The metabolism and anti-atherogenic properties of HDL

Cardioprotective functions of HDLs

Multiple human population studies have established the concentration of high density lipoprotein (HDL) cholesterol as an independent, inverse predictor of the risk of having a cardiovascular event. Furthermore, HDLs have several well-documented functions with the potential to protect against cardiovascular disease. These include an ability to promote the efflux of cholesterol from macrophages in the artery wall, inhibit the oxidative modification of low density lipoproteins (LDLs), inhibit vascular inflammation, inhibit thrombosis, promote endothelial repair, promote angiogenesis, enhance endothelial function, improve diabetic control, and inhibit hematopoietic stem cell proliferation. There are undoubtedly other beneficial functions of HDLs yet to be identified. The HDL fraction in human plasma is heterogeneous, consisting of several subpopulations of particles of varying size, density, and composition. The functions of the different HDL subpopulations remain largely unknown. Given that therapies that increase the concentration of HDL cholesterol have varying effects on the levels of specific HDL subpopulations, it is of great importance to understand how distribution of different HDL subpopulations contribute to the potentially cardioprotective functions of this lipoprotein fraction. This review summarizes current understanding of the relationship of HDL subpopulations to their cardioprotective properties and highlights the gaps in current knowledge regarding this important aspect of HDL biology.

The secondary structure of apolipoprotein A-I on 9.6-nm reconstituted high-density lipoprotein determined by EPR spectroscopy

Apolipoprotein A-I (ApoA-I) is the major protein component of high-density lipoprotein (HDL), and is critical for maintenance of cholesterol homeostasis. During reverse cholesterol transport, HDL transitions between an array of subclasses, differing in size and composition. This process requires ApoA-I to adapt to changes in the shape of the HDL particle, transiting from an apolipoprotein to a myriad of HDL subclass-specific conformations. Changes in ApoA-I structure cause alterations in HDL-specific enzyme and receptor-binding properties, and thereby direct the HDL particle through the reverse cholesterol transport pathway. In this study, we used site-directed spin label spectroscopy to examine the conformational details of the ApoA-I central domain on HDL. The motional dynamics and accessibility to hydrophobic/hydrophilic relaxation agents of ApoA-I residues 99–163 on 9.6-nm reconstituted HDL was analyzed by EPR. In previous analyses, we examined residues 6–98 and 164–238 (of ApoA-I's 243 residues), and combining these findings with the current results, we have generated a full-length map of the backbone structure of reconstituted HDL-associated ApoA-I. Remarkably, given that the majority of ApoA-I's length is composed of amphipathic helices, we have identified nonhelical residues, specifically the presence of a β-strand (residues 149–157). The significance of these nonhelical residues is discussed, along with the other features, in the context of ApoA-I function in contrast to recent models derived by other methods.

The cardioprotective protein apolipoprotein A1 promotes potent anti-tumorigenic effects

Here, we show that apolipoprotein A1 (apoA1), the major protein component of high density lipoprotein (HDL), through both innate and adaptive immune processes, potently suppresses tumor growth and metastasis in multiple animal tumor models, including the aggressive B16F10L murine malignant melanoma model. Mice expressing the human apoA1 transgene (A1Tg) exhibited increased infiltration of CD11b(+) F4/80(+) macrophages with M1, anti-tumor phenotype, reduced tumor burden and metastasis, and enhanced survival. In contrast, apoA1-deficient (A1KO) mice showed markedly heightened tumor growth and reduced survival. Injection of human apoA1 into A1KO mice inoculated with tumor cells remarkably reduced both tumor growth and metastasis, enhanced survival, and promoted regression of both tumor and metastasis burden when administered following palpable tumor formation and metastasis development. Studies with apolipoprotein A2 revealed the anti-cancer therapeutic effect was specific to apoA1. In vitro studies ruled out substantial direct suppressive effects by apoA1 or HDL on tumor cells. Animal models defective in different aspects of immunity revealed both innate and adaptive arms of immunity contribute to complete apoA1 anti-tumor activity. This study reveals a potent immunomodulatory role for apoA1 in the tumor microenvironment, altering tumor-associated macrophages from a pro-tumor M2 to an anti-tumor M1 phenotype. Use of apoA1 to redirect in vivo elicited tumor-infiltrating macrophages toward tumor rejection may hold benefit as a potential cancer therapeutic.

Diminished antioxidant activity of high-density lipoprotein-associated proteins in chronic kidney disease

Background

Decreased serum arylesterase activity, catalyzed by the high‐density lipoprotein–associated paraoxonase (PON)‐1, is associated with increased oxidant stress and atherosclerosis risk. We sought to determine the prognostic value of serum PON‐1 activity, as monitored by PON or arylesterase activities, in subjects with chronic kidney disease (CKD), particularly in relation to established cardiac biomarkers.

Methods and Results

Serum arylesterase and PON activities were measured in sequential subjects with CKD (n=630; estimated glomerular filtration rate [eGFR] <60 mL/min per 1.73 m²) and an age‐ and sex‐matched control group of non‐CKD subjects (n=315) presenting for cardiac evaluations and prospectively followed for incident (3‐year) major adverse cardiac events (composite of death, nonfatal myocardial infarction, and stroke). Serum arylesterase activity in CKD subjects was lower compared with that in non‐CKD control subjects [median (interquartile range) 94 (77 to 112) versus 103 (85 to 121) μmol(L·min) per mL, P<0.001]; similarly, PON activity in CKD subjects was lower compared with that in non‐CKD control subjects [median (interquartile range) 474 (275 to 936) versus 586 (301 to 1118) nmol(L·min) per mL, P<0.001]. Lower serum arylesterase (hazard ratio 1.8, 95% CI 1.26 to 2.57, P<0.01) was a predictor of poorer outcomes. After adjusting for traditional risk factors and medication use, lower serum arylesterase (hazard ratio 1.55, 95% CI 1.08 to 2.23, P<0.05) still conferred an increased risk of major adverse cardiac events at 3 years.

Conclusions

In patients with CKD, decreased serum arylesterase activity, a measure of diminished antioxidant properties of PON‐1, predicts higher risk of incident long‐term adverse cardiovascular events (heart attack, stroke, or death) in multivariable models adjusting for established clinical and biochemical risk factors.

Inhibitory effects of in vivo oxidized high-density lipoproteins on platelet aggregation: evidence from patients with abetalipoproteinemia

There is evidence that high-density lipoproteins (HDLs) may regulate platelet function, but disparate results exist regarding the effects of oxidized HDLs on platelets. The objective of our study was to determine the role of in vivo oxidized HDLs on platelet aggregation. Platelet aggregation and redox status were investigated in 5 patients with abetalipoproteinemia (ABLP) or homozygous hypobetalipoproteinemia, two rare metabolic diseases characterized by the absence of apolipoprotein B-containing lipoproteins, compared to 5 control subjects. Platelets isolated from plasma of patients with ABLP aggregated 4 to 10 times more than control platelets, depending on the agonist. By contrast, no differences in the extent of platelet aggregation were observed between ABLP platelet-rich plasma (PRP) and control PRP, suggesting the presence of a protective factor in ABLP plasma. ABLP HDLs inhibited agonist-induced platelet aggregation by binding to SR-BI, while control HDLs had no effect. On the other hand, lipoprotein-deficient plasma from patients with ABLP did not inhibit platelet aggregation. Severe oxidative stress was evidenced in patients with ABLP. Compared to control HDLs, ABLP HDLs showed a 40% decrease of α-tocopherol and an 11-fold increased malondialdehyde concentration. These results demonstrate that in vivo oxidized HDLs do not lose their antiaggregatory properties despite oxidation.

Discoidal HDL and apoA-I-derived peptides improve glucose uptake in skeletal muscle

Lipid-free apoA-I and mature spherical HDL have been shown to induce glucose uptake in skeletal muscle. To exploit apoA-I and HDL states for diabetes therapy, further understanding of interaction between muscle and apoA-I is required. This study has examined whether nascent discoidal HDL, in which apoA-I attains a different conformation from mature HDL and lipid-free states, could induce muscle glucose uptake and whether a specific domain of apoA-I can mediate this effect. Using L6 myotubes stimulated with synthetic reconstituted discoidal HDL (rHDL), we show a glucose uptake effect comparable to insulin. Increased plasma membrane GLUT4 levels in ex vivo rHDL-stimulated myofibers from HA-GLUT4-GFP transgenic mice support this observation. rHDL increased phosphorylation of AMP kinase (AMPK) and acetyl-coA carboxylase (ACC) but not Akt. A survey of domain-specific peptides of apoA-I showed that the lipid-free C-terminal 190-243 fragment increases plasma membrane GLUT4, promotes glucose uptake, and activates AMPK signaling but not Akt. This may be explained by changes in α-helical content of 190-243 fragment versus full-length lipid-free apoA-I as assessed by circular dichroism spectroscopy. Discoidal HDL and the 190-243 peptide of apoA-I are potent agonists of glucose uptake in skeletal muscle, and the C-terminal α-helical content of apoA-I may be an important determinant of this effect.

Health effects of olive oil polyphenols: recent advances and possibilities for the use of health claims

The Mediterranean diet and consumption of olive oil have been connected in several studies with longevity and a reduced risk of morbidity and mortality. Lifestyle, such as regular physical activity, a healthy diet, and the existing social cohesion in Southern European countries have been recognised as candidate protective factors that may explain the Mediterranean Paradox. Along with some other characteristics of the Mediterranean diet, the use of olive oil as the main source of fat is common in Southern European countries. The benefits of consuming olive oil have been known since antiquity and were traditionally attributed to its high content in oleic acid. However, it is now well established that these effects must also be attributed to the phenolic fraction of olive oil with its anti-oxidant, anti-inflammatory and anti-microbial activities. The mechanisms of these activities are varied and probably interconnected. For some activities of olive oil phenolic compounds, the evidence is already strong enough to enable the legal use of health claims on foods. This review discusses the health effects of olive oil phenols along with the possibilities of communicating these effects on food labels.

Lipoprotein remodeling generates lipid-poor apolipoprotein A-I particles in human interstitial fluid

Although much is known about the remodeling of high density lipoproteins (HDLs) in blood, there is no information on that in interstitial fluid, where it might have a major impact on the transport of cholesterol from cells. We incubated plasma and afferent (prenodal) peripheral lymph from 10 healthy men at 37°C in vitro and followed the changes in HDL subclasses by nondenaturing two-dimensional crossed immunoelectrophoresis and size-exclusion chromatography. In plasma, there was always initially a net conversion of small pre-β-HDLs to cholesteryl ester (CE)-rich α-HDLs. By contrast, in lymph, there was only net production of pre-β-HDLs from α-HDLs. Endogenous cholesterol esterification rate, cholesteryl ester transfer protein (CETP) concentration, CE transfer activity, phospholipid transfer protein (PLTP) concentration, and phospholipid transfer activity in lymph averaged 5.0, 10.4, 8.2, 25.0, and 82.0% of those in plasma, respectively (all P < 0.02). Lymph PLTP concentration, but not phospholipid transfer activity, was positively correlated with that in plasma (r = +0.63, P = 0.05). Mean PLTP-specific activity was 3.5-fold greater in lymph, reflecting a greater proportion of the high-activity form of PLTP. These findings suggest that cholesterol esterification rate and PLTP specific activity are differentially regulated in the two matrices in accordance with the requirements of reverse cholesterol transport, generating lipid-poor pre-β-HDLs in the extracellular matrix for cholesterol uptake from neighboring cells and converting pre-β-HDLs to α-HDLs in plasma for the delivery of cell-derived CEs to the liver.

Redox-inflammatory synergy in the metabolic syndrome

Metabolic syndrome (MetS) comprises interrelated disease states including obesity, insulin resistance and type 2 diabetes (T2DM), dyslipidemia, and hypertension. Essential to normal physiological function, and yet massively damaging in excess, oxidative stress and inflammation are pivotal common threads among the pathologies of MetS. Increasing evidence indicates that redox and inflammatory dysregulation parallels the syndrome's physiological, biochemical, and anthropometric features, leading many to consider the pro-oxidative, pro-inflammatory milieu an unofficial criterion in itself. Left unchecked, cross-promotion of oxidative stress and inflammation creates a feed-forward cycle that can initiate and advance disease progression. Such redox-inflammatory integration is evident in the pathogenesis of obesity, insulin resistance and T2DM, atherogenic dyslipidemia, and hypertension, and is thus hypothesized to be the "common soil" from which they develop. The present review highlights the synergistic contributions of redox-inflammatory processes to each of the components of the MetS.

Abnormal glucose and lipid control in non-ischemic left ventricular dysfunction

BACKGROUND

Cardiovascular risk factors are classically associated with coronary atherosclerosis. We sought to investigate whether risk factors are also associated with left ventricular (LV) dilatation, contractile impairment and reduced myocardial blood flow (MBF) in patients with non-ischemic LV dysfunction.

METHODS

We studied 81 patients (59 males, age 60 ± 9 years) with mild-to-severe LV dysfunction (mean ejection fraction 37%, range 19%-50%), no history of diabetes and normal coronary arteries. Absolute MBF was measured by positron emission tomography and (13)N-ammonia at rest and after dipyridamole (0.56 mg/kg I.V. over 4 min).

RESULTS

Overt LV dysfunction (LV end-diastolic diameter >60 mm associated with LV ejection fraction <45%) was present in 42 patients (52%); severely depressed hyperemic MBF (<1.09 mL · min(-1) · g(-1)) was present in 41 patients (51%). Using multivariate logistic regression analysis, low high-density lipoprotein cholesterol (HDL-C, P < .036), newly diagnosed non-insulin-dependent diabetes or insulin-resistance (NIDD/IR, P < .019) and the use of diuretics (P = .001) were independently associated with overt LV dysfunction. Low HDL-C (P = .015) and NIDD/IR (P = .048) were also independently associated with severely depressed hyperemic MBF.

CONCLUSIONS

Low HDL-C and NIDD/IR are associated with more severe LV impairment and reduced hyperemic MBF in non-ischemic LV dysfunction.

Autoantibodies to apolipoprotein A-1 in cardiovascular diseases: current perspectives

Immune-mediated inflammation plays a major role in atherosclerosis and atherothrombosis, two essential features for cardiovascular disease (CVD) development, currently considered as the leading cause of death in the western world. There is accumulating evidence showing that humoral autoimmunity might play an important role in CVD and that some autoantibodies could represent emerging cardiovascular risk factors. Recent studies demonstrate that IgG autoantibodies against apolipoprotein A-1 (apoA-1) are raised in many diseases associated with a high cardiovascular risk, such as systemic lupus erythematosus, acute coronary syndrome, rheumatoid arthritis, severe carotid stenosis, and end-stage renal disease. In this work, we aimed at reviewing current data in the literature pointing to anti-apolipoprotein A-1 antibodies (anti-apoA-1 IgG) as a possible prognostic and diagnostic biomarker of cardiovascular risk and appraising their potential role as active mediators of atherogenesis.

Effects of the Iowa and Milano mutations on apolipoprotein A-I structure and dynamics determined by hydrogen exchange and mass spectrometry

The Iowa point mutation in apolipoprotein A-I (G26R) leads to a systemic amyloidosis condition, and the Milano mutation (R173C) is associated with hypoalphalipoproteinemia, a reduced plasma level of high-density lipoprotein. To probe the structural effects that lead to these outcomes, we used amide hydrogen-deuterium exchange coupled with a fragment separation/mass spectrometry analysis (HX MS). The Iowa mutation inserts an arginine residue into the nonpolar face of an α-helix that spans residues 7-44 and causes changes in structure and structural dynamics. This helix unfolds, and other helices in the N-terminal helix bundle domain are destabilized. The segment encompassing residues 116-158, largely unstructured in wild-type apolipoprotein A-I, becomes helical. The helix spanning residues 81-115 is destabilized by 2 kcal/mol, increasing the small fraction of time it is transiently unfolded to ≥1%, which allows proteolysis at residue 83 in vivo over time, releasing an amyloid-forming peptide. The Milano mutation situated on the polar face of the helix spanning residues 147-178 destabilizes the helix bundle domain only moderately, but enough to allow cysteine-mediated dimerization that leads to the altered functionality of this variant. These results show how the HX MS approach can provide a powerful means of monitoring, in a nonperturbing way and at close to amino acid resolution, the structural, dynamic, and energetic consequences of biologically interesting point mutations.

Cholesteryl ester transfer protein inhibitors for dyslipidemia: focus on dalcetrapib

Among the noteworthy recent stories in the management and prevention of atherosclerotic cardiovascular disease (CVD) is the saga of the development of pharmacological inhibitors of cholesteryl ester transfer protein (CETP). Inhibiting CETP significantly raises plasma concentrations of high-density lipoprotein cholesterol, which has long been considered a marker of reduced CVD risk. However, the first CETP inhibitor, torcetrapib, showed a surprising increase in CVD events, despite a dramatic increase in high-density lipoprotein cholesterol levels. This paradox was explained by putative off-target effects not related to CETP inhibition that were specific to torcetrapib. Subsequently, three newer CETP inhibitors, namely dalcetrapib, anacetrapib, and evacetrapib, were at various phases of clinical development in 2012. Each of these had encouraging biochemical efficacy and safety profiles. Dalcetrapib even had human arterial imaging results that tended to look favorable. However, the dalcetrapib development program was recently terminated, presumably because interim analysis of a large CVD outcome trial indicated no benefit. These events raise important questions regarding the validity of the mechanism of CETP inhibition and the broader issue of whether pharmacological raising of high-density lipoprotein cholesterol itself is a useful strategy for CVD risk reduction.

Rationale for cholesteryl ester transfer protein inhibition

PURPOSE OF REVIEW

Raising HDL cholesterol (HDL-C) has become an attractive therapeutic target to lower cardiovascular risk in addition to statins. Inhibition of the cholesteryl ester transfer protein (CETP), which mediates the transfer of cholesteryl esters from HDL to apolipoprotein B-containing particles, leads to a substantial increase in HDL-C levels. Various CETP inhibitors are currently being evaluated in phase II and phase III clinical trials. However, the beneficial effect of CETP inhibition on cardiovascular outcome remains to be established.

RECENT FINDINGS

Torcetrapib, the first CETP inhibitor tested in a phase III clinical trial (ILLUMINATE), failed in 2006 because of an increase in all-cause mortality and cardiovascular events that subsequently were attributed to nonclass-related off-target effects (particularly increased blood pressure and low serum potassium) related to the stimulation of aldosterone production. Anacetrapib, another potent CETP inhibitor, raises HDL-C levels by approximately 138% and decreases LDL cholesterol (LDL-C) levels by approximately 40%, without the adverse off-targets effects of torcetrapib (DEFINE study). The CETP modulator dalcetrapib raises HDL-C levels by approximately 30% (with only minimal effect on LDL-C levels) and proved safety in the dal-VESSEL and dal-PLAQUE trials involving a total of nearly 600 patients. Evacetrapib, a relatively new CETP inhibitor, exhibited favorable changes in the lipid profile in a phase II study.

SUMMARY

The two ongoing outcome trials, dal-OUTCOMES (dalcetrapib) and REVEAL (anacetrapib), will provide more conclusive answers for the concept of reducing cardiovascular risk by raising HDL-C with CETP inhibition.

Apolipoprotein A-I helical structure and stability in discoidal high-density lipoprotein (HDL) particles by hydrogen exchange and mass spectrometry

To understand high-density lipoprotein (HDL) structure at the molecular level, the location and stability of α-helical segments in human apolipoprotein (apo) A-I in large (9.6 nm) and small (7.8 nm) discoidal HDL particles were determined by hydrogen-deuterium exchange (HX) and mass spectrometry methods. The measured HX kinetics of some 100 apoA-I peptides specify, at close to amino acid resolution, the structural condition of segments throughout the protein sequence and changes in structure and stability that occur on incorporation into lipoprotein particles. When incorporated into the large HDL particle, the nonhelical regions in lipid-free apoA-I (residues 45-53, 66-69, 116-146, and 179-236) change conformation from random coil to α-helix so that nearly the entire apoA-I molecule adopts helical structure (except for the terminal residues 1-6 and 237-243). The amphipathic α-helices have relatively low stability, in the range 3-5 kcal/mol, indicating high flexibility and dynamic unfolding and refolding in seconds or less. A segment encompassed by residues 125-158 exhibits bimodal HX labeling indicating co-existing helical and disordered loop conformations that interchange on a time scale of minutes. When incorporated around the edge of the smaller HDL particle, the increase in packing density of the two apoA-I molecules forces about 20% more residues out of direct contact with the phospholipid molecules to form disordered loops, and these are the same segments that form loops in the lipid-free state. The region of disc-associated apoA-I that binds the lecithin-cholesterol acyltransferase enzyme is well structured and not a protruding unstructured loop as reported by others.

Folded functional lipid-poor apolipoprotein A-I obtained by heating of high-density lipoproteins: relevance to high-density lipoprotein biogenesis

HDL (high-density lipoproteins) remove cell cholesterol and protect from atherosclerosis. The major HDL protein is apoA-I (apolipoprotein A-I). Most plasma apoA-I circulates in lipoproteins, yet ~5% forms monomeric lipid-poor/free species. This metabolically active species is a primary cholesterol acceptor and is central to HDL biogenesis. Structural properties of lipid-poor apoA-I are unclear due to difficulties in isolating this transient species. We used thermal denaturation of human HDL to produce lipid-poor apoA-I. Analysis of the isolated lipid-poor fraction showed a protein/lipid weight ratio of 3:1, with apoA-I, PC (phosphatidylcholine) and CE (cholesterol ester) at approximate molar ratios of 1:8:1. Compared with lipid-free apoA-I, lipid-poor apoA-I showed slightly altered secondary structure and aromatic packing, reduced thermodynamic stability, lower self-associating propensity, increased adsorption to phospholipid surface and comparable ability to remodel phospholipids and form reconstituted HDL. Lipid-poor apoA-I can be formed by heating of either plasma or reconstituted HDL. We propose the first structural model of lipid-poor apoA-I which corroborates its distinct biophysical properties and postulates the lipid-induced ordering of the labile C-terminal region. In summary, HDL heating produces folded functional monomolecular lipid-poor apoA-I that is distinct from lipid-free apoA-I. Increased adsorption to phospholipid surface and reduced C-terminal disorder may help direct lipid-poor apoA-I towards HDL biogenesis.

HDL-C: does it matter? An update on novel HDL-directed pharmaco-therapeutic strategies

It has long been recognized that elevated levels of low-density lipoprotein cholesterol (LDL-C) increase the risk of cardiovascular disease (CHD) and that pharmacologic therapy to decrease LDL-C significantly reduces cardiovascular events. Despite the effectiveness of statins for CHD risk reduction, even optimal LDL-lowering therapy alone fails to avert 60% to 70% of CHD cases. A low plasma concentration of high-density lipoprotein cholesterol (HDL-C) is also associated with increased risk of CHD. However, the convincing epidemiologic data linking HDL cholesterol (HDL-C) to CHD risk in an inverse correlation has not yet translated into clinical trial evidence supporting linearity between HDL-C increases and CHD risk reduction. It is becoming clear that a functional HDL is a more desirable target than simply increasing HDL-C levels. Discoveries in the past decade have shed light on the complex metabolic and antiatherosclerotic pathways of HDL. These insights, in turn, have fueled the development of new HDL-targeted drugs, which can be classified according to four different therapeutic approaches: directly augmenting the concentration of apolipoprotein A-I (apo A-I), the major protein constituent of HDL; indirectly augmenting the concentration of apo A-I and HDL cholesterol; mimicking the functionality of apo A-I and enhancing reverse cholesterol transport. This review discusses the latest in novel HDL directed therapeutic strategies.

Cholesteryl ester transfer protein inhibition as a strategy to reduce cardiovascular risk

Human and rabbit plasma contain a cholesteryl ester transfer protein (CETP) that promotes net mass transfers of cholesteryl esters from high density lipoproteins (HDL) to other plasma lipoprotein fractions. As predicted, inhibition of CETP in both humans and rabbits increases the concentration of cholesterol in the potentially protective HDL fraction, while decreasing it in potentially proatherogenic non-HDL fractions. Inhibition of CETP in rabbits also inhibits the development of diet-induced atherosclerosis. However, use of the CETP inhibitor torcetrapib in humans did not reduce atheroma in three imaging trials and caused an excess of deaths and cardiovascular events in a large clinical outcome trial. The precise explanation for the harm caused by torcetrapib is unknown but may relate to documented, potentially harmful effects unrelated to inhibition of CETP. More recently, a trial using the weak CETP inhibitor dalcetrapib, which raises HDL levels less effectively than torcetrapib and does not lower non-HDL lipoprotein levels, was terminated early for reasons of futility. There was no evidence that dalcetrapib caused harm in that trial. Despite these setbacks, the hypothesis that CETP inhibitors will be antiatherogenic in humans is still being tested in studies with anacetrapib and evacetrapib, two CETP inhibitors that are much more potent than dalcetrapib and that do not share the off-target adverse effects of torcetrapib.

Association between vitamin D status and metabolic syndrome risk among Korean population: based on the Korean National Health and Nutrition Examination Survey IV-2, 2008

AIMS

Low serum 25-hydroxyvitamin D (25(OH)D) levels have been linked to metabolic syndrome. However, community-based data for healthy Korean individuals are lacking. We aimed to assess the vitamin D status and the association of 25(OH)D deficiency with metabolic syndrome in the South Korean population (latitude 33-38°N).

METHODS

In this population-based study, we assessed 5559 South Korean adults selected from the Korean National Health and Nutrition Examination Survey IV-2, 2008. We used multiple logistic regression analysis to assess the association between vitamin D deficiency and metabolic syndrome.

RESULTS

The prevalence of vitamin D deficiency (<20 ng/mL) was 56.0%. Subjects with vitamin D deficiency were younger and had higher education, lower physical activity, and lower alcohol consumption than those with normal vitamin D levels. The overall risk of metabolic syndrome was not associated with 25(OH)D concentration. The adjusted OR of reduced high density lipoprotein cholesterol (HDL-C) decreased across the quintiles of 25(OH)D concentrations (OR=0.72; 95% confidence interval=0.54-0.95 for comparisons of lowest vs. highest quintile; P for trend=0.003).

CONCLUSIONS

A high prevalence of vitamin D deficiency was noted in the general South Korean population. Serum 25(OH)D concentration was inversely associated with the risk of having reduced HDL-C.

MicroRNAs in metabolism and metabolic disorders

MicroRNAs (miRNAs) have recently emerged as key regulators of metabolism. For example, miR-33a and miR-33b have a crucial role in controlling cholesterol and lipid metabolism in concert with their host genes, the sterol-regulatory element-binding protein (SREBP) transcription factors. Other metabolic miRNAs, such as miR-103 and miR-107, regulate insulin and glucose homeostasis, whereas miRNAs such as miR-34a are emerging as key regulators of hepatic lipid homeostasis. The discovery of circulating miRNAs has highlighted their potential as both endocrine signalling molecules and disease markers. Dysregulation of miRNAs may contribute to metabolic abnormalities, suggesting that miRNAs may potentially serve as therapeutic targets for ameliorating cardiometabolic disorders.

MicroRNAs in metabolism and metabolic disorders

MicroRNAs (miRNAs) have recently emerged as key regulators of metabolism. For example, miR-33a and miR-33b have a crucial role in controlling cholesterol and lipid metabolism in concert with their host genes, the sterol-regulatory element-binding protein (SREBP) transcription factors. Other metabolic miRNAs, such as miR-103 and miR-107, regulate insulin and glucose homeostasis, whereas miRNAs such as miR-34a are emerging as key regulators of hepatic lipid homeostasis. The discovery of circulating miRNAs has highlighted their potential as both endocrine signalling molecules and disease markers. Dysregulation of miRNAs may contribute to metabolic abnormalities, suggesting that miRNAs may potentially serve as therapeutic targets for ameliorating cardiometabolic disorders.

Effect of dalcetrapib plus pravastatin on lipoprotein metabolism and high-density lipoprotein composition and function in dyslipidemic patients: results of a phase IIb dose-ranging study

BACKGROUND

Cholesteryl ester transfer protein (CETP) is involved in high-density lipoprotein (HDL) remodeling and transfer of lipids between HDL particles and other lipoproteins. Epidemiologic studies show that both elevated HDL-cholesterol (HDL-C) and reduced CETP activity attenuate cardiovascular risk, making inhibition or modulation of CETP a potential therapeutic target. This study analyzed the effect of dalcetrapib on lipoprotein profile, CETP activity, and cellular cholesterol efflux when co-administered with pravastatin in patients with low or average HDL-C.

METHODS

Patients were randomized in a double-blind fashion to receive placebo or dalcetrapib 300, 600, or 900 mg once daily for 12 weeks. All patients were concomitantly treated to their low-density lipoprotein cholesterol target with pravastatin. Lipoprotein profile was analyzed by nuclear magnetic resonance spectroscopy and polyacrylamide gradient gel electrophoresis. Composition of the HDL fraction was assessed after polyethylene glycol precipitation. Contribution of this fraction to cholesterol efflux was assessed using radiolabeled donor cells.

RESULTS

Co-administration of dalcetrapib with pravastatin increased HDL-C, apolipoproteins (apo) A-I and A-II, and CETP mass, and decreased CETP activity. A relative increase in large HDL and low-density lipoprotein subparticle fractions was observed. High-density lipoprotein composition showed increased association of esterified cholesterol, free cholesterol, phospholipids, apo A-I, and apo E. Adenosine 5'-triphosphate-binding cassette A1- and scavenger receptor type BI-mediated cholesterol efflux increased.

CONCLUSIONS

Dalcetrapib up to 600 mg, combined with pravastatin, increased HDL-C and altered lipoprotein profile, HDL composition, and HDL function, with little further change at a 900-mg dose. The impact on cardiovascular events in dyslipidemic patients is being evaluated.

HDL cholesterol and bone mineral density: is there a genetic link?

Overwhelming evidence has linked cardiovascular disease and osteoporosis, but the shared root cause of these two diseases of the elderly remains unknown. Low levels of high density lipoprotein cholesterol (HDL) and bone mineral density (BMD) are risk factors for cardiovascular disease and osteoporosis respectively. A number of correlation studies have attempted to determine if there is a relationship between serum HDL and BMD but these studies are confounded by a number of variables including age, diet, genetic background, gender and hormonal status. Collectively, these data suggest that there is a relationship between these two phenotypes, but that the nature of this relationship is context specific. Studies in mice plainly demonstrate that genetic loci for BMD and HDL co-map and transgenic mouse models have been used to show that a single gene can affect both serum HDL and BMD. Work completed to date has demonstrated that HDL can interact directly with both osteoblasts and osteoclasts, but no direct evidence links bone back to the regulation of HDL levels. Understanding the genetic relationship between BMD and HDL has huge implications for understanding the clinical relationship between CVD and osteoporosis and for the development of safe treatment options for both diseases.

The Srb1+1050T allele is associated with metabolic syndrome in children but not with cholesteryl ester plasma concentrations of high-density lipoprotein subclasses

BACKGROUND

Low cholesterol and phospholipid plasma levels of some high-density lipoprotein (HDL) subclasses have been described in children with metabolic syndrome. Scavenger receptor class B type I (SR-BI) has been proposed to be at the origin of such HDL alterations because of its key role on cholesteryl esters-HDL metabolism. However, the possible contribution of SR-BI has not been specifically explored in this kind of patients.

METHODS

Plasma lipid concentrations of HDL subclasses, i.e., triglycerides (TG), phosphatidylcholine (Ph), free cholesterol (FC), and total cholesterol (TC), were determined by enzymatic staining on polyacrylamide gradient gels (PAGE) in 39 pediatric patients with metabolic syndrome and 65 children as controls. Cholesteryl esters were estimated by the difference between TC and FC. Proteins of HDL subclasses were also stained for the assessment of the relative size distribution of HDL. For statistical analysis, the study population was grouped by Srb1 +1050C-->T polymorphism (rs5888) as carriers or noncarriers of the T allele, and data were corrected by metabolic syndrome status.

RESULTS

The Srb1 +1050T allele was associated with metabolic syndrome [odds ratio (OR)=2.18 (1.12-4.22), P=0.02]. Plasma TG corresponding to HDL3a, as well as the relative proportion of this HDL subclass, were slightly higher in carriers of the T allele as compared to CC homozygous subjects. Cholesteryl esters plasma concentrations of all HDL subclasses were comparable between T allele carriers and noncarriers after correction by metabolic syndrome status.

CONCLUSIONS

Srb1 +1050T was associated with metabolic syndrome, but T carrier subjects did not show important differences concerning HDL subclasses as compared to noncarriers.

Safety and efficacy of dalcetrapib on atherosclerotic disease using novel non-invasive multimodality imaging (dal-PLAQUE): a randomised clinical trial

BACKGROUND

Dalcetrapib modulates cholesteryl ester transfer protein (CETP) activity to raise high-density lipoprotein cholesterol (HDL-C). After the failure of torcetrapib it was unknown if HDL produced by interaction with CETP had pro-atherogenic or pro-inflammatory properties. dal-PLAQUE is the first multicentre study using novel non-invasive multimodality imaging to assess structural and inflammatory indices of atherosclerosis as primary endpoints.

METHODS

In this phase 2b, double-blind, multicentre trial, patients (aged 18-75 years) with, or with high risk of, coronary heart disease were randomly assigned (1:1) to dalcetrapib 600 mg/day or placebo for 24 months. Randomisation was done with a computer-generated randomisation code and was stratified by centre. Patients and investigators were masked to treatment. Coprimary endpoints were MRI-assessed indices (total vessel area, wall area, wall thickness, and normalised wall index [average carotid]) after 24 months and (18)F-fluorodeoxyglucose ((18)F-FDG) PET/CT assessment of arterial inflammation within an index vessel (right carotid, left carotid, or ascending thoracic aorta) after 6 months, with no-harm boundaries established before unblinding of the trial. Analysis was by intention to treat. This trial is registered at ClinicalTrials.gov, NCT00655473.

FINDINGS

189 patients were screened and 130 randomly assigned to placebo (66 patients) or dalcetrapib (64 patients). For the coprimary MRI and PET/CT endpoints, CIs were below the no-harm boundary or the adverse change was numerically lower in the dalcetrapib group than in the placebo group. MRI-derived change in total vessel area was reduced in patients given dalcetrapib compared with those given placebo after 24 months; absolute change from baseline relative to placebo was -4·01 mm(2) (90% CI -7·23 to -0·80; nominal p=0·04). The PET/CT measure of index vessel most-diseased-segment target-to-background ratio (TBR) was not different between groups, but carotid artery analysis showed a 7% reduction in most-diseased-segment TBR in the dalcetrapib group compared with the placebo group (-7·3 [90% CI -13·5 to -0·8]; nominal p=0·07). Dalcetrapib did not increase office blood pressure and the frequency of adverse events was similar between groups.

INTERPRETATION

Dalcetrapib showed no evidence of a pathological effect related to the arterial wall over 24 months. Moreover, this trial suggests possible beneficial vascular effects of dalcetrapib, including the reduction in total vessel enlargement over 24 months, but long-term safety and clinical outcomes efficacy of dalcetrapib need to be analysed.

FUNDING

F Hoffmann-La Roche Ltd.

Update on HDL receptors and cellular cholesterol transport

Efflux is central to maintenance of tissue and whole body cholesterol homeostasis. The discovery of cell surface receptors that bind high-density lipoprotein (HDL) with high specificity and affinity to promote cholesterol release has significantly advanced our understanding of cholesterol efflux. We now know that 1) cells have several mechanisms to promote cholesterol release, including a passive mechanism that depends on the physico-chemical properties of cholesterol molecules and their interactions with phospholipids; 2) a variety of HDL particles can interact with receptors to promote cholesterol transport from tissues to the liver for excretion; and 3) interactions between HDL and receptors show functional synergy. Therefore, efflux efficiency depends both on the arrays of receptors on tissue cells and HDL particles in serum.

LDL-apheresis depletes apoE-HDL and pre-β1-HDL in familial hypercholesterolemia: relevance to atheroprotection

Subnormal HDL-cholesterol (HDL-C) and apolipoprotein (apo)AI levels are characteristic of familial hypercholesterolemia (FH), reflecting perturbed intravascular metabolism with compositional anomalies in HDL particles, including apoE enrichment. Does LDL-apheresis, which reduces HDL-cholesterol, apoAI, and apoE by adsorption, induce selective changes in HDL subpopulations, with relevance to atheroprotection? Five HDL subpopulations were fractionated from pre- and post-LDL-apheresis plasmas of normotriglyceridemic FH subjects (n = 11) on regular LDL-apheresis (>2 years). Apheresis lowered both plasma apoE (-62%) and apoAI (-16%) levels, with preferential, genotype-independent reduction in apoE. The mass ratio of HDL2:HDL3 was lowered from ~1:1 to 0.72:1 by apheresis, reflecting selective removal of HDL2 mass (80% of total HDL adsorbed). Pre-LDL-apheresis, HDL2 subpopulations were markedly enriched in apoE, consistent with ~1 copy of apoE per 4 HDL particles. Large amounts (50-66%) of apoE-HDL were removed by apheresis, preferentially in the HDL2b subfraction (-50%); minor absolute amounts of apoE-HDL were removed from HDL3 subfractions. Furthermore, pre-β1-HDL particle levels were subnormal following removal (-53%) upon apheresis, suggesting that cellular cholesterol efflux may be defective in the immediate postapheresis period. In LDL-receptor (LDL-R) deficiency, LDL-apheresis may enhance flux through the reverse cholesterol transport pathway and equally attenuate potential biglycan-mediated deposition of apoE-HDL in the arterial matrix.

Evacetrapib is a novel, potent, and selective inhibitor of cholesteryl ester transfer protein that elevates HDL cholesterol without inducing aldosterone or increasing blood pressure

Cholesteryl ester transfer protein (CETP) catalyses the exchange of cholesteryl ester and triglyceride between HDL and apoB containing lipoprotein particles. The role of CETP in modulating plasma HDL cholesterol levels in humans is well established and there have been significant efforts to develop CETP inhibitors to increase HDL cholesterol for the treatment of coronary artery disease. These efforts, however, have been hampered by the fact that most CETP inhibitors either have low potency or have undesirable side effects. In this study, we describe a novel benzazepine compound evacetrapib (LY2484595), which is a potent and selective inhibitor of CETP both in vitro and in vivo. Evacetrapib inhibited human recombinant CETP protein (5.5 nM IC(50)) and CETP activity in human plasma (36 nM IC(50)) in vitro. In double transgenic mice expressing human CETP and apoAI, evacetrapib exhibited an ex vivo CETP inhibition ED(50) of less than 5 mg/kg at 8 h post oral dose and significantly elevated HDL cholesterol. Importantly, no blood pressure elevation was observed in rats dosed with evacetrapib at high exposure multiples compared with the positive control, torcetrapib. In addition, in a human adrenal cortical carcinoma cell line (H295R cells), evacetrapib did not induce aldosterone or cortisol biosynthesis whereas torcetrapib dramatically induced aldosterone and cortisol biosynthesis. Our data indicate that evacetrapib is a potent and selective CETP inhibitor without torcetrapib-like off-target liabilities. Evacetrapib is currently in phase II clinical development.

Anti-atherogenic mechanisms of high density lipoprotein: effects on myeloid cells

In some settings increasing high density lipoprotein (HDL) levels has been associated with a reduction in experimental atherosclerosis. This has been most clearly seen in apolipoprotein A-I (apoA-I) transgenic mice or in animals infused with HDL or its apolipoproteins. A major mechanism by which these treatments are thought to delay progression or cause regression of atherosclerosis is by promoting efflux of cholesterol from macrophage foam cells. In addition, HDL has been described as having anti-inflammatory and other beneficial effects. Some recent research has linked anti-inflammatory effects to cholesterol efflux pathways but likely multiple mechanisms are involved. Macrophage cholesterol efflux may have a role in facilitating emigration of macrophages from lesions during regression. While macrophages can mediate cholesterol efflux by several pathways, studies in knockout mice or cells point to the importance of active efflux mediated by ATP binding cassette transporter (ABC) A1 and G1. In addition to traditional roles in macrophages, these transporters have been implicated in the control of hematopoietic stem cell proliferation, monocytosis and neutrophilia, as well as activation of monocytes and neutrophils. Thus, HDL and cholesterol efflux pathways may have important anti-atherogenic effects at all stages of the myeloid cell/monocyte/dendritic cell/macrophage lifecycle. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Biological activities of HDL subpopulations and their relevance to cardiovascular disease

The concept of raising high-density lipoprotein (HDL) has been the focus of increasing attention as a strategy to reduce cardiovascular disease. HDL particles are, however, highly heterogeneous in structure, intravascular metabolism and biological activity. In this review, we describe major HDL subpopulations and discuss new findings on the antiatherogenic properties of HDL particles. Across the HDL subpopulation spectrum, small, dense, protein-rich HDLs display potent atheroprotective properties, which can be attributed to specific clusters of proteins and lipids; such activities can be compromised under conditions of atherogenic dyslipidemia. Comprehensive structural and compositional analyses of HDL may provide key information to identify subpopulations displaying specific biological functions and acquiring deficient functionality, with the potential to reveal novel biomarkers of cardiovascular risk and new pharmacological targets.

Disruption of the murine procollagen C-proteinase enhancer 2 gene causes accumulation of pro-apoA-I and increased HDL levels

Given the increased prevalence of cardiovascular disease in the world, the search for genetic variations that impact risk factors associated with the development of this disease continues. Multiple genetic association studies demonstrate that procollagen C-proteinase enhancer 2 (PCPE2) modulates HDL levels. Recent studies revealed an unexpected role for this protein in the proteolytic processing of pro-apolipoprotein (apo) A-I by enhancing the cleavage of the hexapeptide extension present at the N-terminus of apoA-I. To investigate the role of the PCPE2 protein in an in vivo model, PCPE2-deficient (PCPE2 KO) mice were examined, and a detailed characterization of plasma lipid profiles, apoA-I, HDL speciation, and function was done. Results of isoelectric focusing (IEF) electrophoresis together with the identification of the amino terminal peptides DEPQSQWDK and WHVWQQDEPQSQWDVK, representing mature apoA-I and pro-apoA-I, respectively, in serum from PCPE2 KO mice confirmed that PCPE2 has a role in apoA-I maturation. Lipid profiles showed a marked increase in plasma apoA-I and HDL-cholesterol (HDL-C) levels in PCPE2 KO mice compared with wild-type littermates, regardless of gender or diet. Changes in HDL particle size and electrophoretic mobility observed in PCPE2 KO mice suggest that the presence of pro-apoA-I impairs the maturation of HDL. ABCA1-dependent cholesterol efflux is defective in PCPE2 KO mice, suggesting that the functionality of HDL is altered.

Progress and challenges in translating the biology of atherosclerosis

Atherosclerosis is a chronic disease of the arterial wall, and a leading cause of death and loss of productive life years worldwide. Research into the disease has led to many compelling hypotheses about the pathophysiology of atherosclerotic lesion formation and of complications such as myocardial infarction and stroke. Yet, despite these advances, we still lack definitive evidence to show that processes such as lipoprotein oxidation, inflammation and immunity have a crucial involvement in human atherosclerosis. Experimental atherosclerosis in animals furnishes an important research tool, but extrapolation to humans requires care. Understanding how to combine experimental and clinical science will provide further insight into atherosclerosis and could lead to new clinical applications.

Primary prevention of coronary heart disease: integration of new data, evolving views, revised goals, and role of rosuvastatin in management. A comprehensive survey

A recent explosion in the amount of cardiovascular risk and incipient, undetected subclinical cardiovascular pathology has swept across the globe. Nearly 70% of adult Americans are overweight or obese; the prevalence of visceral obesity stands at 53% and continues to rise. At any one time, 55% of the population is on a weight-loss diet, and almost all fail. Fewer than 15% of adults or children exercise sufficiently, and over 60% engage in no vigorous activity. Among adults, 11%-13% have diabetes, 34% have hypertension, 36% have prehypertension, 36% have prediabetes, 12% have both prediabetes and prehypertension, and 15% of the population with either diabetes, hypertension, or dyslipidemia are undiagnosed. About one-third of the adult population, and 80% of the obese, have fatty livers. With 34% of children overweight or obese, prevalence having doubled in just a few years, type 2 diabetes, hypertension, dyslipidemia, and fatty livers in children are at their highest levels ever. Half of adults have at least one cardiovascular risk factor. Not even 1% of the population attains ideal cardiovascular health. Despite falling coronary death rates for decades, coronary heart disease (CHD) death rates in US women 35 to 54 years of age may now be increasing because of the obesity epidemic. Up to 65% of patients do not have their conventional risk biomarkers under control. Only 30% of high risk patients with CHD achieve aggressive low density lipoprotein (LDL) targets. Of those patients with multiple risk factors, fewer than 10% have all of them adequately controlled. Even when patients are titrated to evidence-based targets, about 70% of cardiac events remain unaddressed. Undertreatment is also common. About two-thirds of high risk primary care patients are not taking needed medications for dyslipidemia. Poor patient adherence, typically below 50%, adds further difficulty. Hence, after all such fractional reductions are multiplied, only a modest portion of total cardiovascular risk burden is actually being eliminated, and the full potential of risk reduction remains unrealized. Worldwide the situation is similar, with the prevalence of metabolic syndrome approaching 50%. Primordial prevention, resulting from healthful lifestyle habits that do not permit the appearance of risk factors, is the preferred method to lower cardiovascular risk. Lowering the prevalence of obesity is the most urgent matter, and is pleiotropic since it affects blood pressure, lipid profiles, glucose metabolism, inflammation, and atherothrombotic disease progression. Physical activity also improves several risk factors, with the additional potential to lower heart rate. Given the current obstacles, success of primordial prevention remains uncertain. At the same time, the consequences of delay and inaction will inevitably be disastrous, and the sense of urgency mounts. Since most CHD events arise in a large subpopulation of low- to moderate-risk individuals, identifying a high proportion of those who will go on to develop events with accuracy remains unlikely. Without a refinement in risk prediction, the current model of targeting high-risk individuals for aggressive therapy may not succeed alone, especially given the rising burden of risk. Estimating cardiovascular risk over a period of 10 years, using scoring systems such as Framingham or SCORE, continues to enjoy widespread use and is recommended for all adults. Limitations in the former have been of concern, including the under- or over-estimation of risk in specific populations, a relatively short 10-year risk horizon, focus on myocardial infarction and CHD death, and exclusion of family history. Classification errors may occur in up to 37% of individuals, particularly women and the young. Several different scoring systems are discussed in this review. The use of lifetime risk is an important conceptual advance, since ≥90% of young adults with a low 10-year risk have a lifetime risk of ≥39%; over half of all American adults have a low 10-year risk but a high lifetime risk. At age 50 the absence of traditional risk factors is associated with extremely low lifetime risk and significantly greater longevity. Pathological and epidemiological data confirm that atherosclerosis begins in early childhood, and advances seamlessly and inexorably throughout life. Risk factors in childhood are similar to those in adults, and track between stages of life. When indicated, aggressive treatment should begin at the earliest indication, and be continued for years. For those patients at intermediate risk according to global risk scores, C-reactive protein (CRP), coronary artery calcium (CAC), and carotid intima-media thickness (CIMT) are available for further stratification. Using statins for primary prevention is recommended by guidelines, is prevalent, but remains underprescribed. Statin drugs are unrivaled, evidence-based, major weapons to lower cardiovascular risk. Even when low density lipoprotein cholesterol (LDL-C) targets are attained, over half of patients continue to have disease progression and clinical events. This residual risk is of great concern, and multiple sources of remaining risk exist. Though clinical evidence is incomplete, altering or raising the blood high density lipoprotein cholesterol (HDL-C) level continues to be pursued. Of all agents available, rosuvastatin produces the greatest reduction in LDL-C, LDL-P, and improvement in apoA-I/apoB, together with a favorable safety profile. Several recent proposals and methods to lower cardiovascular risk are reviewed. A combination of approaches, such as the addition of lifetime risk, refinement of risk prediction, guideline compliance, novel treatments, improvement in adherence, and primordial prevention, including environmental and social intervention, will be necessary to lower the present high risk burden.

Reverse cholesterol transport revisited: contribution of biliary versus intestinal cholesterol excretion

Reverse cholesterol transport (RCT) is usually defined as high-density lipoprotein-mediated transport of excess cholesterol from peripheral tissues, including cholesterol-laden macrophages in vessel walls, to the liver. From the liver, cholesterol can then be removed from the body via secretion into the bile for eventual disposal via the feces. According to this paradigm, high plasma high-density lipoprotein levels accelerate RCT and hence are atheroprotective. New insights in individual steps of the RCT pathway, in part derived from innovative mouse models, indicate that the classical concept of RCT may require modification.

Lipid-Free Apolipoprotein A-I and Discoidal Reconstituted High-Density Lipoproteins Differentially Inhibit Glucose-Induced Oxidative Stress in Human Macrophages

Objective—

The goal of this study was to investigate the mechanisms by which apolipoprotein (apo) A-I, in the lipid-free form or as a constituent of discoidal reconstituted high-density lipoproteins ([A-I]rHDL), inhibits high-glucose–induced redox signaling in human monocyte-derived macrophages (HMDM).

Methods and Results—

HMDM were incubated under normal (5.8 mmol/L) or high-glucose (25 mmol/L) conditions with native high-density lipoproteins (HDL) lipid-free apoA-I from normal subjects and from subjects with type 2 diabetes (T2D) or (A-I)rHDL. Superoxide (O 2 − ) production was measured using dihydroethidium fluorescence. NADPH oxidase activity was assessed using lucigenin-derived chemiluminescence and a cyotochrome c assay. p47phox translocation to the plasma membrane, Nox2, superoxide dismutase 1 (SOD1), and SOD2 mRNA and protein levels were determined by real-time polymerase chain reaction and Western blotting. Native HDL induced a time-dependent inhibition of O 2 − generation in HMDM incubated with 25 mmol/L glucose. Lipid-free apoA-I and (A-I)rHDL increased SOD1 and SOD2 levels and attenuated 25 mmol/L glucose-mediated increases in cellular O 2 − , NADPH oxidase activity, p47 translocation, and Nox2 expression. Lipid-free apoA-I mediated its effects on Nox2, SOD1, and SOD2 via ABCA1. (A-I)rHDL-mediated effects were via ABCG1 and scavenger receptor BI. Lipid-free apoA-I from subjects with T2D inhibited reactive oxygen species generation less efficiently than normal apoA-I.

Conclusion—

Native HDL, lipid-free apoA-I and (A-I)rHDL inhibit high-glucose–induced redox signaling in HMDM. The antioxidant properties of apoA-I are attenuated in T2D.

Triglyceride-rich lipoproteins and high-density lipoprotein cholesterol in patients at high risk of cardiovascular disease: evidence and guidance for management

Even at low-density lipoprotein cholesterol (LDL-C) goal, patients with cardiometabolic abnormalities remain at high risk of cardiovascular events. This paper aims (i) to critically appraise evidence for elevated levels of triglyceride-rich lipoproteins (TRLs) and low levels of high-density lipoprotein cholesterol (HDL-C) as cardiovascular risk factors, and (ii) to advise on therapeutic strategies for management. Current evidence supports a causal association between elevated TRL and their remnants, low HDL-C, and cardiovascular risk. This interpretation is based on mechanistic and genetic studies for TRL and remnants, together with the epidemiological data suggestive of the association for circulating triglycerides and cardiovascular disease. For HDL, epidemiological, mechanistic, and clinical intervention data are consistent with the view that low HDL-C contributes to elevated cardiovascular risk; genetic evidence is unclear however, potentially reflecting the complexity of HDL metabolism. The Panel believes that therapeutic targeting of elevated triglycerides (≥ 1.7 mmol/L or 150 mg/dL), a marker of TRL and their remnants, and/or low HDL-C (<1.0 mmol/L or 40 mg/dL) may provide further benefit. The first step should be lifestyle interventions together with consideration of compliance with pharmacotherapy and secondary causes of dyslipidaemia. If inadequately corrected, adding niacin or a fibrate, or intensifying LDL-C lowering therapy may be considered. Treatment decisions regarding statin combination therapy should take into account relevant safety concerns, i.e. the risk of elevation of blood glucose, uric acid or liver enzymes with niacin, and myopathy, increased serum creatinine and cholelithiasis with fibrates. These recommendations will facilitate reduction in the substantial cardiovascular risk that persists in patients with cardiometabolic abnormalities at LDL-C goal.

Triglyceride-rich lipoproteins and high-density lipoprotein cholesterol in patients at high risk of cardiovascular disease: evidence and guidance for management

Even at low-density lipoprotein cholesterol (LDL-C) goal, patients with cardiometabolic abnormalities remain at high risk of cardiovascular events. This paper aims (i) to critically appraise evidence for elevated levels of triglyceride-rich lipoproteins (TRLs) and low levels of high-density lipoprotein cholesterol (HDL-C) as cardiovascular risk factors, and (ii) to advise on therapeutic strategies for management. Current evidence supports a causal association between elevated TRL and their remnants, low HDL-C, and cardiovascular risk. This interpretation is based on mechanistic and genetic studies for TRL and remnants, together with the epidemiological data suggestive of the association for circulating triglycerides and cardiovascular disease. For HDL, epidemiological, mechanistic, and clinical intervention data are consistent with the view that low HDL-C contributes to elevated cardiovascular risk; genetic evidence is unclear however, potentially reflecting the complexity of HDL metabolism. The Panel believes that therapeutic targeting of elevated triglycerides (≥1.7 mmol/L or 150 mg/dL), a marker of TRL and their remnants, and/or low HDL-C (<1.0 mmol/L or 40 mg/dL) may provide further benefit. The first step should be lifestyle interventions together with consideration of compliance with pharmacotherapy and secondary causes of dyslipidaemia. If inadequately corrected, adding niacin or a fibrate, or intensifying LDL-C lowering therapy may be considered. Treatment decisions regarding statin combination therapy should take into account relevant safety concerns, i.e. the risk of elevation of blood glucose, uric acid or liver enzymes with niacin, and myopathy, increased serum creatinine and cholelithiasis with fibrates. These recommendations will facilitate reduction in the substantial cardiovascular risk that persists in patients with cardiometabolic abnormalities at LDL-C goal.

Pressure perturbation calorimetry of lipoproteins reveals an endothermic transition without detectable volume changes. Implications for adsorption of apolipoprotein to a phospholipid surface

Plasma lipoproteins are assemblies of lipids and apolipoproteins that mediate lipid transport and metabolism. High-density lipoproteins (HDL) remove excess cell cholesterol and provide protection against atherosclerosis. Important aspects of metabolic HDL remodeling, including apolipoprotein dissociation and lipoprotein fusion, are mimicked in thermal denaturation. We report the first study of the protein-lipid complexes by pressure perturbation calorimetry (PPC) beyond 100 °C. In PPC, volume expansion coefficient α(v)(T) is measured during heating; in proteins, α(v)(T) is dominated by hydration. Calorimetric studies of reconstituted HDL and of human high-density, low-density, and very low-density lipoproteins reveal that apolipoprotein unfolding, dissociation, and lipoprotein fusion are endothermic transitions without detectable volume changes. This may result from the limited applicability of PPC to slow kinetically controlled transitions such as thermal remodeling of lipoproteins and/or from the possibility that this remodeling causes no significant changes in the solvent structure and, hence, may not involve large transient solvent exposure of apolar moieties. Another conclusion is that apolipoprotein A-I in solution adsorbs to the phospholipid surface; protein hydration is preserved upon such adsorption. We posit that adsorption to a phospholipid surface helps recruit free apolipoprotein to the plasma membrane and facilitate HDL biogenesis.

Apolipoprotein A-I structural organization in high-density lipoproteins isolated from human plasma

High density lipoproteins (HDL) mediate cholesterol transport and protection from cardiovascular disease. Although synthetic HDLs have been studied for 30 years, the structure of human plasma-derived HDL, and its major protein apolipoprotein (apo)A-I, is unknown. We separated normal human HDL into 5 density subfractions and then further isolated those containing predominantly apoA-I (LpA-I). Using cross-linking chemistry and mass spectrometry, we found that apoA-I adopts a structural framework in these particles that closely mirrors that in synthetic HDL. We adapted established structural models for synthetic HDL to generate the first detailed models of authentic human plasma HDL in which apoA-I adopts a symmetrical cage-like structure. The models suggest that HDL particle size is modulated via a twisting motion of the resident apoA-I molecules. This understanding offers insights into how apoA-I structure modulates HDL function and its interactions with other apolipoproteins.

HDL and cardiovascular disease: atherogenic and atheroprotective mechanisms

The lipoprotein HDL has two important roles: first, it promotes reverse cholesterol transport, and second, it modulates inflammation. Epidemiological studies show that HDL-cholesterol levels are inversely correlated with the risk of cardiovascular events. However, many patients who experience a clinical event have normal, or even high, levels of HDL cholesterol. Measuring HDL-cholesterol levels provides information about the size of the HDL pool, but does not predict HDL composition or function. The main component of HDL, apolipoprotein A-I (apo A-I), is largely responsible for reverse cholesterol transport through the macrophage ATP-binding cassette transporter ABCA1. Apo A-I can be damaged by oxidative mechanisms, which render the protein less able to promote cholesterol efflux. HDL also contains a number of other proteins that are affected by the oxidative environment of the acute-phase response. Modification of the protein components of HDL can convert it from an anti-inflammatory to a proinflammatory particle. Small peptides that mimic some of the properties of apo A-I have been shown in preclinical models to improve HDL function and reduce atherosclerosis without altering HDL-cholesterol levels. Robust assays to evaluate the function of HDL are needed to supplement the measurement of HDL-cholesterol levels in the clinic.