study)

Apolipoprotein (apo) AI is distributed within high-density lipoproteins (HDL) between different types of particles, one containing both apoAI and apoAII (LpAI:AII), the other containing no apoAII (LpAI). We investigated the associations between LpAI and LpAI:AII with several factors such as body mass index (BMI), waist to hip ratio (WHR), alcohol intake, cigarette consumption and physical activity, in three French and one Northern Irish male populations included in a prospective study (PRIME study). LpAI and LpAI:AII were associated with variations in all environmental factors, except LpAI:AII, which was not associated with WHR. These relationships were unchanged after adjustment for other environmental factors, but slightly modified after adjustment for triglyceride levels. LpAI decreased when BMI, WHR and cigarette smoking increased, and increased with alcohol consumption and physical activity. LpAI:AII had a similar variation except for the absence of LpAI:AII modification associated with WHR variation. The associations between LpAI and BMI, alcohol consumption and cigarette smoking were largely dependent on HDL-cholesterol as indicated by the lack of any significance when the adjustment for HDL-cholesterol was made. Conversely, after adjustment for HDL-cholesterol, the significant association between LpAI:AII and BMI disappeared, while the associations between LpAI:AII and alcohol consumption, cigarette smoking and physical activity remained significant. These results suggest that the mechanisms of LpAI and LpAI:AII modulations differ according to each environmental factor, some dependent on the lipid content of lipoproteins and others not, but LpAI and LpAI:AII levels seem independent of triglyceride concentration.

Quantification of human plasma phospholipid transfer protein (PLTP): relationship between PLTP mass and phospholipid transfer activity

A sensitive sandwich-type enzyme-linked immunosorbent assay (ELISA) for human plasma phospholipid transfer protein (PLTP) has been developed using a monoclonal capture antibody and a polyclonal detection antibody. The ELISA allows for the accurate quantification of PLTP in the range of 25-250 ng PLTP/assay. Using the ELISA, the mean plasma PLTP concentration in a Finnish population sample (n = 159) was determined to be 15.6 +/- 5.1 mg/l, the values ranging from 2.30 to 33.4 mg/l. PLTP mass correlated positively with HDL-cholesterol (r = 0.36, P < 0.001), apoA-I (r = 0.37, P < 0.001), apoA-II (r = 0.20, P < 0.05), Lp(A-I) (r=0.26, P=0.001) and Lp(A-I/A-II) particles (r=0.34, P<0.001), and negatively with body mass index (BMI) (r = -0.28, P < 0.001) and serum triacylglycerol (TG) concentration (r = -0.34, P < 0.001). PLTP mass did not correlate with phospholipid transfer activity as measured with a radiometric assay. The specific activity of PLTP, i.e. phospholipid transfer activity divided by PLTP mass, correlated positively with plasma TG concentration (r=0.568, P<0.001), BMI (r=0.45, P<0.001), apoB (r = 0.45, P < 0.001). total cholesterol (r=0.42, P < 0.001), LDL-cholesterol (r = 0.34, P < 0.001) and age (r = 0.36, P < 0.001), and negatively with HDL-cholesterol (r= -0.33, P < 0.001), Lp(A-I) (r= -0.21, P < 0.01) as well as Lp(A-I/A-II) particles (r = -0.32, P < 0.001). When both PLTP mass and phospholipid transfer activity were adjusted for plasma TG concentration, a significant positive correlation was revealed (partial correlation, r = 0.31, P < 0.001). The results suggest that PLTP mass and phospholipid transfer activity are strongly modulated by plasma lipoprotein composition: PLTP mass correlates positively with parameters reflecting plasma high density lipoprotein (HDL) levels, but the protein appears to be most active in subjects displaying high TG concentration.

Reverse cholesterol transport in diabetes mellitus

There are epidemiological data and experimental animal models relating the development of premature atherosclerosis with defects of the reverse cholesterol transport (RCT) system. In this regard, the plasma concentrations of the high density lipoprotein (HDL) subfractions, of cholesteryl ester transfer protein (CETP), as well as the activity of the enzyme lecithin-cholesterol acyl transferase (LCAT) play critical roles. However, there has been plenty of evidence that atherosclerosis in diabetes mellitus (DM) is ascribed to a greater arterial wall cell uptake of modified apoB-containing lipoproteins whereas a primary or predominant defect of the RCT system is still a subject of debate. In other words, in spite of the fact that in DM the composition and rates of metabolism of the HDL particles are greatly altered and display a diminished in vitro efficiency to remove cell cholesterol, definitive in vivo demonstration of the importance of this fact in atherogenesis is lacking. Furthermore, the roles played by LCAT and CETP in RCT in DM are difficult to interpret because the in vitro procedures of measurement utilized have either been inadequate, or inappropriately interpreted. Knock-out or transgenic mice are much needed models to investigate the roles of LCAT, CETP, phospholipid transfer protein (PLTP), and of a CETP inhibitor in the development of atherosclerosis of experimental DM.

DNA sequences responsible for reduced promoter activity of human phospholipid transfer protein by fibrate

Phospholipid transfer protein (PLTP) plays an important role in plasma lipid and lipoprotein metabolism. We have previously cloned and characterized the promoter region of the human PLTP gene. The present study was conducted to determine if the promoter activity of the human PLTP gene is affected by fibrate, a hypolipidemic drug, and to identify DNA sequences that are responsible for the effect. The results indicated that the promoter activity of the PLTP gene was significantly reduced by fenofibrate, and the area that was mainly responsive to the reducing effect by fibrate was located between -377 and -230 of the 5'-flanking region. The DNA sequence analysis suggested that each area of the DNA sequences from -342 to -323 and from -322 to -299 has two repeated sequences, which are inverted and homologous to the recognition motif of peroxisome proliferator-activated receptor (PPAR), namely the PPAR-responsive element (PPRE). Mutagenesis of these PPRE-like sequences, especially that at -322 to -299, abolished most of the reducing effects of fibrate on the PLTP promoter activity. These findings strongly suggest that the PPRE-like elements are responsible for the reduced promoter activity of the human PLTP gene by fibrate.

Serum phospholipid transfer protein activity and genetic variation of the PLTP gene

The inverse relationship between serum levels of high density lipoproteins (HDL) and risk of coronary heart disease is well established. The phospholipid transfer protein (PLTP) promotes the transfer of phospholipids between lipoproteins and modulates HDL size and composition. It thus plays a central role in HDL metabolism. Serum PLTP activity was measured in 400 healthy Finnish individuals in order to determine normal PLTP serum values. PLTP activity increased with age (P<0.001), so that the PLTP activity was 3.81+/-0.84 micromol/ml per h (mean +/- S.D., n = 52) for men and 3.97+/-0.11 micromol/ml per h (n = 52) for women in the youngest age group (25-35 years), while it was 6.77+/-0.17 micromol/ml per h (n = 45) for men and 6.68+/-0.15 micromol/ml per h (n = 40) for women in the oldest age group (56-65 years). PLTP activity correlated significantly (P<0.001) with body mass index (r = 0.22), serum total cholesterol (r = 0.17), the ratio of HDL-cholesterol/total cholesterol (r = -0.20), triglycerides (r = 0.20), apo A-II (r = 0.20), and gamma glutamyl transferase (r = 0.22) values. Serum PLTP activity correlated negatively (r = -0.20, P<0.001) with levels of apolipoprotein A-I in HDL particles that contained only apo A-I [Lp(A-I) particles]. The allelic frequencies of six intragenic polymorphisms, -79G/T, -56G/A, -37T/C, -31A/G, Phe2Leu, Arg121Trp, and two neutral polymorphisms, located in the immediate vicinity of the PLTP gene were determined. There were no significant associations between these polymorphisms and serum PLTP activity.

Introduction of the human PLTP transgene suppresses the atherogenic diet-induced increase in plasma phospholipid transfer activity in C57BL/6 mice

The human plasma phospholipid transfer protein (PLTP) has been shown to facilitate the transfer of phospholipids between lipoproteins and convert high-density lipoproteins into larger and smaller particles in vitro. To explore the lipid transport function in vivo, transgenic C57BL/6 mice that express the human PLTP gene, driven by its natural promoter, were generated. Little difference in PLTP activity and lipoprotein lipids was observed between transgenic mice and non-transgenic control mice fed the chow diet. In response to an atherogenic high-fat, high-cholesterol, cholic acid containing diet, the PLTP activity increased significantly with time in control mice (62% in males and 34% in females after the high-fat diet for 18 weeks). In contrast, the PLTP activity did not change appreciably in the transgenic mice fed the atherogenic diet. Thus, the introduction of the human transgene suppressed the diet-induced increase in plasma PLTP activity, as evidenced by a decrease in PLTP mRNA in a variety of tissues. High-density lipoprotein levels decreased in mice fed the atherogenic diet, but there was a proportionally greater decrease in transgenic animals than in controls. After 18 weeks on the atherogenic diet, the transgenic animals had high-density lipoprotein-cholesterol and PLTP activity approximately one-half of that of control animals. Non-denaturing gradient gel electrophoresis of plasma indicated that the atherogenic diet decreased the high-density lipoprotein size distribution in control mice. However, high-density lipoprotein particle size distribution of the transgenic mice was shifted to smaller particles compared with control animals (P < 0.001). These findings suggest that PLTP activity can modulate the effects of an atherogenic diet on high-density lipoproteins.

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

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

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

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

Mass concentration of plasma phospholipid transfer protein in normolipidemic, type IIa hyperlipidemic, type IIb hyperlipidemic, and non-insulin-dependent diabetic subjects as measured by a specific ELISA

Mean plasma phospholipid transfer protein (PLTP) concentrations were measured for the first time by using a competitive enzyme-linked immunosorbent assay. PLTP mass levels and phospholipid transfer activity values, which were significantly correlated among normolipidemic plasma samples (r=0.787, P<0.0001), did not differ between normolipidemic subjects (3.95+/-1.04 mg/L and 575+/-81 nmol. mL-1. h-1, respectively; n=30), type IIa hyperlipidemic patients (4. 06+/-0.84 mg/L and 571+/-43 nmol. mL-1. h-1, respectively; n=36), and type IIb hyperlipidemic patients (3.90+/-0.79 mg/L and 575+/-48 nmol. mL-1. h-1, respectively; n=33). No significant correlations with plasma lipid parameters were observed among the various study groups. In contrast, plasma concentrations of the related cholesteryl ester transfer protein (CETP) were higher in type IIa and type IIb patients than in normolipidemic controls, and significant, positive correlations with total and low density lipoprotein cholesterol levels were noted. Interestingly, plasma PLTP mass concentration and plasma phospholipid transfer activity were significantly higher in patients with non-insulin-dependent diabetes mellitus (n=50) than in normolipidemic controls (6.76+/-1. 93 versus 3.95+/-1.04 mg/L, P<0.0001; and 685+/-75 versus 575+/-81 nmol. mL-1. h-1, P<0.0001, respectively). In contrast, CETP levels did not differ significantly between the 2 groups. Among non-insulin-dependent diabetes mellitus patients, PLTP levels were positively correlated with fasting glycemia and glycohemoglobin levels (r=0.341, P=0.0220; and r=0.382, P=0.0097, respectively) but not with plasma lipid parameters. It is proposed that plasma PLTP mass levels are related to glucose metabolism rather than to lipid metabolism.

High density associated enzymes: their role in vascular biology

Enzymes associated with circulating HDL include lecithin: cholesterol acyl transferase, phospholipid transfer protein, cholesterol ester transfer protein, paraoxonase 1 and platelet activating factor acetylhydrolase. Together with lipoprotein lipase and hepatic lipase these enzymes produce important lipoprotein remodeling and modulate their structure and function and therefore their role in artery wall metabolism.

The effects of ethyl alcohol on the concentration of some lipids in mouse organs

1. The administration of 5% and 10% ethyl alcohol to mice in 7-, 14- and 28-day periods resulted in an increase in triglycerides, total lipids and cholesterol concentration in the liver and a decrease in the muscle. 2. The smallest changes were in the kidney.

Remodeling of HDL by phospholipid transfer protein: demonstration of particle fusion by 1H NMR spectroscopy

There is evidence that phospholipid transfer protein (PLTP) can increase reverse cholesterol transport by inducing favorable subclass distribution in the high density lipoprotein (HDL) fraction. This includes generation of initial cholesterol acceptor particles, pre beta-HDL, and of enlarged particles that are rapidly cleared from the circulation. However, partly because of methodological difficulties, the mechanisms behind the PLTP-mediated interconversion of HDL particles are not fully understood. In this communication, we describe the use of a novel methodology, based on 1H NMR spectroscopy, to study the PLTP-induced size changes in the HDL particles. In accordance with native gradient gel electrophoresis, the 1H NMR data revealed a gradual production of enlarged HDL particles in the HDL3+ PLTP mixtures. In addition, according to a physical model for lipoprotein particles, relating the frequency shifts observable with NMR to the size of the lipoprotein particles, the NMR data demonstrated that PLTP-mediated HDL remodeling involves fusion of the HDL particles.

Determination of biological markers for alcohol abuse

Alcoholism is one of the most frequent addictions and an important subject in forensic medicine and clinical toxicology. Several laboratory abnormalities are associated with excessive alcohol consumption. They are useful in the diagnosis of alcoholism especially during the follow-up of various treatment programs. The biological markers mostly used for diagnosis of alcoholism are presented. Especially, methods for the determination of the following diagnostic tools are reviewed: congener alcohols, gamma-glutamyltransferase, aspartate and alanine aminotransferase, beta-hexosaminidase, erythrocyte aldehyde dehydrogenase, alpha-amino-n-butyric acid to leucine ratio, macrocytosis, carbohydrate-deficient transferrin, (apo)lipoproteins, fatty acid ethyl esters, blood acetate, acetaldehyde adducts, 5-hydroxytryptophol, dolichol and condensation products. No laboratory test exists that is reliable enough for the exact diagnosis of alcoholism. The combination of physician interview, questionnaire and laboratory markers is necessary for the diagnosis of alcoholism.