Plasma lipid transfer proteins and cardiovascular disease. The Framingham Heart Study

Plasma proteome mediate the impact of PM2.5 on stroke: A 2-step Mendelian randomization study

The objectives of this study were to measure the mediation effect of plasma proteins and to clarify their mediating role in the relationship between stroke risk and particulate matter 2.5 (PM2.5) exposure. The possible mediating role of plasma proteins on the causative link between PM2.5 exposure and stroke incidence were examined using a two-step Mendelian randomization (MR) approach based on two-sample Mendelian randomization (TSMR). The findings revealed a significant positive causal relationship between PM2.5 exposure and stroke, with an inverse variance weighted odds ratio of 1.219 (95 % CI: 1.002 - 1.482, P < 0.05). Additionally, a positive causal association was identified between PM2.5 exposure and several plasma proteins, including FAM134B, SAP, ITGB7, Elafin, and DCLK3. Among these, FAM134B, ITGB7, Elafin, and DCLK3 also demonstrated a positive causal association with stroke, whereas only SAP was found to be negatively causally associated with stroke. Remarkably, four plasma proteins, namely DCLK3, FAM134B, Elafin, and ITGB7, were identified as mediators, accounting for substantial proportions (14.5 %, 13.6 %, 11.1 %, and 9.9 %) of the causal association between PM2.5 and stroke. These results remained robust across various sensitivity analyses. Consequently, the study highlights the significant and independent impact of PM2.5 on stroke risk and identifies specific plasma proteins as potential targets for preventive interventions against PM2.5-induced stroke.

The role of genetically-influenced phospholipid transfer protein activity in lipoprotein metabolism and coronary artery disease

BACKGROUND

Phospholipid transfer protein (PLTP) transfers surface phospholipids between lipoproteins and as such plays a role in lipoprotein metabolism, but with unclear effects on coronary artery disease (CAD) risk. We aimed to investigate the associations of genetically-influenced PLTP activity with 1-H nuclear magnetic resonance (1H-NMR) metabolomic measures and with CAD. Furthermore, using factorial Mendelian randomization (MR), we examined the potential additional effect of genetically-influenced PLTP activity on CAD risk on top of genetically-influenced low-density lipoprotein-cholesterol (LDL-C) lowering.

METHODS

Using data from UK Biobank, genetic scores for PLTP activity and LDL-C were calculated and dichotomised based on the median, generating four groups with combinations of high/low PLTP activity and high/low LDL-C levels for the factorial MR. Linear and logistic regressions were performed on 168 metabolomic measures (N = 58,514) and CAD (N = 318,734, N-cases=37,552), respectively, with results expressed as β coefficients (in standard deviation units) or odds ratios (ORs) and 95% confidence interval (CI).

RESULTS

Irrespective of the genetically-influenced LDL-C, genetically-influenced low PLTP activity was associated with a higher HDL particle concentration (β [95% CI]: 0.03 [0.01, 0.05]), smaller HDL size (-0.14 [-0.15, -0.12]) and higher triglyceride (TG) concentration (0.04 [0.02, 0.05]), but not with CAD (OR 0.99 [0.97, 1.02]). In factorial MR analyses, genetically-influenced low PLTP activity and genetically-influenced low LDL-C had independent associations with metabolomic measures, and genetically-influenced low PLTP activity did not show an additional effect on CAD risk.

CONCLUSIONS

Low PLTP activity associates with higher HDL particle concentration, smaller HDL particle size and higher TG concentration, but no association with CAD risk was observed.

Integrated omics approach for the identification of HDL structure-function relationships in PCSK9-related familial hypercholesterolemia

BACKGROUND

The role of proprotein convertase subtilisin/kexin type 9 (PCSK9) in dyslipidemia may go beyond its immediate effects on low-density lipoprotein receptor (LDL-R) activity.

OBJECTIVE

This study aimed to assess PCSK9-derived alterations of high-density lipoprotein (HDL) physiology, which bear a potential to contribute to cardiovascular risk profile.

METHODS

HDL was isolated from 33 patients with familial autosomal dominant hypercholesterolemia (FH), including those carrying PCSK9 gain-of-function (GOF) genetic variants (FH-PCSK9, n = 11), together with two groups of dyslipidemic patients employed as controls and carrying genetic variants in the LDL-R not treated (ntFH-LDLR, n = 11) and treated (tFH-LDLR, n = 11) with statins, and 11 normolipidemic controls. Biological evaluations paralleled by proteomic, lipidomic and glycomic analyses were applied to characterize functional and compositional properties of HDL.

RESULTS

Multiple deficiencies in the HDL function were identified in the FH-PCSK9 group relative to dyslipidemic FH-LDLR patients and normolipidemic controls, which involved reduced antioxidative, antiapoptotic, anti-thrombotic and anti-inflammatory activities. By contrast, cellular cholesterol efflux capacity of HDL was unchanged. In addition, multiple alterations of the proteomic, lipidomic and glycomic composition of HDL were found in the FH-PCSK9 group. Remarkably, HDLs from FH-PCSK9 patients were systematically enriched in several lysophospholipids as well as in A2G2S2 (GP13) glycan and apolipoprotein A-IV. Based on network analysis of functional and compositional data, a novel mosaic structure-function model of HDL biology involving FH was developed.

CONCLUSION

Several metrics of anti-atherogenic HDL functionality are altered in FH-PCSK9 patients paralleled by distinct compositional alterations. These data provide a first-ever overview of the impact of GOF PCSK9 genetic variants on structure-function relationships in HDL.

Alterations of HDL's to piHDL's Proteome in Patients with Chronic Inflammatory Diseases, and HDL-Targeted Therapies

Chronic inflammatory diseases, such as rheumatoid arthritis, steatohepatitis, periodontitis, chronic kidney disease, and others are associated with an increased risk of atherosclerotic cardiovascular disease, which persists even after accounting for traditional cardiac risk factors. The common factor linking these diseases to accelerated atherosclerosis is chronic systemic low-grade inflammation triggering changes in lipoprotein structure and metabolism. HDL, an independent marker of cardiovascular risk, is a lipoprotein particle with numerous important anti-atherogenic properties. Besides the essential role in reverse cholesterol transport, HDL possesses antioxidative, anti-inflammatory, antiapoptotic, and antithrombotic properties. Inflammation and inflammation-associated pathologies can cause modifications in HDL's proteome and lipidome, transforming HDL from atheroprotective into a pro-atherosclerotic lipoprotein. Therefore, a simple increase in HDL concentration in patients with inflammatory diseases has not led to the desired anti-atherogenic outcome. In this review, the functions of individual protein components of HDL, rendering them either anti-inflammatory or pro-inflammatory are described in detail. Alterations of HDL proteome (such as replacing atheroprotective proteins by pro-inflammatory proteins, or posttranslational modifications) in patients with chronic inflammatory diseases and their impact on cardiovascular health are discussed. Finally, molecular, and clinical aspects of HDL-targeted therapies, including those used in therapeutical practice, drugs in clinical trials, and experimental drugs are comprehensively summarised.

Systematic Mendelian randomization using the human plasma proteome to discover potential therapeutic targets for stroke

Stroke is the second leading cause of death with substantial unmet therapeutic needs. To identify potential stroke therapeutic targets, we estimate the causal effects of 308 plasma proteins on stroke outcomes in a two-sample Mendelian randomization framework and assess mediation effects by stroke risk factors. We find associations between genetically predicted plasma levels of six proteins and stroke (P ≤ 1.62 × 10-4). The genetic associations with stroke colocalize (Posterior Probability >0.7) with the genetic associations of four proteins (TFPI, TMPRSS5, CD6, CD40). Mendelian randomization supports atrial fibrillation, body mass index, smoking, blood pressure, white matter hyperintensities and type 2 diabetes as stroke risk factors (P ≤ 0.0071). Body mass index, white matter hyperintensity and atrial fibrillation appear to mediate the TFPI, IL6RA, TMPRSS5 associations with stroke. Furthermore, thirty-six proteins are associated with one or more of these risk factors using Mendelian randomization. Our results highlight causal pathways and potential therapeutic targets for stroke.

Expressing the Human Cholesteryl Ester Transfer Protein Minigene Improves Diet-Induced Fatty Liver and Insulin Resistance in Female Mice

Mounting evidence has shown that CETP has important physiological roles in adapting to chronic nutrient excess, specifically, to protect against diet-induced insulin resistance. However, the underlying mechanisms for the protective roles of CETP in metabolism are not yet clear. Mice naturally lack CETP expression. We used transgenic mice with a human CETP minigene (huCETP) controlled by its natural flanking region to further understand CETP-related physiology in response to obesity. Female huCETP mice and their wild-type littermates were fed a high-fat diet for 6 months. Blood lipid profile and liver lipid metabolism were studied. Insulin sensitivity was analyzed with euglycemic-hyperinsulinemic clamp studies combined with ³H-glucose tracer techniques. While high-fat diet feeding induced obesity for huCETP mice and their wild-type littermates lacking CETP expression, insulin sensitivity was higher for female huCETP mice than for their wild-type littermates. There was no difference in insulin sensitivity for male huCETP mice vs. littermates. The increased insulin sensitivity in females was largely caused by the better insulin-mediated suppression of hepatic glucose production. In huCETP females, CETP in the circulation decreased HDL-cholesterol content and increased liver cholesterol uptake and liver cholesterol and oxysterol contents, which was associated with the upregulation of LXR target genes in long-chain polyunsaturated fatty acid biosynthesis and PPARα target genes in fatty acid β-oxidation in the liver. The upregulated fatty acid β-oxidation may account for the improved fatty liver and liver insulin action in female huCETP mice. This study provides further evidence that CETP has beneficial physiological roles in the metabolic adaptation to nutrient excess by promoting liver fatty acid oxidation and hepatic insulin sensitivity, particularly for females.

Inducible phospholipid transfer protein deficiency ameliorates atherosclerosis

BACKGROUND AND AIMS

Atherosclerosis progression and regression studies are related to its prevention and treatment. Although we have gained extensive knowledge on germline phospholipid transfer protein (PLTP) deficiency, the effect of inducible PLTP deficiency in atherosclerosis remains unexplored.

METHODS

We generated inducible PLTP (iPLTP)-knockout (KO) mice and measured their plasma lipid levels after feeding a normal chow or a Western-type diet. Adenovirus associated virus-proprotein convertase subtilisin/kexin type 9 (AAV-PCSK9) was used to induce hypercholesterolemia in the mice. Collars were placed around the common carotid arteries, and atherosclerosis progression and regression in the carotid arteries and aortic roots were evaluated.

RESULTS

On a normal chow diet, iPLTP-KO mice exhibited decreased cholesterol, phospholipid, apoA-I, and apoB levels compared with control mice. Furthermore, the overall amount of high-density lipoprotein (HDL) particles was reduced in these mice, but this effect was more profound for larger HDL particles. On a Western-type diet, iPLTP-KO mice again exhibited reduced levels of all tested lipids, even though the basal lipid levels were increased. Additionally, these mice displayed significantly reduced atherosclerotic plaque sizes with increased plaque stability. Importantly, inducible PLTP deficiency significantly ameliorated atherosclerosis by reducing the size of established plaques and the number of macrophages in the plaques without causing lipid accumulation in the liver.

CONCLUSIONS

Induced PLTP deficiency in adult mice reduces plasma total cholesterol and triglycerides, prevents atherosclerosis progression, and promotes atherosclerosis regression. Thus, PLTP inhibition is a promising therapeutic approach for atherosclerosis.

The Role of Phospholipid Transfer Protein in the Development of Atherosclerosis

PURPOSE OF REVIEW

Phospholipid transfer protein (PLTP), a member of lipid transfer protein family, is an important protein involved in lipid metabolism in the circulation. This article reviews recent PLTP research progresses, involving lipoprotein metabolism and atherogenesis.

RECENT FINDINGS

PLTP activity influences atherogenic and anti-atherogenic lipoprotein levels. Human serum PLTP activity is a risk factor for human cardiovascular disease and is an independent predictor of all-cause mortality. PLTP deficiency reduces VLDL and LDL levels and attenuates atherosclerosis in mouse models, while PLTP overexpression exerts an opposite effect. Both PLTP deficiency and overexpression result in reduction of HDL which has different size, inflammatory index, and lipid composition. Moreover, although both PLTP deficiency and overexpression reduce cholesterol efflux capacity, but this effect has no impact in macrophage reverse cholesterol transport in mice. Furthermore, PLTP activity is related with metabolic syndrome, thrombosis, and inflammation. PLTP could be target for the treatment of dyslipidemia and atherosclerosis, although some potential off-target effects should be noted.

Cholesteryl ester transfer protein inhibitors in precision medicine

Dyslipidemia is associated with atherosclerosis and cardiovascular disease development, posing serious risks to human health. Cholesteryl ester transfer protein (CETP) is responsible for exchange of neutral lipids, such as cholesteryl ester and TG, between plasma high density lipoprotein (HDL) particles and Apolipoprotein B-100 (ApoB-100) containing lipoprotein particles. Genetic studies suggest that single-nucleotide polymorphism (SNPs) with loss of activity CETP is associated with increased HDL-C, reduced LDL-C, and cardiovascular risk. In animal studies, mostly in rabbits, which have similar CETP activity to humans, inhibition of CETP through antisense oligonucleotides reduced aortic arch atherosclerosis. Concerning this notion, inhibiting the CETP is considered as a promise approach to reduce cardiovascular events, and several CETP inhibitors have been recently studied as a cholesterol modifying agent to reduce cardiovascular mortality in high risk cardiovascular disease patients. However, in Phase III cardiovascular outcome trials, three CETP inhibitors, named Torcetrapib, Dalcetrapib, and Evacetrapib, did not provide expected cardiovascular benefits and failed to improve outcomes of patient with cardiovascular diseases (CVD). Although REVEAL trail has recently shown that Anacetrapib could reduce major coronary events, it was also shown to induce excessive lipid accumulation in adipose tissue; thereby, the further regulatory approval will not be sought. On the other hand, growing evidence indicated that the function of CETP inhibitors on modulating the cardiovascular events are determined by correlated single nucleotide polymorphism (SNP) in the ADCY9 gene. However, the underlying mechanisms whereby CETP inhibitors interact with the genotype are not yet elucidated, which could potentially be related to the genotype-dependent cholesterol efflux capacity of HDL particles. In the present review, we summarize the current understanding of the functions of CETP and the outcomes of the phase III randomized controlled trials of CETP inhibitors. In addition, we also put forward the implications from results of the trials which potentially suggest that the CETP inhibitors could be a promising precise therapeutic medicine for CVD based on genetic background.

Cholesteryl Ester Transfer Protein Impairs Triglyceride Clearance via Androgen Receptor in Male Mice

Elevated postprandial triacylglycerols (TAG) are an important risk factor for cardiovascular disease. Men have higher plasma TAG and impaired TAG clearance compared to women, which may contribute to sex differences in risk of cardiovascular disease. Understanding mechanisms of sex differences in TAG metabolism may yield novel therapeutic targets to prevent cardiovascular disease. Cholesteryl ester transfer protein (CETP) is a lipid shuttling protein known for its effects on high‐density lipoprotein (HDL) cholesterol levels. Although mice lack CETP, we previously demonstrated that transgenic CETP expression in female mice alters TAG metabolism. The impact of CETP on TAG metabolism in males, however, is not well understood. Here, we demonstrate that CETP expression increases plasma TAG in males, especially in very‐low density lipoprotein (VLDL), by impairing postprandial plasma TAG clearance compared to wild‐type (WT) males. Gonadal hormones were required for CETP to impair TAG clearance, suggesting a role for sex hormones for this effect. Testosterone replacement in the setting of gonadectomy was sufficient to restore the effect of CETP on TAG. Lastly, liver androgen receptor (AR) was required for CETP to increase plasma TAG. Thus, expression of CETP in males raises plasma TAG by impairing TAG clearance via testosterone signaling to AR. Further understanding of how CETP and androgen signaling impair TAG clearance may lead to novel approaches to reduce TAG and mitigate risk of cardiovascular disease.

Preβ1-high-density lipoprotein metabolism is delayed in patients with chronic kidney disease not on hemodialysis

BACKGROUND

Preβ1-high-density lipoprotein (HDL) is a lipid-poor cholesterol acceptor that is converted to lipid-rich HDL by lecithin-cholesterol acyltransferase (LCAT). In patients receiving hemodialysis, preβ1-HDL metabolism is hampered even if HDL cholesterol is normal. Hemodialysis may affect preβ1-HDL metabolism by releasing lipases from the vascular wall due to heparin.

OBJECTIVES

We investigated whether preβ1-HDL metabolism is delayed in patients with chronic kidney disease (CKD) who are not receiving hemodialysis.

METHODS

We examined 44 patients with Stage 3 or higher CKD and 22 healthy volunteers (Control group). The patients with CKD were divided into those without renal replacement therapy (CKD group, n = 22) and those undergoing continuous ambulatory peritoneal dialysis (CAPD group, n = 22). Plasma preβ1-HDL concentrations were determined by immunoassay. During incubation at 37°C, we used 5,5-dithio-bis (2-nitrobenzoic acid) (DTNB) to inhibit LCAT activity and defined the conversion halftime of preβ1-HDL (CHT_preβ1) as the time required for the difference in preβ1-HDL concentration in the presence and absence of 5,5-DTNB to reach half the baseline concentration.

RESULTS

The absolute and relative preβ1-HDL concentrations were higher, and CHT_preβ1 was longer in the CKD and CAPD groups than in the Control group. Preβ1-HDL concentration was significantly correlated with CHT_preβ1 but not with LCAT activity in patients with CKD and CAPD.

CONCLUSION

Preβ1-HDL metabolism is delayed in patients with CKD who are not on hemodialysis. This preβ1-HDL metabolic delay may progress as renal function declines.

Association of Serum Cholesterol Ester Transfer Protein Levels with Taq IB Polymorphism in Acute Coronary Syndrome

Information on the relationship between circulating cholesteryl ester transfer protein (CETP) levels and coronary heart disease (CHD) incidence (and also, therefore, acute coronary syndrome [ACS]) is conflicting. Many studies have been published concerning this relationship, most of which have incompatible results. In our study, we aimed to determine serum CETP levels in subject individuals with ACS and healthy control individuals, and the association of those levels with Taq IB polymorphism. The current study was conducted with 62 hospitalized patients who had been diagnosed with ACS and 26 controls. All subjects were selected from a previous study of which we are among the coauthors. Serum CETP levels were determined by quantitative enzyme-linked immunosorbent assay (ELISA). The mean serum CETP levels in all patients were significantly higher than those in controls. CETP TaqIB polymorphism affected serum CETP levels, with higher serum CETP for the GA genotype in both groups than in other genotypes. Although the AA genotype showed higher CETP levels than the GG genotype in patients with ACS, the GG showed higher CETP than the AA in healthy controls. Our results support an association between high serum CETP and ACS incidence. Our study helped address some of the controversies regarding the relationship of serum CETP mass to atherosclerosis, in addition to the association of ACS occurrence with circulating CETP levels.

Impact of Phospholipid Transfer Protein in Lipid Metabolism and Cardiovascular Diseases

PLTP plays an important role in lipoprotein metabolism and cardiovascular disease development in humans; however, the mechanisms are still not completely understood. In mouse models, PLTP deficiency reduces cardiovascular disease, while its overexpression induces it. Therefore, we used mouse models to investigate the involved mechanisms. In this chapter, the recent main progresses in the field of PLTP research are summarized, and our focus is on the relationship between PLTP and lipoprotein metabolism, as well as PLTP and cardiovascular diseases.

Modified lipoproteins in periodontitis: a link to cardiovascular disease?

There is a strong association between periodontal disease and atherosclerotic cardiovascular disorders. A key event in the development of atherosclerosis is accumulation of modified lipoproteins within the arterial wall. We hypothesise that patients with periodontitis have an altered lipoprotein profile towards an atherogenic form. Therefore, the present study aims at identifying modifications of plasma lipoproteins in periodontitis. Lipoproteins from ten female patients with periodontitis and gender- and age-matched healthy controls were isolated by density-gradient ultracentrifugation. Proteins were separated by 2D gel-electrophoresis and identified by map-matching or by nano-LC followed by MS. Apolipoprotein (Apo) A-I (ApoA-I) methionine oxidation, Oxyblot, total antioxidant capacity and a multiplex of 71 inflammation-related plasma proteins were assessed. Reduced levels of apoJ, phospholipid transfer protein, apoF, complement C3, paraoxonase 3 and increased levels of α-1-antichymotrypsin, apoA-II, apoC-III were found in high-density lipoprotein (HDL) from the patients. In low-density lipoprotein (LDL)/very LDL (VLDL), the levels of apoL-1 and platelet-activating factor acetylhydrolase (PAF-AH) as well as apo-B fragments were increased. Methionine oxidation of apoA-I was increased in HDL and showed a relationship with periodontal parameters. α-1 antitrypsin and α-2-HS glycoprotein were oxidised in LDL/VLDL and antioxidant capacity was increased in the patient group. A total of 17 inflammation-related proteins were important for group separation with the highest discriminating proteins identified as IL-21, Fractalkine, IL-17F, IL-7, IL-1RA and IL-2. Patients with periodontitis have an altered plasma lipoprotein profile, defined by altered protein levels as well as post-translational and other structural modifications towards an atherogenic form, which supports a role of modified plasma lipoproteins as central in the link between periodontal and cardiovascular disease (CVD).

Shotgun proteomic analysis reveals proteome alterations in HDL of patients with cholesteryl ester transfer protein deficiency

BACKGROUND

We previously reported that the patients with cholesteryl ester transfer protein (CETP) deficiency (CETP-D) show marked changes in the size and lipid compositions of high-density lipoprotein (HDL) and that they are not protected from atherosclerotic cardiovascular diseases, despite increased serum HDL-cholesterol (HDL-C) levels. HDL particles carry a variety of proteins, some of which are known to have antiatherogenic functions.

OBJECTIVE

This study aimed to investigate the protein composition of HDL particles in patients with CETP-D.

METHODS

Eight patients with complete deficiency of CETP and 8 normolipidemic healthy subjects were enrolled. We performed shotgun proteomic analysis to investigate the proteome of ultracentrifugally isolated HDL.

RESULTS

We identified 79 HDL-associated proteins involved in lipid metabolism, protease inhibition, complement regulation, and acute-phase response, including 5 potential newly identified HDL-associated proteins such as angiopoietin-like3 (ANGPTL3). Spectral counts of apolipoprotein (apo) E were increased in patients with CETP-D compared with controls (60.3 ± 6.9 vs 43.7 ± 2.5, P < .001), which is concordant with our previous report. Complement regulatory proteins such as C3, C4a, C4b, and C9 were also significantly enriched in HDL from patients with CETP-D. Furthermore, apoC-III and ANGPTL3, both of which are now known to associate with increased atherosclerotic cardiovascular diseases, were enriched in patients with CETP-D compared with normolipidemic subjects (35.9 ± 5.3 vs 27.1 ± 3.7, 2.3 ± 1.1 vs 0.4 ± 1.1, respectively; P < .01).

CONCLUSION

We have characterized HDL-associated proteins in patients with CETP-D. We identified a significant increase in the amount of apoE, apoC-III, ANGPTL3, and complement regulatory proteins. These proteomic changes might be partly responsible for the enhanced atherogenicity of patients with CETP-D.

CETP Inhibition Improves HDL Function but Leads to Fatty Liver and Insulin Resistance in CETP-Expressing Transgenic Mice on a High-Fat Diet

In clinical trials, inhibition of cholesteryl ester transfer protein (CETP) raises HDL cholesterol levels but does not robustly improve cardiovascular outcomes. Approximately two-thirds of trial participants are obese. Lower plasma CETP activity is associated with increased cardiovascular risk in human studies, and protective aspects of CETP have been observed in mice fed a high-fat diet (HFD) with regard to metabolic outcomes. To define whether CETP inhibition has different effects depending on the presence of obesity, we performed short-term anacetrapib treatment in chow- and HFD-fed CETP transgenic mice. Anacetrapib raised HDL cholesterol and improved aspects of HDL functionality, including reverse cholesterol transport, and HDL's antioxidative capacity in HFD-fed mice was better than in chow-fed mice. Anacetrapib worsened the anti-inflammatory capacity of HDL in HFD-fed mice. The HDL proteome was markedly different with anacetrapib treatment in HFD- versus chow-fed mice. Despite benefits on HDL, anacetrapib led to liver triglyceride accumulation and insulin resistance in HFD-fed mice. Overall, our results support a physiologic importance of CETP in protecting from fatty liver and demonstrate context selectivity of CETP inhibition that might be important in obese subjects.

Plasma Phospholipid Transfer Protein Promotes Platelet Aggregation

It remains unclear whether plasma phospholipid transfer protein (PLTP) is involved in hyper-coagulation or hypo-coagulation. This study investigated the direct effect of PLTP on platelet aggregation and the underlying mechanism. Washed platelets from humans or mice and mouse platelet-rich plasma and human recombinant PLTP were isolated. PLTP is present in human platelets. We assessed adenosine diphosphate (ADP)-, collagen- and thrombin-induced platelet aggregation, phosphatidylserine externalization and photothrombosis-induced cerebral infarction in mice. PLTP over-expression increased platelet aggregation, while PLTP deficiency had the opposing reaction. Human recombinant PLTP increased both mouse and human platelet aggregation in a dose-dependent manner. Phosphatidylserine externalization provides a water/lipid surface for the interaction of coagulation factors, which accelerates thrombosis. Compared with wild-type controls, platelets from PLTP transgenic mice had significantly more phosphatidylserine on the exterior surface of the plasma membrane, whereas platelets from PLTP-deficient mice had significantly less phosphatidylserine on the surface, thus PLTP influences fibrinogen binding on the plasma membrane. Moreover, recombinant PLTP together with ADP significantly increased phosphatidylserine exposure on the plasma membrane of PLTP-deficient platelets, thereby increasing fibrinogen binding. PLTP over-expression significantly accelerated the incidence of photothrombosis-induced infarction in mice, whereas PLTP deficiency significantly reduced the frequency of infarction. We concluded that PLTP promotes phosphatidylserine externalization at the plasma membrane of platelets and accelerates ADP- or collagen-induced platelet aggregation. This effect plays an important role in the initiation of thrombin generation and platelet aggregation under sheer stress conditions. Thus, PLTP is involved in hyper-coagulation. Therefore, PLTP inhibition could be a novel approach for countering thrombosis.

Genetically elevated high-density lipoprotein cholesterol through the cholesteryl ester transfer protein gene does not associate with risk of Alzheimer's disease

Introduction

There is conflicting evidence whether high-density lipoprotein cholesterol (HDL-C) is a risk factor for Alzheimer's disease (AD) and dementia. Genetic variation in the cholesteryl ester transfer protein (CETP) locus is associated with altered HDL-C. We aimed to assess AD risk by genetically predicted HDL-C.

Methods

Ten single nucleotide polymorphisms within the CETP locus predicting HDL-C were applied to the International Genomics of Alzheimer's Project (IGAP) exome chip stage 1 results in up 16,097 late onset AD cases and 18,077 cognitively normal elderly controls. We performed instrumental variables analysis using inverse variance weighting, weighted median, and MR-Egger.

Results

Based on 10 single nucleotide polymorphisms distinctly predicting HDL-C in the CETP locus, we found that HDL-C was not associated with risk of AD (P > .7).

Discussion

Our study does not support the role of HDL-C on risk of AD through HDL-C altered by CETP. This study does not rule out other mechanisms by which HDL-C affects risk of AD.

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CETP SNPs were not associated with AD in a large sample of AD cases/controls.

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Genetically predicted HDL-C through CETP does not associate with AD.

Plasma lecithin:cholesterol acyltransferase and phospholipid transfer protein activity independently associate with nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a highly prevalent condition which contributes to atherogenic apolipoprotein B dyslipoproteinemias. Lecithin:cholesterol acyltransferase (LCAT) and phospholipid transfer protein (PLTP) are both synthesized by the liver and are important in lipid metabolism. Here, we interrogated the impact of NAFLD on plasma LCAT and PLTP activities.

METHODS

Plasma LCAT activity (exogenous substrate assay) and PLTP activity (phospholipid vesicles-HDL assay) were determined in 348 subjects (279 men; 81 subjects with type 2 diabetes (T2DM); 123 with metabolic syndrome (MetS)). A Fatty Liver Index (FLI) ≥60 was used as a proxy of NAFLD. Insulin resistance was determined by homoeostasis model assessment (HOMA-IR).

RESULTS

A total of 147 participants had an FLI ≥60 coinciding with T2DM and MetS (P < 0.001 for each). Plasma LCAT activity and PLTP activity were on average 12% and 5% higher, respectively, in subjects with an FLI ≥ 60 (P < 0.001 for each). In age- and sex-adjusted partial linear regression analysis, LCAT activity and PLTP activity were positively related to various obesity measures and HOMA-IR (P < 0.001 for each). In multivariable linear regression analyses adjusted for age and sex, LCAT activity was associated with an FLI ≥ 60 independent of T2DM and MetS, the waist/hip ratio, or HOMA-IR (β = 0.307 to 0.366, P < 0001 for all models). PLTP activity was also associated with an FLI ≥ 60 independent of these variables (β = 0.151 to 0223, P = 0.013 to 0.001).

CONCLUSION

NAFLD, as inferred from an FLI≥60, confers higher plasma LCAT and to a lesser extent PLTP activity, even when taking account of T2DM, MetS, central obesity and insulin resistance.

Alteration of HDL Protein Composition with Hemodialysis Initiation

BACKGROUND AND OBJECTIVES

HDL particles obtained from patients on chronic hemodialysis exhibit lower cholesterol efflux capacity and are enriched in inflammatory proteins compared with those in healthy individuals. Observed alterations in HDL proteins could be due to effects of CKD, but also may be influenced by the hemodialysis procedure, which stimulates proinflammatory and prothrombotic pathways.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We compared HDL-associated proteins in 143 participants who initiated hemodialysis within the previous year with those of 110 participants with advanced CKD from the Hemodialysis Fistula Maturation Study. We quantified concentrations of 38 HDL-associated proteins relative to total HDL protein using targeted mass spectrometry assays that included a stable isotope-labeled internal standard. We used linear regression to compare the relative abundances of HDL-associated proteins after adjustment and required a false discovery rate q value ≤10% to control for multiple testing. We further assessed the association between hemodialysis initiation and cholesterol efflux capacity in a subset of 80 participants.

RESULTS

After adjustment for demographics, comorbidities, and other clinical characteristics, eight HDL-associated proteins met the prespecified false discovery threshold for association. Recent hemodialysis initiation was associated with higher HDL-associated concentrations of serum amyloid A1, A2, and A4; hemoglobin-β; haptoglobin-related protein; cholesterylester transfer protein; phospholipid transfer protein; and apo E. The trend for participants recently initiating hemodialysis for lower cholesterol efflux capacity compared with individuals with advanced CKD did not reach statistical significance.

CONCLUSIONS

Compared with advanced CKD, hemodialysis initiation within the previous year is associated with higher concentrations of eight HDL proteins related to inflammation and lipid metabolism. Identified associations differ from those recently observed for nondialysis-requiring CKD. Hemodialysis initiation may further impair cholesterol efflux capacity. Further work is needed to clarify the clinical significance of the identified proteins with respect to cardiovascular risk.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2018_07_25_CJASNPodcast_18_8_W.mp3.

Prodomain of Furin Promotes Phospholipid Transfer Protein Proteasomal Degradation in Hepatocytes

BACKGROUND

Phospholipid transfer protein (PLTP) is one of the major modulators of lipoprotein metabolism and atherosclerosis development; however, little is known about the regulation of PLTP. The effect of hepatic prodomain of furin (profurin) expression on PLTP processing and function is investigated.

METHODS AND RESULTS

We used adenovirus expressing profurin in mouse liver to evaluate PLTP activity, mass, and plasma lipid levels. We coexpressed PLTP and profurin in human hepatoma cell line cells and studied their interaction. We found profurin expression significantly reduced plasma lipids, plasma PLTP activity, and mass in all tested mouse models, compared with controls. Moreover, the expression of profurin dramatically reduced liver PLTP activity and protein level. We further explored the mechanism using in vivo and ex vivo approaches. We found that profurin can interact with intracellular PLTP and promote its ubiquitination and proteasomal degradation, resulting in less PLTP secretion from the hepatocytes. Furin does not cleave PLTP; instead, it forms a complex with PLTP, likely through its prodomain.

CONCLUSIONS

Our study reveals that hepatic PLTP protein is targeted for proteasomal degradation by profurin expression, which could be a novel posttranslational mechanism underlying PLTP regulation.

Phospholipid transfer protein: its impact on lipoprotein homeostasis and atherosclerosis

Phospholipid transfer protein (PLTP) is one of the major modulators of lipoprotein metabolism and atherosclerosis development in humans; however, we still do not quite understand the mechanisms. In mouse models, PLTP overexpression induces atherosclerosis, while its deficiency reduces it. Thus, mouse models were used to explore the mechanisms. In this review, I summarize the major progress made in the PLTP research field and emphasize its impact on lipoprotein metabolism and atherosclerosis, as well as its regulation.

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.

Overexpression and deletion of phospholipid transfer protein reduce HDL mass and cholesterol efflux capacity but not macrophage reverse cholesterol transport

Phospholipid transfer protein (PLTP) may affect macrophage reverse cholesterol transport (mRCT) through its role in the metabolism of HDL. Ex vivo cholesterol efflux capacity and in vivo mRCT were assessed in PLTP deletion and PLTP overexpression mice. PLTP deletion mice had reduced HDL mass and cholesterol efflux capacity, but unchanged in vivo mRCT. To directly compare the effects of PLTP overexpression and deletion on mRCT, human PLTP was overexpressed in the liver of wild-type animals using an adeno-associated viral (AAV) vector, and control and PLTP deletion animals were injected with AAV-null. PLTP overexpression and deletion reduced plasma HDL mass and cholesterol efflux capacity. Both substantially decreased ABCA1-independent cholesterol efflux, whereas ABCA1-dependent cholesterol efflux remained the same or increased, even though preβ HDL levels were lower. Neither PLTP overexpression nor deletion affected excretion of macrophage-derived radiocholesterol in the in vivo mRCT assay. The ex vivo and in vivo assays were modified to gauge the rate of cholesterol efflux from macrophages to plasma. PLTP activity did not affect this metric. Thus, deviations in PLTP activity from the wild-type level reduce HDL mass and ex vivo cholesterol efflux capacity, but not the rate of macrophage cholesterol efflux to plasma or in vivo mRCT.

Alterations in high-density lipoprotein proteome and function associated with persistent organic pollutants

There is a growing body of evidence that persistent organic pollutants (POPs) may increase the risk for cardiovascular disease (CVD), but the mechanisms remain unclear. High-density lipoprotein (HDL) acts protective against CVD by different processes, and we have earlier found that HDL from subjects with CVD contains higher levels of POPs than healthy controls. In the present study, we have expanded analyses on the same individuals living in a contaminated community and investigated the relationship between the HDL POP levels and protein composition/function. HDL from 17 subjects was isolated by ultracentrifugation. HDL protein composition, using nanoliquid chromatography tandem mass spectrometry, and antioxidant activity were analyzed. The associations of 16 POPs, including polychlorinated biphenyls (PCBs) and organochlorine pesticides, with HDL proteins/functions were investigated by partial least square and multiple linear regression analysis. Proteomic analyses identified 118 HDL proteins, of which ten were significantly (p<0.05) and positively associated with the combined level of POPs or with highly chlorinated PCB congeners. Among these, cholesteryl ester transfer protein and phospholipid transfer protein, as well as the inflammatory marker serum amyloid A, were found. The serum paraoxonase/arylesterase 1 activity was inversely associated with POPs. Pathway analysis demonstrated that up-regulated proteins were associated with biological processes involving lipoprotein metabolism, while down-regulated proteins were associated with processes such as negative regulation of proteinases, acute phase response, platelet degranulation, and complement activation. These results indicate an association between POP levels, especially highly chlorinated PCBs, and HDL protein alterations that may result in a less functional particle. Further studies are needed to determine causality and the importance of other environmental factors. Nevertheless, this study provides a first insight into a possible link between exposure to POPs and risk of CVD.

Serum Lipid Transfer Proteins in Hypothyreotic Patients Are Inversely Correlated with Thyroid-Stimulating Hormone (TSH) Levels

Background

Plasma cholesteryl ester transfer protein (CETP) activity is often decreased in patients with hypothyroidism, whereas less is known about the phospholipid transfer protein (PLTP). We aimed to evaluate simultaneously serum CETP and PLTP activity in patients diagnosed with hypothyroidism.

Material/Methods

The selection criteria for control group members (without thyroid dysfunction) in this case to case study were levels of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides similar to those in study group patients (101 patients diagnosed with hypothyroidism). Serum CETP and PLTP activities were measured by homogenous fluorometric assays using synthetic donor particle substrates.

Results

Serum CETP and PLTP activities in hypothyreotic patients were lower (p<0.001) compared with those in healthy subjects. This lowering was associated with significant changes in HDL-C subclasses: decrease in HDL₂- and increase in HDL₃ cholesterol levels. Multiple linear regression analyses adjusted for age, sex, body mass index, smoking habits, and alcohol drinking showed a strong association between hypothyroidism and activity of lipid transfer proteins. A linear inverse relationship between thyroid-stimulating hormone (TSH) and CETP (r=−0.21; p<0.01) and between TSH and PLTP (r=−0.24; p<0.001) was shown. There also was a positive correlation (p<0.001) between CETP and HDL₂ cholesterol (r=0.27) and between PLTP and HDL₂ cholesterol (r=0.37). A negative correlation between CETP and HDL₃ cholesterol (r=−0.22: p<0.01) and between PLTP and HDL₃ cholesterol (r=−0.24; p<0.001) has been demonstrated as well.

Conclusions

The decreased HDL₂ and increased HDL₃ cholesterol levels in subjects with hypothyroidism are consequences of decreased activity of lipid transfer proteins. These changes are early symptoms of lipid disturbances in hypothyroidism.

Re-evaluation of cholesteryl ester transfer protein function in atherosclerosis based upon genetics and pharmacological manipulation

PURPOSE OF REVIEW

To re-evaluate the functions of plasma cholesteryl ester transfer protein (CETP) in atherosclerosis based upon recent findings from human genetics and pharmacological CETP manipulation.

RECENT FINDINGS

CETP is involved in the transfer of cholesteryl ester from HDL to apolipoprotein B-containing lipoproteins, a key step of reverse cholesterol transport (RCT). CETP inhibitors have been developed to raise serum HDL-cholesterol (HDL-C) levels and reduce cardiovascular events. However, outcome studies of three CETP inhibitors (torcetrapib, dalcetrapib and evacetrapib) were prematurely terminated because of increased mortality or futility despite marked increases in HDL-cholesterol and decreases in LDL-cholesterol except for dalcetrapib. Patients with CETP deficiency show remarkable changes in HDL and LDL and are sometimes accompanied by atherosclerotic cardiovascular diseases. Recent prospective epidemiological studies demonstrated atheroprotective roles of CETP. CETP inhibition induces formation of small dense LDL and possibly dysfunctional HDL and downregulates hepatic scavenger receptor class B type I (SR-BI). Therefore, CETP inhibitors may interrupt LDL receptor and SR-BI-mediated cholesterol delivery back to the liver.

SUMMARY

For future drug development, the opposite strategy, namely enhancers of RCT via CETP and SR-BI activation as well as the inducers of apolipoprotein A-I or HDL production might be a better approach rather than delaying HDL metabolism by inhibiting a main stream of RCT in vivo.

Serum CETP and PLTP activity in middle-aged men living in urban or rural area of the Lower Silesia region. PURE Poland sub-study

INTRODUCTION

The dependence of lipid transfer proteins on significant pro-atherogenic factors is unclear. The aim of the study was to evaluate serum cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activity in relation to lipid disturbances in men living in an urban or rural area.

MATERIAL AND METHODS

A group of 427 men, volunteers for the Prospective Urban Rural Epidemiology (PURE) sub-study - 263 urban inhabitants (aged 51.9 ±6.0) and 164 residents of villages (aged 51.1 ±5.9) - were examined. In the multivariable linear regression model, the following factors were included as potential confounders: age, body mass index (BMI), smoking, alcohol consumption, hs-C-reactive protein reaction (hs-CRP) and co-existence of chronic diseases.

RESULTS

In multiple linear regression models, site of residence (urban or rural area) was the most important independent and consistent predictor of CETP and PLTP activity; β coefficients (95% CI) for CETP (0.18) and PLTP (-0.29) were significant at levels of p < 0.001. Three-way analysis of variance showed no effect of smoking or moderate alcohol consumption on lipid transfer proteins; however, CETP activity showed an interaction effect between these risk factors. In the group of all men, CETP activity was significantly and positively correlated with total cholesterol (r = 0.24), low-density lipoprotein cholesterol (r = 0.18), and non-high density lipoprotein cholesterol (r = 0.21), whereas PLTP activity was correlated with BMI (r = 0.12). Body mass index in rural men was higher than in the urban male population.

CONCLUSIONS

Increased PLTP activity, recognized as a pro-atherogenic factor, and decreased CETP activity, known as a protective factor, both observed in men living in rural areas, are probably conditioned by nutritional and/or genetic factors.

Rationale and Design of the PROSPECTIVE Trial: Probucol Trial for Secondary Prevention of Atherosclerotic Events in Patients with Prior Coronary Heart Disease

BACKGROUND

Reduction of serum LDL-cholesterol by statins was shown to improve clinical outcomes in patients with coronary heart disease (CHD). Although intensive statin therapy significantly reduced cardiovascular risks, atherosclerotic cardiovascular events have not been completely prevented. Therefore, effective pharmacologic therapy is necessary to improve "residual risks" in combination with statins. Probucol has a potent antioxidative effect, inhibits the oxidation of LDL, and reduces xanthomas. Probucol Trial for Secondary Prevention of Atherosclerotic Events in Patients with Prior Coronary Heart Disease (PROSPECTIVE) is a multicenter, randomized, prospective study designed to test the hypothesis that the addition of probucol to other lipid-lowering drugs will prevent cerebro- and cardiovascular events in patients with prior coronary events and high LDL cholesterol levels.

STUDY DESIGN

The study will recruit approximately 860 patients with a prior CHD and dyslipidemia with LDL-C level ≥140 mg/dl without any medication and those treated with any lipid-lowering drugs with LDL-C level ≥100 mg/dl. Lipid-lowering agents are continuously administered during the study period in control group, and probucol (500 mg/day, 250 mg twice daily) is added to lipid-lowering therapy in the test group. The efficacy and safety of probucol with regard to the prevention of cerebro- and cardiovascular events and the intima-media thickness of carotid arteries as a surrogate marker will be evaluated.

SUMMARY

PROSPECTIVE will determine whether the addition of probucol to other lipid-lowering drugs improves cerebro- and cardiovascular outcomes in patients with prior coronary heart disease. Furthermore, the safety of a long-term treatment with probucol will be clarified.

The controversy over the use of cholesteryl ester transfer protein inhibitors: is there some light at the end of the tunnel?

BACKGROUND

According to epidemiological studies, there is no clear relationship between the plasma cholesteryl ester transfer protein (CETP) concentration and the development of atherosclerosis in human populations. Although some studies suggest that increased CETP activity relates to undesirable profiles of plasma lipoproteins, promoting an anti-atherogenic plasma lipoprotein profile by drugs that inhibit CETP has not succeeded in preventing atherosclerosis in humans.

MATERIALS AND METHODS

This review describes 28 investigations in human populations dealing with plasma CETP, 11 in mice that express human CETP and seven in animals (six in rabbits and one in mice) in which plasma CETP activity was inhibited by drugs.

RESULTS

Present review shows that models in mice expressing human CETP are not illuminating because they report increase as well reduction of atherosclerosis. However, investigations in rabbits and mice that develop severe hypercholesterolaemia clearly indicate that impairment of the plasma CETP activity elicits protection against the development of atherosclerosis; in all of these experiments are attained substantial reductions of the atherogenic lipoproteins, namely, plasma apoB containing lipoproteins.

CONCLUSION

These models are strong indicators that the benefit in preventing atherosclerosis should be earned in cases of hyperlipidemia by CETP inhibitors.

Elevated CETP Lipid Transfer Activity is Associated with the Risk of Venous Thromboembolism

Aim: Cholesteryl ester transfer protein (CETP) is an important lipid transfer factor in plasma that enhances prothrombinase activity in purified systems. This study was conducted to test the association of plasma CETP activity with venous thrombosis (VTE) and to address the procoagulant mechanism of CETP activity in prothrombinase assays.

Methods: We measured CETP lipid transfer activity in plasmas of 49 male VTE patients and in plasmas of matched controls. CETP procoagulant activity was tested in purified prothrombinase systems.

Results: CETP lipid transfer activity levels were significantly higher in VTE patients than in controls (p = 0.0008). A subset of patients carrying the CETP mutations Ala373Pro and Arg451Gln, which were also linked to the VTE risk, showed significantly higher plasma CETP activity than the non-carriers. The plasma CETP activity negatively correlated with APTT, suggesting that the CETP activity is associated with plasma coagulability. Recombinant (r) CETP bound to both factor Xa (Kd = 15 nM) and Gla-domainless factor Xa (Kd = 59 nM), whereas rCETP enhanced prothrombin activation by factor Xa, but not by Gla-domainless factor Xa. rCETP also required factor Va for enhancement of prothrombinase activity. When we addressed the effects of mutations in CETP on prothrombinase activity, Gln451-rCETP was found to have five-fold higher thrombin generation activity than wt-rCETP or Pro373-rCETP.

Conclusions: Elevated CETP lipid transfer activity in plasma was associated with the risk of VTE. Gln451-CETP, which is linked to VTE, has much higher procoagulant activity than wt-CETP. CETP might act as a physiologic procoagulant by mechanisms that involve its direct binding to factor Xa.

HDL functionality in reverse cholesterol transport--Challenges in translating data emerging from mouse models to human disease

Whereas LDL-derived cholesterol accumulates in atherosclerotic lesions, HDL particles are thought to facilitate removal of cholesterol from the lesions back to the liver thereby promoting its fecal excretion from the body. Because generation of cholesterol-loaded macrophages is inherent to atherogenesis, studies on the mechanisms stimulating the release of cholesterol from these cells and its ultimate excretion into feces are crucial to learn how to prevent lesion development or even induce lesion regression. Modulation of this key anti-atherogenic pathway, known as the macrophage-specific reverse cholesterol transport, has been extensively studied in several mouse models with the ultimate aim of applying the emerging knowledge to humans. The present review provides a detailed comparison and critical analysis of the various steps of reverse cholesterol transport in mouse and man. We attempt to translate this in vivo complex scenario into practical concepts, which could serve as valuable tools when developing novel HDL-targeted therapies.

Postprandial Studies Uncover Differing Effects on HDL Particles of Overt and Subclinical Hypothyroidism

BACKGROUND

Overt hypothyroidism (OH) is associated with abnormal lipid metabolism and endothelial dysfunction under fasting conditions. The balance of evidence suggests similar but less marked abnormalities in subclinical hypothyroidism (SCH). There are few data regarding the metabolic and vascular effects of OH or SCH under postprandial conditions.

METHODS

This was a cross-sectional study, carried out in a teaching hospital. Subjects with OH (n = 21), SCH (n = 28), and controls (n = 44) matched for age, sex, and body mass index (BMI) were studied under fasting and postprandial conditions. Postprandial lipid metabolism with particular emphasis on intestinally derived lipoproteins, HDL cholesterol (HDL), and endothelial function were compared in subjects with OH and SCH who were matched for age, sex, and BMI. Apolipoprotein B48 (Apo B48), a measure of intestinally derived lipoprotein, was measured by enzyme-linked immunosorbent assay. HDL was subfractionated into HDL2 and HDL3 by rapid ultracentrifugation. Functional aspects of HDL were determined by monitoring the activities of cholesteryl-ester-transfer-protein (CETP) and lecithin-cholesterol-acyl-transferase (LCAT). Systemic and HDL-associated inflammation was assessed by measuring serum-amyloid-A (SAA) levels. Endothelial function was assessed by flow-mediated dilatation (FMD) of the brachial artery in response to hyperemia of the forearm.

RESULTS

There were no significant between-group differences in LDL cholesterol or triglyceride concentration. Peak Apo B48 levels were greater in OH (p < 0.001) and SCH (p < 0.05) compared with control subjects. HDL area under the curve (AUC) was lower postprandially in SCH (p < 0.001) but not OH compared with control subjects. HDL2- and HDL3-associated CETP AUC was lower only in OH (p < 0.005) compared with controls. FMD was reduced in OH (p < 0.05) compared with SCH and controls postprandially.

CONCLUSION

Postprandial lipoprotein and vascular abnormalities differ between OH and SCH. Although both are characterized by increased intestinally derived lipoprotein particles, HDL is reduced only in SCH. Maintained HDL in OH probably reflects reduced CETP activity, which was not observed in SCH. Postprandial endothelial dysfunction is abnormal only in OH, and this effect does not appear to reflect increased inflammation.

Did we abandon probucol too soon?

PURPOSE OF REVIEW

Probucol is a potent antioxidative drug that has been used for prevention and treatment of atherosclerotic cardiovascular diseases and xanthoma. Probucol has been used as a lipid-lowering drug for a long time especially in Japan, although Western countries quitted its use because of the reduction in serum HDL-cholesterol (HDL-C). This review highlights both basic and clinical studies that provide new insights into the pleiotropic effects of probucol.

RECENT FINDINGS

Recently, the mechanisms for the pharmacologic actions of probucol have been elucidated at the molecular level with a special focus on HDL metabolism and its functions. Probucol enhances plasma cholesteryl ester transfer protein activity and hepatic scavenger receptor class B type I, causing a decrease in HDL-C. It also accelerates the antioxidative function of HDL via increase in paraoxonase 1 activity. Recent retrospective analyses of probucol-treated patients with heterozygous familial hypercholesterolemia and those after coronary revascularization demonstrated a strong beneficial effect of probucol on secondary prevention of cardiovascular events and mortality.

SUMMARY

Probucol has pleiotropic and beneficial therapeutic effects on cardiovascular system. Although statins are effective for lowering LDL-cholesterol (LDL-C) and reducing coronary heart disease risk, probucol should be considered as an option in case statins are not effective.

Cholesteryl Ester Transfer Protein Inhibitors - Future Soon to be REVEALed

Reduction of the remaining residual cardiovascular risk is a clinical unmet need currently being addressed through a combination of further reduction of plasma concentrations of low-density lipoproteins (LDLs) and increasing plasma concentrations of high-density lipoproteins (HDLs). This brief review sets out the so-called HDL hypothesis and summarises the clinical results of the family of drugs, which function to raise plasma HDL concentration through inhibition of cholesteryl ester transfer proteins (CEPT).

PLTP activity inversely correlates with CAAD: effects of PON1 enzyme activity and genetic variants on PLTP activity

Recent studies have failed to demonstrate a causal cardioprotective effect of HDL cholesterol levels, shifting focus to the functional aspects of HDL. Phospholipid transfer protein (PLTP) is an HDL-associated protein involved in reverse cholesterol transport. This study sought to determine the genetic and nongenetic predictors of plasma PLTP activity (PLTPa), and separately, to determine whether PLTPa predicted carotid artery disease (CAAD). PLTPa was measured in 1,115 European ancestry participants from a case-control study of CAAD. A multivariate logistic regression model was used to elucidate the relationship between PLTPa and CAAD. Separately, a stepwise linear regression determined the nongenetic clinical and laboratory characteristics that best predicted PLTPa. A final stepwise regression considering both nongenetic and genetic variables identified the combination of covariates that explained maximal PLTPa variance. PLTPa was significantly associated with CAAD (7.90 × 10(-9)), with a 9% decrease in odds of CAAD per 1 unit increase in PLTPa (odds ratio = 0.91). Triglyceride levels (P = 0.0042), diabetes (P = 7.28 × 10(-5)), paraoxonase 1 (PON1) activity (P = 0.019), statin use (P = 0.026), PLTP SNP rs4810479 (P = 6.38 × 10(-7)), and PCIF1 SNP rs181914932 (P = 0.041) were all significantly associated with PLTPa. PLTPa is significantly inversely correlated with CAAD. Furthermore, we report a novel association between PLTPa and PON1 activity, a known predictor of CAAD.

Dialysis Modalities and HDL Composition and Function

Lipid abnormalities may have an effect on clinical outcomes of patients on dialysis. Recent studies have indicated that HDL dysfunction is a hallmark of ESRD. In this study, we compared HDL composition and metrics of HDL functionality in patients undergoing hemodialysis (HD) or peritoneal dialysis (PD) with those in healthy controls. We detected a marked suppression of several metrics of HDL functionality in patients on HD or PD. Compositional analysis revealed that HDL from both dialysis groups shifted toward a more proinflammatory phenotype with profound alterations in the lipid moiety and protein composition. With regard to function, cholesterol efflux and anti-inflammatory and antiapoptotic functions seemed to be more severely suppressed in patients on HD, whereas HDL-associated paraoxonase activity was lowest in patients on PD. Quantification of enzyme activities involved in HDL metabolism suggested that HDL particle maturation and remodeling are altered in patients on HD or PD. In summary, our study provides mechanistic insights into the formation of dysfunctional HDL in patients with ESRD who are on HD or PD.

Elevated baseline plasma phospholipid protein (PLTP) levels are an independent predictor of long-term all-cause mortality in patients with diabetes mellitus and known or suspected coronary artery disease

OBJECTIVES

To investigate the long-term prognostic significance of baseline plasma PLTP levels in a group of well-characterized male patients with diabetes mellitus and known or suspected coronary artery disease referred for coronary angiography.

BACKGROUND

PLTP is a plasma protein that mediates the net transfer and exchange of phospholipids between lipoproteins. It has been implicated in the pathogenesis of atherosclerosis and elevated plasma levels have been reported in patients with diabetes mellitus.

METHODS

Baseline plasma PLTP levels were measured in 154 male patients with diabetes mellitus who were referred for coronary angiography and followed prospectively for 5 years for the development of all-cause mortality.

RESULTS

After adjustment for a variety of baseline clinical, angiographic and laboratory parameters, plasma PLTP levels (analyzed as a continuous variable) were an independent predictor of all-cause mortality at 5 years (HR, 1.55; 95% CI, 1.22-2.00; P = 0.0009). Furthermore, in 3 additional multivariate models that also included a wide variety of contemporary biomarkers with established prognostic efficacy (i.e., ST2, GDF-15, Cystatin C, Fibrinogen, and NT-proBNP), PLTP remained an independent predictor of all-cause mortality at 5 years.

CONCLUSIONS

Elevated baseline plasma levels of PLTP are associated with an increased risk of long-term all-cause mortality in patients with diabetes and known or suspected coronary disease. Furthermore, this association is independent of a variety of clinical, angiographic, and laboratory variables, including a whole host of contemporary biomarkers with established prognostic efficacy.

Low-normal thyroid function and novel cardiometabolic biomarkers

The concept is emerging that low-normal thyroid function, i.e., either higher thyroid-stimulating hormone or lower free thyroxine levels within the euthyroid reference range, could contribute to the development of atherosclerotic cardiovascular disease. It is possible that adverse effects of low-normal thyroid function on cardiovascular outcome may be particularly relevant for specific populations, such as younger people and subjects with high cardiovascular risk. Low-normal thyroid function probably relates to modest increases in plasma total cholesterol, low density lipoprotein cholesterol, triglycerides and insulin resistance, but effects on high density lipoprotein (HDL) cholesterol and non-alcoholic fatty liver disease are inconsistent. Low-normal thyroid function may enhance plasma cholesteryl ester transfer, and contribute to an impaired ability of HDL to inhibit oxidative modification of LDL, reflecting pro-atherogenic alterations in lipoprotein metabolism and HDL function, respectively. Low-normal thyroid function also confers lower levels of bilirubin, a strong natural anti-oxidant. Remarkably, all these effects of low-normal thyroid functional status appear to be more outspoken in the context of chronic hyperglycemia and/or insulin resistance. Collectively, these data support the concept that low-normal thyroid function may adversely affect several processes which conceivably contribute to the pathogenesis of atherosclerotic cardiovascular disease, beyond effects on conventional lipoprotein measures.

Increased large VLDL particles confer elevated cholesteryl ester transfer in diabetes

BACKGROUND

Plasma cholesteryl ester transfer (CET), reflecting transfer of cholesteryl esters from high density lipoproteins (HDL) towards apolipoprotein B-containing lipoproteins, may promote atherosclerosis development, and is elevated in Type 2 diabetes mellitus (T2DM). We determined the extent to which the relationship of plasma CET with very low density lipoprotein (VLDL) and low density lipoprotein (LDL) subfractions is modified in T2DM.

MATERIALS AND METHODS

Plasma CET, cholesteryl ester transfer protein (CETP) mass, as well as VLDL and LDL subfractions (nuclear magnetic resonance spectroscopy) were determined in 62 patients with T2DM and 53 nondiabetic subjects.

RESULTS

Plasma CET and CETP mass were increased in T2DM, coinciding higher triglycerides and large VLDL particles (all P < 0·02). Plasma CET was positively related to the VLDL and the LDL particle concentration in age-, sex- and diabetes status-adjusted analysis (both P < 0·001). Multivariable linear regression analysis demonstrated an independent positive interaction between the presence of T2DM and the VLDL concentration on plasma CET (β = 0·238, P = 0·033). The relationship of plasma CET with the VLDL concentration was also positively modified by plasma glucose (β = 0·211, P = 0·004) and glycated haemoglobin (β = 0·190, P = 0·012). Of the individual VLDL subfractions, a positive interaction of diabetes status with large VLDL on plasma CET was observed (β = 0·280, P = 0·003). Neither the relationship of the LDL particle concentration nor of CETP mass with plasma CET was modified by the presence of T2DM (P > 0·15).

CONCLUSION

Abnormalities in the concentration and composition of large VLDL particles are likely to contribute to elevated plasma CET in T2DM.

Phospholipid transfer protein destabilizes mouse atherosclerotic plaque

OBJECTIVE

Phospholipid transfer protein (PLTP) accelerates the development of atherosclerosis in mouse models. We examined the role of PLTP in atherosclerotic plaque stability.

APPROACH AND RESULTS

We prepared apolipoprotein E and PLTP double-knockout (PLTP(-/-)ApoE(-/-)) mice. PLTP deficiency significantly decreased lesion size and reduced monocyte/macrophage infiltration, as well as macrophage apoptosis in lesion areas. Moreover, it increased fibrous content in plaques, which suggests that PLTP may affect atherosclerotic plaque stability. Importantly, PLTP overexpression mediated by adenovirus had the reverse effect. It promoted the accumulation of reactive oxygen species in macrophages, which could lead to cell apoptosis and increased the production of inflammatory cytokines and chemokines. PLTP overexpression could promote receptor-interacting protein 3 recruitment of macrophages in cytoplasm, which could induce reactive oxygen species, thus inducing atherogenesis.

CONCLUSIONS

PLTP plays an important role in modulating the stability of atherosclerotic plaques. The receptor-interacting protein 3- reactive oxygen species signal pathway could be involved in this PLTP-mediated process.

CETP inhibitors and cardiovascular disease: Time to think again

Inhibition of cholesteryl ester transfer protein (CETP) lowers plasma low-density lipoprotein cholesterol concentration and raises high-density lipoprotein (HDL) cholesterol, suggesting it might prevent cardiovascular disease (CVD). From the outset, however, the concept has been controversial owing to uncertainty about its effects on HDL function and reverse cholesterol transport (RCT). Although there has long been good evidence that CETP inhibition reduces atherosclerosis in rabbits, the first information on CETP as a CVD risk factor in a prospectively followed cohort was not published until after the first Phase 3 trial of a CETP inhibitor had begun. The worrying finding that CVD incidence was related inversely to plasma CETP has since been reproduced in each of five further prospective cohort studies. Similar results were obtained in subjects on or off statin therapy, for first and second CVD events, and for mortality as well as CVD morbidity. Additionally, two recent studies have found alleles of the CETP gene that lower hepatic CETP secretion to be associated with an increased risk of myocardial infarction. Meanwhile, CETP gene transfer in mice was found to increase RCT from peripheral macrophages in vivo, and human plasma with high CETP activity was shown to have a greater capacity to remove cholesterol from cultured cells than plasma with low activity. This mounting evidence for a protective function of CETP has been given remarkably little attention, and indeed was not mentioned in several recent reviews.  It appears to show that CETP inhibition does not test the HDL hypothesis as originally hoped, and raises a pressing ethical issue regarding two Phase 3 trials of inhibitors, involving more than forty thousand subjects, which are currently in progress. As the weight of evidence now clearly supports an adverse effect of CETP inhibition on CVD, an urgent review is needed to determine if these trials should be discontinued.

Enhanced cholesterol efflux to HDL through the ABCA1 transporter in hypertriglyceridemia of type 2 diabetes

OBJECTIVE

Our objective was to examine the role of hypertriglyceridemia on the capacity of HDL to facilitate ABCA-1 mediated cholesterol efflux in type 2 diabetes (T2DM).

METHODS

HDL mediated cholesterol efflux through the ABCA-1 transporter was measured using BHK cell lines in samples of 71 participants with T2DM in the presence or absence of high triglyceride levels (TG). Additionally, HDL mediated efflux was measured in 13 diabetic and non-diabetic participants fasting and four hours after a high-fat test challenge.

RESULTS

HDL mediated cholesterol efflux function was increased in participants with T2DM with hypertriglyceridemia when compared to participants with T2DM without hypertriglyceridemia (efflux ratio mean±standard deviation (SD), T2DM+TG: 1.17±0.25 vs. T2DM - TG: 1.03±0.19, p=0.0098). In the fat challenge study, we observed a significant increase in ABCA-1 mediated cholesterol efflux capacity following an ingestion of high-fat test meal by participants in both groups of T2DM (n=6, efflux ratio, mean±SD, pre: 0.86±0.4 vs. post: 1.34±0.6, p=0.01) and non-diabetic participants (n=7, efflux ratio mean±SD pre: 1.24±0.31 vs. post: 1.39±0.42, p=0.04) that was partly explained by the difference in CETP activity (r=0.6, p=0.03).

CONCLUSION

Our study suggests that high triglyceride levels facilitate ABCA-1 mediated efflux function of HDL in part by activating CETP.

Periodontal disease and stroke: a meta-analysis of cohort studies

This review aimed to determine the association between periodontal disease and stroke incidence by a meta-analysis of cohort studies. Cohort studies that evaluated the incidence of stroke (fatal or non-fatal, ischaemic or haemorrhagic) and baseline periodontal status and calculated relative risk values were included. The quality of the included studies was assessed using an evaluation grid. The analyses were conducted separately for three outcomes: periodontitis, gingivitis and loss of teeth. Adjusted values of relative risk or of hazard ratio were used to assess risk values in each study. Random effects meta-analyses were conducted when data could be pooled. From the 743 references retrieved, only nine cohort studies were suitable for inclusion in this review. Quality scores of the studies varied greatly. Three prospective studies, which used reliable indicators of periodontal disease, obtained the highest scores. Conversely, three studies that used a subjective evaluation of stroke incidence or diagnosed stroke without imaging obtained the lowest score. The results of the meta-analyses varied depending on the outcome considered and the type of stroke. The risk of stroke was significantly increased by the presence of periodontitis [relative risk 1.63 (1.25, 2.00)]. Tooth loss was also a risk factor for stroke [relative risk 1.39 (1.13, 1.65)]. The risk of stroke did not vary significantly with the presence of gingivitis. This review shows that periodontitis and tooth loss are associated with the occurrence of stroke.