Decreased PLTP mass but elevated PLTP activity linked to insulin resistance in HTG: effects of bezafibrate therapy

Association of phospholipid transfer protein (PLTP) and the effect of genetic variant rs5072 on hypertriglyceridemia and atherogenic dyslipidemia in children and adolescents from Southeastern Mexico

INTRODUCTION

Dyslipidemia is characterized by changes in lipid and lipoprotein levels in the blood where phospholipid transfer protein (PLTP) helps to regulate and modulate the size of high-density lipoproteins (HDL), working on the reverse transport of cholesterol. ApoA-1 is the primary protein component of HDL, and certain genetic variants like rs5072, have been associated with hypertriglyceridemia in children. This study aimed to explore the association between PLTP concentrations and the effect of the genetic variant APOA1 rs5072 on hypertriglyceridemia and atherogenic dyslipidemia (AD) in the pediatric population of Southeastern Mexico.

MATERIALS AND METHODS

A cross-sectional study was carried out with a case-control design for 364 pediatric patients between 2 and 17 years old in Chiapas and Tabasco, Mexico. Serum samples were used to evaluate PLTP concentrations using ELISA kits, and DNA from peripheral blood samples was used to study genetic variation using q-PCR with TaqMan® probes. For statistical analysis, Student t-test for media comparison, Chi-square for frequency and Pearson analysis for correlation was performed. The software SNPStats was used for inheritance models.

RESULTS

Children with hypertriglyceridemia had higher levels of PLTP (8.3 ± 6.5 ng/ml) than the control group (6.4 ± 4.5 ng/ml). Similarly, the pediatric patients with AD had higher PLTP levels of 8.0 ± 6 ng/ml, mainly in children with high triglycerides who were between 10 and 17 years old (9.7 ± 8.0 ng/ml). Also, it was found that the genetic variant rs5072 had a protective effect against hypertriglyceridemia (OR = 0.61, p = 0.024) in the over-dominant inheritance model.

CONCLUSION

PLTP levels increase in pediatric patients aged 10 to 17 years with a diagnosis of hypertriglyceridemia and AD. The genetic variant rs5072 has a protective effect in hypertriglyceridemia.

Phospholipid transfer protein (PLTP) deficiency attenuates high fat diet induced obesity and insulin resistance

Increased phospholipid transfer protein (PLTP) activity has been found to be associated with obesity, and metabolic syndrome in humans. However, whether or not PLTP has a direct effect on insulin sensitivity and obesity is largely unknown. Here we analyzed the effect by using PLTP knockout (PLTP^-/-) mouse model. Although, PLTP^-/- mice have normal body-weight-gain under chow diet, these mice were protected from high-fat-diet-induced obesity and insulin resistance, compared with wild type mice. In order to understand the mechanism, we evaluated insulin receptor and Akt activation and found that PLTP deficiency significantly enhanced phosphorylated insulin receptor and Akt levels in high-fat-diet fed mouse livers, adipose tissues, and muscles after insulin stimulation, while total Akt and insulin receptor levels were unchanged. Moreover, we found that the PLTP deficiency induced significantly more GLUT4 protein in the plasma membranes of adipocytes and muscle cells after insulin stimulation. Finally, we found that PLTP-deficient hepatocytes had less sphingomyelins and free cholesterols in the lipid rafts and plasma membranes than that of controls and this may provide a molecular basis for PLTP deficiency-mediated increase in insulin sensitivity. We have concluded that PLTP deficiency leads to an improvement in tissue and whole-body insulin sensitivity through modulating lipid levels in the plasma membrane, especially in the lipid rafts.

Capsaicin Supplementation Improved Risk Factors of Coronary Heart Disease in Individuals with Low HDL-C Levels

Low high-density lipoprotein cholesterol (HDL-C) is associated with an increased risk of coronary heart disease (CHD). This study aimed to evaluate the effects of capsaicin intervention on the serum lipid profile in adults with low HDL-C. In a randomized, double-blind, controlled clinical trial, 42 eligible subjects were randomly assigned to the capsaicin (n = 21, 4 mg of capsaicin daily) or to the control group (n = 21, 0.05 mg of capsaicin daily) and consumed two capsaicin or control capsules, which contained the powder of the skin of different peppers, twice daily for three months. Thirty-five subjects completed the trial (18 in the capsaicin group and 17 in the control group). The baseline characteristics were similar between the two groups. Compared with the control group, fasting serum HDL-C levels significantly increased to 1.00 ± 0.13 mmol/L from 0.92 ± 0.13 mmol/L in the capsaicin group (p = 0.030), while levels of triglycerides and C-reactive protein and phospholipid transfer protein activity moderately decreased (all p < 0.05). Other lipids, apolipoproteins, glucose, and other parameters did not significantly change. In conclusion, capsaicin improved risk factors of CHD in individuals with low HDL-C and may contribute to the prevention and treatment of CHD.

Overnutrition Determines LPS Regulation of Mycotoxin Induced Neurotoxicity in Neurodegenerative Diseases

Chronic neurodegenerative diseases are now associated with obesity and diabetes and linked to the developing and developed world. Interests in healthy diets have escalated that may prevent neurodegenerative diseases such as Parkinson's and Alzheimer's disease. The global metabolic syndrome involves lipoprotein abnormalities and insulin resistance and is the major disorder for induction of neurological disease. The effects of bacterial lipopolysaccharides (LPS) on dyslipidemia and NAFLD indicate that the clearance and metabolism of fungal mycotoxins are linked to hypercholesterolemia and amyloid beta oligomers. LPS and mycotoxins are associated with membrane lipid disturbances with effects on cholesterol interacting proteins, lipoprotein metabolism, and membrane apo E/amyloid beta interactions relevant to hypercholesterolemia with close connections to neurological diseases. The influence of diet on mycotoxin metabolism has accelerated with the close association between mycotoxin contamination from agricultural products such as apple juice, grains, alcohol, and coffee. Cholesterol efflux in lipoproteins and membrane cholesterol are determined by LPS with involvement of mycotoxin on amyloid beta metabolism. Nutritional interventions such as diets low in fat/carbohydrate/cholesterol have become of interest with relevance to low absorption of lipophilic LPS and mycotoxin into lipoproteins with rapid metabolism of mycotoxin to the liver with the prevention of neurodegeneration.

Fibrates and fish oil, but not corn oil, up-regulate the expression of the cholesteryl ester transfer protein (CETP) gene

Cholesteryl ester transfer protein (CETP) is a plasma protein that reduces high density lipoprotein (HDL)-cholesterol (chol) levels and may increase atherosclerosis risk. n-3 and n-6 polyunsaturated fatty acids (PUFAs) are natural ligands, and fibrates are synthetic ligands for peroxisome proliferator activated receptor-alpha (PPARα), a transcription factor that modulates lipid metabolism. In this study, we investigated the effects of PUFA oils and fibrates on CETP expression. Hypertriglyceridemic CETP transgenic mice were treated with gemfibrozil, fenofibrate, bezafibrate or vehicle (control), and normolipidemic CETP transgenic mice were treated with fenofibrate or with fish oil (FO; n-3 PUFA rich), corn oil (CO, n-6 PUFA rich) or saline. Compared with the control treatment, only fenofibrate significantly diminished triglyceridemia (50%), whereas all fibrates decreased the HDL-chol level. Elevation of the CETP liver mRNA levels and plasma activity was observed in the fenofibrate (53%) and gemfibrozil (75%) groups. Compared with saline, FO reduced the plasma levels of nonesterified fatty acid (26%), total chol (15%) and HDL-chol (20%). Neither of the oil treatments affected the plasma triglyceride levels. Compared with saline, FO increased the plasma adiponectin level and reduced plasma leptin levels, whereas CO increased the leptin levels. FO, but not CO, significantly increased the plasma CETP mass (90%) and activity (23%) as well as increased the liver level of CETP mRNA (28%). In conclusion, fibrates and FO, but not CO, up-regulated CETP expression at both the mRNA and protein levels. We propose that these effects are mediated by the activation of PPARα, which acts on a putative PPAR response element in the CETP gene.

Effects of fenofibrate on lipid profiles, cholesterol ester transfer activity, and in-stent intimal hyperplasia in patients after elective coronary stenting

Background

The association between modulation of detailed lipoprotein profiles and cholesterol ester transfer (CET) activity by peroxisome proliferator-activated receptor (PPAR)-a agonists in patients with coronary artery disease remains unclear. We assessed lipid profiles, plasma CET activity, and in-stent intimal hyperplasia after fenofibrate treatment in patients who underwent elective coronary stenting.

Methods

Forty-three consecutive patients who underwent elective coronary stenting were randomized to the fenofibrate group (300 mg/day for 25 weeks, n = 22) or the control group (n = 21). At baseline and follow up, CET activity and lipoprotein profiles were measured, and quantitative coronary angiography was performed.

Results

In the fenofibrate group, the levels of large very low-density lipoprotein cholesterol, and small low-density lipoprotein (LDL) cholesterol decreased and those of small high-density lipoprotein (HDL) cholesterol increased. Besides, CET activity decreased independent of the effect of fenofibrate on total and LDL cholesterol. The reduction of CET activity significantly correlated with the increase in LDL particle size (r = 0.47, P = 0.03) and the decrease of triglycerides in large HDL subclasses (r = 0.48, P = 0.03). Although there were no significant differences in restenosis parameters between the two groups, low CET activity significantly correlated with the inhibition of neointimal hyperplasia (r = 0.56, P = 0.01).

Conclusions

Fenofibrate inhibited CET activity and thereby improved atherogenic lipoprotein profiles, and reduced intimal hyperplasia after coronary stenting.

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

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 40-80 years, with known cardiovascular disease and low HDL-C (<1.0 mmol/l), were randomized to receive, after an initial 6 week dietary run-in phase, either ATOR 20 mg (n = 41) or ROSU 10 mg (n = 39). The doses were up-titrated (in 6 week intervals) to 80 mg of ATOR or 40 mg 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.

Altered phospholipid transfer protein gene expression and serum lipid profile by topotecan

Camptothecin (CPT) and its structural analogues including topotecan and irinotecan, are inhibitors of topoisomerase I. These drugs are clinically active against a broad spectrum of cancers. To understand the genesis of chemotherapeutic resistance to the CPT family of anticancer drugs, we examined by gene expression profiling the pharmacological response to topotecan in the human hepatoma HepG2 cells and found a striking induction of the phospholipid transfer protein (PLTP) gene expression by topotecan. We showed that activation of PLTP gene expression is specific to CPT and its analogues including specific enantiomers that inhibit topoisomerase I. PLTP-mediated lipid transfer to high-density lipoprotein (HDL) is thought to be important for shuttling and redistribution of lipids between lipoproteins, which are normally returned to the liver for metabolism via the reverse cholesterol transport pathway. Hence, we asked whether elevated PLTP levels might increase the transfer of drugs into HDL. We observed that CPT was not accumulated in HDL and other lipoproteins. In addition, topotecan treatment in mice caused a marked reduction in serum HDL that was accompanied by an increase in triglyceride and cholesterol levels. These results showed that PLTP does not mediate the transfer of topoisomerase I inhibitors to serum lipoproteins. However, elevated serum PLTP levels following treatment with topoisomerase I inhibitors in cancer patients may serve as a biomarker for monitoring the development of hypertriglyceridemia and acute pancreatitis.

Plasma triglyceride levels and body mass index values are the most important determinants of prebeta-1 HDL concentrations in patients with various types of primary dyslipidemia

OBJECTIVE

Experimental studies have shown that the prebeta-1 subclass of high-density lipoprotein particles (prebeta-1 HDL) may play an important role in the reverse cholesterol transport pathway as the initial acceptors of cellular cholesterol. The aim of the present study was the direct comparison of prebeta-1 HDL values in individuals with various types of primary dyslipidemias.

METHODS

Four hundred and eighty-six unrelated individuals were included in the study. According to their lipid values study participants were subdivided into four groups: control group (n=206), type IIA dyslipidemia group (n=148), type IIB dyslipidemia group (n=49) and type IV dyslipidemia group (n=83).

RESULTS

All dyslipidemic patients displayed higher concentrations of prebeta-1 HDL compared to control individuals. However, patients with dyslipidemias characterized by an abnormal catabolism of triglyceride-rich lipoproteins (such as dyslipidemias of type IIB and IV) tend to have higher prebeta-1 HDL values compared to patients with hypercholesterolemia, and this increase is proportional to the degree of hypertriglyceridemia. In addition, patients with metabolic syndrome exhibited significantly higher levels of prebeta-1 HDL compared to individuals that do not fulfill the criteria for the diagnosis of this syndrome. Multiple regression analysis revealed that serum triglyceride concentrations and body mass index (BMI) values were the most important determinants of prebeta-1 HDL levels in our population.

CONCLUSION

All dyslipidemic patients exhibit increased prebeta-1 HDL concentrations as compared to normolipidemic individuals. Whether this increase represents a defensive mechanism against atherosclerosis or it is indicative of impaired maturation of HDL particles and thus of a defective reverse cholesterol transport mechanism remains to be established.

Ciprofibrate increases cholesteryl ester transfer protein gene expression and the indirect reverse cholesterol transport to the liver

Background

CETP is a plasma protein that modulates atherosclerosis risk through its HDL-cholesterol reducing action. The aim of this work was to examine the effect of the PPARα agonist, ciprofibrate, on the CETP gene expression, in the presence and absence of apolipoprotein (apo) CIII induced hypertriglyceridemia, and its impact on the HDL metabolism.

Results

Mice expressing apo CIII and/or CETP and non-transgenic littermates (CIII, CIII/CETP, CETP, non-Tg) were treated with ciprofibrate during 3 weeks. Drug treatment reduced plasma triglycerides (30-43%) and non-esterified fatty acids (19-47%) levels. Cholesterol (chol) distribution in plasma lipoprotein responses to ciprofibrate treatment was dependent on the genotypes. Treated CIII expressing mice presented elevation in VLDL-chol and reduction in HDL-chol. Treated CETP expressing mice responded with reduction in LDL-chol whereas in non-Tg mice the LDL-chol increased. In addition, ciprofibrate increased plasma post heparin lipoprotein lipase activity (1.3-2.1 fold) in all groups but hepatic lipase activity decreased in treated CETP and non-Tg mice. Plasma CETP activity and liver CETP mRNA levels were significantly increased in treated CIII/CETP and CETP mice (30-100%). Kinetic studies with ³H-cholesteryl ether (CEt) labelled HDL showed a 50% reduction in the ³H-CEt found in the LDL fraction in ciprofibrate treated compared to non-treated CETP mice. This means that ³H-CEt transferred from HDL to LDL was more efficiently removed from the plasma in the fibrate treated mice. Accordingly, the amount of ³H-CEt recovered in the liver 6 hours after HDL injection was increased by 35%.

Conclusion

Together these data showed that the PPARα agonist ciprofibrate stimulates CETP gene expression and changes the cholesterol flow through the reverse cholesterol transport, increasing plasma cholesterol removal through LDL.

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

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 (HbA(1c)), 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.

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

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-beta-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, PLTP activity, EST, and CET were higher (P=0.04 to <0.001), whereas adiponectin was lower in MetS subjects (P<0.01). Pre-beta-HDL and pre-beta-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-beta-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 importance of free fatty acids in the development of Type 2 diabetes

The recent increase in the prevalence of obesity has been associated with a coincident rise in the prevalence of Type 2 diabetes, whereas weight loss has been shown to decrease the risk of Type 2 diabetes. The pathophysiological mechanisms that have been proposed to explain this link are fundamentally concerned with insulin resistance and the decline in pancreatic B-cell function that accompanies an increase in visceral obesity. They involve the rise in the plasma concentrations of free fatty acids (FFAs) that are associated with an increase in fat mass. Elevated levels of FFAs can lead to insulin resistance, and evidence is growing that B-cell function is impaired through lipotoxicity. Factors such as tumour necrosis factor-alpha (TNF-alpha) and adiponectin, released from adipose tissue, can also modulate insulin resistance. Many interventions that are helpful in treating or preventing Type 2 diabetes, such as weight loss and certain pharmacological interventions, reduce circulating FFA concentrations to a greater or lesser extent. Recent study results suggest that peroxisome proliferator-activated receptor (PPAR)gamma agonists have an effect on the development of Type 2 diabetes. However, in light of concerns over the apparent increase in congestive heart failure with PPARgamma agonists, their place in the prevention of Type 2 diabetes remains to be determined.

Low phospholipid transfer protein (PLTP) is a risk factor for peripheral atherosclerosis

OBJECTIVE

Phospholipid transfer protein (PLTP) facilitates cholesterol efflux from cells, intravascular HDL remodelling and transfer of vitamin E and endotoxin. In humans, the relationship of PLTP to atherosclerosis is unknown. However, strong coronary risk factors like obesity, diabetes, cigarette smoking and inflammation increase circulating levels of active PLTP. The aim of the present, cross-sectional study was to analyze the relationship of PLTP to peripheral arterial disease, a marker of generalized atherosclerosis, independently of potentially confounding factors like obesity, diabetes and smoking.

METHODS

We performed a case control study in 153 patients with symptomatic peripheral arterial disease (PAD) and 208 controls free of vascular disease. Smokers and patients with diabetes mellitus were excluded. A lipoprotein-independent assay was used for measurement of circulating bioactive PLTP and an ELISA utilizing a monoclonal antibody was used to analyze PLTP mass.

RESULTS

PLTP activity was significantly decreased in patients with PAD 5.5 (4.6-6.4)(median (25th-75th percentile)) versus 5.9 (5.1-6.9) micromol/mL/h in controls (p=0.001). In contrast, PLTP mass was similar in patients with PAD 8.5 microg/mL (7.3-9.5) and in controls 8.3 microg/mL (6.9-9.7) (p=0.665). Multivariate logistic regression analysis revealed that PLTP activity is independently associated with the presence of PAD. PLTP activity was similar in patients with and without lipid-lowering drugs (p=0.396).

CONCLUSION

Our results show that in non-diabetic, non-smoking subjects low rather than high PLTP activity is a marker for the presence of peripheral arterial disease and that distribution of PLTP between high-activity and low-activity forms may be compromised in atherosclerosis.

Concerted actions of cholesteryl ester transfer protein and phospholipid transfer protein in type 2 diabetes: effects of apolipoproteins

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.

Fenofibrate increases HDL-cholesterol by reducing cholesteryl ester transfer protein expression

In addition to efficiently decreasing VLDL-triglycerides (TGs), fenofibrate increases HDL-cholesterol levels in humans. We investigated whether the fenofibrate-induced increase in HDL-cholesterol is dependent on the expression of the cholesteryl ester transfer protein (CETP). To this end, APOE*3-Leiden (E3L) transgenic mice without and with the human CETP transgene, under the control of its natural regulatory flanking regions, were fed a Western-type diet with or without fenofibrate. Fenofibrate (0.04% in the diet) decreased plasma TG in E3L and E3L.CETP mice (-59% and -60%; P < 0.001), caused by a strong reduction in VLDL. Whereas fenofibrate did not affect HDL-cholesterol in E3L mice, fenofibrate dose-dependently increased HDL-cholesterol in E3L.CETP mice (up to +91%). Fenofibrate did not affect the turnover of HDL-cholesteryl ester (CE), indicating that fenofibrate causes a higher steady-state HDL-cholesterol level without altering the HDL-cholesterol flux through plasma. Analysis of the hepatic gene expression profile showed that fenofibrate did not differentially affect the main players in HDL metabolism in E3L.CETP mice compared with E3L mice. However, in E3L.CETP mice, fenofibrate reduced hepatic CETP mRNA (-72%; P < 0.01) as well as the CE transfer activity in plasma (-73%; P < 0.01). We conclude that fenofibrate increases HDL-cholesterol by reducing the CETP-dependent transfer of cholesterol from HDL to (V)LDL, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool.

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

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

Plasma phospholipid transfer protein activity is decreased in type 2 diabetes during treatment with atorvastatin: a role for apolipoprotein E?

Plasma phospholipid transfer protein (PLTP) plays an important role in lipoprotein metabolism. PLTP activity is elevated in patients with diabetes, a condition with strongly elevated risk for coronary heart disease. The aim of this study was to test the hypothesis that statins reduce PLTP activity and to examine the potential role of apolipoprotein E (apoE). PLTP activity and apoE were measured in patients with type 2 diabetes from the DALI (Diabetes Atorvastatin Lipid Intervention) Study, a 30-week randomized double-blind placebo-controlled trial with atorvastatin (10 and 80 mg daily). At baseline, PLTP activity was positively correlated with waist circumference, HbA(1c), glucose, and apoE (all P < 0.05). Atorvastatin treatment resulted in decreased PLTP activity (10 mg atorvastatin: -8.3%, P < 0.05; 80 mg atorvastatin: -12.1%, P < 0.002). Plasma apoE decreased by 28 and 36%, respectively (P < 0.001). The decrease in apoE was strongly related to the decrease in PLTP activity (r = 0.565, P < 0.001). The change in apoE remained the sole determinant of the change in PLTP activity in a multivariate model. The activity of PLTP in type 2 diabetes is decreased by atorvastatin. The association between the decrease in PLTP activity and apoE during statin treatment supports the hypothesis that apoE may prevent PLTP inactivation.

The effect of sensitisation to insulin with pioglitazone on fasting and postprandial lipid metabolism, lipoprotein modification by lipases, and lipid transfer activities in type 2 diabetic patients

AIMS/HYPOTHESIS

Insulin resistance is thought to be central to the pathogenesis of diabetic dyslipidaemia. We hypothesised that improving insulin sensitivity would improve fasting and postprandial triglyceride metabolism in patients with type 2 diabetes. To this aim we studied fasting and postprandial lipaemia in type 2 diabetic patients before and after sensitisation to insulin with pioglitazone, compared with that observed in patients on an insulin-providing regime.

METHODS

In a double-blind placebo-controlled protocol, 22 patients with type 2 diabetes were randomly allocated to receive either pioglitazone (45 mg/day) or glibenclamide (5 mg/day), for a 20-week period. Fasting and postprandial lipid metabolism were investigated at baseline and at the end of the treatment period. A group of non-diabetic subjects was also studied.

RESULTS

Compared with glibenclamide treatment, pioglitazone treatment decreased fasting triglyceride, glucose and insulin levels and the homeostasis model assessment score of insulin resistance. Decreased fasting triglyceride after pioglitazone treatment was due to reduced VLDL triglyceride, particularly VLDL-2. Lipoprotein lipase activity was unchanged by pioglitazone treatment but hepatic lipase showed a significant decrease. Pioglitazone treatment lowered total postprandial triglyceride, as well as chylomicron- and chylomicron-remnant retinyl palmitate levels to normal. Glucose disposal improved but remained abnormal.

CONCLUSIONS/INTERPRETATION

Insulin sensitisation with pioglitazone has major effects in restoring postprandial lipaemia to normal, while also correcting fasting hypertriglyceridaemia; both factors may have consequences for atherogenic risk in diabetes.

Lipid transfer proteins (LTP) and atherosclerosis

This review deals with four lipid transfer proteins (LTP): three are involved in cholesteryl ester (CE) synthesis or transport, the fourth deals with plasma phospholipid (PL) transfer. Experimental models of atherosclerosis, clinical and epidemiological studies provided information as to the relationship of these LTP(s) to atherosclerosis, which is the main focus of this review. Thus, inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) 1 and 2 decreases cholesterol absorption, plasma cholesterol and aortic cholesterol esterification in the aorta. The discovery that tamoxifen is a potent ACAT inhibitor explained the plasma cholesterol lowering of the drug. The use of ACAT inhibition in humans is under current investigation. As low cholesteryl ester transfer protein (CETP) activity is connected with high HDL-C, several CETP inhibitors were tried in rabbits, with variable results. A new CETP inhibitor, Torcetrapib, was tested in humans and there was a 50-100% increase in HDL-C. Lecithin cholesterol acyl-transferase (LCAT) influences oxidative stress, which can be lowered by transient LCAT gene transfer in LCAT-/- mice. Phospholipid transfer protein (PLTP) deficiency reduced apo B production in apo E-/- mice, as well as oxidative stress in four models of mouse atherosclerosis. In conclusion, the ability to increase HDL-C so markedly by inhibitors of CETP introduces us into a new era in prevention and treatment of coronary heart disease (CHD).

Active and low-active forms of serum phospholipid transfer protein in a normal Finnish population sample

Human serum phospholipid transfer protein (PLTP) exists as a catalytically active (HA-PLTP) and a low-active (LA-PLTP) form. In this study, the association of PLTP activity and the concentrations of both forms with lipid and carbohydrate parameters were investigated. In a random Finnish population sample, serum PLTP concentration (n=250) was 6.56 +/- 1.45 mg/l, the mean lipoprotein-independent (PLTPexo) phospholipid transfer activity was 6.59 +/- 1.66 micromol/ml/h, and the mean lipoprotein-dependent (PLTPendo) activity was 1.37 +/- 0.29 micromol/ml/h. Of the serum PLTP concentration, approximately 46% was in a catalytically active form. HA-PLTP concentration correlated positively with serum PLTPexo activity (r=0.380, P <0.001), HDL cholesterol (r=0.291, P <0.001), and apolipoprotein A-I (r=0.187, P <0.01). Of the potential regulatory factors for PLTP, apolipoprotein E showed a weak positive correlation with serum PLTPexo (r=0.154, P <0.05) and PLTPendo (r=0.192, P <0.01) activity but not with PLTP concentration. Weak associations were also observed between PLTP parameters and determinants of glucose homeostasis (glucose, insulin, and homeostasis model assessment for insulin resistance). The present data on PLTP activity and concentration reveal novel connections of the two PLTP forms to lipid and carbohydrate metabolism.

Study of agreement between LDL size as measured by nuclear magnetic resonance and gradient gel electrophoresis

LDL particle size can be measured by gradient gel electrophoresis (GGE) and NMR. The agreement between the two methods has not been extensively evaluated. Therefore, we measured LDL size by NMR and GGE in 324 individuals (152 with type 1 diabetes and 172 controls). The Spearman correlation between both methods was 0.39 [95% confidence interval (CI) = 0.29, 0.48]. The average difference was 5.38 nm (NMR being smaller), but it increased with increasing LDL size. Less than 50% of people classified as pattern B on GGE were classified as pattern B on NMR (kappa = 0.31; 95% CI = 0.17, 0.45). Agreement was lower for diabetic subjects compared with controls, for women compared with men, and for subjects with triglycerides less than 1.30 mmol/l compared with subjects with triglycerides greater than 1.30 mmol/l. External validation showed that cholesteryl ester transfer rate was related to LDL size on GGE in all subgroups and to LDL size on NMR only in men and nondiabetic subjects. Our findings show that agreement between NMR- and GGE-based LDL size is far from perfect and is not consistent across subgroups of patients. In particular, the two methods should not be assumed to be interchangeable in women and diabetic subjects. Whether NMR or GGE predicts cardiovascular disease risk better has not yet been evaluated.

Emerging roles for phospholipid transfer protein in lipid and lipoprotein metabolism

PURPOSE OF REVIEW

This review highlights the recent key advances in our understanding of the role of phospholipid transfer protein in lipid and lipoprotein metabolism.

RECENT FINDINGS

The overexpression of human phospholipid transfer protein in mice is associated with an increase in atherosclerosis. This is consistent with earlier studies using mouse models suggesting that phospholipid transfer protein was pro-atherogenic. The presence of phospholipid transfer protein in macrophages and atherosclerotic lesions suggests that it could be either anti-atherogenic by facilitating lipid efflux or pro-atherogenic by facilitating lipid retention. Phospholipid transfer protein may also be a key player in reverse cholesterol transport, as it interacts with the adenosine triphosphate-binding cassette transporter A1 and facilitates lipid efflux from peripheral cells. Both the release of chymase, a neutral protease, from mast cells and the oxidation of HDL by hypochlorous acid can impair the function of phospholipid transfer protein in reverse cholesterol transport. Studies of phospholipid transfer protein-mediated phospholipid transfer activity in humans support a role for phospholipid transfer protein in hypertriglyceridemia, obesity, diabetes, inflammation and coronary artery disease, and in the modulation of LDL particle density and size. Furthermore, recent evidence suggests that phospholipid transfer protein may play a role in reproductive processes, in lipid and lipoprotein metabolism in the central nervous system, and in neurodegenerative disease.

SUMMARY

Phospholipid transfer protein is emerging as a multifaceted and multifunctional player in lipid and lipoprotein metabolism, but much additional work will be required to understand the significance of these recent findings for clinical practice.