A Commentary on the Development and Validation of novel automatable assay for cholesterol efflux capacity

The determination of functionality or quality of HDL is assuming a central stage in the prediction of cardiovascular diseases (CVD). To assess HDL quality, several attempts have been made to develop an automated, cost-effective CEC system with few operational steps that might be used in clinical settings for large throughput testing. The work of Dr. Ohkawa and co-workers seems to address this issue and provide a solution for the same (Bioscience Reports (2023) 43 BSR20221519, https://doi.org/10.1042/BSR20221519). Earlier work from the author's lab utilized a radioisotope and cell-free CEC assay known as the immobilized liposome-bound gel beads (ILGs) method. However, this assay required a centrifugation step to separate the cells and was not suitable for automation. To overcome these limitations, two very important changes were made (i) magnetic beads were used instead of gel beads which allowed them to avoid the centrifugation process that would allow ease of setting up an autonomous analyzer; (ii) porous magnetic beads were coated with liposomes containing fluorescently tagged cholesterol instead radiolabeled cholesterol. These two changes can be considered not only significant but also novel as they were highly suitable for CEC testing. The authors reported the successful development of a simple Immobilized liposome-based magnetic beads (ILM) automated system to measure CEC which provided both consistent performance and satisfactory correlation with the other methods.  Thus, we feel this study will open newer avenues for measuring the quality of HDL in addition to the quantity of HDL-cholesterol in clinical settings in a more robust way.

Structure-based mechanism and inhibition of cholesteryl ester transfer protein

PURPOSE OF REVIEW

Cholesteryl ester transfer proteins (CETP) regulate plasma cholesterol levels by transferring cholesteryl esters (CEs) among lipoproteins. Lipoprotein cholesterol levels correlate with the risk factors for atherosclerotic cardiovascular disease (ASCVD). This article reviews recent research on CETP structure, lipid transfer mechanism, and its inhibition.

RECENT FINDINGS

Genetic deficiency in CETP is associated with a low plasma level of low-density lipoprotein cholesterol (LDL-C) and a profoundly elevated plasma level of high-density lipoprotein cholesterol (HDL-C), which correlates with a lower risk of atherosclerotic cardiovascular disease (ASCVD). However, a very high concentration of HDL-C also correlates with increased ASCVD mortality. Considering that the elevated CETP activity is a major determinant of the atherogenic dyslipidemia, i.e., pro-atherogenic reductions in HDL and LDL particle size, inhibition of CETP emerged as a promising pharmacological target during the past two decades. CETP inhibitors, including torcetrapib, dalcetrapib, evacetrapib, anacetrapib and obicetrapib, were designed and evaluated in phase III clinical trials for the treatment of ASCVD or dyslipidemia. Although these inhibitors increase in plasma HDL-C levels and/or reduce LDL-C levels, the poor efficacy against ASCVD ended interest in CETP as an anti-ASCVD target. Nevertheless, interest in CETP and the molecular mechanism by which it inhibits CE transfer among lipoproteins persisted. Insights into the structural-based CETP-lipoprotein interactions can unravel CETP inhibition machinery, which can hopefully guide the design of more effective CETP inhibitors that combat ASCVD. Individual-molecule 3D structures of CETP bound to lipoproteins provide a model for understanding the mechanism by which CETP mediates lipid transfer and which in turn, guide the rational design of new anti-ASCVD therapeutics.

Scavenging dicarbonyls with 5'-O-pentyl-pyridoxamine increases HDL net cholesterol efflux capacity and attenuates atherosclerosis and insulin resistance

OBJECTIVE

Oxidative stress contributes to the development of insulin resistance (IR) and atherosclerosis. Peroxidation of lipids produces reactive dicarbonyls such as Isolevuglandins (IsoLG) and malondialdehyde (MDA) that covalently bind plasma/cellular proteins, phospholipids, and DNA leading to altered function and toxicity. We examined whether scavenging reactive dicarbonyls with 5'-O-pentyl-pyridoxamine (PPM) protects against the development of IR and atherosclerosis in Ldlr^-/- mice.

METHODS

Male or female Ldlr^-/- mice were fed a western diet (WD) for 16 weeks and treated with PPM versus vehicle alone. Plaque extent, dicarbonyl-lysyl adducts, efferocytosis, apoptosis, macrophage inflammation, and necrotic area were measured. Plasma MDA-LDL adducts and the in vivo and in vitro effects of PPM on the ability of HDL to reduce macrophage cholesterol were measured. Blood Ly6C^hi monocytes and ex vivo 5-ethynyl-2'-deoxyuridine (EdU) incorporation into bone marrow CD11b+ monocytes and CD34+ hematopoietic stem and progenitor cells (HSPC) were also examined. IR was examined by measuring fasting glucose/insulin levels and tolerance to insulin/glucose challenge.

RESULTS

PPM reduced the proximal aortic atherosclerosis by 48% and by 46% in female and male Ldlr^-/- mice, respectively. PPM also decreased IR and hepatic fat and inflammation in male Ldlr^-/- mice. Importantly, PPM decreased plasma MDA-LDL adducts and prevented the accumulation of plaque MDA- and IsoLG-lysyl adducts in Ldlr^-/- mice. In addition, PPM increased the net cholesterol efflux capacity of HDL from Ldlr^-/- mice and prevented both the in vitro impairment of HDL net cholesterol efflux capacity and apoAI crosslinking by MPO generated hypochlorous acid. Moreover, PPM decreased features of plaque instability including decreased proinflammatory M1-like macrophages, IL-1β expression, myeloperoxidase, apoptosis, and necrotic core. In contrast, PPM increased M2-like macrophages, Tregs, fibrous cap thickness, and efferocytosis. Furthermore, PPM reduced inflammatory monocytosis as evidenced by decreased blood Ly6C^hi monocytes and proliferation of bone marrow monocytes and HSPC from Ldlr^-/- mice.

CONCLUSIONS

PPM has pleotropic atheroprotective effects in a murine model of familial hypercholesterolemia, supporting the therapeutic potential of reactive dicarbonyl scavenging in the treatment of IR and atherosclerotic cardiovascular disease.

Associations of total urinary arsenic with total cholesterol and high-density lipoprotein among 12-17-year-old participants from the 2009-2016 NHANES cycles: A cross-sectional study

INTRODUCTION

Hypertension and diabetes are highly prevalent among US adults. Arsenic exposure is associated with these cardiometabolic morbidities but the relationship between arsenic exposure and cholesterol markers of cardiometabolic disease has not been elucidated, especially at younger ages, when many chronic diseases may initiate. This study examined the association of total urinary arsenic with total cholesterol (TC) and high-density lipoprotein cholesterol (HDL) and explored effect modification by weight status.

METHODS

The study sample consisted of 12-17-year-old participants with complete data from the 2009-2016 National Health and Nutrition Examination Survey cycles. The cross-sectional associations of creatinine-adjusted total urinary arsenic with TC and HDL were assessed using multivariable linear regression models with survey weights. Three models were built, adjusting for varying combinations of age, gender, race/ethnicity, weight status, survey cycle, family income to poverty ratio, reference person education level, arsenobetaine, and dimethylarsinic acid (DMA). Model adjustments for arsenobetaine approximated inorganic arsenic exposure, and further adjustment for DMA approximated unmethylated inorganic arsenic exposure. We also explored weight status (underweight/healthy, overweight, and obese) as a potential effect modifier of these relationships using stratified analyses and interaction tests.

RESULTS

The final analytical sample consisted of 1,177 12-17-year-old participants. After adjusting for covariates and arsenobetaine, creatinine-adjusted arsenic was positively associated with HDL levels (β = 0.063; 95% CI: 0.007, 0.119). Upon further adjustment for DMA, creatinine-adjusted arsenic was positively associated with HDL levels (β = 0.079; 95% CI: 0.015, 0.143) and TC levels (β = 0.258; 95% CI: 0.002, 0.515). No effect modification by weight status was observed.

CONCLUSIONS

We found a positive association of approximated unmethylated inorganic arsenic exposure with TC, and contrary to our expectation, with HDL. There was no effect modification by weight status. Our findings should be confirmed by conducting longitudinal studies among adolescents exposed to low-level arsenic and focusing specifically on urinary inorganic arsenic concentrations.

Aptamer/AuNPs encoders endow precise identification and discrimination of lipoprotein subclasses

Lipoproteins are composed of lipid and apolipoproteins in conjunction with noncovalent bonds. Different lipoprotein categories, particularly Low-Density Lipoprotein (LDL), High-Density Lipoprotein (HDL) and Very Low-Density Lipoprotein (VLDL) disagree in roles for the occurrence and development of cardiovascular disease, and their exact discrimination are critically required. Herein, a multiplexed sensor platform combined with an encoder system is introduced for accurate analysis of multiple lipoproteins in complex matrix. Three encoders, i.e., bare AuNPs, AuNPs-anti-LDL aptamer (AuNPs-apt) and AuNPs-non-aptamer DNA (AuNPs-n), facilitate precise discrimination for lipoprotein subclasses at a fairly low level of 0.490 nM. The binding of single-stranded DNA (ssDNA) with AuNPs prevents them from gathering in a relatively higher level of salt. In targets stimuli, the weaker binding between ssDNA and AuNPs is destroyed to certain degrees depending on the differential affinities among DNA, AuNPs, and multifarious proteins. It results in distinct aggregation states of encoders to cause diverse ultraviolet absorption, which may be statistically characterized to achieve highly facile and precise identification for lipoprotein subclasses. Remarkably, LDL at 0.05-37.5 μg/mL could be identified by the encoder system. 11 typical proteins including three lipoprotein subclasses in human serum were also precisely discriminated. Furthermore, the accurate identification of lipoprotein subclasses with different molar ratios from real clinical serum samples were obtained.

HDL and cancer - causality still needs to be confirmed? Update 2020

An inverse correlation between high-density lipoprotein cholesterol (HDL-C) and cancer risk has been shown by several epidemiological studies. Some studies have even suggested that HDL-C can be used as a prognostic marker in patients with certain types of cancer. However, whether reduced HDL-C level is a consequential or causal factor in the development and progression of cancer remains a controversial issue. In this review, we update and summarize recent advances that highlight the role of HDL and some of its components in prognosis, diagnosis and treatment of cancer.

Serum amyloid A-induced blood-brain barrier dysfunction associated with decreased claudin-5 expression in rat brain endothelial cells and its inhibition by high-density lipoprotein in vitro

The blood-brain barrier (BBB) is the multicellular interface located between the peripheral circulation and the brain parenchyma. BBB dysfunction is reported in many CNS diseases, such cognitive impairment, depression, Alzheimer's disease (AD), and multiple sclerosis (MS). Emerging evidence indicates that liver-derived inflammatory mediators are upregulated in neurological diseases with BBB dysfunction. Serum amyloid A (SAA), an acute phase protein secreted by hepatocytes, could be a candidate inflammatory signaling molecule transmitted from the liver to the brain; however, its contribution to BBB dysfunction is poorly understood. The present study aimed to elucidate the involvement of SAA in BBB impairment in an in vitro BBB model using rat brain microvascular endothelial cells (RBECs). We demonstrated that Apo-SAA significantly decreased transendothelial electrical resistance (TEER) and increased sodium fluorescein (Na-F) permeability in RBEC monolayers. Apo-SAA also decreased claudin-5 expression levels in RBECs. Furthermore, the Apo-SAA-mediated impairment of the BBB with decreased claudin-5 expression was inhibited by the addition of a high-density lipoprotein (HDL) related to SAA in plasma. These findings suggest that HDL counteracts the effects of SAA on BBB function. Therefore, the functional imbalance between SAA and HDL may induce BBB impairment, thereby triggering development of neuroinflammation. SAA could be a significant endogenous mediator in the liver-to-brain inflammation axis.

The anti-inflammatory properties of HDLs are impaired in gout

OBJECTIVE

We sought to determine whether high-density lipoprotein (HDL) function was altered in gout patients.

RESEARCH DESIGN AND METHODS

The study included 95 gout patients and 68 healthy controls. The concentrations of interleukin (IL)-1β and IL-9 were measured by ELISA, and indicators such as blood uric acid, liver and kidney function, blood glucose, and blood lipids were detected. To test for the anti-inflammatory and reverse cholesterol transport (RCT) function of HDL, 11 gout patients and 11 healthy controls were randomly selected for the BioVision cholesterol efflux test, which detects the RCT activity of HDL. To assess the anti-inflammatory function of HDL, cells in co-culture with HDL were treated with inflammatory stimuli such as tumor necrosis factor-α (TNF-α), and then, the cells were assayed for the expression of intercellular adhesion molecules (ICAMs) and vascular cell adhesion molecule-1 (VCAM-1).

RESULTS

In total, this study enrolled 163 participants, including 95 non-hyperlipidemic gout patients and 68 healthy controls. IL-1β and IL-9 levels were significantly higher in the gout group than in the control group (85.26 ± 23.16 vs. 41.47 ± 6.48 and 33.77 ± 12.68 vs. 23.66 ± 4.53, respectively, P < 0.001). Additionally, plasma IL-1β and IL-9 levels were increased along with those of blood uric acid (R² = 0.4116 and R² = 0.4150, respectively, P < 0.001). Compared with the healthy controls, gout patients showed no differences in plasma apoA-1 levels or in the cholesterol efflux assay. Gout patients had increased ICAM-1 expression compared with the healthy controls (88.79 ± 3.68 vs. 86.27 ± 4.64, P < 0.05), but no difference in VCAM-1 expression was found (0.87 ± 0.43 vs. 0.98 ± 0.96, P > 0.05). In this assay, higher values indicate less suppression of ICAM-1 induction, which correlates with a reduced anti-inflammatory capacity.

CONCLUSIONS

The anti-inflammatory activities of HDLs are impaired in gout patients. Key Points • Gout patients show chronic inflammation. • The anti-inflammatory activity of high-density lipoprotein is impaired in gout patients.

Cardiac apoptosis caused by elevated cholesterol level in experimental autoimmune myocarditis

It has been reported that cholesterol-lowing agents can ameliorate severity of myocarditis. However, the beneficial effect of the agents has been claimed to be independent of cholesterol reduction as there is no significant change in the plasma cholesterol level in myocarditis. In the present study, using experimental autoimmune myocarditis (EAM) rats as an animal model, we demonstrated that EAM induced elevation of cholesterol level and impaired cholesterol efflux capacity in the cardiac tissue. Moreover, serum high-density lipoprotein (HDL) content was reduced and HDL function associated protein Paraoxonase 1 (PON1) activity was decreased. Besides, the major structural protein within HDL, Apolipoprotein A1 (ApoA1) expression in the cardiac tissues was significantly reduced while the level of serum ApoA1 was not significantly altered. Importantly, cholesterol depleting agent methyl-β-cyclodextrin (MβCD) alleviated the development of EAM, as monitored by decreased ratio of heart weight to body weight (HW/BW), decreased infiltration of inflammatory cells and collagen deposition, improved cardiac function, reduced expression of apoptosis-related protein Bax, Fas, FasL and caspase-3 and increased level of anti-apoptotic protein Bcl-2. These results suggest that reduction of cholesterol level in cardiac tissue could suppress EAM-induced cardiac apoptosis through both intrinsic and extrinsic apoptotic pathways.

Androgen deprivation therapy improves the in vitro capacity of high-density lipoprotein (HDL) to receive cholesterol and other lipids in patients with prostate carcinoma

Background

Androgen deprivation therapy (ADT) is widely used in the treatment of testosterone-dependent prostate carcinomas. ADT often increases plasma LDL and HDL cholesterol and triglycerides. The aim was to test whether ADT changes the transfer of lipids to HDL, an important aspect of this metabolism and HDL protective functions, and related parameters.

Methods

Sixteen volunteers with advanced prostate carcinoma submitted to pharmacological ADT or orchiectomy had plasma collected shortly before and after 6 months of ADT. In vitro transfer of lipids to HDL was performed by incubating plasma with donor emulsion containing radioactive lipids by 1 h at 37 °C. After chemical precipitation of apolipoprotein B-containing lipoprotein, the radioactivity of HDL fraction was counted.

Results

ADT reduced testosterone to nearly undetectable levels and markedly diminished PSA. ADT increased the body weight but glycemia, triglycerides, LDL and HDL cholesterol, HDL lipid composition and CETP concentration were unchanged. However, ADT increased the plasma unesterified cholesterol concentration (48 ± 12 vs 56 ± 12 mg/dL, p = 0.019) and LCAT concentration (7.15 ± 1.81 vs 8.01 ± 1.55μg/mL, p = 0.020). Transfer of unesterified (7.32 ± 1.09 vs 8.18 ± 1.52%, p < 0.05) and esterified cholesterol (6.15 ± 0.69 vs 6.94 ± 1.29%, p < 0.01) and of triglycerides (6.37 ± 0.43 vs 7.18 ± 0.91%, p < 0.001) to HDL were increased after ADT. Phospholipid transfer was unchanged.

Conclusion

Increase in transfer of unesterified and esterified cholesterol protects against cardiovascular disease, as shown previously, and increased LCAT favors cholesterol esterification and facilitates the reverse cholesterol transport. Thus, our results suggest that ADT may offer anti-atherosclerosis protection by improving HDL functional properties. This could counteract, at least partially, the eventual worse effects on plasma lipids.

High-density lipoproteins during sepsis: from bench to bedside

High-density lipoproteins (HDLs) represent a family of particle characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver conferring them a cardioprotective function. HDLs also display pleiotropic properties including antioxidant, anti-apoptotic, anti-thrombotic, anti-inflammatory, or anti-infectious functions. Clinical data demonstrate that HDL cholesterol levels decrease rapidly during sepsis and that these low levels are correlated with morbi-mortality. Experimental studies emphasized notable structural and functional modifications of HDL particles in inflammatory states, including sepsis. Finally, HDL infusion in animal models of sepsis improved survival and provided a global endothelial protective effect. These clinical and experimental studies reinforce the potential of HDL therapy in human sepsis. In this review, we will detail the different effects of HDLs that may be relevant under inflammatory conditions and the lipoprotein changes during sepsis and we will discuss the potentiality of HDL therapy in sepsis.

Cerebrovascular amyloid Angiopathy in bioengineered vessels is reduced by high-density lipoprotein particles enriched in Apolipoprotein E

Background

Several lines of evidence suggest that high-density lipoprotein (HDL) reduces Alzheimer’s disease (AD) risk by decreasing vascular beta-amyloid (Aβ) deposition and inflammation, however, the mechanisms by which HDL improve cerebrovascular functions relevant to AD remain poorly understood.

Methods

Here we use a human bioengineered model of cerebral amyloid angiopathy (CAA) to define several mechanisms by which HDL reduces Aβ deposition within the vasculature and attenuates endothelial inflammation as measured by monocyte binding.

Results

We demonstrate that HDL reduces vascular Aβ accumulation independently of its principal binding protein, scavenger receptor (SR)-BI, in contrast to the SR-BI-dependent mechanism by which HDL prevents Aβ-induced vascular inflammation. We describe multiple novel mechanisms by which HDL acts to reduce CAA, namely: i) altering Aβ binding to collagen-I, ii) forming a complex with Aβ that maintains its solubility, iii) lowering collagen-I protein levels produced by smooth-muscle cells (SMC), and iv) attenuating Aβ uptake into SMC that associates with reduced low density lipoprotein related protein 1 (LRP1) levels. Furthermore, we show that HDL particles enriched in apolipoprotein (apo)E appear to be the major drivers of these effects, providing new insights into the peripheral role of apoE in AD, in particular, the fraction of HDL that contains apoE.

Conclusion

The findings in this study identify new mechanisms by which circulating HDL, particularly HDL particles enriched in apoE, may provide vascular resilience to Aβ and shed new light on a potential role of peripherally-acting apoE in AD.

High-density lipoprotein cholesterol efflux capacity and cardiovascular risk in autoimmune and non-autoimmune diseases

Functional assessment of cholesterol efflux capacity (CEC) to high-density lipoprotein (HDL) is an emerging tool for evaluating morbidity and mortality associated with cardiovascular disease (CVD). By promoting macrophage reverse cholesterol transport (RCT), HDL-mediated CEC is believed to play an important role in atherosclerotic lesion progression in the vessel wall. Furthermore, recent evidence indicates that the typical inverse associations between various forms of CEC and CV events may be strongly modulated by environmental systemic factors and traditional CV risk factors, in addition to autoimmune diseases. These factors influence the complex and dynamic composition of HDL particles, which in turn positively or negatively affect HDL-CEC. Herein, we review recent findings connecting HDL-CEC to traditional CV risk factors and cardiometabolic conditions (non-autoimmune diseases) as well as autoimmune diseases, with a specific focus on how these factors may influence the associations between HDL-CEC and CVD risk.

Association of cholesterol uptake capacity, a novel indicator for HDL functionality, and coronary plaque properties: An optical coherence tomography-based observational study

BACKGROUND

Cholesterol efflux from atherosclerotic lesion is a key function of high-density lipoprotein (HDL). Recently, we established a simple, high-throughput, cell-free assay to evaluate the capacity of HDL to accept additional cholesterol, which is herein referred to as "cholesterol uptake capacity (CUC)".

OBJECTIVE

To clarify the cross-sectional relationship between CUC and coronary plaque properties.

METHODS

We enrolled 135 patients to measure CUC and assess the morphological features of angiographic stenosis by optical coherence tomography (OCT). We estimated the extent of the lipid-rich plaque by multiplying the mean lipid arc by lipid length (lipid index). The extent of the OCT-detected macrophage accumulation in the target plaque was semi-quantitatively estimated using a grading system.

RESULTS

Lipid-rich plaque lesions were identified in 125 patients (92.6%). CUC was inversely associated with the lipid index (R = -0.348, P < 0.0001). In addition, CUC was also inversely associated with macrophage score (R = -0.327, P < 0.0001). Conversely, neither circulating levels of HDL cholesterol nor apoA1 showed a similar relationship.

CONCLUSIONS

We demonstrated that CUC was inversely related to lipid-rich plaque burden and the extent of macrophage accumulation, suggesting that CUC could be useful for cardiovascular risk stratification.

Assessment of HDL Cholesterol Removal Capacity: Toward Clinical Application

While there is a controversy regarding the causal relationship between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD), recent studies have demonstrated that the cholesterol efflux capacity (CEC) of HDL is associated with the incidence of CVD. However, there are several limitations to current assays of CEC. First, CEC measurements are not instantly applicable in clinical settings, because CEC assay methods require radiolabeled cholesterol and cultured cells, and these procedures are time consuming. Second, techniques to measure CEC are not standardized. Third, the condition of endogenous cholesterol donors would not be accounted for in the CEC assays. Recently, we established a simple, high-throughput, cell-free assay system to evaluate the capacity of HDL to accept additional cholesterol, which is herein referred to as "cholesterol uptake capacity (CUC)". We demonstrated that CUC represents a residual cardiovascular risk in patients with optimal low-density lipoprotein cholesterol control independently of traditional risk factors, including HDL-C. Establishing reproducible approaches for the cholesterol removal capacity of HDL is required to validate the impact of dysfunctional HDL on cardiovascular risk stratification in the "real world".

HDL in Endocrine Carcinomas: Biomarker, Drug Carrier, and Potential Therapeutic

High-density lipoprotein (HDL) have long been studied for their protective role against cardiovascular diseases, however recently relationship between HDL and cancer came into focus. Several epidemiological studies have shown an inverse correlation between HDL-cholesterol (HDL-C) and cancer risk, and some have even implied that HDL-C can be used as a predictive measure for survival prognosis in for specific sub-population of certain types of cancer. HDL itself is an endogenous nanoparticle capable of removing excess cholesterol from the periphery and returning it to the liver for excretion. One of the main receptors for HDL, scavenger receptor type B-I (SR-BI), is highly upregulated in endocrine cancers, notably due to the high demand for cholesterol by cancer cells. Thus, the potential to exploit administration of cholesterol-free reconstituted or synthetic HDL (sHDL) to deplete cholesterol in endocrine cancer cell and stunt their growth of use chemotherapeutic drug loaded sHDL to target payload delivery to cancer cell has become increasingly attractive. This review focuses on the role of HDL and HDL-C in cancer and application of sHDLs as endocrine cancer therapeutics.

Potential causal associations of serum 25-hydroxyvitamin D with lipids: a Mendelian randomization approach of the HUNT study

Observational studies have shown consistent associations between higher circulating 25-hydroxyvitamin D [25(OH)D] levels and favorable serum lipids. We sought to investigate if such associations were causal. A Mendelian randomization (MR) study was conducted on a population-based cohort comprising 56,435 adults in Norway. A weighted 25(OH)D allele score was generated based on vitamin D-increasing alleles of rs2282679, rs12785878 and rs10741657. Linear regression analyses of serum lipid levels on the allele score were performed to assess the presence of causal associations of serum 25(OH)D with the lipids. To quantify the causal effects, the inverse-variance weighted method was used for calculating MR estimates based on summarized data of individual single-nucleotide polymorphisms. The MR estimate with 95% confidence interval (CI) represents percentage difference in the lipid level per genetically determined 25 nmol/L increase in 25(OH)D. The 25(OH)D allele score demonstrated a clear association with high-density lipoprotein (HDL) cholesterol (p = 0.007) but no association with total or non-HDL cholesterol or triglycerides (p ≥ 0.27). The MR estimate showed 2.52% (95% CI 0.79-4.25%) increase in HDL cholesterol per genetically determined 25 nmol/L increase in 25(OH)D, which was stronger than the corresponding estimate of 1.83% (95% CI 0.85-2.81%) from the observational analysis. The MR estimates for total cholesterol (0.60%, 95% CI - 0.73 to 1.94%), non-HDL cholesterol (0.04%, 95% CI - 1.79 to 1.88%) and triglycerides (- 2.74%, 95% CI - 6.16 to 0.67%) showed no associations. MR analysis of data from a population-based cohort suggested a causal and positive association between serum 25(OH)D and HDL cholesterol.

Reconstituted Discoidal High-Density Lipoproteins: Bioinspired Nanodiscs with Many Unexpected Applications

PURPOSE OF REVIEW

Summarize the initial discovery of discoidal high-density lipoprotein (HDL) in human plasma and review more recent innovations that span the use of reconstituted nanodisc HDL for membrane protein characterization to its use as a drug carrier and a novel therapeutic agent for cardiovascular disease.

RECENT FINDINGS

Using a wide variety of biophysical techniques, the structure and composition of endogenous discoidal HDL have now largely been solved. This has led to the development of new methods for the in vitro reconstitution of nanodisc HDL, which have proven to have a wide variety of biomedical applications. Nanodisc HDL has been used as a platform for mimicking the plasma membrane for the reconstitution and investigation of the structures of several plasma membrane proteins, such as cytochrome P450s and ABC transporters. Nanodisc HDL has also been designed as drug carriers to transport amphipathic, as well as hydrophobic small molecules, and has potential therapeutic applications for several diseases. Finally, nanodisc HDL itself like native discoidal HDL can mediate cholesterol efflux from cells and are currently being tested in late-stage clinical trials for cardiovascular disease. The discovery of the characterization of native discoidal HDL has inspired a new field of synthetic nanodisc HDL, which has offered a growing number of unanticipated biomedical applications.

Plasma lipoproteome in Alzheimer's disease: a proof-of-concept study

Background

Although total plasma lipoproteome consists of proteins that have shown promises as biomarkers that can identify Alzheimer's disease (AD), effect sizes are modest. The objective of this study is to provide initial proof-of-concept that the plasma lipoproteome more likely differ between AD cases and controls when measured in individual plasma lipoprotein fractions than when measured as total in immunodepleted plasma.

Methods

We first developed a targeted proteomics method based on selected reaction monitoring (SRM) and liquid chromatography and tandem mass spectrometry for measurement of 120 tryptic peptides from 79 proteins that are commonly present in plasma lipoproteins. Then in a proof-of concept case-control study of 5 AD cases and 5 sex- and age-matched controls, we applied the targeted proteomic method and performed relatively quantification of 120 tryptic peptides in plasma lipoprotein fractions (fractionated by sequential gradient ultracentrifugation) and in immunodepleted plasma (of albumin and IgG). Unadjusted p values from two-sample t-tests and overall fold change was used to evaluate a peptide relative difference between AD cases and controls, with lower p values (< 0.05) or greater fold differences (> 1.05 or < 0.95) suggestive of greater peptide/protein differences.

Results

Within-day and between-days technical precisions (mean %CV [SD] of all SRM transitions) of the targeted proteomic method were 3.95% (2.65) and 9.31% (5.59), respectively. Between-days technical precisions (mean % CV [SD]) of the entire plasma lipoproteomic workflow including plasma lipoprotein fractionation was 27.90% (14.61). Ten tryptic peptides that belonged to 5 proteins in plasma lipoproteins had unadjusted p values < 0.05, compared to no peptides in immunodepleted plasma. Furthermore, 27, 32, 17, and 20 tryptic peptides in VLDL, IDL, LDL and HDL, demonstrated overall peptide fold differences > 1.05 or < 0.95, compared to only 6 tryptic peptides in immunodepleted plasma. The overall comparisons, therefore, suggested greater peptide/protein differences in plasma lipoproteome when measured in individual plasma lipoproteins than as total in immunodepleted plasma. Specifically, protein complement C3's peptide IHWESASLLR, had unadjusted p values of 0.00007, 0.00012, and 0.0006 and overall 1.25, 1.17, 1.14-fold changes in VLDL, IDL, and LDL, respectively. After positive False Discovery Rate (pFDR) adjustment, the complement C3 peptide IHWESASLLR in VLDL remained statistically different (adjusted p value < 0.05).

Discussion

The findings may warrant future studies to investigate plasma lipoproteome when measured in individual plasma lipoprotein fractions for AD diagnosis.

Feasibility of a plasma bioassay to assess oxidative protection of low-density lipoproteins by high-density lipoproteins

BACKGROUND

Traditionally, the impact of lipoproteins on vascular disease has been evaluated in light of their quantity, that is, cholesterol content, in plasma. However, recent studies of high-density lipoproteins (HDLs) have focused on functionality with regard to atheroprotection. For example, bioassays have emerged to assess the ability of HDL, in its near native plasma environment, to promote cholesterol removal (efflux) from cells. As a result, attention has focused on developing plasma-based assays for other putative HDL protective functions including protecting low-density lipoproteins (LDLs) from oxidative damage.

OBJECTIVE

To determine the feasibility of such an assay in a complex sample such as plasma, we evaluated the contribution of HDL vs other plasma factors in preventing LDL oxidation.

METHODS

We separated normolipidemic human plasma by gel filtration chromatography and assessed each fraction for its ability to prevent LDL modification by water soluble radical and copper-initiated oxidation mechanisms.

RESULTS

Using proteomics and selective precipitation methods, we identified major antioxidative contributions for fibrinogen, immunoglobulin G, albumin, and small soluble molecules like uric acid and ascorbate, with albumin being especially dominant in copper-initiated mechanisms. HDL particles were minor contributors (∼1%-2%) to the antioxidant capacity of plasma, irrespective of oxidation mechanism.

CONCLUSIONS

Given the overwhelming background of antioxidant capacity inherent to highly abundant plasma proteins, specific bioassays of HDL antioxidative function will likely require its complete separation from plasma.

Eicosapentaenoic Acid-Enriched High-Density Lipoproteins Exhibit Anti-Atherogenic Properties

BACKGROUND

It has previously been reported that oral administration of purified eicosapentaenoic acid (EPA) generates EPA-rich high-density lipoprotein (HDL) particles with a variety of anti-inflammatory properties. In this study, the mechanism underlying the anti-atherogenic effects of EPA-rich HDL using reconstituted HDL (rHDL) was investigated.Methods and Results:rHDL was generated by the sodium cholate dialysis method, using apolipoprotein A-1 protein, cholesterol, and various concentrations of EPA-phosphatidylcholine (PC) or egg-PC. Increased EPA-PC contents in rHDL resulted in decreased particle size. Next, the effects of rHDL containing various amounts (0-100% of total PC) of EPA-PC on vascular cell adhesion molecule-1 (VCAM-1) expression in human umbilical vein endothelial cells (HUVECs) was examined. Cytokine-stimulated VCAM-1 expression was inhibited in a dose-dependent manner based on the amount of EPA-PC in rHDL. Surprisingly, the incubation of HUVECs with EPA-rich rHDL resulted in the production of resolvin E3 (RvE3), an anti-inflammatory metabolite derived from EPA. Incubation with EPA-PC alone did not adequately induce RvE3 production, suggesting that RvE3 production requires an endothelial cell-HDL interaction. The increased anti-inflammatory effects of EPA-rich HDL may be explained by EPA itself and RvE3 production. Furthermore, the increase in EPA-PC content enhanced cholesterol efflux.

CONCLUSIONS

The EPA-enriched HDL particles exhibit cardioprotective properties via the production of anti-inflammatory lipid metabolites and the increase in cholesterol efflux.

Regression of coronary atherosclerosis with infusions of the high-density lipoprotein mimetic CER-001 in patients with more extensive plaque burden

BACKGROUND

CER-001 is an engineered pre-beta high-density lipoprotein (HDL) mimetic, which rapidly mobilizes cholesterol. Infusion of CER-001 3 mg/kg exhibited a potentially favorable effect on plaque burden in the CHI-SQUARE (Can HDL Infusions Significantly Quicken Atherosclerosis Regression) study. Since baseline atheroma burden has been shown as a determinant for the efficacy of HDL infusions, the degree of baseline atheroma burden might influence the effect of CER-001.

METHODS

CHI-SQUARE compared the effect of 6 weekly infusions of CER-001 (3, 6 and 12 mg/kg) vs. placebo on coronary atherosclerosis in 369 patients with acute coronary syndrome (ACS) using serial intravascular ultrasound (IVUS). Baseline percent atheroma volume (B-PAV) cutoff associated with atheroma regression following CER-001 infusions was determined by receiver-operating characteristics curve analysis. 369 subjects were stratified according to the cutoff. The effect of CER-001 at different doses was compared to placebo in each group.

RESULTS

A B-PAV ≥30% was the optimal cutoff associated with PAV regression following CER-001 infusions. CER-001 induced PAV regression in patients with B-PAV ≥30% but not in those with B-PAV <30% (-0.45%±2.65% vs. +0.34%±1.69%, P=0.01). Compared to placebo, the greatest PAV regression was observed with CER-001 3mg/kg in patients with B-PAV ≥30% (-0.96%±0.34% vs. -0.25%±0.31%, P=0.01), whereas there were no differences between placebo (+0.09%±0.36%) versus CER-001 in patients with B-PAV <30% (3 mg/kg; +0.41%±0.32%, P=0.39; 6 mg/kg; +0.27%±0.36%, P=0.76; 12 mg/kg; +0.32%±0.37%, P=0.97).

CONCLUSIONS

Infusions of CER-001 3 mg/kg induced the greatest atheroma regression in ACS patients with higher B-PAV. These findings identify ACS patients with more extensive disease as most likely to benefit from HDL mimetic therapy.

Association of High-Density Lipoprotein Subclasses with Carotid Intima-Media Thickness: Shimane CoHRE Study

AIMS

Recent studies suggested that subclasses of high-density lipoprotein (HDL) may be a better biomarker to predict the risk of atherosclerotic disorders. We aimed to examine the association of HDL2- and HDL3-cholesterol (HDL2-C and HDL3-C) with carotid intima-media thickness (IMT) using a new method to quantify the HDL-C subclasses.

METHODS

Participants were 657 Japanese subjects (434 women) who received a health examination (mean age: 73 years). Serum samples were analyzed by the homogenous assay for HDL-C and HDL3-C. HDL2-C was calculated indirectly by subtracting HDL3-C from HDL-C. HDL3-C measured by this assay was well correlated with that measured by ultracentrifugation (r=0.898, p＜0.001). The maximum IMT (max-IMT) and plaque score (PS) were evaluated by ultrasonography following the standard protocol.

RESULTS

HDL3-C was associated with age both in men (r=－0.322, p＜0.0001) and women (r=－0.315, p＜0.0001). In a simple regression analysis, max-IMT showed an inverse association with HDL3-C, whereas no significant association was observed with HDL2-C. A multiple linear regression analysis indicated, however, that the association between HDL3-C and max-IMT was not significant in both aged and younger populations when age was included in the analysis. Further, not only HDL2-C but also HDL3-C was not a significant predictor of 'atherosclerotic arteries' defined as the max-IMT ≥1.5 mm. Similar results were observed in the analysis on PS.

CONCLUSIONS

Neither HDL3-C nor HDL2-C was significantly associated with carotid atherosclerosis in the Japanese population in this study.

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

BACKGROUND AND AIMS

The 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.

METHODS

Here, 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.

RESULTS

For 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.

CONCLUSIONS

These 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.

A selective peroxisome proliferator-activated receptor δ agonist PYPEP suppresses atherosclerosis in association with improvement of the serum lipoprotein profiles in human apolipoprotein B100 and cholesteryl ester transfer protein double transgenic mice

OBJECTIVE

Although peroxisome proliferator-activated receptor (PPAR) δ agonists have been shown to improve the serum lipoprotein profiles in humans, the impact of the changes in these lipoprotein profiles on atherosclerosis remains to be elucidated. The aim of this study was to investigate the relationship between the selective PPARδ agonist-induced alterations of serum lipoprotein profiles and the development of atherosclerosis in human apolipoprotein B100 and cholesterol ester transfer protein double transgenic (hApoB100/hCETP-dTg) mice with human-like hypercholesterolemic dyslipidemia.

METHODS

hApoB100/hCETP-dTg mice fed an atherogenic diet received a novel PPARδ agonist (PYPEP) or vehicle for 18 weeks, followed by evaluation of atherosclerosis. Serum samples were collected during the treatment period at least at 3-week intervals to determine the lipoprotein levels and the levels of an inflammatory marker, macrophage chemotactic protein-1 (MCP-1), and to analyze the lipoprotein profile by fast protein liquid chromatography. The cholesterol efflux capacity of high-density lipoprotein (HDL) was examined using [(3)H]-cholesterol labeled macrophages.

RESULTS

Compared with vehicle treatment, PYPEP treatment caused increases in the serum levels of HDL cholesterol and apolipoprotein A-I (ApoA-I), as well as reductions in the serum non-HDL cholesterol and MCP-1 levels. The HDL fraction from the PYPEP-treated group maintained its cholesterol efflux capacity and showed an increased population of smaller HDL particles. PYPEP substantially suppressed atherosclerotic lesion progression, and the lesion areas had significant correlations with non-HDL cholesterol, HDL cholesterol, ApoA-I and MCP-1 by Pearson's correlation analysis. A multiple regression analysis revealed that non-HDL cholesterol and ApoA-I were significantly associated with the atherosclerotic lesion area.

CONCLUSION

A novel PPARδ agonist, PYPEP, suppressed atherosclerotic lesion progression by improving the serum lipoprotein profiles, including increased levels of ApoA-I and functional HDL particles, as well as a reduced non-HDL cholesterol level, in hApoB100/hCETP-dTg mice with human-like hypercholesterolemic dyslipidemia.

Apolipoprotein A-I: A Molecule of Diverse Function

Apolipoprotein A-I (apo A-I) an indispensable component and a major structural protein of high-density lipoprotein (HDL), plays a vital role in reverse cholesterol transport and cellular cholesterol homeostasis since its identification. Its multifunctional role in immunity, inflammation, apoptosis, viral, bacterial infection etc. has crossed its boundary of its potential of protecting cardiovascular system and lowering cardiovascular disease risk, attributing HDL to be known as a protective fat removal particle. Its structural homology with prostacyclin stabilization factor has contributed to its anti-clotting and anti-aggregatory effect on platelet which has potentiated its cardio-protective role as well as its therapeutic efficacy against Alzheimer's disease. The binding affinity and neutralising action against endotoxin lipopolysaccharide, reduces the toxic manifestations of septic shock. As a negative acute phase protein, it blocks T-cell signalling of macrophages. However the recently identified anti-tumor activity of apo A-I has been highlighted in various models of melanoma, lung cancer, ovarian cancer, lymphoblastic leukaemia, gastric as well as pancreatic cancers. These cancer fighting effects are directed towards regression of tumor size and distant metastasis by its immuno modulatory activity as well as its clearing effect on serum lysophospholipids. This lowering effect on lysophospholipid concentration is utilized by apo A-I mimetic peptides to be used in retarding tumor cell proliferation and as a potential cancer therapeutic agent. Not only that, it inhibits the tumor associated neo-angiogenesis as well as brings down the matrix degrading enzymes associated with tumor metastasis. However this efficient therapeutic potential of apo A-I as an anti tumor agent awaits further future experimental studies in humans.

Imaging and force measurement of LDL and HDL by AFM in air and liquid

The size and biomechanical properties of lipoproteins are tightly correlated with their structures/functions. While atomic force microscopy (AFM) has been used to image lipoproteins the force measurement of these nano-sized particles is missing. We detected that the sizes of LDL and HDL in liquid are close to the commonly known values. The Young's modulus of LDL or HDL is ∼0.4 GPa which is similar to that of some viral capsids or nanovesicles but greatly larger than that of various liposomes. The adhesive force of LDL or HDL is small (∼200 pN). The comparison of AFM detection in air and liquid was also performed which is currently lacking. Our data may provide useful information for better understanding and AFM detection of lipoproteins.

Decreased consumption of sugar-sweetened beverages improved selected biomarkers of chronic disease risk among US adults: 1999 to 2010

Consumption of sugar-sweetened beverages (SSBs) increased greatly from the late 1970s to the early part of this decade. Although recent data show that consumption of SSB may now be declining, consumption levels still remain much higher than recommended. Using data from the National Health and Nutrition Examination Survey, we assessed trends in intakes of SSB and levels of chronic disease biomarkers from 1999 to 2010 and examined the associations of SSB intake and biomarkers of chronic disease risk. We hypothesized that SSB intake will decrease and biomarkers of chronic disease risk will improve, therefore indicating that high intake of SSB is associated with greater chronic disease risk. Univariate analysis showed that from 1999 to 2010, SSB consumption decreased (P for trend = .0026), high-density lipoprotein increased (P for trend < .0001), low-density lipoprotein decreased (P for trend = .0007), and C-reactive protein decreased (P for trend = .0096). Using multivariate analysis, we showed that higher intakes of SSB were associated with lower high-density lipoprotein (P for trend < .0001), in an unadjusted model and all models with increasing numbers of covariates, and higher C-reactive protein (P for trend < .05), in an unadjusted model and in models with age, race/ethnicity, sex, education level, and poverty income ratio adjustments. We conclude that SSB consumption is associated with biomarkers of chronic disease risk, independent of demographic and lifestyle factors.

Severe coronary disease in an adult considered at low cardiovascular disease risk with a healthy lifestyle

Lipoprotein(a) [Lp(a)] is a lipoprotein subclass well-known among the lipid community to accelerate atherosclerosis and promote thrombosis through incompletely understood mechanism. We report a case of a young man with a healthy lifestyle and no major coronary or vascular risk factors who presented to the emergency department with an acute coronary syndrome and was ultimately found to have severe coronary artery disease. A diagnostic workup revealed elevated Lp(a). He was treated with consequent reduction in Lp(a) concentration. This case highlights the need to better understand atypical lipoproteins, how they relate to cardiovascular disease, the implications for screening family members, and the need to standardize patient management guidelines for the purpose of mortality risk reduction.