High-density lipoproteins differentially modulate cytokine-induced expression of E-selectin and cyclooxygenase-2

Beneficial effects of high-density lipoprotein (HDL) on stent biocompatibility and the potential value of HDL infusion therapy following percutaneous coronary intervention

Several epidemiological studies have shown a clear inverse relationship between serum levels of high-density lipoprotein cholesterol (HDL-C) and the risk of atherosclerotic cardiovascular disease (ASCVD), even at low-density lipoprotein cholesterol levels below 70 mg/dL. There is much evidence from basic and clinical studies that higher HDL-C levels are beneficial, whereas lower HDL-C levels are detrimental. Thus, HDL is widely recognized as an essential anti-atherogenic factor that plays a protective role against the development of ASCVD. Percutaneous coronary intervention is an increasingly common treatment choice to improve myocardial perfusion in patients with ASCVD. Although drug-eluting stents have substantially overcome the limitations of conventional bare-metal stents, there are still problems with stent biocompatibility, including delayed re-endothelialization and neoatherosclerosis, which cause stent thrombosis and in-stent restenosis. According to numerous studies, HDL not only protects against the development of atherosclerosis, but also has many anti-inflammatory and vasoprotective properties. Therefore, the use of HDL as a therapeutic target has been met with great interest. Although oral medications have not shown promise, the developed HDL infusions have been tested in clinical trials and have demonstrated viability and reproducibility in increasing the cholesterol efflux capacity and decreasing plasma markers of inflammation. The aim of the present study was to review the effect of HDL on stent biocompatibility in ASCVD patients following implantation and discuss a novel therapeutic direction of HDL infusion therapy that may be a promising candidate as an adjunctive therapy to improve stent biocompatibility following percutaneous coronary intervention.

Multifaced Roles of HDL in Sepsis and SARS-CoV-2 Infection: Renal Implications

High-density lipoproteins (HDLs) are a class of blood particles, principally involved in mediating reverse cholesterol transport from peripheral tissue to liver. Omics approaches have identified crucial mediators in the HDL proteomic and lipidomic profile, which are involved in distinct pleiotropic functions. Besides their role as cholesterol transporter, HDLs display anti-inflammatory, anti-apoptotic, anti-thrombotic, and anti-infection properties. Experimental and clinical studies have unveiled significant changes in both HDL serum amount and composition that lead to dysregulated host immune response and endothelial dysfunction in the course of sepsis. Most SARS-Coronavirus-2-infected patients admitted to the intensive care unit showed common features of sepsis disease, such as the overwhelmed systemic inflammatory response and the alterations in serum lipid profile. Despite relevant advances, episodes of mild to moderate acute kidney injury (AKI), occurring during systemic inflammatory diseases, are associated with long-term complications, and high risk of mortality. The multi-faceted relationship of kidney dysfunction with dyslipidemia and inflammation encourages to deepen the clarification of the mechanisms connecting these elements. This review analyzes the multifaced roles of HDL in inflammatory diseases, the renal involvement in lipid metabolism, and the novel potential HDL-based therapies.

Initial serum cholesterol level as a potential marker for post cardiac arrest patient outcomes

AIM

Cholesterol and lipoproteins have many roles during systemic inflammation in critically ill patients. Many previous studies have reported that low levels of cholesterol are associated with poor outcomes in these patients. The aim of this study was to investigate the association of initial total cholesterol with predicting neurologic outcome of post-cardiac arrest patients.

METHODS

This was a retrospective observational study of out-of-hospital-cardiac arrest (OHCA) survivors who had serum cholesterol levels at admission. Multivariate regression analysis was performed to investigate total cholesterol and its association with neurologic outcome. Area under receiver operator characteristic curve (AUROC) was assessed and cut off values for predicting good or poor neurologic outcomes were analysed.

RESULTS

A total of 355 patients were analysed. Lower total cholesterol was significantly associated with poor neurologic outcome [OR: 0.99 (95% CI: 0.98-0.99), p < 0.01] in the multivariate analysis. Cholesterol was also useful to screening for poor neurologic outcome [AUROC: 0.70 (95%CI: 0.63-0.77)]. Patients with cholesterol lower than 71 mg/dL had poor neurologic outcome with a specificity of 100%.

CONCLUSIONS

Initial cholesterol level is an easily obtained biomarker that showed association with neurologic outcomes of post cardiac arrest patients.

Serum E-selectin concentration is associated with risk of metabolic syndrome in females

OBJECTIVES

Traits of metabolic syndrome (MetS) and biomarkers of inflammation and endothelial dysfunction were examined. We investigated the differences of various biomarkers among individuals with or without Mets in a gender-specific manner. The gender-specific associations between E-selectin and MetS were further evaluated.

METHODS

A total of 205 patients were recruited from the outpatient clinics of Tri-Service General Hospital, Taipei, Taiwan. Inclusion criteria were age between 20-75 years and BMI < 35 kg/m2. Demographic, anthropometric and MetS index data were compared between genders. Markers of inflammation and endothelial dysfunction were compared between individuals with or without MetS by gender.

RESULTS

Age-adjusted E-selectin values showed significant positive correlations with BMI, waist-hip ratio, fasting plasma glucose, systolic and diastolic blood pressure, triglycerides, TNF-α, hsCRP and ICAM-1, and inverse correlation with HDL cholesterol. E-selectin levels were positively correlated with numbers of MetS components in females (P < 0.001) but not in males (P = 0.125).

CONCLUSIONS

Increased E-selectin levels are significantly associated with increased MetS risk in females, but not in males.

High-Density Lipoprotein, Mean Platelet Volume, and Uric Acid as Biomarkers for Outcomes in Patients With Sepsis: An Observational Study

BACKGROUND

We conducted an observational study evaluating the association between uric acid, mean platelet volume (MPV), and high-density lipoprotein (HDL) with complications and outcomes of patients with sepsis in a critical care setting.

METHODS

We followed patients with a diagnosis of severe sepsis and septic shock for a maximum of 28 days. Main outcomes assessed included length of stay (LOS), the need for renal replacement therapy (RRT), assisted mechanical ventilation (AMV), and vasopressor support as well as in-unit mortality.

RESULTS

The overall average age of the 37 patients enrolled was 48.1 (19.8) years; among them, 37.8% were male. Abdominal related (43.2%) and pulmonary (29.7%) were the main sites of infection. The overall Acute Physiology and Chronic Health Evaluation 2 (APACHE-2) median score was 19 (9-24). Acute kidney injury (AKI) was observed in 46.9% of the sample. In all, 54.1% required vasopressor support, 54.1% AMV, and 35.1% RRT. Patients with bacteremia were significantly more likely to require vasopressor support and those with urinary tract infections were significantly younger. We found increasing ΔMPV levels, higher APACHE-2 scores, lower HDL values, and a reduced age to be associated with a longer LOS. Higher scores on the APACHE-2 scale and lower levels of HDL significantly associated with higher odds for developing AKI. The need for vasopressor support was significantly associated with higher values of 72-hour MPV and with higher levels of baseline uric acid and lower values of initial HCO₃. Initial and 72-hour levels of MPV and higher scores in the APACHE-2 were all significantly correlated with the need for AMV. An increased probability of dying during follow-up was significantly correlated with increasing age.

CONCLUSION

We were able to establish significant associations between our candidate biomarkers and relevant outcomes for patients with sepsis. Our results support the use of these low-cost biomarkers in the assessment of prognosis of patients with sepsis.

Pharmacological Intervention to Modulate HDL: What Do We Target?

The cholesterol concentrations of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) have traditionally served as risk factors for cardiovascular disease. As such, novel therapeutic interventions aiming to raise HDL cholesterol have been tested in the clinical setting. However, most trials led to a significant increase in HDL cholesterol with no improvement in cardiovascular events. The complexity of the HDL particle, which exerts multiple physiological functions and is comprised of a number of subclasses, has raised the question as to whether there should be more focus on HDL subclass and function rather than cholesterol quantity. We review current data regarding HDL subclasses and subclass-specific functionality and highlight how current lipid modifying drugs such as statins, cholesteryl ester transfer protein inhibitors, fibrates and niacin often increase cholesterol concentrations of specific HDL subclasses. In addition this review sets out arguments suggesting that the HDL3 subclass may provide better protective effects than HDL2.

The Changing Face of HDL and the Best Way to Measure It

BACKGROUND

HDL cholesterol (HDL-C) is a commonly used lipid biomarker for assessing cardiovascular health. While a central focus has been placed on the role of HDL in the reverse cholesterol transport (RCT) process, our appreciation for the other cardioprotective properties of HDL continues to expand with further investigation into the structure and function of HDL and its specific subfractions. The development of novel assays is empowering the research community to assess different aspects of HDL function, which at some point may evolve into new diagnostic tests.

CONTENT

This review discusses our current understanding of the formation and maturation of HDL particles via RCT, as well as the newly recognized roles of HDL outside RCT. The antioxidative, antiinflammatory, antiapoptotic, antithrombotic, antiinfective, and vasoprotective effects of HDL are all discussed, as are the related methodologies for assessing these different aspects of HDL function. We elaborate on the importance of protein and lipid composition of HDL in health and disease and highlight potential new diagnostic assays based on these parameters.

SUMMARY

Although multiple epidemiologic studies have confirmed that HDL-C is a strong negative risk marker for cardiovascular disease, several clinical and experimental studies have yielded inconsistent results on the direct role of HDL-C as an antiatherogenic factor. As of yet, our increased understanding of HDL biology has not been translated into successful new therapies, but will undoubtedly depend on the development of alternative ways for measuring HDL besides its cholesterol content.

HDL in sepsis - risk factor and therapeutic approach

High-density lipoprotein (HDL) is a key component of circulating blood and plays essential roles in regulation of vascular endothelial function and immunity. Clinical data demonstrate that HDL levels drop by 40-70% in septic patients, which is associated with a poor prognosis. Experimental studies using Apolipoprotein A-I (ApoAI) null mice showed that HDL deficient mice are susceptible to septic death, and overexpressing ApoAI in mice to increase HDL levels protects against septic death. These clinical and animal studies support our hypothesis that a decrease in HDL level is a risk factor for sepsis, and raising circulating HDL levels may provide an efficient therapy for sepsis. In this review, we discuss the roles of HDL in sepsis and summarize the efforts of using synthetic HDL as a potential therapy for sepsis.

Effect of extractions from Ephedra sinica Stapf on hyperlipidemia in mice

The aim of the present study was to investigate the hypolipidemic and antioxidant potential of ephedra extractions in diet-induced hyperlipidemic mice. Mice were fed a diet high in fat to establish the hyperlipidemic model. A total of 48 mice were randomly divided into six groups, which included the normal control, model control, positive control, ephedra alkaloid, ephedra polysaccharide and ephedra non-alkaloid groups. Intragastric administration of the respective treatments was provided continuously for four weeks and the body weight was recorded weekly. The total levels of cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C) and malondialdehyde (MDA), and the activity levels of superoxide dismutase (SOD), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum were recorded. In addition, changes in liver morphology and organ coefficients (ratio of organ to body weight) were evaluated, while the acute toxicity reactions of ephedra extractions were investigated using the modified Spearman-Karber method. Compared with the mice in the model control group, the weight, liver coefficient, serum levels of TC, TG and MDA, and activities of ALT and AST were significantly lower (P<0.05) in the mice in the ephedra non-alkaloid group. However, the level of HDL-C and the activity of SOD were markedly higher (P<0.05). Fatty degeneration of the liver in the ephedra alkaloid and non-alkaloid groups was notably improved compared with the model control group. The mean lethal dose (LD₅₀) of ephedra alkaloids was 610 mg/kg, and the maximum tolerated dose of oral ephedra non-alkaloids in the mice was 367.5-fold larger than the clinical dosage in humans. In conclusion, ephedra non-alkaloids have therapeutic potential for the treatment of hyperlipidemia, since they are able to improve lipid metabolism and are relatively safe for use under the maximum tolerated dose.

HDL and endothelial protection

High-density lipoproteins (HDLs) represent a family of particles characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver. In addition to this function, HDLs display pleiotropic effects including antioxidant, anti-apoptotic, anti-inflammatory, anti-thrombotic or anti-proteolytic properties that account for their protective action on endothelial cells. Vasodilatation via production of nitric oxide is also a hallmark of HDL action on endothelial cells. Endothelial cells express receptors for apoA-I and HDLs that mediate intracellular signalling and potentially participate in the internalization of these particles. In this review, we will detail the different effects of HDLs on the endothelium in normal and pathological conditions with a particular focus on the potential use of HDL therapy to restore endothelial function and integrity.

Apolipoprotein A-I mimetic peptide 4F attenuates kidney injury, heart injury, and endothelial dysfunction in sepsis

Kidney injury, heart injury, and cytokine-induced vascular hyperpermeability are associated with high rates of morbidity and mortality in sepsis. Although the mechanism remains unknown, apolipoprotein A-I (apoA-I) mimetic peptide 4F reduces inflammation and protects HDL levels, which are reduced in sepsis. We hypothesized that 4F also protects kidneys and hearts in a rat model of cecal ligation and puncture (CLP). We divided Wistar rats into groups: sham-operated (control), CLP, and CLP+4F (10 mg/kg body wt ip, 6 h after CLP). At 24 h post-CLP, we evaluated cardiac function, mean arterial pressure (MAP), heart rate (HR), baroreflex sensitivity, total cholesterol, LDL, HDL, serum cytokines, and inulin clearance. We performed immunoblotting for protein regulators of vascular permeability (Slit2 and Robo4) and endothelial nitric oxide synthase (eNOS) in kidney tissue. We evaluated heart mitochondria with electron microscopy. Although there was no difference in MAP, the HR was significantly higher in CLP rats than in control and CLP+4F rats. In CLP+4F rats, baroreflex sensitivity and cardiac function were completely protected from the effects of CLP, as was glomerular filtration; heart mitochondria morphology was improved; sepsis-induced changes in serum cholesterol, LDL, HDL, and apoA-I were less common; all cytokines were lower than in CLP rats; and expression of Slit2, Robo4, and eNOS was completely restored. Administration of 4F inhibits inflammatory responses and strengthens the vascular barrier, protecting kidneys and hearts in an HDL-dependent manner. To determine the extent of the protective effect of 4F, further studies are needed.

High density lipoproteins and endothelial functions: mechanistic insights and alterations in cardiovascular disease

Prospective population studies in the primary prevention setting have shown that reduced plasma levels of HDL cholesterol are associated with an increased risk of coronary disease and myocardial infarction. Experimental and translational studies have further revealed several potential anti-atherogenic effects of HDL, including protective effects on endothelial cell functions. HDL has been suggested to protect endothelial cell functions by prevention of oxidation of LDL and its adverse endothelial effects. Moreover, HDL from healthy subjects can directly stimulate endothelial cell production of nitric oxide and anti-inflammatory, anti-apoptotic, and anti-thrombotic effects as well as endothelial repair processes. However, several recent clinical trials using HDL cholesterol-raising agents, such as torcetrapib, dalcetrapib, and niacin, did not demonstrate a significant reduction of cardiovascular events in patients with coronary disease. Of note, growing evidence suggests that the vascular effects of HDL can be highly heterogeneous and vasoprotective properties of HDL are altered in patients with coronary disease. Characterization of underlying mechanisms and understanding of the clinical relevance of this "HDL dysfunction" is currently an active field of cardiovascular research. Notably, in some recent studies no clear association of higher HDL cholesterol levels with a reduced risk of cardiovascular events was observed in patients with already established coronary disease. A greater understanding of mechanisms of action of HDL and its altered vascular effects is therefore critical within the context of HDL-targeted therapies. In this review, we will address different effects of HDL on endothelial cell functions potentially relevant to atherosclerotic vascular disease and explore molecular mechanisms leading to "dysfunctional HDL".

Cardiovascular disease risk reduction by raising HDL cholesterol--current therapies and future opportunities

Since the first discovery of an inverse correlation between high-density lipoprotein-cholesterol (HDL-C) levels and coronary heart disease in the 1950s the life cycle of HDL, its role in atherosclerosis and the therapeutic modification of HDL-C levels have been major research topics. The Framingham study and others that followed could show that HDL-C is an independent cardiovascular risk factor and that the increase of HDL-C of only 10 mg·L(-1) leads to a risk reduction of 2-3%. While statin therapy and therefore low-density lipoprotein-cholesterol (LDL-C) reduction could lower coronary heart disease considerably; cardiovascular morbidity and mortality still occur in a significant portion of subjects already receiving therapy. Therefore, new strategies and therapies are needed to further reduce the risk. Raising HDL-C was thought to achieve this goal. However, established drug therapies resulting in substantial HDL-C increase are scarce and their effect is controversial. Furthermore, it is becoming increasingly evident that HDL particle functionality is at least as important as HDL-C levels since HDL particles not only promote reverse cholesterol transport from the periphery (mainly macrophages) to the liver but also exert pleiotropic effects on inflammation, haemostasis and apoptosis. This review deals with the biology of HDL particles, the established and future therapeutic options to increase HDL-C and discusses the results and conclusions of the most important studies published in the last years. Finally, an outlook on future diagnostic tools and therapeutic opportunities regarding coronary artery disease is given.

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.

Human apolipoprotein A-I induces cyclooxygenase-2 expression and prostaglandin I-2 release in endothelial cells through ATP-binding cassette transporter A1

High-density lipoprotein (HDL) can induce cyclooxygenase-2 (COX-2) expression and prostacyclin I-2 (PGI-2) release in endothelial cells to exert multiple antiatherogenic functions. This effect has been attributed mainly to the role of sphingosine-1-phosphate (S1P) integrated in HDL. However, whether apolipoprotein A-I (apoA-I), the major apolipoprotein of HDL, could induce COX-2 expression and PGI-2 release still remains unclear. In the present study, we selectively delipidated HDL and confirmed that apoA-I could facilitate COX-2 expression and PGI-2 production in human umbilical vein endothelial cells (HUVECs). ApoA-I, but not trypsinized apoA-I, induced COX-2 expression in a time- and dose-dependent manner consistent with a key role for apoA-I in this process. Additionally, cotreatment of apoA-I with S1P further enhanced COX-2 expression and PGI-2 production in HUVECs. These effects triggered by apoA-I were not inhibited by pertussis toxin, consistent with SIP receptor independent pathway for apoA-I effect. Moreover, we demonstrated that the activation of p38 mitogen-activated protein kinase (MAPK), extracellular receptor kinase (ERK) 1/2, and JAK2 pathways by apoA-I was involved in the expression of COX-2 and the release of PGI-2 in HUVECs, and these effects were inhibited by their specific inhibitors, respectively. Small interfering RNA experiments showed that ATP binding-cassette transporter A1 (ABCA1) was required for COX-2 expression and PGI-2 release induced by apoA-I. Thus our results indicate that apoA-I induces COX-2 expression and PGI-2 release through ABCA1 and the activation of intracellular p38 MAPK, ERK1/2, as well as JAK2 pathways, and apoA-I can reinforce these effects with S1P in HUVECs. These novel effects of apoA-I could in part mediate antiatherogenic effects of HDL.

The HDL proteome in acute coronary syndromes shifts to an inflammatory profile

Inflammation is a major factor underlying acute coronary syndromes (ACS). HDL particles may be remodeled, becoming functionally defective, under the inflammatory conditions seen in ACS. Shotgun proteomics was used to monitor changes in the HDL proteome between male age-matched control, stable CAD, and ACS subjects (n=10/group). HDL was isolated by ultracentrifugation and separated by 1D-gel followed by LC-MS/MS. We identified 67 HDL-associated proteins, 20 of which validated recently identified proteins including vitronectin and complement C4B, and 5 of which were novel. Using gene ontology analysis, we found that the HDL-proteome consisted of proteins involved in cholesterol homeostasis (~50%), with significant contributions by proteins involved in lipid binding, antioxidant, acute-phase response, immune response, and endopeptidase/protease inhibition. Importantly, levels of apoA-IV were significantly reduced in ACS patients, whereas levels of serum amyloid A (SAA) and complement C3 (C3) were significantly increased (spectral counting; t-test p≤0.05), as confirmed by immunoblot or ELISA. Despite differences in protein composition, ABCA1, ABCG1, and SR-BI mediated cholesterol efflux assays did not indicate that HDL from ACS patients is functionally deficient as compared to controls, when corrected for apoA-I mass. Our results support that the HDL proteome differs between control, CAD and ACS patients. Increased abundance of SAA, C3, and other inflammatory proteins in HDL from ACS patients suggests that HDL reflects a shift to an inflammatory profile which, in turn, might alter the protective effects of HDL on the atherosclerotic plaque. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Activation of intracellular signaling systems by high-density lipoproteins

The proteosome of high-density lipoprotein particles is quite complex and consists of up to 75 different proteins and enzymes. The specific protein cargo of HDL particles regulates their functionality. In addition to their documented capacity to engage in reverse cholesterol transport, reduce oxidized lipid, and function as apoprotein donors, HDL particles can activate a variety of signaling systems in endothelial cells, smooth muscle cells, and platelets. The HDLs can deliver sphingolipids to the surface of these cell types and activate sphingosine phosphate receptors. Sphingosine phosphate receptors are coupled to numerous different intracellular signaling cascades exerting roles in vasodilatation, inflammation, cell migration and apoptosis, inhibition of platelet activation, and endothelial adhesion molecule expression, among other functions. The ability of HDL to influence such a diverse array of cellular functions lends biological plausibility to the substantial epidemiological and clinical evidence suggesting that the HDLs are unique among lipoproteins in that they are vasculoprotective and antiatherogenic.

Raising HDL cholesterol in women

High-density lipoprotein cholesterol (HDL-C) concentration is essential in the determination of coronary heart disease (CHD) risk in women. This is especially true in the postmenopausal state, where lipid profiles and CHD risk mimic that of age-matched men. Thus, interventions designed to reduce CHD risk by raising HDL-C levels may have particular significance during the transition to menopause. This review discusses HDL-C-raising therapies and the role of HDL in the primary prevention of CHD in women. Lifestyle-based interventions such as dietary change, aerobic exercise regimens, and smoking cessation are initial steps that are effective in raising HDL-C, and available data suggest women respond similarly to men with these interventions. When combined with pharmacotherapy, the effects of these lifestyle alterations are further amplified. Though studies demonstrating gender-specific differences in therapy are limited, niacin continues to be the most effective agent in raising HDL-C levels, especially when used in combination with fibrate or statin therapy. Emerging treatments such as HDL mimetic therapy show much promise in further raising HDL-C levels and improving cardiovascular outcomes.

Gender differences in cardiovascular disease: hormonal and biochemical influences

OBJECTIVE

Atherosclerosis is a complex process characterized by an increase in vascular wall thickness owing to the accumulation of cells and extracellular matrix between the endothelium and the smooth muscle cell wall. There is evidence that females are at lower risk of developing cardiovascular disease (CVD) as compared to males. This has led to an interest in examining the contribution of genetic background and sex hormones to the development of CVD. The objective of this review is to provide an overview of factors, including those related to gender, that influence CVD.

METHODS

Evidence analysis from PubMed and individual searches concerning biochemical and endocrine influences and gender differences, which affect the origin and development of CVD.

RESULTS

Although still controversial, evidence suggests that hormones including estradiol and androgens are responsible for subtle cardiovascular changes long before the development of overt atherosclerosis.

CONCLUSION

Exposure to sex hormones throughout an individual's lifespan modulates many endocrine factors involved in atherosclerosis.

High-density lipoprotein metabolism and endothelial function

PURPOSE OF REVIEW

High-density lipoprotein (HDL) protects against atherosclerosis, transporting cholesterol from peripheral cells to the liver, where it is excreted into the bile. However, HDL also has prominent vascular protective effects.

RECENT FINDINGS

Recent studies have uncovered mechanisms through which HDL decreases vascular inflammation, boosts nitric oxide production, and inhibits thrombosis. The discovery that dysfunctional HDL can also have proinflammatory effects has uncovered a new aspect of HDL biology.

SUMMARY

Low-density lipoprotein is the primary target for drug therapy of dyslipidemias. Drugs that increase HDL also affect additional metabolic pathways. Development of selective drugs targeting key aspects of HDL metabolism may enable us to alter the composition of HDL and inhibit atherogenesis.

High-density lipoproteins, platelets and the pathogenesis of atherosclerosis

1. Prospective and interventional studies demonstrate an inverse relationship between plasma high-density lipoprotein (HDL)-cholesterol and the incidence of coronary artery disease. Although the atheroprotective effects of HDL are usually attributed to the reverse cholesterol transport, in which HDL shuttles cholesterol from cells in the arterial wall to the liver, other mechanisms are also under investigation. 2. Platelets are involved in both the initiation and progression of atherosclerotic lesions. In addition, the formation of thrombi over ruptured atherosclerotic plaques results in the narrowing or complete occlusion of coronary arteries. Current experimental evidence suggests that HDL may exert antiplatelet effects and thereby counteract the development of atherothrombotic vascular disease. 3. In vitro studies show that HDL inhibits agonist-stimulated platelet aggregation, fibrinogen binding, granule secretion and liberation of thromboxane A(2). Inhibitory effects of HDL are mediated, in part, by scavenger receptor type B1 and/or the apolipoprotein E receptor apoER2/LRP8 and are linked to the induction of intracellular signalling cascades encompassing stimulation of protein kinase C, cytoplasmatic alkalization and generation of nitric oxide. 4. Populational studies demonstrate that there is an inverse association between plasma HDL levels and recurrent venous thromboembolism. In addition, HDL-cholesterol has been identified as an independent predictor of acute platelet thrombus formation. The administration of reconstituted HDL particles in humans attenuates ex vivo platelet activation. 5. The present review summarizes recent advances in understanding HDL-platelet interactions and discusses the potential use of HDL-like particles in the therapy of thrombosis.

High-density lipoprotein cholesterol levels and prognosis in advanced heart failure

BACKGROUND

High-density lipoproteins (HDLs) influence the generation of prostacyclin via cyclooxygenase stimulation. Prostaglandins represent an important compensatory pathway in advanced heart failure (HF). Whether HDL levels discriminate prognosis in HF remains unknown.

METHODS

We prospectively evaluated the prognostic relationship of HDL levels in severe HF by examining 132 consecutive patients listed for heart transplantation (52 +/- 11 years of age, 80% men, 79% white, mean follow-up 18 months). Using population mean HDL levels (HDL <33 mg/dl [n = 47] vs > or =33 mg/dl [n = 85]), patients were grouped and followed for the primary composite end-points of HF hospitalizations or death, stratified by underlying etiology (non-ischemic, n = 52; ischemic, n = 80).

RESULTS

Patients with HDL <33 mg/dl had lower serum sodium (135 vs 137 mEq/liter, p = 0.008), higher total bilirubin (1.3 vs 0.7 mg/dl, p < 0.001) and higher uric acid (7.6 vs 6.7 mg/dl, p = 0.048) levels, but similar serum creatinine compared with the > or =33 mg/dl HDL group. Survival analysis, using a Cox proportional hazards model, revealed reduced HDL (<33 mg/dl) as the most significant independent predictor of HF hospitalizations or death, independent of underlying etiology. Low-cholesterol and low-density lipoprotein (LDL)-cholesterol alone were not found to be independently predictive of outcome.

CONCLUSIONS

Lower HDL levels correlate with adverse prognosis independent of etiology and predict clinical worsening or death in advanced HF. Further study is warranted as to whether these findings represent a clinical marker or suggest a potential therapeutic target.

Accelerated atherosclerosis in inflammatory rheumatic diseases

Over recent years it has become clear that patients with inflammatory rheumatic diseases are at increased risk of developing atherosclerosis. The exact causes for this are probably related in part to a general adverse effect of inflammation on atherogenesis, and in part to immune mechanisms specific to individual rheumatic diseases. This review discusses proposed mechanisms of accelerated atherosclerosis, including abnormal lipid and lipoprotein profiles, oxidative stress, enhanced apoptosis, thrombophilia, immune complexes, and increased mononuclear cell infiltration of atherosclerotic lesions, and local generation of cytokines.

Multiple actions of high-density lipoprotein

PURPOSE OF REVIEW

The most accepted property of high-density lipoprotein is reverse cholesterol transport. However, other beneficial actions may contribute to the antiatherogenic role of high-density lipoprotein. This review addresses the action of high-density lipoprotein beyond reverse cholesterol transport.

RECENT FINDINGS

High-density lipoprotein cholesterol levels are inversely associated with coronary heart disease and other forms of vascular disease. Apart from transferring excess cholesterol to the liver, high-density lipoprotein exhibits favorable effects on oxidation, inflammation, thrombosis and endothelial function. Some of these actions are at least in part attributed to high-density lipoprotein-associated enzymes, such as paraoxonase and platelet-activating factor acetylhydrolase. However, high-density lipoprotein can become dysfunctional and proatherogenic under certain circumstances.

SUMMARY

Current data suggest that high-density lipoprotein possesses various properties beyond reverse cholesterol transport. However, many issues on the exact role of high-density lipoprotein remain unknown. Future research is needed.

Oleanolic acid induces prostacyclin release in human vascular smooth muscle cells through a cyclooxygenase-2-dependent mechanism

Oleanolic acid is a triterpenoid that may contribute to the cardio-protective effects of olive oil. Our goal was to assess whether oleanolic acid could modulate eicosanoid biosynthesis and to determine the mechanism involved in this effect. Human coronary smooth muscle cells (SMC) were treated with oleanolic acid, erythrodiol, or hydroxytyrosol and eicosanoid release was measured by enzyme immunoassay. Cyclooxygenase (Cox)-1 and Cox-2 protein and messenger sRNA levels were analyzed by Western blot and real-time PCR, respectively. Mitogen-activated protein kinase (MAPK) pathways were assessed using specific antibodies. Oleanolic acid induced prostaglandin I2 (PGI2) release by human coronary SMC, an effect that was prevented by celecoxib (a specific inhibitor of Cox-2). The increased PGI2 was time-and dose-dependent and was associated to the up-regulation of Cox-2. No effects were observed on thromboxane A2. Erythrodiol but not hydroxytyrosol upregulated Cox-2 expression and induced PGI2 synthesis. Oleanolic acid induced an early phosphorylation of p38 MAPK and p42/44 MAPK but not c-Jun N-terminal kinase-1 (JNK-1). SB203580 (p38MAPK inhibitor) and U0126 (MAPK kinase1/2 inhibitor) abrogated the upregulation of Cox-2 and PGI2 release induced by oleanolic acid. A peptide inhibitor of JNK-1 (L-JNKI1) did not produce any effect. The induction of Cox-2 was preceded by an early activation of cAMP regulatory element-binding protein, a key transcription factor involved in Cox-2 transcriptional upregulation. Therefore, oleanolic acid contributes to vascular homeostasis by inducing PGI2 release in a Cox-2-dependent manner. Oleanolic acid could be regarded as a bioactive molecule that may contribute to the beneficial effects of the Mediterranean diet.

Low HDL-C predicts the onset of transplant vasculopathy in pediatric cardiac recipients on pravastatin therapy

The levels and protein/lipid compositions of major lipoprotein particles of 19 pediatric cardiac transplant recipients (4-18 yr of age) were studied in this prospective, open clinical follow-up study before and at one yr of pravastatin therapy (10 mg/day). The recipients were grouped into those with (n = 6; group A) and those without (n = 13; group B) angiographically detectable vasculopathy. Twenty-one pediatric non-transplant controls were studied at baseline. At baseline, the group A recipients had 29% lower HDL-C concentrations (p = 0.031) and 29% higher apoB-100/apoA-I ratios (p = 0.034) than the group B recipients. At one yr of pravastatin, the respective figures were 29% (p = 0.013) and 33% (p = 0.005). Compared with the healthy pediatric controls, the transplant recipients had significantly higher serum TG before pravastatin [median (range): 1.3 mmol/L (0.6-3.2) vs. 0.7 mmol/L (0.3-2.4), p = 0.0002] and at one yr [1.3 mmol/L (0.5-3.5) vs. 0.7 mmol/L (0.3-2.4), p = 0.0004]. The baseline apoB-100/apoA1 ratios of the recipients were 33% higher (p = 0.005). In conclusion, low HDL-C and high apoB-100/apoA-I ratio were associated with angiographically detectable vasculopathy. Even though pravastatin effectively lowered the TC and LDL-C and improved compositional properties of LDL and HDL(2) particles, it failed to normalize the elevated TG and, in some patients, to prevent the progression of transplant vasculopathy.

Inhibition of CETP activity by torcetrapib reduces susceptibility to diet-induced atherosclerosis in New Zealand White rabbits

Cholesteryl ester transfer protein (CETP) inhibitors increase high density lipoprotein-cholesterol (HDL-C) in animals and humans, but whether CETP inhibition will be antiatherogenic is still uncertain. We tested the CETP inhibitor torcetrapib in rabbits fed an atherogenic diet at a dose sufficient to increase HDL-C by at least 3-fold (207 +/- 32 vs. 57 +/- 6 mg/dl in controls at 16 weeks). CETP activity was inhibited by 70-80% throughout the study. Non-HDL-C increased in both groups, but there was no difference apparent by the study's end. At 16 weeks, aortic atherosclerosis was 60% lower in torcetrapib-treated animals (16.4 +/- 3.4% vs. 39.8 +/- 5.4% in controls) and aortic cholesterol content was reduced proportionally. Sera from a separate group of rabbits administered torcetrapib effluxed 48% more cholesterol from Fu5AH cells than did sera from control animals, possibly explaining the reduced aortic cholesterol content. Regression analyses indicated that lesion area in the torcetrapib-treated group was strongly correlated with the ratio of total plasma cholesterol to HDL-C but not with changes in other lipid or lipoprotein levels. CETP inhibition with torcetrapib retards atherosclerosis in rabbits, and the reduced lesion area is associated with increased levels of HDL-C.

High density lipoprotein subfractions: isolation, composition, and their duplicitous role in oxidation

The plasma HDLs represent a major class of cholesterol-transporting lipoprotein that can be divided into two distinct subfractions, HDL(2) and HDL(3), by ultracentrifugation. Existing methods for the subfractionation of HDL requires lengthy ultracentrifugations, making them unappealing for large-scale studies. We describe a method that subfractionates HDL from plasma in only 6 h, representing a substantial decrease in total isolation time. The subfractions so isolated were assessed for a variety of lipid and protein components, in addition to their susceptibility to oxidation, both alone and in combination with VLDL and LDL. We report for the first time a prooxidant role for HDL during VLDL oxidation, in which HDL donates preformed hydroperoxides to VLDL in a cholesteryl ester transfer protein (CETP)-dependent process. Examination of the participation of HDL in LDL oxidation has reinforced its classic role as a potent antioxidant. Furthermore, we have also implicated the second major HDL-associated enzyme, LCAT, in these processes, whereby it acts as a potent prooxidant during VLDL oxidation but as an antioxidant during LDL oxidation. Thus, we have identified a potentially duplicitous role for HDL in the pathogenesis of atherosclerosis, attributable to both CETP and LCAT.

The PGH-synthase system and isozyme-selective inhibition

Virtually all human cell types can express both cyclooxygenase (COX)-1 and COX-2 under appropriate circumstances. Both isoforms can subserve physiologic and pathophysiologic roles when coupled with the appropriate stimuli and downstream prostaglandin (PG)H2-isomerases and prostanoid receptors. Although the ratio of maximal biosynthetic capacity of human platelets to the basal rate of production of thromboxane A2 is approximately 5000, this ratio is much lower in the case of PGI2, thus dictating quite different requirements for the extent and duration of COX inhibition in human platelets and vascular endothelial cells to detect functional and clinical effects. The development of low-dose aspirin as an antiplatelet agent has been instrumental in characterizing the role of platelet COX-1 in atherothrombosis. Similarly, though quite unexpectedly, the development of coxibs as anti-inflammatory agents has been instrumental in elucidating the role of endothelial COX-2 in vascular occlusion. Because of differential requirements for the inhibition of thromboxane A2 versus PGI2 biosynthesis in vivo, most traditional nonsteroidal anti-inflammatory drugs tend to mimic the effects of coxibs, rather than aspirin, on prostanoid-dependent cardiovascular homeostasis.

Characterization of a new mouse model for human apolipoprotein A-I/C-III/A-IV deficiency

Human data raised the possibility that coronary heart disease is associated with mutations in the apolipoprotein gene cluster APOA1/C3/A4 that result in multideficiency of cluster-encoded apolipoproteins and hypoalphalipoproteinemia. To test this hypothesis, we generated a mouse model for human apolipoprotein A-I (apoA-I)/C-III/A-IV deficiency. Homozygous mutants (Apoa1/c3/a4(-/-)) lacking the three cluster-encoded apolipoproteins were viable and fertile. In addition, feeding behavior and growth were apparently normal. Total cholesterol (TC), high density lipoprotein cholesterol (HDLc), and triglyceride levels in the plasma of fasted mutants fed a regular chow were 32% (P < 0.001), 17% (P < 0.001), and 70% (P < 0.01), respectively, those of wild-type mice. When fed a high-fat Western-type (HFW) diet, Apoa1/c3/a4(-/-) mice showed a further decrease in HDLc concentration and a moderate increase in TC, essentially in non-HDL fraction. The capacity of Apoa1/c3/a4(-/-) plasma to promote cholesterol efflux in vitro was decreased to 75% (P < 0.001), and LCAT activity was decreased by 38% (P < 0.01). Despite the very low total plasma cholesterol, the imbalance in lipoprotein distribution caused small but detectable aortic lesions in one-third of Apoa1/c3/a4(-/-) mice fed a HFW diet. In contrast, none of the wild-type mice had lesions. These results demonstrate that Apoa1/c3/a4(-/-) mice display clinical features similar to human apoA-I/C-III/A-IV deficiency (i.e., marked hypoalphalipoproteinemia) and provide further support for the apoa1/c3/a4 gene cluster as a minor susceptibility locus for atherosclerosis in mice.

Circulating markers of endothelial function in cardiovascular disease

Endothelial dysfunction is a key event in cardiovascular disease. Measurement of endothelial dysfunction in vivo presents a major challenge, but has important implications since it may identify the clinical need for therapeutic intervention, specifically in primary prevention. Several biological markers have been used as indicators of endothelial dysfunction. The soluble adhesion molecules sICAM-1 and sVCAM-1 lack specificity and are increased in inflammatory processes. Both markers are increased in coronary artery disease. sICAM-1 level predicts the risk for cardiovascular disease or diabetes mellitus in healthy individuals. sE-selectin is specific for the endothelium and is increased in coronary artery disease and diabetes mellitus. sE-selectin is also associated with diabetic risk. The endothelium-specific marker, soluble thrombomodulin, is associated with severity of coronary artery disease, stroke or peripheral occlusive arterial disease and is not increased in healthy or asymptomatic subjects. Interestingly, thrombomodulin decreases during treatment of hypercholesterolemia or hyperhomocysteinemia. In contrast, von Willebrand factor is the best endothelial biomarker and predicts risk for ischemic heart disease or stroke.

High-Density Lipoprotein Cholesterol-Raising Strategies

There is a distinct inverse relationship between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease risk. HDL-C mediates cholesterol efflux from the vasculature and promotes anti-oxidant, anti-inflammatory, and anti-thrombotic effects. There are multiple lifestyle and therapeutic interventions that raise HDL-C, and there is increasing evidence that these interventions improve cardiovascular outcomes. Recent findings regarding the role of HDL-C in cholesterol metabolism offer new strategies designed to target atherosclerosis. This review highlights the utility of existing HDL-C-raising strategies and examines new potential therapies.

HDL: the 'new' target of cardiovascular medicine

Clinical, experimental and epidemiological research has shown the undeniable causal relationship between low HDL plasma concentrations and cardiovascular disease. Low HDL levels are present in about 10% of the general population and represent the most frequent form of dyslipidemia in patients with coronary disease. Reduced HDL concentrations seem to be unable to eliminate efficiently the cholesterol excess at vascular wall level, contributing to the onset of the inflammatory response that typically occurs in the pathogenesis of atherosclerosis right from its earliest stages. The results of numerous studies quite convincingly suggest that HDL is capable of exerting anti-inflammatory activity either directly or by modulating the expression of a number of acute phase proteins. Although the therapeutic options currently available for raising HDL levels still show modest efficacy, both in experimental and pre-clinical fields, genetic investigation and specifically aimed pharmacological treatment have produced more encouraging results, shedding some light on the concrete possibility of being able to treat this disease in the very near future.

Inflammation: cause of vascular disease and malnutrition in dialysis patients

Inflammation occurs in response to tissue injury or the presence of foreign antigens and is important in the mobilization of specific immunologic and nonimmunologic defenses against injury. The vascular endothelium is altered to allow immune competent cells to access the interstitial space. Muscle and visceral proteins are catabolized and the amino acids are used either to supply energy or as substrates for the production of acute-phase proteins that play a role in defense. Restoration of muscle mass is impaired while inflammation is on going. Lipids are mobilized. Although serving a vital role in allowing host survival from acute injury or infection, if unimpeded, or if triggered inappropriately, the acute-phase response may instead lead to increased vascular injury and progressive loss of muscle and visceral protein pools causing malnutrition. Markers of inflammation (C reactive protein [CRP] or interleukin-6 [IL-6] levels) are associated with cardiovascular risk in the general population and in dialysis patients. Hypoalbuminemia also is associated with cardiovascular risk in dialysis patients. Although albumin is considered a marker of nutrition, changes in albumin levels are associated with increased levels of acute-phase proteins. Persistent changes in albumin levels are caused by reduced albumin synthesis associated with inflammation and not decreased normalized protein catabolic rate. The cause(s) of inflammation must be identified and treated to resolve malnutrition and reduce cardiovascular risk.

The impact of heparin compounds on cellular inflammatory responses: a construct for future investigation and pharmaceutical development

Atherosclerotic disease is recognized as a chronic inflammatory disorder with intermittent and widely variable phases of cellular proliferation and heightened thrombotic activity. The multi-tiered links between inflammation, atherogenesis and thrombogenesis provide a unique opportunity for research and development of pharmaceuticals which target one or more critical pathobiologic steps (Fig. 1). The purpose of the following review on heparin compounds is to comprehensively examine the multi-cellular, pleuripotential effects of a commonly used anticoagulant drug in the context of normal and disease-altered vascular responses and illustrate possible constructs for avenues of subsequent investigation in the field of atherothrombosis. The overview is divided into five integrated parts; antiinflammatory properties of the normal vessel wall, the relationship between glycosaminoglycans and inflammation, heparin-mediated effects on cellular inflammatory responses, association between molecular weight and antiinflammatory capabilities, and oral heparin compounds for achieving prolonged cell-based inhibition.

Roles for prostaglandins in the steroidogenic response of human granulosa cells to high-density lipoproteins

In human granulosa-lutein cells, high-density lipoproteins (HDL) can stimulate progesterone synthesis. The objective of the present study was to establish whether prostaglandins (PGs) participate in the steroidogenic response to HDL. Both HDL and apolipoprotein AI (ApoAI) stimulated concentration-dependent increases in PGE2, cAMP and progesterone accumulation. The minimum concentrations of HDL and ApoAI required to elevate PGE2 production were the same as those required to stimulate cAMP accumulation and progesterone synthesis. Concentrations of PGE2 were elevated within 10 min in cells exposed to HDL and rose progressively over 24 h, whereas cAMP and progesterone were only increased significantly after 24 h of treatment with HDL. Co-treatment with prostaglandin H synthase inhibitors (meclofenamic acid and indomethacin) abolished the cAMP and progesterone responses to both HDL and ApoAI. Hence, the ability of HDL to stimulate progesterone synthesis can be mimicked by ApoAI and appears to involve increased generation of one or more luteotrophic PGs, possibly acting via cAMP.

Reconstituted high-density lipoprotein attenuates organ injury and adhesion molecule expression in a rodent model of endotoxic shock

The salutary effects of high-density lipoproteins (HDLs) in animal and human models of endotoxic shock have in the past been attributed to the ability of this lipoprotein to bind to lipopolysaccharide. However, the precise mechanisms for the protective effect of HDL are unclear. The first objective of this study was to determine the effects of HDLs on the organ injury and dysfunction associated with acute severe endotoxemia. Second, to gain insight into the mechanism of action of HDL, we also investigated the effect of HDLs on 1) the expression of P-selectin and intercellular adhesion molecule-1 in the kidneys of rats treated with endotoxin and 2) the rise in the plasma levels of tumor necrosis factor-alpha (TNF-alpha). Rats were given Escherichia coli lipopolysaccharide (6 mg/kg i.v.), pretreated with either vehicle (n = 9) or reconstituted HDL (rHDL; apolipoprotein A-I/phosphatidylcholine proteoliposomes, n = 10), and were monitored for 6 h. Here we report that rHDL attenuates the renal injury and dysfunction caused by endotoxin in the rat. In addition, rHDL reduced the degree of histological tissue injury in the lung, liver and intestine and attenuated the expression of P-selectin and intercellular adhesion molecule-1 in the renal glomerulus. Interestingly, pretreatment of rats with rHDL did not prevent the hypotension nor the rise in plasma levels of TNF-alpha (at 90 min) caused by endotoxin. Thus, rHDL reduces the organ injury/dysfunction, but does not affect the circulatory failure, nor the rise in plasma levels of TNF-alpha caused by endotoxin in the rat. We propose that the mechanisms of these beneficial effects of HDL may be related to direct inhibition of adhesion molecule expression.

Simvastatin potenciates PGI2 release induced by HDL in human VSMC: effect on Cox-2 up-regulation and MAPK signalling pathways activated by HDL

High density lipoproteins (HDL) induce prostacyclin (PGI(2)) release in vascular smooth muscle cells (VSMC) by up-regulation of cyclooxygenase-2 (Cox-2). Our goal was to analyse the mechanisms underlying this effect, and its potential modulation by HMG-CoA reductase inhibition in human VSMC. The contribution of mitogen-activated protein kinase (MAPK) signalling pathways was assessed by Western blot analysis and using specific inhibitors [PD098059 for p42/44 MAPK kinase (MEK); SB203580 for p38 MAPK or L-JNKI1 for c-Jun N-terminal kinase-1 (JNK-1)]. HDL-induced PGI(2) release was inhibited by rofecoxib (a specific Cox-2 inhibitor, 5 microM). HDL induced the early activation of p42 MAPK, p38 MAPK and JNK-1. p42/44 MAPK was the major pathway involved in both Cox-2 up-regulation and PGI(2) synthesis; p38 MAPK was also involved in both processes while JNK inhibition only affected PGI(2) synthesis. Pertussis toxin (an inhibitor of Galphai/Galphao proteins) prevented MAPK activation and inhibited both Cox-2 up-regulation and PGI(2) release. Genistein (a tyrosine kinase inhibitor) inhibited PGI(2) release without affecting MAPK activation or Cox-2 up-regulation. Simvastatin (0.1-1 microM) increased HDL-induced PGI(2) release ( approximately 45% at 1 microM) but did not significantly modify early MAPK activation or Cox-2 expression. Simvastatin alone did not significantly affect PGI(2) release. Our results suggest that mechanisms associated with G protein-coupled receptor activation, trigger Cox-2 up-regulation and PGI(2) release via multiple MAPK signalling pathways in VSMC. The mechanism is independent of tyrosine kinase receptors, although cytosolic tyrosine kinases could activate Cox-2 post-translationally. The potential contribution of HDL to vascular homeostasis, via increases in PGI(2) synthesis, could be enhanced by HMG-CoA reductase inhibitors.