Antioxidative Activity of HDL Particle Subspecies Is Impaired in Hyperalphalipoproteinemia: Relevance of Enzymatic and Physicochemical Properties

Excessive Consumption of Alcoholic Beverages and Extremely High Levels of High-Density Lipoprotein Cholesterol (HALP) in the ELSA-Brasil Cohort Baseline

BACKGROUND

It has already been established that the consumption of alcoholic beverages increases high-density lipoprotein cholesterol (HDL-C) levels in dose-response.

METHODS AND RESULTS

A cross-sectional analysis was carried out with 6132 participants of both sexes aged between 35 and 74 years, who were active and retired workers from six Brazilian states. Heavy drinkers were categorized by sex: men > 210 g/week and women > 140 g/week; moderate drinkers: men ≤ 209 g/week and women ≤ 139 g/week. The HDL-C level was dichotomized into normal (40 mg/dL-82.9 mg/dL) and extremely high (≥83 mg/dL). We used binary logistic regression to assess associations between baseline alcohol intake and HDL-C, which were adjusted for sex, age, income, physical activity, kilocalories and body mass index (BMI), and we found an positive association between extremely high HDL-C and the excessive consumption of alcoholic beverages. These participants were mostly women with a high income, lower waist circumference, kilocalorie consumption and also a higher consumption in all categories of alcoholic beverages.

CONCLUSION

Excessive alcohol consumption was associated with a higher probability of extremely high HDL-C.

HDL and Oxidation

In this chapter, we will focus on HDLs' activity of inhibiting LDL oxidation and neutralizing some other oxidants. ApoA-I was known as the main antioxidant component in HDLs. The regulation of antioxidant capacity of HDL is mainly exhibited in regulation of apoA-I and alterations at the level of the HDL lipidome and the modifications of the proteome, especially MPO and PON1. HDL oxidation will influence the processes of inflammation and cholesterol transport, which are important processes in atherosclerosis, metabolic diseases, and many other diseases. In a word, HDL oxidation might be an effective antioxidant target in treatment of many diseases.

Regional Fat Distributions Are Associated With Subclinical Right Ventricular Dysfunction in Adults With Uncomplicated Obesity

Objective

Obesity is a prominent public health problem that has increased cardiovascular mortality risks. However, the specific effects of obesity, independent of comorbidities, on cardiac structure and function have not been well clarified, especially those effects on the right ventricle (RV). Cardiovascular magnetic resonance (CMR) tissue tracking can assess detailed RV mechanical features. This study aimed to evaluate RV strain using CMR in uncomplicated obese adults and assess its association with fat distributions.

Methods

A total of 49 obese patients and 30 healthy controls were included. The RV global systolic function and strain parameters based on CMR were assessed. Body fat distributions were measured with dual X-ray absorptiometry. RV function indices of obese patients were compared with those of healthy controls. Correlations among related body fat distribution parameters and RV function indices were conducted with multivariable linear regression.

Results

Compared with healthy controls, the obese group had impaired RV strain with lower global longitudinal peak strain (PS), longitudinal peak systolic strain rate (PSSR), circumferential and longitudinal peak diastolic strain rates (PDSR) (all P < 0.05), while LV and RV ejection fractions were not significantly different between the two groups (P > 0.05). Multivariable linear regression analysis demonstrated that android fat% was independently associated with longitudinal PS (β = −0.468, model R² = 0.219), longitudinal PDSR (β = −0.487, model R² = 0.237), and circumferential PSSR (β = −0.293, model R² = 0.086). Trunk fat% was independently associated with longitudinal PSSR (β = −0.457, model R² = 0.209). In addition, the strongest correlations of circumferential PDSR were BMI and gynoid fat% (β = −0.278, β = 0.369, model R² = 0.324).

Conclusions

Extensive subclinical RV dysfunction is found in uncomplicated obese adults. BMI, as an index of overall obesity, is independently associated with subclinical RV dysfunction. In addition, central obesity (android fat and trunk fat distributions) has a negative effect on subclinical RV function, while peripheral obesity (gynoid fat distribution) may have a positive effect on it.

Clinical Trials Registration

Effect of lifestyle intervention on metabolism of obese patients based on smart phone software (ChiCTR1900026476).

HDL subgroups and their paraoxonase-1 activity in the obese, overweight and normal weight subjects

BACKGROUND

Obesity and overweight are significant public health problems because of higher risk for coronary artery disease (CAD). It is very important to determine new predictive markers to identify the CAD risk in obese and overweight. To aim this, we analysed HDL-C subgroups (HDL2-C and HDL3-C) and their paraoxonase-1 (PON-1) activity in obese, overweight and normal weight subjects.

METHOD

71 obese, 40 overweight and 30 healthy subjects as a control group were enrolled the study. Serum lipids levels were determined with enzymatic colorimetric method. Further, PON-1 activities and HDL-C levels were determined by spectrophotometric methods. Non-HDL3-C concentrations were calculated with the subtraction of HDL3-C from total HDL-C.

RESULTS

The mean serum levels of total HDL-C, HDL3-C, Non-HDL3-C and ApoA1 were higher in control group than obese and overweight groups. There were a statistically significant difference between obese and control group in terms of Lp(a), hsCRP and HOMA index. Higher total PON-1, non-HDL3 PON-1 and HDL3 PON-1 activities were found in the control group compared with obese and overweight groups. Total HDL was weakly negative correlated with the HOMA index, BMI and waist circumference. There was a weak negative correlation between non-HDL3-C and waist circumference.

CONCLUSION

Altered HDL-subgroups pattern and decreased PON-1 activities may cause increased risk for CVD in obese and overweight individuals. Therefore determination of HDL subgroups and their PON-1 activity may improve risk prediction compared with measuring total HDL-C levels and its PON-1 activity alone. Body weight and insulin resistance appear to have a role in the decreased HDL-C levels and PON-1activity in obese. Further studies should be conducted to shed more light on impacts of these markers in CVD.

High-density lipoproteins (HDL): Novel function and therapeutic applications

The failure of high-density lipoprotein (HDL)-raising agents to reduce cardiovascular disease (CVD) together with recent findings of increased cardiovascular mortality in subjects with extremely high HDL-cholesterol levels provide new opportunities to revisit our view of HDL. The concept of HDL function developed to explain these contradictory findings has recently been expanded by a role played by HDL in the lipolysis of triglyceride-rich lipoproteins (TGRLs) by lipoprotein lipase. According to the reverse remnant-cholesterol transport (RRT) hypothesis, HDL critically contributes to TGRL lipolysis via acquirement of surface lipids, including free cholesterol, released from TGRL. Ensuing cholesterol transport to the liver with excretion into the bile may reduce cholesterol influx in the arterial wall by accelerating removal from circulation of atherogenic, cholesterol-rich TGRL remnants. Such novel function of HDL opens wide therapeutic applications to reduce CVD in statin-treated patients, which primarily involve activation of cholesterol flux upon lipolysis.

Excess weight mediates changes in HDL pool that reduce cholesterol efflux capacity and increase antioxidant activity

BACKGROUND AND AIM

Obesity-related decline in high-density lipoprotein (HDL) functions such as cholesterol efflux capacity (CEC) has supported the notion that this lipoprotein dysfunction may contribute for atherogenesis among obese patients. We investigated if potentially other HDL protective actions may be affected with weight gain and these changes may occur even before the obesity range in a cross-sectional analysis.

METHODS AND RESULTS

Lipid profile, body mass index (BMI), biochemical measurements, and carotid intima-media thickness (cIMT) were obtained in this cross-sectional study with 899 asymptomatic individuals. Lipoproteins were separated by ultracentrifugation and HDL physical-chemical characterization, CEC, antioxidant activity, anti-inflammatory activity, HDL-mediated platelet aggregation inhibition were measured in a randomly-selected subgroup (n = 101). Individuals with increased HDL-C had an attenuated increase in cIMT with elevation of BMI (interaction effect β = -0.054; CI 95% -0.0815, -0.0301). CEC, HDL-C, HDL size and HDL-antioxidant activity were negatively associated with cIMT. BMI was inversely correlated with HDL-mediated inhibition of platelet aggregation (Spearman's rho -0.157, p < 0.03) and CEC (Spearman's rho -0.32, p < 0.001), but surprisingly it was directly correlated with the antioxidant activity (Spearman's rho 0.194, p = 0.052). Thus, even in non-obese, non-diabetic individuals, increased BMI is associated with a wide change in protective functions of HDL, reducing CEC and increasing antioxidant activity. In these subjects, decreased HDL concentration, size or function are related to increased atherosclerotic burden.

CONCLUSION

Our findings demonstrate that in non-obese, non-diabetic individuals, the increasing values of BMI are associated with impaired protective functions of HDL and concomitant increase in atherosclerotic burden.

Free cholesterol transfer to high-density lipoprotein (HDL) upon triglyceride lipolysis underlies the U-shape relationship between HDL-cholesterol and cardiovascular disease

BACKGROUND

Low concentrations of high-density lipoprotein cholesterol (HDL-C) represent a well-established cardiovascular risk factor. Paradoxically, extremely high HDL-C levels are equally associated with elevated cardiovascular risk, resulting in the U-shape relationship of HDL-C with cardiovascular disease. Mechanisms underlying this association are presently unknown. We hypothesised that the capacity of high-density lipoprotein (HDL) to acquire free cholesterol upon triglyceride-rich lipoprotein (TGRL) lipolysis by lipoprotein lipase underlies the non-linear relationship between HDL-C and cardiovascular risk.

METHODS

To assess our hypothesis, we developed a novel assay to evaluate the capacity of HDL to acquire free cholesterol (as fluorescent TopFluor® cholesterol) from TGRL upon in vitro lipolysis by lipoprotein lipase.

RESULTS

When the assay was applied to several populations markedly differing in plasma HDL-C levels, transfer of free cholesterol was significantly decreased in low HDL-C patients with acute myocardial infarction (-45%) and type 2 diabetes (-25%), and in subjects with extremely high HDL-C of >2.59 mmol/L (>100 mg/dL) (-20%) versus healthy normolipidaemic controls. When these data were combined and plotted against HDL-C concentrations, an inverse U-shape relationship was observed. Consistent with these findings, animal studies revealed that the capacity of HDL to acquire cholesterol upon lipolysis was reduced in low HDL-C apolipoprotein A-I knock-out mice and was negatively correlated with aortic accumulation of [³H]-cholesterol after oral gavage, attesting this functional characteristic as a negative metric of postprandial atherosclerosis.

CONCLUSIONS

Free cholesterol transfer to HDL upon TGRL lipolysis may underlie the U-shape relationship between HDL-C and cardiovascular disease, linking HDL-C to triglyceride metabolism and atherosclerosis.

Retinal Vein Occlusion is Associated with Low Blood High-Density Lipoprotein Cholesterol: A Nationwide Cohort Study

PURPOSE

To investigate association between the development of retinal vein occlusion (RVO) and blood high-density lipoprotein cholesterol (HDL-C).

DESIGN

A retrospective, nationwide, population-based cohort study.

METHODS

This study was set in the Republic of Korea and included 23,149,403 people ≥20 years of age who underwent the Korean National Health Screening Program examination between January 2009 and December 2012. Among them, the RVO group was composed of patients with an initial diagnosis of RVO made between 2009 and 2015 (n = 117,639). The earliest claim with an RVO diagnostic code was considered as the incident time. The predictive value of HDL-C level for RVO was analyzed using hazard ratios. The primary outcome measure was the incident cases of RVO.

RESULTS

Subjects with RVO were generally older; had high body mass index, waist circumference, fasting blood glucose, blood pressure, total and low-density lipoprotein cholesterol, and triglyceride values, and low glomerular filtration rate and HDL-C values; and were more likely to experience diabetes mellitus and hypertension compared with the non-RVO group. The fully adjusted hazard ratio of RVO was 1.12 (95% confidence interval 1.10-1.14) in the lowest quartile of HDL-C versus in the highest quartile. The association between the development of RVO and HDL-C was higher those with a younger age, male sex, current smoking habit, diabetes mellitus, and hypercholesterolemia. In addition, we observed a significant synergistic effect of low HDL-C level with obesity and hypertension.

CONCLUSION

This is the first nationwide population-based epidemiologic study evaluating the association between HDL-C level and the risk of RVO development. A significant association between low HDL-C and RVO development was found.

Glycosylation of human plasma lipoproteins reveals a high level of diversity, which directly impacts their functional properties

AIMS

Human plasma lipoproteins are known to contain various glycan structures whose composition and functional importance are starting to be recognized. We assessed N-glycosylation of human plasma HDL and LDL and the role of their glycomes in cellular cholesterol metabolism.

METHODS

N-glycomic profiles of native and neuraminidase-treated HDL and LDL were obtained using HILIC-UHPLC-FLD. Relative abundance of the individual chromatographic peaks was quantitatively expressed as a percentage of total integrated area and N-glycan structures present in each peak were elucidated by MALDI-TOF MS. The capacity of HDL to mediate cellular efflux of cholesterol and the capacity of LDL to induce cellular accumulation of cholesteryl esters were evaluated in THP-1 cells.

RESULTS

HILIC-UHPLC-FLD analysis of HDL and LDL N-glycans released by PNGase F resulted in 22 and 18 distinct chromatographic peaks, respectively. The majority of N-glycans present in HDL (~70%) and LDL (~60%) were sialylated with one or two sialic acid residues. The most abundant N-glycan structure in both HDL and LDL was a complex type biantennary N-glycan with one sialic acid (A2G2S1). Relative abundances of several N-glycan structures were dramatically altered by the neuraminidase treatment, which selectively removed sialic acid residues. Native HDL displayed significantly greater efficacy in removing cellular cholesterol from THP-1 cells as compared to desialylated HDL (p < 0.05). Cellular accumulation of cholesteryl esters in THP-1 cells was significantly higher after incubations with desialylated LDL particles as compared to native LDL (p < 0.05).

CONCLUSIONS

N-glycome of human plasma lipoproteins reveals a high level of diversity, which directly impacts functional properties of the lipoproteins.

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.

Antioxidative activity of high-density lipoprotein (HDL): Mechanistic insights into potential clinical benefit

Uptake of low-density lipoprotein (LDL) particles by macrophages represents a key step in the development of atherosclerotic plaques, leading to the foam cell formation. Chemical modification of LDL is however necessary to induce this process. Proatherogenic LDL modifications include aggregation, enzymatic digestion and oxidation. LDL oxidation by one-electron (free radicals) and two-electron oxidants dramatically increases LDL affinity to macrophage scavenger receptors, leading to rapid LDL uptake and fatty streak formation. Circulating high-density lipoprotein (HDL) particles, primarily small, dense, protein-rich HDL3, provide potent protection of LDL from oxidative damage by free radicals, resulting in the inhibition of the generation of pro-inflammatory oxidized lipids. HDL-mediated inactivation of lipid hydroperoxides involves their initial transfer from LDL to HDL and subsequent reduction to inactive hydroxides by redox-active Met residues of apolipoprotein A-I. Several HDL-associated enzymes are present at elevated concentrations in HDL3 relative to large, light HDL2 and can be involved in the inactivation of short-chain oxidized phospholipids. Therefore, HDL represents a multimolecular complex capable of acquiring and inactivating proatherogenic lipids. Antioxidative function of HDL can be impaired in several metabolic and inflammatory diseases. Structural and compositional anomalies in the HDL proteome and lipidome underlie such functional deficiency. Concomitant normalization of the metabolism, circulating levels, composition and biological activities of HDL particles, primarily those of small, dense HDL3, can constitute future therapeutic target.

Paraoxonase-1 activity is positively related to phospholipid transfer protein activity in type 2 diabetes mellitus: Role of large HDL particles

OBJECTIVES

High density lipoprotein (HDL)-associated paraoxonase-1 (PON-1) exerts anti-oxidative properties, whereas phospholipid transfer protein (PLTP) is able to convert mature HDL into larger and smaller HDL particles. Here we tested associations of PON-1 with PLTP in type 2 diabetes mellitus (T2DM), a condition characterized by lower PON-1 activity and higher PLTP activity.

DESIGN AND METHODS

Serum PON-1 (arylesterase activity), plasma PLTP activity (liposome-vesicle HDL system), and (apo)lipoproteins were measured in 81 T2DM subjects (mean age 59±9years; 31 women; no insulin treatment). In 48 participants, HDL subfractions were measured by nuclear magnetic resonance spectroscopy.

RESULTS

In univariate correlation analysis, PON-1 activity was positively related to PLTP activity (r=0.348, p=0.001). PLTP activity was positively related to blood pressure, body mass index and triglycerides, whereas PON-1 activity was positively to HDL cholesterol and apoA-I (p<0.05 to <0.01 for each). Both PLTP activity and PON-I activity were positively related to large HDL particles (r=0.379, p=0.008 and r=0.411, p=0.004, respectively). In multivariable linear regression analysis, PON-1 activity was associated with PLTP activity independent of clinical covariates and HDL cholesterol or apoA-I (β=0.340, p=0.001 and β=0.320, p=0.003, respectively). The association of PON-1 activity with PLTP activity was lost in analysis which included large HDL particles (large HDL: β=0.411, p=0.004).

CONCLUSIONS

PON-1 activity is positively related to PLTP activity in T2DM, raising the possibility that PLTP could act to maintain PON-1. This association may in part be attributable to a common relationship of PON-1 and PLTP with large HDL particles.

Dysfunctional HDL and atherosclerotic cardiovascular disease

High-density lipoproteins (HDLs) protect against atherosclerosis by removing excess cholesterol from macrophages through the ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette transporter G1 (ABCG1) pathways involved in reverse cholesterol transport. Factors that impair the availability of functional apolipoproteins or the activities of ABCA1 and ABCG1 could, therefore, strongly influence atherogenesis. HDL also inhibits lipid oxidation, restores endothelial function, exerts anti-inflammatory and antiapoptotic actions, and exerts anti-inflammatory actions in animal models. Such properties could contribute considerably to the capacity of HDL to inhibit atherosclerosis. Systemic and vascular inflammation has been proposed to convert HDL to a dysfunctional form that has impaired antiatherogenic effects. A loss of anti-inflammatory and antioxidative proteins, perhaps in combination with a gain of proinflammatory proteins, might be another important component in rendering HDL dysfunctional. The proinflammatory enzyme myeloperoxidase induces both oxidative modification and nitrosylation of specific residues on plasma and arterial apolipoprotein A-I to render HDL dysfunctional, which results in impaired ABCA1 macrophage transport, the activation of inflammatory pathways, and an increased risk of coronary artery disease. Understanding the features of dysfunctional HDL or apolipoprotein A-I in clinical practice might lead to new diagnostic and therapeutic approaches to atherosclerosis.

Oxidized high-density lipoprotein impairs endothelial progenitor cells' function by activation of CD36-MAPK-TSP-1 pathways

AIMS

High-density lipoprotein (HDL) levels inversely correlate with cardiovascular events due to the protective effects on vascular wall and stem cells, which are susceptible to oxidative modifications and then lead to potential pro-atherosclerotic effects. We proposed that oxidized HDL (ox-HDL) might lead to endothelial progenitor cells (EPCs) dysfunction and investigated underlying mechanisms.

RESULTS

ox-HDL was shown to increase apoptosis and intracellular reactive oxygen species levels, but to reduce migration, angiogenesis, and cholesterol efflux of EPCs in a dose-dependent manner. p38 mitogen-activated protein kinase (MAPK) and NF-κB were activated after ox-HDL stimulation, which also upregulated thrombospondin-1 (TSP-1) expression without affecting vascular endothelial growth factor. Effects caused by ox-HDL could be significantly attenuated by pretreatment with short hairpin RNA-mediated CD36 knockdown or probucol. Data of in vivo experiments and the inverse correlation of ox-HDL and circulating EPC numbers among patients with coronary artery diseases (CAD) or CAD and type 2 diabetes also supported it. Meanwhile, HDL separated from such patients could significantly increase cultured EPC's caspase 3 activity, further supporting our proposal.

INNOVATION

This is the most complete study to date of how ox-HDL would impair EPCs function, which was involved with activation of CD36-p38 MAPK-TSP-1 pathways and proved by not only the inverse relationship between ox-HDL and circulating EPCs in clinic but also pro-apoptotic effects of HDL separated from patients' serum.

CONCLUSION

Activation of CD36-p38 MAPK-TSP-1 pathways contributes to the pathological effects of ox-HDL on EPCs' dysfunction, which might be one of the potential etiological factors responsible for the disturbed neovascularization in chronic ischemic disease.

Will Lipidation of ApoA1 through Interaction with ABCA1 at the Intestinal Level Affect the Protective Functions of HDL?

The relationship between levels of high-density lipoprotein cholesterol (HDL-C) and cardiovascular (CV) risk is well recognized; however, in recent years, large-scale phase III studies with HDL-C-raising or -mimicking agents have failed to demonstrate a clinical benefit on CV outcomes associated with raising HDL-C, casting doubt on the "HDL hypothesis." This article reviews potential reasons for the observed negative findings with these pharmaceutical compounds, focusing on the paucity of translational models and relevant biomarkers related to HDL metabolism that may have confounded understanding of in vivo mechanisms. A unique function of HDL is its ability to interact with the ATP-binding cassette transporter (ABC) A1 via apolipoprotein (Apo) A1. Only recently, studies have shown that this process may be involved in the intestinal uptake of dietary sterols and antioxidants (vitamin E, lutein and zeaxanthin) at the basolateral surface of enterocytes. This parameter should be assessed for HDL-raising drugs in addition to the more documented reverse cholesterol transport (RCT) from peripheral tissues to the liver. Indeed, a single mechanism involving the same interaction between ApoA1 and ABCA1 may encompass two HDL functions previously considered as separate: antioxidant through the intestinal uptake of antioxidants and RCT through cholesterol efflux from loaded cells such as macrophages.

Effect of open-label infusion of an apoA-I-containing particle (CER-001) on RCT and artery wall thickness in patients with FHA

Reverse cholesterol transport (RCT) contributes to the anti-atherogenic effects of HDL. Patients with the orphan disease, familial hypoalphalipoproteinemia (FHA), are characterized by decreased tissue cholesterol removal and an increased atherogenic burden. We performed an open-label uncontrolled proof-of-concept study to evaluate the effect of infusions with a human apoA-I-containing HDL-mimetic particle (CER-001) on RCT and the arterial vessel wall in FHA. Subjects received 20 infusions of CER-001 (8 mg/kg) during 6 months. Efficacy was assessed by measuring (apo)lipoproteins, plasma-mediated cellular cholesterol efflux, fecal sterol excretion (FSE), and carotid artery wall dimension by MRI and artery wall inflammation by (18)F-fluorodeoxyglucose-positron emission tomography/computed tomography scans. We included seven FHA patients: HDL-cholesterol (HDL-c), 13.8 [1.8-29.1] mg/dl; apoA-I, 28.7 [7.9-59.1] mg/dl. Following nine infusions in 1 month, apoA-I and HDL-c increased directly after infusion by 27.0 and 16.1 mg/dl (P = 0.018). CER-001 induced a 44% relative increase (P = 0.018) in in vitro cellular cholesterol efflux with a trend toward increased FSE (P = 0.068). After nine infusions of CER-001, carotid mean vessel wall area decreased compared with baseline from 25.0 to 22.8 mm(2) (P = 0.043) and target-to-background ratio from 2.04 to 1.81 (P = 0.046). In FHA-subjects, CER-001 stimulates cholesterol mobilization and reduces artery wall dimension and inflammation, supporting further evaluation of CER-001 in FHA patients.

Serum paraoxonase-1 activity is more closely related to HDL particle concentration and large HDL particles than to HDL cholesterol in Type 2 diabetic and non-diabetic subjects

OBJECTIVES

We determined relationships of the anti-oxidative enzyme, paraoxonase-1 (PON-1), with high density lipoprotein (HDL) subfractions, and tested whether these relationships are stronger than those with HDL cholesterol and apolipoprotein A-I (apoA-I) in subjects with and without type 2 diabetes mellitus (T2DM).

DESIGN AND METHODS

Serum PON-1 (arylesterase activity) and HDL subfractions (nuclear magnetic resonance spectroscopy) were determined in 67 T2DM patients and in 56 non-diabetic subjects.

RESULTS

PON-1 activity, HDL cholesterol and apoA-I were decreased in T2DM (all p<0.05). The HDL particle concentration was unaltered, but large HDL particles, medium HDL particles and HDL particle size were decreased, whereas small HDL particles were increased in T2DM (all p<0.05). PON-1 was more closely related to HDL cholesterol than to apoA-I (p=0.001). In turn, the positive relationship of PON-1 with the HDL particle concentration and with large HDL particles was stronger than that with HDL cholesterol (both p<0.01). The inverse relationship of PON-1 with T2DM was only modestly attenuated by HDL cholesterol or HDL particle characteristics.

CONCLUSIONS

PON-1 activity is more closely related to the HDL particle concentration or large HDL particles than to HDL cholesterol. Impaired PON-1 activity in T2DM is not to a considerable extent explained by altered HDL subfraction levels.

Low normal free T4 confers decreased high-density lipoprotein antioxidative functionality in the context of hyperglycaemia

OBJECTIVES

Low normal thyroid function may promote the development of atherosclerotic cardiovascular disease by thus far poorly defined mechanisms. We tested the impact of thyroid function on HDL antioxidative capacity, a metric of its antiatherogenic functionality, in euthyroid subjects with varying degrees of glucose tolerance.

DESIGN AND SUBJECTS

Seventy subjects with Type 2 diabetes mellitus (T2DM), 37 subjects with impaired fasting glucose (IFG) and 31 subjects with normal fasting glucose (NFG) (revised NCEP-ATPIII criteria) participated in a cross-sectional study.

MEASUREMENTS

HDL antioxidative capacity (standardized for HDL cholesterol) was measured as the percentage inhibition of low-density lipoprotein oxidation in vitro.

RESULTS

TSH, free T4 and HDL antioxidative capacity were not different among NFG, IFG and T2DM subjects (P > 0·25 for each). HDL antioxidative capacity was correlated positively with free T4 (r = 0·320, P = 0·007), and negatively with plasma glucose (r = -0·394, P < 0·001) in T2DM only. Taking account of age and sex, the relationship of HDL antioxidative functionality with free T4 was modified by glucose tolerance status (P = 0·040 and P = 0·008 for interactions of IFG and T2DM with free T4 respectively). Prevailing plasma glucose also interacted positively with free T4 on HDL antioxidative capacity (P = 0·054).

CONCLUSIONS

In the context of chronic hyperglycaemia, low free T4 within the euthyroid range confers diminished HDL antioxidative capacity, a pathophysiologically relevant metric of HDL functionality.

High-density lipoprotein subfractions display proatherogenic properties in overweight and obese children

BACKGROUND

In adults, obesity-driven inflammation can lead to increased cardiovascular disease (CVD). However, information regarding childhood obesity and its inflammatory sequelae is less well defined. Serum amyloid-A (SAA) is an inflammatory molecule that rapidly associates with high-density lipoproteins (HDLs) and renders them dysfunctional. Therefore, SAA may be a useful biomarker to identify increased CVD potential in overweight and obese children.

METHODS

Young Hearts 2000 is a cross-sectional cohort study in which 92 children who were obese were matched for age and sex with 92 overweight and 92 lean children. HDL(2) and HDL(3) (HDL(2&3)) were isolated from plasma by a three-step rapid-ultracentrifugation procedure. SAA was measured in serum and HDL(2&3) by an enzyme-linked immunosorbent assay procedure, and the activities of cholesterol ester transfer protein (CETP) and lecithin cholesteryl acyltransferase (LCAT) were measured by fluorimetric assays.

RESULTS

Trends across the groups indicated that SAA increased in serum and HDL(2&3) as BMI increased, as did HDL(2)-CETP and HDL(2)-LCAT activities.

CONCLUSION

These results have provided evidence that overweight and obese children are exposed to an inflammatory milieu that impacts the antiatherogenic properties of HDL and that could increase CVD risk. This supports the concept that it is important to target childhood obesity to help minimize future cardiovascular events.

High-density lipoprotein (HDL) particle subpopulations in heterozygous cholesteryl ester transfer protein (CETP) deficiency: maintenance of antioxidative activity

Cholesteryl ester transfer protein (CETP) deficiency causes elevated high-density lipoprotein-cholesterol (HDL-C) levels; its impact on HDL functionality however remains elusive. We compared functional and compositional properties of HDL derived from 9 Caucasian heterozygous CETP mutation carriers (splice-site mutation in intron 7 resulting in premature truncation) with those of 9 age- and sex-matched normolipidemic family controls. As expected, HDL-C levels were increased 1.5-fold, and CETP mass and activity were decreased by −31% and −38% respectively, in carriers versus non-carriers. HDL particles from carriers were enriched in CE (up to +19%, p<0.05) and depleted of triglycerides (TG; up to −54%, p<0.01), resulting in a reduced TG/CE ratio (up to 2.5-fold, p<0.01). In parallel, the apoA-I content was increased in HDL from carriers (up to +22%, p<0.05). Both the total HDL fraction and small, dense HDL3 particles from CETP-deficient subjects displayed normal antioxidative activity by attenuating low-density lipoprotein oxidation with similar efficacy on a particle mass basis as compared to control HDL3. Consistent with these data, circulating levels of systemic biomarkers of oxidative stress (8-isoprostanes) were similar between the two groups. These findings support the contention that HDL functionality is maintained in heterozygous CETP deficiency despite modifications in lipid and protein composition.

HDL inflammation and atherosclerosis: current and future perspectives

The role of high-density lipoprotein (HDL) in the genesis and evolution of cardiovascular disease is a topical and interesting issue. Reduced HDL concentrations appear to be unable to efficiently eliminate the cholesterol excess at the vascular wall level, contributing to the onset of the inflammatory response that typically occurs in the pathogenesis of atherosclerosis from its earliest stages. In the last decade, many studies have explored the possibility of reducing cardiovascular risk through modulation of HDL levels, glimpsing new fascinating therapeutic horizons. This review summarizes recent findings on HDL and cardiovascular disease, mainly with an educational objective, considering the biochemical, cellular and molecular aspects of these particles.

High-density lipoprotein therapeutics and cardiovascular prevention

The field of cardiovascular prevention has long anticipated the evolution of high-density lipoprotein (HDL) therapy from unproven metabolic tweaking to pillar of risk reduction on par with low-density lipoprotein control. However, the convincing epidemiologic data linking HDL cholesterol (HDL-C) and cardiovascular disease risk in an inverse correlation has not yet translated into clinical trial evidence supporting linearity between HDL-C increases and risk reduction, or identifying obvious goals of therapy. Although HDL-C-increasing lifestyle maneuvers and established HDL drugs such as niacin and fibrates are likely to protect the vasculature, the negative results obtained in trials of a cholesteryl ester transfer protein inhibitor remind us that HDL-C increases are not always beneficial. It is becoming clear that a functional HDL is a more desirable target than simply increasing HDL-C levels. The larger objective of improving HDL functionality (with or without HDL-C level changes) is bound to become the guiding principle for pharmaceutical research in this area. Several new compounds currently being tested bridge the classical aim of increasing HDL-C levels with the novel target of improving HDL function.

HDL 2 particles are associated with hyperglycaemia, lower PON1 activity and oxidative stress in type 2 diabetes mellitus patients

OBJECTIVES

In this study we examined the relationship of oxidative stress and hyperglycaemia to antioxidative capacity of high-density cholesterol (HDL-C) particles in type 2 diabetes mellitus (DM).

DESIGN AND METHODS

Oxidative stress status parameters (superoxide anion (O2(-)), superoxide dismutase (SOD) activity and paraoxonase (PON1) status were assessed in 114 patients with type 2 DM and 91 healthy subjects. HDL particle diameters were determined by non-denaturing polyacrylamide gradient (3-31%) gel electrophoresis.

RESULTS

Patients had significantly higher concentrations of oxidative stress parameter O2(-)(p<0.001) and antioxidative defence, SOD activity (p<0.001). Paraoxonase activity was significantly lower in diabetics (p<0.001). The PON1(192) phenotype distribution among study groups was not significantly different. HDL 3 phenotype was significantly prevalent among patients (p<0.001). Paraoxonase activity was significantly lower in patients with predominantly HDL 2 particles than in controls.

CONCLUSIONS

The results of our current study indicate that the diabetic HDL 2 phenotype is associated with hyperglycaemia, lower PON1 activity and elevated oxidative stress.

Antiatherogenic function of HDL particle subpopulations: focus on antioxidative activities

Oxidative stress, an emerging risk factor for premature atherosclerosis and cardiovascular disease, mediates the formation of proinflammatory, pro-atherogenic oxidized low-density lipoprotein (oxLDL) in the arterial intima. Circulating HDL particles, and particularly small, dense, protein-rich HDL3, may provide potent protection of LDL in vivo from oxidative damage by free radicals in the arterial intima, resulting in the inhibition of the generation of proinflammatory oxidized lipids, primarily lipid hydroperoxides (LOOH) but also short-chain oxidized phospholipids (oxPL). HDL-mediated inactivation of LOOH involves initial transfer of phospholipid hydroperoxides (PLOOH) from LDL to HDL3, which is governed by the rigidity of the surface monolayer of HDL, and subsequent reduction of PLOOH by redox-active Met residues of apolipoprotein A-I (apoA-I) with the formation of phospholipid hydroxides (PLOH) and methionine sulphoxides. HDL-associated enzymes may in turn contribute to the hydrolytic inactivation of short-chain oxPL. Mounting evidence suggests that the integrated antioxidative activity of HDL appear to be defective in atherogenic dyslipidaemias involving low HDL-cholesterol levels; anomalies in the proteome and lipidome of HDL particles in dyslipidaemic patients may underlie such functional deficiency. Pharmacological normalization of HDL metabolism concomitantly with correction of circulating levels, composition and biological activities of HDL particles, with enrichment in apoA-I and reduction in HDL surface rigidity, may constitute an efficacious therapeutic approach to attenuate atherosclerosis in dyslipidaemic patients at high cardiovascular risk.

Oxidized high-density lipoprotein is associated with protein-energy wasting in maintenance hemodialysis patients

BACKGROUND AND OBJECTIVES

Oxidized HDL (oxHDL) may behave as proinflammatory HDL because of reduced anti-inflammatory capacity and is considered a risk factor for mortality in patients on maintenance hemodialysis (MHD). The study presented here assessed the effect of oxHDL on protein-energy wasting (PEW) in MHD patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This prospective study examined a cohort of MHD patients (n = 176) who were not taking lipid-lowering drugs. Blood samples were obtained to measure albumin, lipids, high-sensitivity C-reactive protein (hsCRP), oxidized LDL (oxLDL), and oxHDL. PEW was assessed by subjective global assessment (SGA) and geriatric nutritional risk index (GNRI). Measurements and assessment of nutritional status were followed up 1 year later.

RESULTS

OxHDL was significantly increased in patients with PEW at baseline. High oxHDL and high hsCRP were significantly associated with PEW, and receiver operating characteristic curves for oxHDL and hsCRP showed statistically similar accuracy for predicting SGA-positive status. According to multivariate regression models, high oxHDL had a significant influence on PEW in patients, particularly those with high hsCRP. Decreased changes in GNRI and high prevalence of SGA-positive status at 1 year were more common in patients with high oxHDL at baseline and 1 year later than in patients with low oxHDL at both time points.

CONCLUSIONS

A high oxHDL state may be associated with PEW estimated by GNRI and SGA, particularly concomitant with inflammation in MHD patients.

Catabolism of lipoproteins and metabolic syndrome

PURPOSE OF REVIEW

Metabolic syndrome is very common and is associated with significantly increased risk for both cardiovascular disease and type 2 diabetes. At present, no unifying mechanism can explain it. However, insulin resistance is a key feature of this syndrome, plays a key role in triglyceride metabolism and contributes to dyslipidemia and development of type 2 diabetes. Here, we review the mechanisms involved in the overproduction of large VLDL and their catabolism and finally potential therapeutic targets to provide a more complete approach to treatment of these lipid abnormalities.

RECENT FINDINGS

Dyslipidemia plays an important role in the development of atherosclerosis and is mainly associated by the hepatic overproduction of large triglyceride-rich VLDL, low levels of HDL cholesterol and high levels of small, dense, LDL cholesterol particles. It is thus of special interest to understand the mechanism involved in the hepatic synthesis of lipoproteins and the degradation of these lipoproteins that depend, to a large extent, on insulin action.

SUMMARY

The atherogenic lipid abnormalities observed in the metabolic syndrome may require a combination of drugs such as statins and HDL-raising agents to provide a more complete approach to treating dyslipidemia and reducing cardiovascular risk.

Why is HDL functionally deficient in type 2 diabetes?

High-density lipoprotein (HDL) particles exert a spectrum of atheroprotective activities that can be deficient in type 2 diabetes. Key mechanisms leading to the formation of functionally deficient HDL involve 1) HDL enrichment in triglycerides and depletion in cholesteryl esters with conformational alterations of apolipoprotein A-I; 2) glycation of apolipoproteins and/or HDL-associated enzymes; and 3) oxidative modification of HDL lipids, apolipoproteins, and/or enzymes. Available data identify hypertriglyceridemia, with concomitant compositional modification of the HDL lipid core and conformational change of apolipoprotein A-I, as a driving force in functional alteration of HDL particles in type 2 diabetes. Therapeutic options for correcting HDL functional deficiency should target hypertriglyceridemia by normalizing circulating levels of triglyceride-rich lipoproteins.

Fenofibrate therapy ameliorates fasting and postprandial lipoproteinemia, oxidative stress, and the inflammatory response in subjects with hypertriglyceridemia and the metabolic syndrome

OBJECTIVE

The aim of this study was to determine the effects of fenofibrate (160 mg/day) on fasting and postprandial lipoproteins, oxidized fatty acids, and inflammatory mediators in subjects with hypertriglyceridemia and the metabolic syndrome.

RESEARCH DESIGN AND METHODS

Fifty-nine subjects with fasting hypertriglyceridemia (> or = 1.7 and < 6.9 mmol/l) and two or more of the Adult Treatment Panel III criteria for the metabolic syndrome were randomly assigned to fenofibrate (160 mg/day) or placebo in a double-blind, controlled clinical trial.

RESULTS

Fenofibrate treatment lowered fasting triglycerides (-46.1%, P < 0.0001) and postprandial (area under the curve) triglycerides (-45.4%, P < 0.0001) due to significant reductions in postprandial levels of large (-40.8%, P < 0.0001) and medium (-49.5%, P < 0.0001) VLDL particles. The number of fasting total LDL particles was reduced in fenofibrate-treated subjects (-19.0%, P = 0.0033) primarily due to reductions in small LDL particles (-40.3%, P < 0.0001); these treatment differences persisted postprandially. Fasting and postprandial oxidized fatty acids were reduced in fenofibrate-treated subjects compared with placebo-administered subjects (-15.3%, P = 0.0013, and 31.0%, P < 0.0001, respectively), and fenofibrate therapy lowered fasting and postprandial soluble vascular cell adhesion molecule-1 (VCAM-1) (-10.9%, P = 0.0005, and -12.0%, P = 0.0001, respectively) as well as fasting and postprandial soluble intercellular adhesion molecule-1 (ICAM-1) (-14.8%, P < 0.0001, and -15.3%, P < 0.0001, respectively). Reductions in VCAM-1 and ICAM-1 were correlated with reductions in fasting and postprandial large VLDL particles (P < 0.0001) as well as postprandial oxidized fatty acids (P < 0.0005).

CONCLUSIONS

Triglyceride-lowering therapy with fenofibrate reduced fasting and postprandial free fatty acid oxidation and inflammatory responses, and these antiatherosclerotic effects were most highly correlated with reductions in large VLDL particles.

The paradox of dysfunctional high-density lipoprotein

PURPOSE OF REVIEW

This review addresses how, in atherosclerosis or systemic inflammation, HDL can lose its usual atheroprotective characteristics and even paradoxically assume proinflammatory properties.

RECENT FINDINGS

Specific chemical and structural changes within HDL particles can impede reverse cholesterol transport, enhance oxidation of LDL, and increase vascular inflammation. HDL may be viewed as a shuttle that can be either anti-inflammatory or proinflammatory, depending on its cargo of proteins, enzymes, and lipids. Some therapeutic approaches that reduce coronary risk, such as statins and therapeutic lifestyle changes, can favorably moderate the characteristics of proinflammatory HDL. In addition, apolipoprotein A-I mimetic peptides and other compounds that target functional aspects of HDL may offer novel approaches to reduction in cardiovascular risk.

SUMMARY

Current data suggest that under some conditions HDL can become dysfunctional and even proinflammatory, but this characterization can change with resolution of systemic inflammation or use of certain treatments.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

Triglyceride-rich HDL3 from patients with familial hypercholesterolemia are less able to inhibit cytokine release or to promote cholesterol efflux

Familial hypercholesterolemia (FH) is associated with heterogeneity of the onset and severity of coronary heart disease (CHD). In this study, we investigated different low-grade proinflammatory markers and the atheroprotective function of the HDL3 subfraction in FH-patients (n = 13) with identical LDL-receptor mutations and in age- and sex-matched healthy controls (n = 11). Compared with healthy controls, FH-patients had greater gene expressions of the proatherogenic mediators TNF-alpha and IL-8 in circulating peripheral blood mononuclear cells. In addition, they had a higher serum concentration of intercellular adhesion molecule-1 (ICAM-1) and a lower net antioxidant capacity. FH-derived HDL3 with a high level of triglycerides had a reduced capacity to inhibit the release of IL-8 from TNF-alpha-stimulated human umbilical vein endothelial cells (HUVEC) [1.864 mg/L (1.461-2.208 mg/L) vs. 1.466 mg/L (1.225-1.643 mg/L); P < 0.05; median (range)], and a reduced capacity to promote cholesterol efflux from lipid-loaded macrophages [12% (12-14%) vs. 15% (14-18%); P < 0.05; median (range)] compared with HDL3 with a lower triglyceride content. Notably, the degree of inhibition of IL-8 release from HUVEC by HDL3 was correlated with the ability of HDL3 to promote cholesterol efflux (r = -0.80, P = 0.03). In conclusion, compared with healthy controls, FH-patients are characterized by higher levels of low-grade proinflammatory markers, and FH-derived HDL3 with high triglyceride content may be more proatherogenic. These triglyceride rich-HDL3 might be partly responsible for the phenotypic variation among FH-patients with identical LDL-receptor mutations.

Elevated HDL Cholesterol is Functionally Ineffective in Cardiac Transplant Recipients: Evidence for Impaired Reverse Cholesterol Transport

BACKGROUND

Cardiac transplant recipients frequently have high plasma HDL levels but it is unclear whether these promote a cardioprotective profile.

METHODS

Parameters of reverse cholesterol transport and endothelial function were compared in 25 cardiac transplant recipients with low (<1.4 mmol/L; n=11) or high (>1.4 mmol/L; n=14) plasma levels of HDL and in a reference healthy group.

RESULTS

Patients with high HDL had lower levels of triglyceride and prebeta1-HDL and a higher proportion of large HDL particles. When normalized to apoA-I content, non-ABCA1-dependent cholesterol efflux from RAW 264.7 macrophage cells to plasma from high HDL patients was 33% lower when compared to plasma from patients with low HDL, whereas ABCA1-dependent cholesterol efflux was not impaired. Forearm vascular responses to acetylcholine and sodium nitroprusside were not influenced by HDL levels in these patients. Compared to a reference healthy group (n=26), cardiac transplant recipients had higher levels of triglyceride, lower levels of prebeta1-HDL and LCAT, and lower activities of cholesteryl ester transfer protein and phospholipid transfer protein.

CONCLUSIONS

Hyperalphalipoproteinaemia in cardiac transplant recipients is associated with the formation of partially dysfunctional HDL. We conclude that high levels of HDL may not confer cardioprotection in this group of patients.

Cholesteryl ester transfer protein (CETP) inhibition beyond raising high-density lipoprotein cholesterol levels: pathways by which modulation of CETP activity may alter atherogenesis

Raising high-density lipoprotein cholesterol (HDL-C) is a promising strategy in the struggle to prevent cardiovascular disease, and cholesteryl ester transfer protein (CETP) inhibitors have been developed to accomplish this. The first results are encouraging, and, in fact, in rabbits, inhibition of CETP reduces atherosclerosis. Because human data regarding the reduction of atheroma burden require more time, the biochemical mechanisms underlying the putative atheroprotection of CETP inhibitors are currently dissected, and several pathways have emerged. First, CETP inhibition increases HDL-C and reduces low-density lipoprotein cholesterol (LDL-C) levels consistent with CETP lipid transfer activity and its role in reverse cholesterol transport (RCT). This coincides with putative beneficial increases in both HDL and LDL size. However, many aspects regarding the impact of CETP inhibition on the RCT pathway remain elusive, in particular whether the first step concerning cholesterol efflux from peripheral tissues to HDL is influenced. Moreover, the relevance of scavenger receptor BI and consequently the central role of HDL in human RCT is still unclear. Second, CETP inhibition was shown recently to increase antioxidant enzymes associated with HDL, in turn associated with decreased oxidation of LDL. Atheroprotection in man is currently anticipated based on the improvement of these biochemical parameters known to influence atherosclerosis, but final confirmation regarding the impact of CETP inhibition on cardiovascular outcome will have to come from trials evaluating clinical end points.

Low HDL-C: a secondary target of dyslipidemia therapy

Current guidelines for the prevention of coronary heart disease (CHD) focus on lowering low-density lipoprotein cholesterol (LDL-C) as the primary target of lipid-modifying therapy. However, there is increasing interest in high-density lipoprotein cholesterol (HDL-C) as a secondary target of therapy. A wealth of epidemiologic data demonstrate that low levels of HDL-C are associated with an increased risk of CHD events, and data from large-scale clinical trials with statins and fibrates indicate that observed clinical benefits are related, at least in part, to improvements in HDL-C levels. Raising HDL-C levels with therapeutic lifestyle changes and pharmacologic intervention might afford opportunities to further reduce the risk of CHD beyond LDL-C lowering. Statins are first-line pharmacotherapy for dyslipidemia and can also improve HDL-C levels, although the extent to which they modify HDL-C varies. Combining a fibrate or niacin with statin therapy raises HDL-C more than a statin alone but might be associated with reduced tolerability and increased adverse reactions. Several new therapeutic approaches to raising HDL-C are in development, including an HDL mimetic and inhibitors of cholesteryl ester transfer protein. Although lowering LDL-C remains the primary target of lipid-modifying therapy, dyslipidemia therapies that are efficacious for both LDL-C reduction and raising HDL-C might offer further improvements in CHD risk reduction.

Low high-density lipoprotein cholesterol disorders and cardiovascular risk: contribution of associated low-density lipoprotein subclass abnormalities

PURPOSE OF REVIEW

Discuss the contribution of low-density lipoprotein subclass abnormalities to cardiovascular risk among individuals with low high-density lipoprotein cholesterol levels.

RECENT FINDINGS

Low high-density lipoprotein cholesterol levels are commonly encountered among patients with early onset cardiovascular disease. Most often, a low high-density lipoprotein cholesterol level is not an isolated abnormality, but it is usually associated with a number of other lipoprotein abnormalities. Data from the Framingham Offspring Study demonstrate that among subjects with high-density lipoprotein cholesterol, 1.0 mmol/L (39 mg/dL), low-density lipoprotein particle numbers were considerably higher than indicated by the level of low-density lipoprotein cholesterol because these subjects had excess numbers of small cholesterol-depleted low-density lipoprotein particles. Elevated numbers of low-density lipoprotein particles identify individuals at highest risk for atherosclerotic vascular disease and cardiovascular events.

SUMMARY

As high levels of low-density lipoprotein particles are a robust predictor of cardiovascular events, strategies targeted at raising low levels of high-density lipoprotein cholesterol must account for low-density lipoprotein particle interactions.

Defective antioxidative activity of small dense HDL3 particles in type 2 diabetes: relationship to elevated oxidative stress and hyperglycaemia

AIMS/HYPOTHESIS

Elevated oxidative stress, hyperglycaemia, and dyslipidaemia involving low levels of HDL particles are key proatherogenic factors in type 2 diabetes mellitus. We examined the relationship of oxidative stress, and the degree of glycaemia and triglyceridaemia, to antioxidative function of HDL particle subspecies in type 2 diabetes.

SUBJECTS AND METHODS

Five HDL subfractions (2b, 2a, 3a, 3b, 3c) were isolated by density gradient ultracentrifugation from well-controlled type 2 diabetic subjects (n=20) and normolipidaemic, non-diabetic controls (n=10). Specific antioxidative activity (capacity to protect LDL from oxidation on a unit particle mass or on a particle number basis), chemical composition and enzymatic activities were measured in each subfraction. Systemic oxidative stress was assessed as plasma levels of 8-isoprostanes.

RESULTS

Specific antioxidative activity of small dense HDL3b and 3c particles in diabetic patients was significantly diminished (up to -47%, on a particle mass or particle number basis) as compared with controls. Plasma 8-isoprostanes were markedly elevated (2.9-fold) in diabetic patients, were negatively correlated with both specific antioxidative activity of HDL3 subfractions and plasma HDL cholesterol (HDL-C) levels, and were positively correlated with glycaemia and triglyceridaemia. Paraoxonase 1 activity was consistently lower in diabetic HDL subfractions and was positively correlated with HDL3 antioxidative activity. The altered chemical composition of diabetic HDL3 subfractions (core cholesteryl ester depletion, triglyceride enrichment) was equally correlated with diminished antioxidative activity.

CONCLUSIONS/INTERPRETATION

Antioxidative activity of small dense HDL is deficient in type 2 diabetes, is intimately linked to oxidative stress, glycaemia and hypertriglyceridaemia and primarily reflects abnormal intrinsic physicochemical properties of HDL particles.

Human apolipoprotein A-I and A-I mimetic peptides: potential for atherosclerosis reversal

PURPOSE OF REVIEW

Recent publications related to the potential use of apolipoprotein (apo)A-I and apoA-I mimetic peptides in the treatment of atherosclerosis are reviewed.

RECENT FINDINGS

A preliminary report indicating that infusion of apoA-IMilano into humans once weekly for 5 weeks caused a significant decrease in coronary artery atheroma volume has sparked great interest in the potential therapeutic use of apoA-I. Recent studies have revealed that HDL quality (e.g. HDL apolipoprotein and lipid content, including oxidized lipids, particle size and electrophoretic mobility, associated enzymatic activities, inflammatory/anti-inflammatory properties, and ability to promote cholesterol efflux) may be more important than HDL-cholesterol levels. Therefore, when developing new strategies to raise HDL-cholesterol concentrations by interfering with HDL metabolism, one must consider the quality of the resulting HDL. In animal models, raising HDL-cholesterol levels by administering oral phospholipids improved both the quantity and quality of HDL and was associated with lesion regression. An apoA-I mimetic peptide, namely 4F synthesized from D-amino acids (D-4F), administered orally to mice did not raise HDL-cholesterol concentrations but promoted the formation of pre-beta HDL containing increased paraoxonase activity, resulting in significant improvements in HDL's anti-inflammatory properties and ability to promote cholesterol efflux from macrophages in vitro. Oral D-4F also promoted reverse cholesterol efflux from macrophages in vivo.

SUMMARY

The quality of HDL may be more important than HDL-cholesterol levels. ApoA-I and apoA-I mimetic peptides appear to have significant therapeutic potential in atherosclerosis.

Metabolic syndrome is associated with elevated oxidative stress and dysfunctional dense high-density lipoprotein particles displaying impaired antioxidative activity

A metabolic syndrome (MetS) phenotype is characterized by insulin-resistance, atherogenic dyslipidemia, oxidative stress, and elevated cardiovascular risk and frequently involves subnormal levels of high-density lipoprotein (HDL) cholesterol. We evaluated the capacity of physicochemically distinct HDL subfractions from MetS subjects to protect low-density lipoprotein against oxidative stress.MetS subjects presented an insulin-resistant phenotype, with central obesity and elevation in systolic blood pressure and plasma triglyceride, LDL-cholesterol, apolipoprotein B, glucose, and insulin levels. Systemic oxidative stress, assessed as plasma 8-isoprostanes, was significantly higher (3.7-fold) in MetS subjects (n = 10) compared with nonobese normolipidemic controls (n = 11). In MetS, small, dense HDL3a, 3b, and 3c subfractions possessed significantly lower specific antioxidative activity (up to -23%, on a unit particle mass basis) than their counterparts in controls. In addition, HDL2a and 3a subfractions from MetS patients possessed lower total antioxidative activity (up to -41%, at equivalent plasma concentrations). The attenuated antioxidative activity of small, dense HDL subfractions correlated with systemic oxidative stress and insulin resistance and was associated with HDL particles exhibiting altered physicochemical properties (core triglyceride enrichment and cholesteryl ester depletion). We conclude that antioxidative activity of small, dense HDL subfractions of altered chemical composition is impaired in MetS and associated with elevated oxidative stress and insulin resistance. Induction of selective increase in the circulating concentrations of dense HDL subfractions may represent an innovative therapeutic approach for the attenuation of high cardiovascular risk in MetS.