Laboratory investigation of dysfunctional HDL

High-density lipoprotein (HDL) particles are anti-atherosclerotic, by virtue of their functions in reverse cholesterol transportation, anti-inflammation and anti-oxidation. However, recent studies have cast doubt on the cardio-protective role of HDL. Structural modification and composition alteration of HDL due to chronic inflammation and acute phase responses may result in loss of normal biological function and even convert HDL into a pro-inflammatory and pro-oxidative agent. Therefore, the assessment of dysfunctional HDL has become a novel target to investigate the association between HDL and coronary artery disease risk. This review article summarizes the laboratory assessment of dysfunctional HDL.

Qualitative characteristics of HDL in young patients of an acute myocardial infarction

AIM

Recently, the concept that high density lipoprotein (HDL) quality is an important parameter for atheroprotection is gaining ground, though little data exists so far to support it. In an attempt to identify measurable qualitative parameters of HDL associated with increased risk for premature myocardial infarction (MI), we studied the structural characteristics of HDL from patients who survived an MI at a young age (≤35 years).

METHODS AND RESULTS

We studied 20 MI patients and 20 healthy control subjects. HDL of patients had reduced apolipoprotein A-I (apoA-I), apolipoprotein M, and paraoxonase 1 levels and significantly elevated apolipoprotein C-III (apoCIII) levels (all p<0.05). Specifically, the HDL apoA-I/apoC-III ratio was 0.24±0.01 in patients versus 4.88±0.90 in controls (p<0.001). These structural alterations correlated with increased oxidation potential of HDL of the MI group compared to controls (2.5-fold, p=0.026). Electron microscopy showed no significant difference in average HDL particle diameter between the two groups though a significant difference existed in HDL diameter distribution, suggesting the presence of different HDL subpopulations in MI and control subjects. Indeed, non-denaturing two-dimensional electrophoresis revealed that MI patients had reduced pre-β1(α), pre-β1(b) and α(2), and elevated α(1), α(3), and pre-α(4) HDL.

CONCLUSIONS

Reduction in the HDL apoA-I/apoC-III ratio, changes in the HDL subpopulation distribution and an increase in HDL oxidation potential correlated with the development of MI in young patients. The possibility that such changes may serve as markers for the early identification of young individuals at high risk for an acute coronary event should be further explored.

Association between moderately oxidized low-density lipoprotein and high-density lipoprotein particle subclass distribution in hemodialyzed and post-renal transplant patients

Disturbances in the metabolism of lipoprotein profiles and oxidative stress in hemodialyzed (HD) and post-renal transplant (Tx) patients are proatherogenic, but elevated concentrations of plasma high-density lipoprotein (HDL) reduce the risk of cardiovascular disease. We investigated the concentrations of lipid, lipoprotein, HDL particle, oxidized low-density lipoprotein (ox-LDL) and anti-ox-LDL, and paraoxonase-1 (PON-1) activity in HD (n=33) and Tx (n=71) patients who were non-smokers without active inflammatory disease, liver disease, diabetes, or malignancy. HD patients had moderate hypertriglyceridemia, normocholesterolemia, low HDL-C, apolipoprotein A-I (apoA-I) and HDL particle concentrations as well as PON-1 activity, and increased ox-LDL and anti-ox-LDL levels. Tx patients had hypertriglyceridemia, hypercholesterolemia, moderately decreased HDL-C and HDL particle concentrations and PON-1 activity, and moderately increased ox-LDL and anti-ox-LDL levels as compared to the reference, but ox-LDL and anti-ox-LDL levels and PON-1 activity were more disturbed in HD patients. However, in both patient groups, lipid and lipoprotein ratios (total cholesterol (TC)/HDL-C, LDL-C/HDL-C, triglyceride (TG)/HDL-C, HDL-C/non-HDL-C, apoA-I/apoB, HDL-C/apoA-I, TG/HDL) were atherogenic. The Spearman's rank coefficient test showed that the concentration of ox-LDL correlated positively with HDL particle level (R=0.363, P=0.004), and negatively with TC (R=-0.306, P=0.012), LDL-C (R=-0.283, P=0.020), and non-HDL-C (R=-0.263, P=0.030) levels in Tx patients. Multiple stepwise forward regression analysis in Tx patients demonstrated that ox-LDL concentration, as an independent variable, was associated significantly positively with HDL particle level. The results indicated that ox-LDL and decreased PON-1 activity in Tx patients may give rise to more mildly-oxidized HDLs, which are less stable, easily undergo metabolic remodeling, generate a greater number of smaller pre-β-HDL particles, and thus accelerate reverse cholesterol transport, which may be beneficial for Tx patients. Further studies are necessary to confirm this.

Nicotinic acid has anti-atherogenic and anti-inflammatory properties on advanced atherosclerotic lesions independent of its lipid-modifying capabilities

Inflammation contributes to atherosclerotic plaque initiation and progression. Recent studies suggest that nicotinic acid has anti-inflammatory effects independent of its lipid-modifying capabilities. We assessed the hypothesis that administration of nicotinic acid to older apolipoprotein E (apoE)-deficient mice with established lesions will reduce lesion size and plaque inflammation independent of its lipid-modifying effects. Therefore nicotinic acid was administered to 27-week-old apo E-deficient mice exhibiting advanced atherosclerotic lesions within the innominate artery. After 27 weeks of treatment both animal groups had no significant changes in plasma lipid levels. Mice treated with nicotinic acid (n = 22) demonstrated a 30% reduction in total lesion area compared with controls (n = 20). Furthermore, they revealed a more stable plaque composition with an increase in fibrous cap thickness and a reduction in the size of the necrotic core. Immunohistochemistry demonstrated a reduced accumulation of macrophages and a reduced expression of vascular cell adhesion molecule-1 and tissue factor. Additionally, administration of nicotinic acid significantly reduced tumor necrosis factor alpha expression in the thoracic aorta as demonstrated by real-time PCR. In conclusion, these data suggest that long-term administration of nicotinic acid has anti-atherogenic and anti-inflammatory properties on advanced atherosclerotic lesions, which are independent of its lipid-modifying actions.

Uremia alters HDL composition and function

Functional impairment of HDL may contribute to the excess cardiovascular mortality experienced by patients with renal disease, but the effect of advanced renal disease on the composition and function of HDL is not well understood. Here, we used mass spectrometry and biochemical analyses to study alterations in the proteome and lipid composition of HDL isolated from patients on maintenance hemodialysis. We identified a significant increase in the amount of acute phase protein serum amyloid A1, albumin, lipoprotein-associated phospholipase A2, and apoC-III composing uremic HDL. Furthermore, uremic HDL contained reduced phospholipid and increased triglyceride and lysophospholipid. With regard to function, these changes impaired the ability of uremic HDL to promote cholesterol efflux from macrophages. In summary, the altered composition of HDL in renal disease seems to inhibit its cardioprotective properties. Assessing HDL composition and function in renal disease may help identify patients at increased risk for cardiovascular disease.

Abnormal high-density lipoproteins in overweight adolescents with atherogenic dyslipidemia

OBJECTIVE

This study aimed to evaluate high-density lipoprotein functionality and the cardiovascular risk factor profile in the overweight pediatric population. We hypothesized that overweight adolescents with low high-density lipoprotein cholesterol and elevated triglyceride plasma levels have metabolic abnormalities and dysfunctional high-density lipoprotein particles, similar to those reported in adults.

PATIENTS AND METHODS

Overweight adolescents with (group 1 [n = 21]) and without (group 2 [n = 36]) atherogenic dyslipidemia (high-density lipoprotein cholesterol: ≤ 40 mg/dL and triglycerides: ≥ 150 mg/dL) and normal-weight normolipidemic subjects, as a reference (group 3 [n = 36]), were included. The cardiovascular risk factor profile (lipids, lipoproteins, high-sensitivity C-reactive protein, and insulin), high-density lipoprotein subclass distribution, composition, and cholesterol efflux capacity were studied.

RESULTS

Group 1 adolescents showed abnormalities in high-density lipoprotein subclass distribution and high-density lipoprotein chemical composition, as well as a significantly lower capacity to promote cholesterol efflux (14.8 ± 2.8, 16.5 ± 3.8, 20.4 ± 3.5, for groups 1, 2 and 3, respectively). High-density lipoprotein(2a) (R(2) = 0.212, β = 0.472, P < .0001) and the Tanner score (R(2) = 0.054, β = -0.253, P = .02) were the independent predictors of cholesterol efflux. Group 1 also showed a higher degree of cardiovascular abnormalities (an adverse lipoprotein profile, greater insulin resistance and systemic inflammation; and lower low-density lipoprotein size) than group 2, even after BMI and Tanner score adjustment.

CONCLUSIONS

This study suggests that atherogenic dyslipidemia identifies overweight adolescents with quantitative, qualitative, and functional high-density lipoprotein abnormalities. Atherogenic dyslipidemia seems to be a marker of an increased risk for developing cardiovascular disease and indicates that those adolescents should be a target of aggressive prevention programs and lipid management guidelines.

Consumption of high-oleic acid ground beef increases HDL-cholesterol concentration but both high- and low-oleic acid ground beef decrease HDL particle diameter in normocholesterolemic men

On the basis of previous results from this laboratory, this study tested the hypothesis that ground beef high in MUFA and low in SFA would increase the HDL-cholesterol (HDL-C) concentration and LDL particle diameter. In a crossover dietary intervention, 27 free-living normocholesterolemic men completed treatments in which five 114-g ground beef patties/wk were consumed for 5 wk with an intervening 4-wk washout period. Patties contained 24% total fat with a MUFA:SFA ratio of either 0.71 (low MUFA, from pasture-fed cattle) or 1.10 (high MUFA, from grain-fed cattle). High-MUFA ground beef provided 3.21 g more 18:1(n-9), 1.26 g less 18:0, 0.89 g less 16:0, and 0.36 g less 18:1(trans) fatty acids per patty than did the low-MUFA ground beef. Both ground beef interventions decreased plasma insulin and HDL(2) and HDL(3) particle diameters and increased plasma 18:0 and 20:4(n-6) (all P ≤ 0.05) relative to baseline values. Only the high-MUFA ground beef intervention increased the HDL-C concentration from baseline (P = 0.02). The plasma TG concentration was positively correlated with the plasma insulin concentration (r = 0.40; P < 0.001) and negatively correlated with HDL-C (r = -0.47; P < 0.001) and plasma 18:0 (r = -0.24; P < 0.01). Plasma insulin and HDL diameters were not correlated (r = 0.01; P > 0.50), indicating that reductions in these measures were not coordinately regulated. The data indicate that dietary beef interventions have effects on risk factors for cardiovascular disease that are independent (insulin, HDL diameters) and dependent (HDL-C) on beef fatty acid composition.

Mechanism of cholesterol efflux in humans after infusion of reconstituted high-density lipoprotein

OBJECTIVES

Infusion of reconstituted HDL (rHDL) leads to changes in HDL metabolism as well as to an increased capacity of plasma to support cholesterol efflux providing an opportunity to investigate mechanisms linking cholesterol efflux to changes in plasma HDL.

METHODS AND RESULTS

Patient plasmas after infusion of rHDL were tested ex vivo for their capacity to stimulate cholesterol efflux. Reconstituted HDL enhanced mobilization of cholesterol from tissues in vivo as shown by rising HDL cholesterol concentrations over the infusion period. Infusion of rHDL in vivo led to increased cholesterol efflux ex vivo; surprisingly, removing apoB-containing lipoproteins while preserving all HDL subfractions eliminated this increase. Infusion of rHDL led to the remodelling of plasma HDL; however, the capacity of plasma to support cholesterol efflux did not correlate with changes in the concentrations of any of HDL subfractions. Unmodified rHDL accounted for only a proportion of the increment in cholesterol efflux capacity. Furthermore, studies using HeLa and BHK cells overexpressing ABCA1, ABCG1, and SR-B1 showed that the contribution of these cellular mediators of cholesterol efflux to the enhanced capacity of plasma for the efflux was minimal.

CONCLUSION

Enhanced cholesterol efflux from tissues requires the presence of apoB-containing lipoproteins and may involve enhanced flow of cholesterol through multiple components of the reverse cholesterol transport pathway rather than being determined by a specific HDL subfraction.

Structure of apolipoprotein A-I N terminus on nascent high density lipoproteins

Apolipoprotein A-I (apoA-I) is the major protein component of high density lipoproteins (HDL) and a critical element of cholesterol metabolism. To better elucidate the role of the apoA-I structure-function in cholesterol metabolism, the conformation of the apoA-I N terminus (residues 6-98) on nascent HDL was examined by electron paramagnetic resonance (EPR) spectroscopic analysis. A series of 93 apoA-I variants bearing single nitroxide spin label at positions 6-98 was reconstituted onto 9.6-nm HDL particles (rHDL). These particles were subjected to EPR spectral analysis, measuring regional flexibility and side chain solvent accessibility. Secondary structure was elucidated from side-chain mobility and molecular accessibility, wherein two major α-helical domains were localized to residues 6-34 and 50-98. We identified an unstructured segment (residues 35-39) and a β-strand (residues 40-49) between the two helices. Residues 14, 19, 34, 37, 41, and 58 were examined by EPR on 7.8, 8.4, and 9.6 nm rHDL to assess the effect of particle size on the N-terminal structure. Residues 14, 19, and 58 showed no significant rHDL size-dependent spectral or accessibility differences, whereas residues 34, 37, and 41 displayed moderate spectral changes along with substantial rHDL size-dependent differences in molecular accessibility. We have elucidated the secondary structure of the N-terminal domain of apoA-I on 9.6 nm rHDL (residues 6-98) and identified residues in this region that are affected by particle size. We conclude that the inter-helical segment (residues 35-49) plays a role in the adaptation of apoA-I to the particle size of HDL.

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.

Helicobacter Pylori infection is a significant risk for modified lipid profile in Japanese male subjects

AIM

Helicobacter Pylori infection was associated with the risk of cardiovascular disease; however, the relation between Helicobacter Pylori infection and the lipid profile has not been fully established.

METHODS

We measured anti-Helicobacter Pylori antibody concentration and lipid profiles in 6,289 Japanese subjects aged 21-64 years (5,077 male and 1,212 female).

RESULTS

The prevalence of Helicobacter Pylori-seropositive subjects was 46.8% and 39.6% in men and women, respectively. Adjusted mean values of low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol in men were significantly higher and lower in Helicobacter Pylori-seropositive than-negative subjects, respectively, (LDL-cholesterol: 129.0±0.8 vs. 125.3±0.7 mg/dL, p< 0.001, HDL-cholesterol: 54.6±0.3 vs. 56.6±0.3 mg/dL, p< 0.01), whereas these associations were not significant in female subjects. Moreover, the odds ratio of Helicobacter Pylori infection for high LDL-cholesteremia and low HDL-cholesteremia in male subjects was 1.23 (95% CI (confidence interval): 1.08-1.40, p< 0.05) and 1.29 (95% CI: 1.03-1.59, p< 0.05), respectively. Female subjects did not have such associations.

CONCLUSIONS

The present study demonstrates that Helicobacter Pylori infection is significantly associated with high LDL-cholesteremia and low HDL-cholesteremia in Japanese male subjects.

Structure/function relationships of apolipoprotein a-I mimetic peptides: implications for antiatherogenic activities of high-density lipoprotein

RATIONALE

Apolipoprotein (apoA)-I mimetic peptides are a promising type of anti-atherosclerosis therapy, but how the structural features of these peptides relate to the multiple antiatherogenic functions of HDL is poorly understood.

OBJECTIVE

To establish structure/function relationships of apoA-I mimetic peptides with their antiatherogenic functions.

METHODS AND RESULTS

Twenty-two bihelical apoA-I mimetic peptides were investigated in vitro for the capacity and specificity of cholesterol efflux, inhibition of inflammatory response of monocytes and endothelial cells, and inhibition of low-density lipoprotein (LDL) oxidation. It was found that mean hydrophobicity, charge, size of hydrophobic face, and angle of the link between the helices are the major factors determining the efficiency and specificity of cholesterol efflux. The peptide with optimal parameters was more effective and specific toward cholesterol efflux than human apoA-I. Charge and size of hydrophobic face were also the major factors affecting antiinflammatory properties, and the presence of cysteine and histidine residues was the main factor determining antioxidant properties. There was no significant correlation between capacities of the peptides to support individual functions; each function had its own optimal set of features.

CONCLUSIONS

None of the peptides was equally effective in all the antiatherogenic functions tested, suggesting that different functions of HDL may have different mechanisms and different structural requirements. The results do suggest, however, that rationalizing the design of apoA-I mimetic peptides may improve their therapeutic value and may lead to a better understanding of mechanisms of various antiatherogenic functions of HDL.

Evaluation of established coronary heart disease on the basis of HDL and non-HDL NMR lipid profiling

A (1)H NMR-based lipid profiling approach was used to investigate the prediction of coronary heart disease (CHD) and examine the confounding effect of factors such as gender, triglycerides, HDL-cholesterol and age levels on the prediction of disease. The HDL and non-HDL lipid profiles in 47 patients with triple vessel disease (TVD) and 41 patients with normal coronary arteries (NCA) both documented angiographically were generated. The presence of CHD was predicted with a sensitivity and specificity of 52% and 75% for HDL model and 78% and 80% for non-HDL, respectively. The lipid constituents of HDL lipoproteins which contributed to the separation between the two groups were the saturated fatty acids, cholesterol, total omega-3 fatty acids, degree of unsaturation, diallylic protons from polyunsaturated fatty acids, linoleic acid and, to a lesser extent, the number of fatty acids, triglycerides, unsaturated fatty acids and phosphatidylcholine. Respectively, for non-HDL, lipoproteins were the saturated fatty acids, number of fatty acids, cholesterol, unsaturated fatty acids and phosphatidylcholine. Gender, triglycerides, HDL-cholesterol and age influenced the lipid constituents of HDL and non-HDL lipoproteins that contributed to the separation between subgroups and confounded the predictive power of the models. NMR-based lipid profiling analysis could contribute to the identification of noninvasive markers for the presence and the development of the disease.

The promise of apolipoprotein A-I mimetics

PURPOSE OF REVIEW

Synthetic high-density lipoprotein (HDL) and apolipoprotein (apo) A-I mimetic peptides emulate many of the atheroprotective biological functions attributed to HDL and can modify atherosclerotic disease processes. Administration of these agents as HDL replacement or modifying therapy has tremendous potential of providing new treatments for cardiovascular disease. Progress in the understanding of these agents is discussed in this review.

RECENT FINDINGS

Prospective, observational, and interventional studies have convincingly demonstrated that elevated serum levels of high-density lipoprotein-cholesterol (HDL-C) are associated with reduced risk for coronary heart disease (CHD). Although traditional pharmacological agents have shown modest utility in raising HDL levels and reducing CHD risk, use of HDL and apo A-I mimetics provides novel therapies to not only increase HDL levels, but to also influence HDL functionality. Evidence developed over the last several years has identified a number of pathways affected by synthetic HDL and apoA-I mimetic peptides, including enhancing reverse cholesterol transport and reducing oxidation and inflammation that directly influence the progression and regression of atherosclerotic disease.

SUMMARY

Clinical trials of relatively short-term synthetic HDL infusion into patients with CHD demonstrate beneficial effects. Use of apo A-I mimetic peptides could potentially overcome some of the limitations associated with use of the intact apo. Studies to establish the most efficacious peptides, optimal dosing regimens, and routes of administration are needed. Use of apo A-I mimetic peptides shows great promise as a therapeutic modality for HDL replacement and enhancing HDL function in treatment of patients with CHD.

Anti-oxidant properties of high-density lipoprotein and atherosclerosis

1. High-density lipoprotein (HDL) is one of the major carriers of cholesterol in the blood. It attracts particular attention because, in contrast with other lipoproteins, many physiological functions of HDL influence the cardiovascular system in favourable ways unless HDL is modified pathologically. 2. The best known function of HDL is the capacity to promote cellular cholesterol efflux from peripheral cells and deliver cholesterol to the liver for excretion, thereby playing a key role in reverse cholesterol transport. The functions of HDL that have recently attracted attention include anti-inflammatory and anti-oxidant activities. High anti-oxidant and anti-inflammatory activities of HDL are associated with protection from cardiovascular disease. 3. Atheroprotective activities, as well as a functional deficiency of HDL, ultimately depend on the protein and lipid composition of HDL. Conversely, these activities are compromised in many pathological states associated with inflammation. 4. The focus of the present review is on the anti-oxidant and anti-inflammatory functions of HDL and its individual components in relation to protection from atherosclerosis.

Benefits and difficulties in measuring HDL subfractions and human paraoxonase-1 activity during statin treatment

Dyslipidaemia including decreased high density lipoprotein cholesterol concentration is one of several factors that have been implicated in increased cardiovascular risk. Since their introduction in the 1980s, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have emerged as the one of the best-selling class of medications to date, with numerous trials demonstrating powerful efficacy in preventing cardiovascular diseases. Although statins have been shown to modestly raise or not alter HDL-cholesterol, their effect on HDL subfractions and on HDL-associated enzymes including human paraoxonase-1 (PON1) has not yet been fully explored. This review summarizes the currently available data on the effect of statins on HDL subfractions and on PON1 activity with a particular emphasis on the clinical relevance of these effects. Moreover, methodological problems of HDL subfraction and PON1 activity determinations are also discussed.

Current status and future directions in lipid management: emphasizing low-density lipoproteins, high-density lipoproteins, and triglycerides as targets for therapy

Current lipid management guidelines are focused on decreasing low-density lipoprotein (LDL-C) levels as the primary target for reducing coronary heart disease (CHD) risk. Yet, many recent studies suggest that low levels of high-density lipoprotein (HDL-C) are a major independent risk factor for cardiovascular diseases. According to several clinical trials, a 1% increase in HDL-C is associated with a 0.7%–3% decrease in CHD events. The direct link between high levels of triglycerides (TG) and CHD, on the other hand, is less well defined. A large reduction in TG is needed to show a difference in CHD events, especially in men. Evidence for a shift in lipid management toward targeting both LDL-C and HDL-C as primary targets for therapy is presented. Currently, the 3-hydroxy-3-methylgutaryl coenzyme A reductase inhibitors (HMG-CoA reductase inhibitors) have proven to significantly decrease LDL-C levels, reduce CHD morbidity/mortality and improve overall survival. However, improvement of survival with statins may be due to other pleiotropic effects beyond LDL-C lowering. Fibric acid derivatives and niacin are primarily used to increase HDL-C levels, although with side effects. Future therapies targeting HDL-C may have profound results on reducing CHD morbidity and mortality. This article highlights existing and future targets in lipid management and is based on available clinical data. There is an urgent need for new treatments using a combination of drugs targeting both LDL-C and HDL-C. Such treatments are expected to have a superior outcome for dyslipidemia therapy, along with TG management.

Signaling by the high-affinity HDL receptor scavenger receptor B type I

Scavenger receptor B type I (SR-BI) plays an important role in mediating cholesterol exchange between cells, high-density lipoprotein (HDL) cholesterol, and other lipoproteins. SR-BI in hepatocytes is essential for reverse cholesterol transport and biliary secretion of HDL cholesterol; thus, it is atheroprotective. More recently, it has been discovered that the HDL-SR-BI tandem serves other functions that also likely contribute to HDL-related cardiovascular protection. A number of the latter mechanisms, particularly in endothelial cells, involve unique direct signal initiation by SR-BI that leads to the activation of diverse kinase cascades. SR-BI signaling occurs in response to plasma membrane cholesterol flux. It requires the C-terminal PDZ-interacting domain of the receptor, which mediates direct interaction with the adaptor molecule PDZK1; and the C-terminal transmembrane domain, which directly binds membrane cholesterol. In endothelium, direct SR-BI signaling in response to HDL results in enhanced production of the antiatherogenic molecule nitric oxide; in a nitric oxide-independent manner, it serves to maintain endothelial monolayer integrity. The role of SR-BI signaling in the numerous other cellular targets of HDL, including hepatocytes, macrophages, and platelets, and the basis by which SR-BI senses plasma membrane cholesterol movement to modify cell behavior are unknown. Further understanding of signaling by SR-BI will optimize the capacity to harness the mechanisms of action of HDL-SR-BI for cardiovascular benefit.

HDL2 can inhibit further oxidative modification of partially oxidized LDL

AIM

To investigate whether HDL(2) can inhibit further oxidative modification of partially oxidized LDL (ox-LDL) by interrupting the chain oxidation reaction after lipid hydroperoxides (LOOH) formation.

METHODS

Following incubation of LDL 400 microg protein/mL phosphate-buffered saline with Cu(2+) for 1.75 h (defined as 0 min), incubation was continued after adding HDL(2) 200 microg protein/mL or HDL(2) 800 microg protein/mL to give both ox-LDL+HDL(2) 200 microg protein/mL or ox-LDL+HDL(2) 800 microg protein/mL. As a control, ox-LDL 200 microg protein/mL and native LDL were prepared. Each sample was subjected to agarose gel electrophoresis and the LOOH in each sample was measured.

RESULTS

When the electrophoretic mobility of native LDL was designated 1, the relative electrophoretic mobility (REM) of ox-LDL increased significantly over time. The REMs of ox-LDL+HDL(2) 800 microg protein/mL from 10 min to 9 h were significantly lower than the REM of ox-LDL at the respective times (p<0.01). LOOH of ox-LDL+HDL(2) 800 microg protein/mL at 1, 3, 6 and 9 h was significantly higher than LOOH in ox-LDL at the respective times (p<0.01). The results of ox-LDL+HDL(2) 200 microg protein/mL were almost the same but to a lesser extent than the results of ox-LDL+HDL(2) 800 microg protein/mL.

CONCLUSION

The present findings suggest that HDL(2) can inhibit further oxidative modification of partially oxidized LDL by interrupting the chain oxidation reaction after LOOH formation in a concentration-dependent manner.

Androgen deficiency and atherosclerosis: The lipid link

The relationship between androgen deficiency and atherosclerosis is complex, poorly understood, and remains controversial. The aim of this review is to evaluate the data in the literature to determine if androgen deficiency modulates lipid profiles and contributes to atherosclerosis development or progression. Studies in animals and humans suggest that androgen deficiency is associated with increased triglycerides (TGs), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C). Although the effects of androgen deficiency on high-density lipoprotein cholesterol (HDL-C) remains controversial, recent data suggest that androgen therapy is associated with increased levels of HDL-C and may improve reverse cholesterol transport. Animal studies suggested that androgen deprivation adversely affect lipid profiles and this was reversed by androgen treatment. Furthermore, androgen treatment of hypogonadal men significantly improved lipid profiles. Emerging data indicate that androgens play an important role in lipid metabolism. Therefore androgens are critical in the prevention and progression of atherosclerosis. Androgen deficiency contributes to increased TGs, TC, LDL-C and reduced HDL-C while androgen treatment results in a favorable lipid profile, suggesting that androgens may provide a protective effect against the development and/or progression of atherosclerosis.

Impaired protection against diabetes and coronary heart disease by high-density lipoproteins in Turks

The issue of whether or not incident type 2 diabetes mellitus and coronary heart disease (CHD) can be predicted by high-density lipoprotein (HDL) cholesterol in both sexes needs investigation. A representative sample of 3035 middle-aged Turkish adults free of CHD at baseline was studied with this purpose prospectively over a mean of 7.8 years. High-density lipoprotein cholesterol levels were found to be correlated in women positively with plasma fibrinogen and weakly with waist girth and C-reactive protein, and to be not correlated with fasting insulin. High-density lipoprotein cholesterol protected men against future CHD risk (for a 12-mg/dL increment: relative risk = 0.80 [95% confidence interval, 0.69-0.95]) after multivariable adjustment in logistic regression analyses for age, smoking status, physical activity grade, hypertension, abdominal obesity, diabetes, and lipid-lowering drugs. However, men were not protected against risk of diabetes. In women, HDL cholesterol was not associated with risk for CHD, whereas intermediate (40-60 mg/dL) compared with lower HDL cholesterol levels proved protective against risk of diabetes (relative risk = 0.57 [95% confidence interval, 0.36-0.90]) after adjustments that included apolipoprotein A-I tertiles. Yet higher serum concentrations failed to yield protection against diabetes. It was concluded that HDL particles confer partially lacking protection against cardiometabolic risk among Turks, and this impairment is modulated by sex. This highly important observation may result from a setting of prevailing chronic subclinical inflammation.

Characterization of metabolic interrelationships and in silico phenotyping of lipoprotein particles using self-organizing maps

Plasma lipid concentrations cannot properly account for the complex interactions prevailing in lipoprotein (patho)physiology. Sequential ultracentrifugation (UCF) is the gold standard for physical lipoprotein isolations allowing for subsequent analyses of the molecular composition of the particles. Due to labor and cost issues, however, the UCF-based isolations are usually done only for VLDL, LDL, and HDL fractions; sometimes with the addition of intermediate density lipoprotein (IDL) particles and the fractionation of HDL into HDL(2) and HDL(3) (as done here; n = 302). We demonstrate via these data, with the lipoprotein lipid concentration and composition information combined, that the self-organizing map (SOM) analysis reveals a novel data-driven in silico phenotyping of lipoprotein metabolism beyond the experimentally available classifications. The SOM-based findings are biologically consistent with several well-known metabolic characteristics and also explain some apparent contradictions. The novelty is the inherent emergence of complex lipoprotein associations; e.g., the metabolic subgrouping of the associations between plasma LDL cholesterol concentrations and the structural subtypes of LDL particles. Importantly, lipoprotein concentrations cannot pinpoint lipoprotein phenotypes. It would generally be beneficial to computationally enhance the UCF-based lipoprotein data as illustrated here. Particularly, the compositional variations within the lipoprotein particles appear to be a fundamental issue with metabolic and clinical corollaries.

Dysfunctional HDL as a diagnostic and therapeutic target

The atheroprotective effects of HDL are mediated by several mechanisms, including its role in reverse cholesterol transport and via its antiinflammatory properties. However, not all HDL is functionally similar. HDL and apolipoprotein A-I may become dysfunctional or even proinflammatory and thus promote atherosclerosis. ApoAI posttranslational modification can have a large impact on its function. Myeloperoxidase modification of apoAI impairs its function as a cholesterol acceptor, and the molecular changes induced by myeloperoxidase have been studied in detail. These studies provide the basis for the development of an oxidant-resistant form of apoAI and clinical measures of HDL modification and dysfunction, which may be useful as a treatment criterion.

Effect of lipid-modifying therapies on the functional quality of high-density lipoproteins: implications for drug development

BACKGROUND

Increasing interest has focused on the development of therapeutic strategies to promote the biological activity of high-density lipoproteins (HDL) to achieve more effective prevention of cardiovascular disease. The highly publicized failure of raising HDL cholesterol with the cholesteryl ester transfer protein inhibitor, torcetrapib, has fueled immense discussion with regard to the potential impact of lipid modifying therapies on the functional quality of HDL particles.

OBJECTIVE/METHOD

To review the literature that has investigated the role of HDL functionality in protection against cardiovascular disease.

CONCLUSION

It remains to be unequivocally demonstrated that therapies that directly target HDL are cardioprotective in humans. Increasing attention on the functional quality of HDL will be essentinal for developing new biomarkers and medical therapies.

Prenatal exposure to cigarette smoke induces diet- and sex-dependent dyslipidemia and weight gain in adult murine offspring

BACKGROUND

Cardiovascular disease (CVD) affects 71 million American adults and remains the leading cause of death in the United States and Europe. Despite studies that suggest that the development of CVD may be linked to intrauterine growth or early events in childhood, little direct experimental evidence supports the notion.

OBJECTIVE

We investigated whether exposure to cigarette smoke in utero alters the risk of developing CVD later in life.

METHODS

We exposed B(6)C(3)F(1) mice (via whole-body inhalation) to either filtered air or mainstream cigarette smoke (MCS, at a particle concentration of 15 mg/m(3)) from gestational day 4 to parturition. Adult offspring were fed a normal chow diet or switched to a high-fat diet 2 weeks before sacrifice. We measured dam and offspring body weight, plasma lipid parameters, lipoprotein subclass particle numbers and sizes, and total antioxidant capacities.

RESULTS

Adult female mice prenatally exposed to MCS demonstrated significantly higher body weight and levels of plasma high-density lipoprotein (HDL) and low-density lipoprotein than did their air-exposed counterparts. When fed a high-fat diet for 2 weeks, males, but not females, exposed prenatally to MCS gained substantially more weight and exhibited dramatic alterations in total cholesterol and HDL levels compared with their air-exposed counterparts.

CONCLUSIONS

These data provide, for the first time, direct experimental evidence supporting the notion that prenatal exposure to cigarette smoke affects offspring weight gain and induces a lipid profile that could alter the offspring's risk of developing CVD later in life.

HDL biogenesis and functions: role of HDL quality and quantity in atherosclerosis

Coronary heart disease (CHD) is a leading cause of death in western societies. In the last few decades, a number of epidemiological studies have shown that a disproportion between atheroprotective and atherogenic lipoproteins in plasma is one of the most important contributors towards atherosclerosis and CHD. Thus, based on the classical view, reduced HDL cholesterol levels independently predict one's risk factor for developing cardiovascular disease, while elevated HDL levels protect from atherosclerosis. However, more recent studies have suggested that the relationship between HDL and cardiovascular risk is more complex and extends beyond the levels of HDL in plasma. These studies challenge the existing view on HDL and cardiovascular risk and trigger a discussion as to whether low HDL is a causal effect for the development of heart disease. In this article we provide a review of the current literature on the biogenesis of HDL and its proposed functions in atheroprotection. In addition, we discuss the significance of both HDL quality and quantity in assessing cardiovascular risk.

HbA1c and serum levels of advanced glycation and oxidation protein products in poorly and well controlled children and adolescents with type 1 diabetes mellitus

Diabetes mellitus is associated with hyperglycemia and with accelerated non-enzymatic glycation, increased oxidative stress and free radical production. The aim of the present study was to evaluate the levels of proteins glycation and oxidation parameters, compare them between poorly and well controlled children with type 1 diabetes mellitus, and determine the impact of glycemic control on these parameters. Blood and serum were obtained from 81 patients with type 1 diabetes mellitus (DM1) (20 patients had long-term good glycemic control [GGC], 61 patients had long-term poor glycemic control [PGC]). Thirty-one healthy children were used as controls. Fructosamine (FAM) was determined by a spectrophotometric method, HbA1c was measured by LPLC, serum advanced glycation end-products (s-AGEs) were determined fluorimetrically, and advanced oxidation protein products (AOPP) were measured spectrophotometrically. We observed significantly higher FAM, HbA1c, s-AGEs and AOPP levels in the patients with DM1 compared with controls, and significantly higher FAM, HbA1c and sAGEs levels in the PGC group compared with the GGC group. AOPP was higher in the PGC group than in the GGC group, but not significantly. In the PGC group we observed significant correlations between HbA1c and HDL-C (r = -0.306, p = 0.01), HbA1c and s-AGEs (r = 0.486, p < 0.001), and HbA1c and AOPP (r = 0.447, p < 0.01). s-AGEs significantly correlated with triacylglycerols (TAG) (r = 0.537, p < 0.001) and AOPP with HDL-C (r = -0.336, p < 0.05), TAG (r = 0.739, p < 0.001) and s-AGEs (r = 0.577, p < 0.001). In conclusion, our results showed both glycative and oxidative stress are increased in the PGC diabetic group compared with controls, they are linked with glycemic control, and probably contribute to the development of diabetic complications. We suggest that the measurement of not only HbA1c but also s-AGEs and AOPP may be useful to predict the risk of development of diabetic complications.

Identification of genetic markers associated with high-density lipoprotein-cholesterol by genome-wide screening in a Japanese population: the Suita study

BACKGROUND

Recent genome-wide association studies (GWAS) have identified genes or loci affecting lipid levels. Given the difference in allele frequencies and linkage disequilibrium patterns across the populations, a GWAS was conducted using the Illumina 550K in a Japanese population (n=900) in search of population-specific genetic variations associated with high-density lipoprotein (HDL)-cholesterol.

METHODS AND RESULTS

Among the 368,274 single nucleotide polymorphisms (SNPs) with a minor allele frequency of at least 0.1, 43 SNPs exceeded the arbitrary threshold of -log(10)P >4.0. The most significant SNP was rs3764261, located 5'upstream of CETP, exhibiting a -log(10)P value of 6.17. Increasing the sample size by genotyping in the additional Suita sample (n=1,810) further improved the level of significance, with each additional copy of the minor allele being associated with an increase in HDL-cholesterol by 6.2 mg/dl (P =3.4x10(-12)). Interestingly, the minor allele was more prevalent in cases with myocardial infarction than in controls (0.221 vs 0.196, nominal P=0.02).

CONCLUSIONS

The association between genetic variants at CETP and HDL-cholesterol was replicated in our sample. None of the genetic variants exerted a greater influence on HDL levels than those at CETP. Associations for the top-ranked SNPs need to be tested for further replication in an independent sample.

Adenoviral expression of human lecithin-cholesterol acyltransferase in nonhuman primates leads to an antiatherogenic lipoprotein phenotype by increasing high-density lipoprotein and lowering low-density lipoprotein

Lecithin-cholesterol acyltransferase (LCAT), a key enzyme in high-density lipoprotein (HDL) metabolism, has been proposed to have atheroprotective properties by promoting reverse cholesterol transport. Overexpression of LCAT in various animal models, however, has led to conflicting results on its overall effect on lipoproteins and atherosclerosis. In this study, the effect of overexpression of LCAT in nonhuman primates on lipoprotein metabolism is examined. Human LCAT was expressed with adenovirus in squirrel monkeys (n = 8), resulting on day 4 in a 22-fold increase of LCAT activity (257 +/- 23 vs 5618 +/- 799 nmol mL(-1) h(-1), P < .0001). At its peak, LCAT was found to nearly double the level of HDL cholesterol from baseline (113 +/- 7 vs 260 +/- 24 mg/dL, P < .01). High-density lipoprotein formed after treatment with the adenovirus was larger in size, as assessed by fast protein liquid chromatography (FPLC) analysis. By kinetic studies, it was determined that there was a decrease in apolipoprotein (Apo) A-I resident time (0.373 +/- 0.027 vs 0.685 +/- 0.045 d(-1), P < .0001) and almost a doubling in the ApoA-I synthetic rate (22 +/- 2 vs 41 +/- 3 mg kg(-1) d(-1), P < .0001), but no overall change in ApoA-I levels. In addition, increased expression of LCAT was associated with a 37% reduction of ApoB levels (12 +/- 1 vs 19 +/- 1 mg/dL, P < .05) due to increased low-density lipoprotein catabolism (fractional catabolic rate = 1.7 +/- 0.1 d(-1) in controls vs 4.2 +/- 0.3 d(-1) in LCAT-treated group, P < .05). In summary, overexpression of LCAT in nonhuman primates leads to an antiatherogenic lipoprotein profile by increasing HDL cholesterol and lowering ApoB, thus making LCAT a potential drug target for reducing atherosclerosis.

Serum levels of soluble receptor for advanced glycation end products and of S100 proteins are associated with inflammatory, autoantibody, and classical risk markers of joint and vascular damage in rheumatoid arthritis

INTRODUCTION

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily of cell surface receptor molecules. High concentrations of three of its putative proinflammatory ligands, S100A8/A9 complex (calprotectin), S100A8, and S100A12, are found in rheumatoid arthritis (RA) serum and synovial fluid. In contrast, soluble RAGE (sRAGE) may prevent proinflammatory effects by acting as a decoy. This study evaluated the serum levels of S100A9, S100A8, S100A12 and sRAGE in RA patients, to determine their relationship to inflammation and joint and vascular damage.

METHODS

Serum sRAGE, S100A9, S100A8 and S100A12 levels from 138 patients with established RA and 44 healthy controls were measured by ELISA and compared by unpaired t test. In RA patients, associations with disease activity and severity variables were analyzed by simple and multiple linear regressions.

RESULTS

Serum S100A9, S100A8 and S100A12 levels were correlated in RA patients. S100A9 levels were associated with body mass index (BMI), and with serum levels of S100A8 and S100A12. S100A8 levels were associated with serum levels of S100A9, presence of anti-citrullinated peptide antibodies (ACPA), and rheumatoid factor (RF). S100A12 levels were associated with presence of ACPA, history of diabetes, and serum S100A9 levels. sRAGE levels were negatively associated with serum levels of C-reactive protein (CRP) and high-density lipoprotein (HDL), history of vasculitis, and the presence of the RAGE 82Ser polymorphism.

CONCLUSIONS

sRAGE and S100 proteins were associated not just with RA inflammation and autoantibody production, but also with classical vascular risk factors for end-organ damage. Consistent with its role as a RAGE decoy molecule, sRAGE had the opposite effects to S100 proteins in that S100 proteins were associated with autoantibodies and vascular risk, whereas sRAGE was associated with protection against joint and vascular damage. These data suggest that RAGE activity influences co-development of joint and vascular disease in rheumatoid arthritis patients.

Is HDL function as important as HDL quantity in the coronary artery disease risk assessment?

Over the past several decades, it has been clearly established that higher plasma concentrations of high-density lipoprotein (HDL) are related to lower risk of coronary artery disease (CAD). According to the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) guidelines, the HDL level of <40 mg/dL is considered low and is one of the CAD risk predictors. However, in the last decade, several studies have indicated the importance of the quality of HDL as another potential measure for CAD risk assessment. The loss of normal biological function of HDL particles as a result of multifactorial actions of chronic inflammation and acute phase responses has suggested a new potential pathway in the pathophysiology of atherosclerosis. The concept of "dysfunctional HDL" or "proinflammatory HDL," which exhibits chameleon-like properties of converting a positive force protecting arteries to a negative one, enhancing atherogenesis is now under active investigation. Measurements of this dysfunctional quality of HDL in cell-based or cell-free assays by analyzing anti-inflammatory functions may link these changes to in vivo assessments of vascular disease. This review provides details on functional and dysfunctional HDL and summarizes recent studies into dysfunctional HDL and its potential links to CAD.

Transferência de lípides para a lipoproteína de alta densidade (HDl) em mulheres com diabetes melito tipo 1

INTRODUÇÃO: Os portadores de diabetes melito tipo 1 (DM1) possuem aumentado risco de doença cardiovascular e, ainda assim, podem apresentar perfil lipídico normal. Para esclarecer se os níveis normais de HDL podem ocultar defeitos na função, foram estudados a transferência de lípides para a HDL em DM1. MÉTODOS: Vinte e uma mulheres jovens portadoras de DM1 foram comparadas com 21 mulheres não-diabéticas. Nanoemulsões foram usadas como doadoras de lípides para HDL: uma marcada com ³H-triglicérides e 14C-colesterol livre e outra com ³H-éster de colesterol e 14C-fosfolípides. Após 1 hora de incubação com amostras de plasma, seguida por precipitação química, o sobrenadante, contendo HDL, teve a radioatividade contada. RESULTADOS: Nenhuma diferença foi encontrada nas transferências dos ésteres de colesterol, triglicérides, colesterol livre e fosfolípides para as HDL. CONCLUSÃO: A transferência de lípides para a HDL não está afetada em portadoras de DM1. Isso sugere que a doença não altera a composição de lipoproteínas e a ação de proteínas de transferência.