High-density Apolipoprotein Research Articles

Large-Scale Analysis of Determinants, Stability, and Heritability of High-Density Lipoprotein Cholesterol Efflux Capacity.

Cholesterol efflux capacity (CEC) has emerged as a biomarker of coronary artery disease risk beyond plasma high-density lipoprotein (HDL) cholesterol (HDL-C) level. However, the determinants of CEC are incompletely characterized. We undertook a large-scale family-based population study to identify clinical, biochemical, and HDL particle parameter determinants of CEC, characterize reasons for the discordancy with HDL-C, quantify its heritability, and assess its stability over 10 to 12 years. CEC was quantified in 1988 individuals from the GRAPHIC (Genetic Regulation of Arterial Pressure of Humans in the Community) cohort, comprising individuals from 2 generations from 520 white nuclear families. Serum lipid and lipoprotein levels were determined by ultracentrifugation or nuclear magnetic resonance and HDL particle size and number quantified by nuclear magnetic resonance. Ninety unrelated individuals had repeat CEC measurements in samples collected after 10 to 12 years. CEC was positively correlated with HDL-C (R=0.62; P<0.0001). Among clinical and biochemical parameters, age, systolic blood pressure, alcohol consumption, serum albumin, triglycerides, phospholipids, and lipoprotein(a) were independently associated with CEC. Among HDL particle parameters, HDL particle number, particle size, and apolipoprotein A-II level were independently associated with CEC. Serum triglyceride level partially explained discordancy between CEC and HDL-C. CEC measurements in samples collected 10 to 12 years apart were strongly correlated (r=0.73; P<0.0001). Heritability of CEC was 0.31 (P=3.89×10-14) without adjustment for HDL-C and 0.13 (P=1.44×10-3) with adjustment. CEC is a stable trait over time, is influenced by specific clinical, serum, and HDL particle parameters factors beyond HDL-C, can be maintained in persons with a low plasma HDL-C by elevated serum triglyceride level, and is modestly independently heritable.

Adiponectin Predicts High-Density Lipoprotein Cholesterol Efflux Capacity in Adults Irrespective of Body Mass Index and Fat Distribution.

Obesity is associated with hypoadiponectemia, dyslipidemia, and increased risk of cardiovascular disease (CVD). Mechanisms linking these conditions remain to be fully understood. Cholesterol efflux capacity (CEC) is a crucial functional property of high-density lipoprotein (HDL) that strongly predicts CVD incidence. We investigated whether age, fat distribution, and other obesity-related factors affect CEC in juvenile and adult overweight/obese participants of the STYJOBS/EDECTA cohort (NCT00482924). We performed an observational study. CEC and its association with body measures and related metabolic parameters was assessed in 683 participants (281 juveniles, of whom 227 were overweight/obese; 402 adults, of whom 197 were overweight/obese). Pearson correlation analysis showed that, after Bonferroni correction, CEC was significantly inversely correlated with body mass index (BMI), carotid diameter, waist circumference, waist-to-hip, waist-to-height ratio, oxidized low-density lipoprotein, and uric acid and with the liver markers alanine-aminotransferase and choline esterase. CEC was positively correlated with HDL cholesterol, total cholesterol, apolipoprotein A1, and adiponectin in adults, whereas in juveniles only apolipoprotein A1 showed a significant positive correlation with CEC. Age-stratified linear regression analyses with CEC as the outcome variable identified adiponectin as the most significant predictor of CEC in adults. The results did not change when either BMI or waist-to-hip ratio as a factor of fat distribution was included in the models. Hypoadiponectemia is a robust predictor of reduced cholesterol efflux capacity in adults irrespective of BMI and fat distribution. Further investigations are needed to assess whether adiponectin is a causal determinant of CEC.

Kidney function is associated with an altered protein composition of high-density lipoprotein

Patients with chronic kidney disease (CKD) exhibit a myriad of metabolic derangements, including dyslipidemia characterized by low plasma concentrations of high-density lipoprotein (HDL)-associated cholesterol. However, the effects of kidney disease on HDL composition have not been comprehensively determined. Here we used a targeted mass spectrometric approach to quantify 38 proteins contained in the HDL particles within a CKD cohort of 509 participants with a broad range of estimated glomerular filtration rates (eGFRs) (CKD stages I-V, and amean eGFR of 45.5 mL/min/1.73m2). After adjusting formultiple testing, demographics, comorbidities, medications, and other characteristics, eGFR was significantly associated with differences in four HDL proteins. Compared to participants with an eGFR of 60mL/min/1.73m2 or more, those with an eGFR under 15mL/min/1.73m2 exhibited 1.89-fold higher retinol-binding protein 4 (95% confidence interval 1.34-2.67), 1.52-fold higher apolipoprotein C-III (1.25-1.84), 0.70-fold lower apolipoprotein L1 (0.55-0.92), and 0.64-fold lower vitronectin (0.48-0.85). Although the HDL apolipoprotein L1was slightly lower among African Americans than among Caucasian individuals, the relationship to eGFR didnot differ by race. After adjustment, no HDL-associated proteins associated with albuminuria. Thus, modest changes in the HDL proteome provide preliminary evidence for an association between HDL proteins and declining kidney function, but this needs to be replicated. Future analyses will determine if HDL proteomics is indeed a clinical predictor of declining kidney function or cardiovascular outcomes.

Structures of apolipoprotein A-I in high density lipoprotein generated by electron microscopy and biased simulations

BackgroundApolipoprotein A-I (apoA-I) in high-density lipoprotein (HDL) is a key protein for the transport of cholesterol from the vascular wall to the liver. The formation and structure of nascent HDL, composed of apoA-I and phospholipids, is critical to this process. MethodsThe HDL was assembled in vitro from apoA-I, cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at a 1:4:50 molar ratio. The structure of HDL was investigated in vitreous samples, frozen at cryogenic temperatures, as well as in negatively stained samples by transmission electron microscopy. Low resolution electron density maps were next used as restraints in biased Monte Carlo simulations of apolipoprotein A-I dimers, with an initial structure derived from atomic resolution X-ray structures. ResultsTwo final apoA-I structure models for the full-length structure of apoA-I dimer in the lipid bound conformation were generated, showing a nearly circular, flat particle with an uneven particle thickness. ConclusionsThe generated structures provide evidence for the discoidal, antiparallel arrangement of apoA-I in nascent HDL, and propose two preferred conformations of the flexible N-termini. General significanceThe novel full-length structures of apoA-I dimers deepens the understanding to the structure-function relationship of nascent HDL with significance for the prevention of lipoprotein-related disease. The biased simulation method used in this study provides a powerful and convenient modelling tool with applicability for structural studies and modelling of other proteins and protein complexes.

Association of SAA gene polymorphism with ischemic stroke in northern Chinese Han population

BackgroundSerum amyloid A protein (SAA) is known as an inflammatory factor and an apolipoprotein that can replace apolipoprotein A-I/II components as the major apolipoprotein of high-density lipoprotein (HDL), which is related to atherosclerosis. The present study is aimed to evaluate whether the SAA gene polymorphism is involved in ischemic stroke in northern Chinese Han population. MethodsIn a case-control study, the participants included 396 patients (239 males, 157 females) with ischemic stroke and 360 healthy subjects (211 males, 149 females). The rs12218 polymorphism of the SAA gene was analyzed by polymerase chain reaction and restriction fragment length polymorphism, while the rs2468844 polymorphism of the SAA gene was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. ResultsThe frequencies of the CC genotype and the C allele of rs12218 were higher in participants with ischemic stroke than in the control group (P=0.020 in males, P=0.001 in large-artery atherosclerosis group, LAA). The frequencies of the AG genotype and the G allele of rs2468844 were higher in participants with ischemic stroke than in the control group (P=0.040 in males, P=0.011 in large-artery atherosclerosis group). Multiple logistic regression analysis revealed the significance of the rs12218 in males and in large-artery atherosclerosis group after adjustment for confounding factors. ConclusionThe rs12218 polymorphism of the SAA gene was associated with ischemic stroke in males and in patients with large-artery atherosclerosis group in northern Chinese Han population.

Cholesterol Efflux Capacity, High-Density Lipoprotein Particle Number, and Incident Cardiovascular Events: An Analysis From the JUPITER Trial (Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin).

Recent failures of drugs that raised high-density lipoprotein (HDL) cholesterol levels to reduce cardiovascular events in clinical trials have led to increased interest in alternative indices of HDL quality, such as cholesterol efflux capacity, and HDL quantity, such as HDL particle number. However, no studies have directly compared these metrics in a contemporary population that includes potent statin therapy and low low-density lipoprotein cholesterol. HDL cholesterol levels, apolipoprotein A-I, cholesterol efflux capacity, and HDL particle number were assessed at baseline and 12 months in a nested case-control study of the JUPITER trial (Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin), a randomized primary prevention trial that compared rosuvastatin treatment to placebo in individuals with normal low-density lipoprotein cholesterol but increased C-reactive protein levels. In total, 314 cases of incident cardiovascular disease (CVD) (myocardial infarction, unstable angina, arterial revascularization, stroke, or cardiovascular death) were compared to age- and gender-matched controls. Conditional logistic regression models adjusting for risk factors evaluated associations between HDL-related biomarkers and incident CVD. Cholesterol efflux capacity was moderately correlated with HDL cholesterol, apolipoprotein A-I, and HDL particle number (Spearman r= 0.39, 0.48, and 0.39 respectively; P<0.001). Baseline HDL particle number was inversely associated with incident CVD (adjusted odds ratio per SD increment [OR/SD], 0.69; 95% confidence interval [CI], 0.56-0.86; P<0.001), whereas no significant association was found for baseline cholesterol efflux capacity (OR/SD, 0.89; 95% CI, 0.72-1.10; P=0.28), HDL cholesterol (OR/SD, 0.82; 95% CI, 0.66-1.02; P=0.08), or apolipoprotein A-I (OR/SD, 0.83; 95% CI, 0.67-1.03; P=0.08). Twelve months of rosuvastatin (20 mg/day) did not change cholesterol efflux capacity (average percentage change -1.5%, 95% CI, -13.3 to +10.2; P=0.80), but increased HDL cholesterol (+7.7%), apolipoprotein A-I (+4.3%), and HDL particle number (+5.2%). On-statin cholesterol efflux capacity was inversely associated with incident CVD (OR/SD, 0.62; 95% CI, 0.42-0.92; P=0.02), although HDL particle number again emerged as the strongest predictor (OR/SD, 0.51; 95% CI, 0.33-0.77; P<0.001). In JUPITER, cholesterol efflux capacity was associated with incident CVD in individuals on potent statin therapy but not at baseline. For both baseline and on-statin analyses, HDL particle number was the strongest of 4 HDL-related biomarkers as an inverse predictor of incident events and biomarker of residual risk. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00239681.

Immunochemical Approach for Monitoring of Structural Transition of ApoA-I upon HDL Formation Using Novel Monoclonal Antibodies

Apolipoprotein A-I (apoA-I) undergoes a large conformational reorganization during remodeling of high-density lipoprotein (HDL) particles. To detect structural transition of apoA-I upon HDL formation, we developed novel monoclonal antibodies (mAbs). Splenocytes from BALB/c mice immunized with a recombinant human apoA-I, with or without conjugation with keyhole limpet hemocyanin, were fused with P3/NS1/1-Ag4-1 myeloma cells. After the HAT-selection and cloning, we established nine hybridoma clones secreting anti-apoA-I mAbs in which four mAbs recognize epitopes on the N-terminal half of apoA-I while the other five mAbs recognize the central region. ELISA and bio-layer interferometry measurements demonstrated that mAbs whose epitopes are within residues 1–43 or 44–65 obviously discriminate discoidal and spherical reconstituted HDL particles despite their great reactivities to lipid-free apoA-I and plasma HDL, suggesting the possibility of these mAbs to detect structural transition of apoA-I on HDL. Importantly, a helix-disrupting mutation of W50R into residues 44–65 restored the immunoreactivity of mAbs whose epitope being within residues 44–65 against reconstituted HDL particles, indicating that these mAbs specifically recognize the epitope region in a random coil state. These results encourage us to develop mAbs targeting epitopes in the N-terminal residues of apoA-I as useful probes for monitoring formation and remodeling of HDL particles.

Abstract 576: Salicylamine, A γ-ketoaldehyde Scavenger, Improves HDL Function and Reduces Atherosclerosis in Apoe Deficient Mice

Background: Lipid peroxidation products impair the cholesterol efflux capacity of high-density lipoprotein (HDL) and promote the development of atherosclerosis. The impact of inhibition of malondialdehyde (MDA)-HDL adduct formation by scavengers on HDL function and whether small molecule aldehyde scavengers protect against the development of atherosclerosis was examined. Methods and Results: Western blot analysis of ApoAI revealed that the amount of ApoAI crosslinking increased with MDA concentration. In the presence of LPS, MDA-HDL (HDL modified by 1mM MDA) versus control HDL stimulated 2- and 1.8-fold more expression of TNF-α and IL-1β in Apoe-/- macrophages demonstrating that MDA-HDL has reduced anti-inflammatory function. HDL-mediated macrophage cholesterol efflux was decreased by ~ 42%, 55%, 70%, and 80%, respectively, for HDL modified with 0.125 mM, 0.25 mM, 0.5 mM, and 1mM MDA, demonstrating that MDA modification of HDL affects its cholesterol efflux capacity in a dose dependent manner. Analysis by Western blot demonstrated that 5mM of salicylamine (SAM) and 5mM of pentylpyridoxamine (PPM), γ-ketoaldehyde scavengers, attenuated MDA mediated crosslinking of apoA-I in HDL (molar ratio of MDA and HDL is 1:5) by 60% and 80 % (P&lt;0.05), respectively. Both SAM and PPM maintained the cholesterol efflux capacity of MDA treated HDL in Apoe-/- macrophages. In addition, pretreatment of LDL with SAM prevented MDA-ApoB adduct formation, and compared to incubation with LDL containing MDA-ApoB adducts, SAM treatment resulted in 57% less cholesterol accumulation in J774 macrophages. Importantly, administration of the ketoaldehyde scavenger, SAM, versus the nonreactive analogue, 4-SAM, to Apoe-/- mice consuming a Western diet for 16 weeks reduced the extent of proximal aortic atherosclerosis by 28% (P&lt;0.05). Conclusions: Treatment with salicylamine, a γ-ketoaldehyde scavenger: 1) inhibits MDA-ApoA1 adduct formation thereby preserving HDL cholesterol efflux capacity; 2) prevents MDA-apoB100 formation resulting in less macrophage cholesterol accumulation; 3) reduces atherosclerosis in Apoe -/- mice. These results support the therapeutic potential of salicylamine in the treatment of atherosclerotic cardiovascular disease.

Scavenger receptor B1 (SR-B1) profoundly excludes high density lipoprotein (HDL) apolipoprotein AII as it nibbles HDL-cholesteryl ester

Reverse cholesterol transport (transfer of macrophage-cholesterol in the subendothelial space of the arterial wall to the liver) is terminated by selective high density lipoprotein (HDL)-cholesteryl ester (CE) uptake, mediated by scavenger receptor class B, type 1 (SR-B1). We tested the validity of two models for this process: "gobbling," i.e. one-step transfer of all HDL-CE to the cell and "nibbling," multiple successive cycles of SR-B1-HDL association during which a few CEs transfer to the cell. Concurrently, we compared cellular uptake of apoAI with that of apoAII, which is more lipophilic than apoAI, using HDL-[3H]CE labeled with [125I]apoAI or [125I]apoAII. The studies were conducted in CHO-K1 and CHO-ldlA7 cells (LDLR-/-) with (CHO-SR-B1) and without SR-B1 overexpression and in human Huh7 hepatocytes. Relative to CE, both apoAI and apoAII were excluded from uptake by all cells. However, apoAII was more highly excluded from uptake (2-4×) than apoAI. To distinguish gobbling versus nibbling mechanisms, media from incubations of HDL with CHO-SR-B1 cells were analyzed by non-denaturing PAGE, size-exclusion chromatography, and the distribution of apoAI, apoAII, cholesterol, and phospholipid among HDL species as a function of incubation time. HDL size gradually decreased, i.e. nibbling, with the concurrent release of lipid-free apoAI; apoAII was retained in an HDL remnant. Our data support an SR-B1 nibbling mechanism that is similar to that of streptococcal serum opacity factor, which also selectively removes CE and releases apoAI, leaving an apoAII-rich remnant.

In situ AFM imaging of apolipoprotein A-I directly derived from plasma HDL

Background and aimsThe major apolipoproteins of plasma lipoproteins play vital roles in the structural integrity and physiological functions of lipoproteins. More than ten structural models of apolipoprotein A-I (apoA-I), the major apolipoprotein of high-density lipoprotein (HDL), have been developed successively. In these models, apoA-I was supposed to organize in a ring-shaped form. To date, however, there is no direct evidence under physiological condition. MethodsHere, atomic force microscopy (AFM) was used to in situ visualize the organization of apoA-I, which was exposed via depletion of the lipid component of plasma HDL pre-immobilized on functionalized mica sheets. ResultsFor the first time, the ring-shaped coarse structure and three detailed structures (crescent-shaped, gapped “O”-shaped, and parentheses-shaped structures, respectively) of apoA-I in plasma HDL, which have the ability of binding scavenger receptors, were directly observed and quantitatively measured by AFM. The three detailed structures probably represent the different extents to which the lipid component of HDL was depleted. Data on lipid depletion of HDL may provide clues to understand lipid insertion of HDL. ConclusionsThese data provide important information for the understanding of the structure/maturation of plasma HDL. Moreover, they suggest a powerful method for directly visualizing the major apolipoproteins of plasma lipoproteins or the protein component of lipoprotein-like lipid-protein complexes.

Methods for Monitoring ABCA1-Dependent Sterol Release.

Releasing sterols to the extracellular milieu is an important part of sterol homeostasis in cells and in the body. ATP-binding cassette transporter A1 (ABCA1) plays an essential role in cellular phospholipid and sterol release to lipid-free or lipid-poor apolipoprotein A-I (apoA-I), the major apolipoprotein in high-density lipoprotein (HDL), and constitutes the first step in the formation of nascent HDL. Loss-of-function mutations in the ABCA1 gene lead to a rare disease known as Tangier disease that causes severe deficiency in plasma HDL level. Mammalian cells receive exogenous cholesterol mainly from low-density lipoprotein. In addition, they synthesize cholesterol endogenously, as well as multiple precursor sterols that are sterol intermediates en route to be converted to cholesterol. HDL contains phospholipids, cholesterol, and precursor sterols, and ABCA1 has an ability to release phospholipids and various sterol molecules. Recent studies using model cell lines showed that ABCA1 prefers to use sterols newly synthesized endogenously as its preferred substrate, rather than cholesterol derived from LDL or cholesterol being recycled within the cells. Here, we describe several methods at the cell culture level to monitor ABCA1-dependent release of sterol molecules to apoA-I present at the cell exterior. Sterol release can be assessed by using a simple colorimetric enzymatic assay, and/or by monitoring the radioactivities of radiolabeled cholesterol incorporated into the cells, and/or of sterols biosynthesized from radioactive acetate, and/or by using gas chromatography-mass spectrometry analysis of various sterols present in medium and in cells. We also discuss the pros and cons of these methods. Together, these methods allow researchers to detect the release not only of cholesterol but also of other sterols present in minor quantities.

Automation of PRM-dependent D3-Leu tracer enrichment in HDL to study the metabolism of apoA-I, LCAT and other apolipoproteins.

We developed an automated quantification workflow for PRM-enabled detection of D3-Leu labeled apoA-I in high-density lipoprotein (HDL) isolated from humans. Subjects received a bolus injection of D3-Leu and blood was drawn at eight time points over three days. HDL was isolated and separated into six size fractions for subsequent proteolysis and PRM analysis for the detection of D3-Leu signal from ∼0.03 to 0.6% enrichment. We implemented an intensity-based quantification approach that takes advantage of high-resolution/accurate mass PRM scans to identify the D3-Leu 2HM3 ion from non-specific peaks. Our workflow includes five modules for extracting the targeted PRM peak intensities (XPIs): Peak centroiding, noise removal, fragment ion matching using Δm/z windows, nine intensity quantification options, and validation and visualization outputs. We optimized the XPI workflow using in vitro synthesized and clinical samples of D0/D3-Leu labeled apoA-I. Three subjects' apoA-I enrichment curves in six HDL size fractions, and LCAT, apoA-II and apoE from two size fractions were generated within a few hours. Our PRM strategy and automated quantification workflow will expedite the turnaround of HDL apoA-I metabolism data in clinical studies that aim to understand and treat the mechanisms behind dyslipidemia.

Potential Mechanisms for Enhanced Activity of Von Willebrand Factor in Patients with Sickle Cell Disease

Sickle cell disease (SCD) is a hemoglobinopathy characterized by vaso-occlusion and hemolysis. Even at disease baseline, von Willebrand factor (VWF) quantity and activity is markedly increased and correlates with the extent of hemolysis [Chen et al. Blood, 2011, 117:3680].VWF is an adhesive plasma protein capable of binding platelets, and secondarily, erythrocytes, and leukocytes. Its adhesive activity is regulated at several levels: being decreased by proteolysis by the metalloprotease ADAMTS13 [Dong et al. Blood, 2002, 100:4033] or by inhibition of self-association into more adhesive forms by high density lipoprotein (HDL) [Chung et al. Blood, 2016, 127:637], or enhanced by oxidative modification [Chen et al. Blood, 2010, 115:706; Fu et al. Blood, 2011, 118:5283]. Here, we explored several potential mechanisms accounting for the increased total active VWF in SCD patients: endothelial activation, enhanced VWF self-association, and defective cleavage of endogenous VWF because of ADAMTS13 dysfunction and/or VWF resistance to cleavage due to oxidation.Methods: We analyzed plasma collected from 12 adult SCD patients at disease baseline; for 3 of these we also have samples collected during vaso-occlusive crisis. We also analyzed multiple crisis samples from one additional patient with no baseline sample. To determine if SCD plasma could activate endothelial cells, we incubated plasma with human umbilical vein endothelial cells (HUVECs) cultured in parallel-plate flow chambers for 20 min at 37˚C then washed the plasma away before perfusing fixed platelets through the chamber. The number and length of platelet-decorated VWF strings were then quantified as a measure of endothelial activation. The plasma levels of VWF, apolipoprotein A-I (ApoA-I, the major apolipoprotein in HDL), myeloperoxidase (MPO), and ADAMTS13 were measured by sandwich ELISA. The activity of ADAMTS13 was evaluated by 1) cleavage of a small VWF A2 peptide substrate; 2) cleavage of multimeric VWF in patient plasma in 1.5 M urea and examining the VWF multimer pattern over time; 3) cleavage of preformed VWF-platelet strings on activated HUVECs; and 4) examining the extent of VWF cleavage in vivo using mass spectrometry (MS). The oxidation of specific methionine residues in VWF and ADAMTS13 from patient plasma was measured by MS as described previously [Chen et al. Blood, 2010, 115:706; Wang et al. JBC, 2015, 290:1422].Results: 1) HUVECs incubated with SCD plasma were activated and produced 2 to 25 fold more VWF strings than cells treated with pooled normal plasma (PNP). Activation was inhibited if the plasma was pre-incubated with hemopexin (0.5 mg/ml), implicating heme as an activator. However, purified heme alone even at high concentration did not activate HUVECs to secrete VWF strings, indicating that heme is required but not sufficient. 2) The ratio of VWF to ApoA-I was markedly elevated in SCD patients, especially during crisis (2.3 ± 0.7 fold of PNP), indicating predisposition to VWF self-association. 3) ADAMTS13 from SCD plasma was defective in cleaving VWF strings (11% to 57% of PNP) and multimeric VWF, but not the A2 peptide substrate. 4) Almost all of the SCD plasma had elevated MPO (3.8 ± 2.5 and 12.8 ± 7.6 fold of PNP in baseline and crisis samples, respectively). 5) Our previous studies showed that HOCl oxidation of VWF Met1606 at the ADAMTS13 cleavage site rendered the VWF noncleavable, and oxidation at other sites increased its platelet-binding activity. We also found that HOCl can inactivate ADAMTS13 by oxidizing Met249 within the metalloprotease domain. We therefore evaluated the extent of VWF Met1606 and ADAMTS13 Met249 oxidation, and VWF cleavage by ADAMTS13 in vivo in patient plasma using tandem MS. We found that ADAMTS13 in SCD plasma had elevated oxidation at Met249 (1.6 ± 0.2 fold of normal controls); VWF cleavage by ADAMTS13 in vivo was decreased by as much as 40% in several of these patients, and the extent of cleavage correlated negatively with the extent of VWF Met1606 oxidation.Summary: Multiple mechanisms contribute to enhanced VWF activity in SCD patients. These include increased secretion by activated endothelial cells, enhanced VWF self-association, and defective cleavage of VWF by endogenous ADAMTS13, partially due to oxidative modification of both VWF and ADAMTS13. DisclosuresNo relevant conflicts of interest to declare.

Predictive Value of Updating te Score Cardiovascular Risk Assessment Engine with Novel Biomarkers in a Type 2 Diabetes Population

AbstractBackground and Aims: The aim of the study was to estimate the predictive value of some new biomarkers in the assessment of cardiovascular disease (CVD) risk in a type 2 diabetes (T2DM) population and to perform a correlation between the SCORE risk results and the risk profile estimated by the use of these biomarkers. Finally, we aimed to establish if the CVD risk assessment can be improved by adding the biomarkers into the SCORE risk equation. Material and Methods: In the study population the CVD risk assessment was performed using the SCORE High Risk Chart. The new individual biomarkers were: estimated glomerular filtration rate (eGFR), urinary albumin excretion (UAE) rate, albumin/creatinine ratio (UACR), cystatin C, plasminogen activator inhibitor-1 (PAI-1), high-sensitivity C-reactive protein (hs-CRP), high density lipoprotein cholesterol (HDL) and apolipoprotein B (apo-B). Results: The SCORE risk prediction model results were significantly altered by adding in the equation apo-B and HDLc values. An increase of one standard deviation of the apo-B values caused the increase of the SCORE results with 0.19 standard deviations while an increase of one standard deviation of the HDLc values decreased the SCORE results with 0.26 standard deviations. Conclusions: Advanced lipid testing, including the measurement of apo-B, provides a more comprehensive cardiac risk assessment and should be used in the development of specifically designed risk-scores for T2DM individuals.

Significance of Lipid-Free and Lipid-Associated ApoA-I in Cellular Cho-lesterol Efflux.

The structure and stability of apolipoprotein (apo)A-I, the major apolipoprotein of human plasma high-density lipoproteins (HDL), determine the efficiency of the protein in the process of HDL generation and affect HDL properties in binding and exchanging its constituents, thus playing an essential role in reverse cholesterol transport. The equilibrium stability of an apoA-I molecule at the lipid interface (12.7 kcal/mol) predicted by a thermodynamic cycle for apolipoprotein folding-unfolding in water and at interface, largely exceeds apoA-I helix stability in HDL against chemical denaturation (3-5 kcal/mol). An ensemble of structures of lipid-bound apoA-I with different stabilities is assumed to exist. The conformational transitions between apoA-I conformers in water and lipid phases correspond to Lumry-Eyring model OL ⇔ CL ⇒ MW, where OL and CL are open and closed structures of HDLbound apoA-I, and MW is the molten globule in water. The model includes the reversible foldingunfolding transitions of N- and C-domains at HDL interface and apolipoprotein irreversible dissociation. We gathered published data on cholesterol efflux for apoA-I proteins with missense mutations in C-domain and calculated the stability of these mutants as a change of free energy relative to a wild type protein. Significant negative correlation was found between this stability and the efficiency of cAMP-stimulated cholesterol efflux. Thus, besides the known role of C-domain hydrophobicity, structure-destabilizing changes may significantly contribute to ABCA1-mediated cholesterol efflux by free apolipoprotein.

Patients with Rheumatoid Arthritis Show Altered Lipoprotein Profiles with Dysfunctional High-Density Lipoproteins that Can Exacerbate Inflammatory and Atherogenic Process.

ObjectiveIn order to identify putative biomarkers in lipoprotein, we compared lipid and lipoprotein properties between rheumatoid arthritis (RA) patients and control with similar age.MethodsWe analyzed four classes of lipoproteins (VLDL, LDL, HDL2, HDL3) from both male (n = 8, 69±4 year-old) and female (n = 25, 53±7 year-old) rheumatoid arthritis (RA) patients as well as controls with similar age (n = 13).ResultsAlthough RA group showed normal levels of total cholesterol (TC), low-density lipoprotein (LDL)-cholesterol, and glucose, however, the RA group showed significantly reduced high-density lipoprotein (HDL)-C level and ratio of HDL-C/TC. The RA group showed significantly elevated levels of blood triglyceride (TG), uric acid, and cholesteryl ester transfer protein (CETP) activity. The RA group also showed elevated levels of advanced glycated end (AGE) products in all lipoproteins and severe aggregation of apoA-I in HDL. As CETP activity and TG contents were 2-fold increased in HDL from RA group, paraoxonase activity was reduced upto 20%. Electron microscopy revealed that RA group showed much less HDL2 particle number than control. LDL from the RA group was severely oxidized and glycated with greater fragmentation of apo-B, especially in female group, it was more atherogenic via phagocytosis.ConclusionLipoproteins from the RA patients showed severely altered structure with impaired functionality, which is very similar to that observed in coronary heart patients. These dysfunctional properties in lipoproteins from the RA patients might be associated with high incidence of cardiovascular events in RA patients.

High-density lipoprotein phospholipid content and apolipoprotein A-I level are determinants of cholesterol efflux capacity in patients with familial hypercholesterolemia

High-density lipoprotein phospholipid content and apolipoprotein A-I level are determinants of cholesterol efflux capacity in patients with familial hypercholesterolemia

Usefulness of the LDL-C/apoB ratio in the overall evaluation of atherogenicity of lipid profile

Context: The ratio of low-density lipoprotein cholesterol to apolipoprotein-B (LDL-C/apoB) conventionally represents an alternative index of LDL particle size. Objective: This study was undertaken to determine the importance of LDL-C/apoB ratio in the overall evaluation of atherogenicity of lipid profile. Methods: The plasma levels of total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), apolipoprotein (apo) A-I, apoB and apoE were measured in 186 apparently healthy men using enzymatic and immunoturbidimetric methods. Results: The subjects with low values of the LDL-C/apoB ratio, indicating a predominance of small dense LDL (sd-LDL) particles in plasma, were characterized by higher TG levels and lower apoE levels. Conclusion: Low levels of apoE are most likely a cause of reduced clearance of TG-rich lipoproteins, which promotes the formation of sd-LDL. Determination of the LDL-C/apoB ratio can be used for monitoring qualitative changes in lipid profile, in addition to traditional lipid variables indicating quantitative changes.

Impaired HDL cholesterol efflux in metabolic syndrome is unrelated to glucose tolerance status: the CODAM study

Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) increase atherosclerotic cardiovascular disease risk. Cholesterol efflux capacity (CEC) is a key metric of the anti-atherosclerotic functionality of high-density lipoproteins (HDL). The present study aimed to delineate if T2DM and MetS cross-sectionally associate with altered CEC in a large high cardiometabolic risk population. CEC was determined from THP-1 macrophage foam cells towards apolipoprotein B-depleted plasma from 552 subjects of the CODAM cohort (288 controls, 126 impaired glucose metabolism [IGM], 138 T2DM). MetS was present in 297 participants. CEC was not different between different glucose tolerance categories but was lower in MetS (P < 0.001), at least partly attributable to lower HDL cholesterol (HDL-C) and apoA-I levels (P < 0.001 for each). Low grade inflammation was increased in IGM, T2DM and MetS as determined by a score comprising 8 different biomarkers (P < 0.05-< 0.001; n = 547). CEC inversely associated with low-grade inflammation taking account of HDL-C or apoA-I in MetS (P < 0.02), but not in subjects without MetS (interaction: P = 0.015). This study demonstrates that IGM and T2DM do not impact the HDL CEC function, while efflux is lower in MetS, partly dependent on plasma HDL-C levels. Enhanced low-grade inflammation in MetS may conceivably impair CEC even independent of HDL-C and apoA-I.

Abstract 389: Covalent Modifications of Apolipoproteins in High Density Lipoprotein by Oxidized Phospholipids Impair the Cholesterol Efflux Function of High Density Lipoprotein and are Detected in Hyperlipidemic Plasma

Oxidized phospholipids (oxPLs) accumulate at sites of oxidative stress and contribute significantly to atherosclerosis and thrombosis. Most oxPLs have electrophilic substituents and are highly likely to form covalent adducts with proteins, thus compromising protein function. Detection of covalent interactions between oxPLs and proteins could provide important information regarding the type of proteins preferentially modified by oxPLs. However, to date, such studies are extremely limited due to significant technical challenges. We now carry out systematic studies on the protein adduction by oxPLs formed in murine and human plasma. Plasma samples were exposed to a physiologically relevant myeloperoxidase/H 2 O 2 /NO 2 – oxidizing system of phagocytes. Protein adduction by the oxPLs generated in plasma was assessed using LC-MS/MS after tryptic digestion and peptide enrichment using a novel method that we developed. We found that HDL apolipoproteins are the major targets of modification by oxPLs in both murine and human plasma. For apoA-I, the most abundant apolipoprotein in HDL, the major modification sites of oxPLs were located in the region (AA144-186), which is critical for the ABCA1 mediated cholesterol efflux to HDL. We further demonstrated that human apoA-I was also heavily crosslinked by specific oxPLs via histidine and lysine residues located in the region (AA144-186) with apoA-I, or other apolipoproteins, including apoA-II, apoA-IV and apoC-I. In vitro experiments demonstrated that oxPLs modification on lipid free apoA-I or nascent HDL (HDL3) dramatically impairs their function as cholesterol efflux mediators. Using hyperlipidemic LDLr-/- mice, we detected a crosslink adduct of apoA-II with apoE by oxPL in murine plasma. To the best of our knowledge, this is the first report for the detection of endogenous protein adducts with oxPLs.