Atheroprotective Effects of High-Density Lipoprotein-Associated Lysosphingolipids

Sepsis and high-density lipoproteins: Pathophysiology and potential new therapeutic targets

In 2020, sepsis has been defined a worldwide health major issue (World Health Organization). Lung, urinary tract and abdominal cavity are the preferred sites of sepsis-linked infection. Research has highlighted that the advancement of sepsis is not only related to the presence of inflammation or microbial or host pattern recognition. Clinicians and researchers now recognized that a severe immunosuppression is also a common feature found in patients with sepsis, increasing the susceptibility to secondary infections. Lipopolysaccharides (LPS) are expressed on the cell surface of Gram-negative, whereas Gram-positive bacteria express peptidoglycan (PGN) and lipoteichoic acid (LTA). The main mechanism by which LPS trigger host innate immune responses is binding to TLR4-MD2 (toll-like receptor4-myeloid differentiation factor 2), whereas, PGN and LTA are exogenous ligands of TLR2. Nucleotide-binding oligomerization domain (NOD)-like receptors are the most well-characterized cytosolic pattern recognition receptors, which bind microbial molecules, endogenous by-products and environmental triggers. It has been demonstrated that high-density lipoproteins (HDL), besides their major role in promoting cholesterol efflux, possess diverse pleiotropic properties, ranging from a modulation of the immune system to anti-inflammatory, anti-apoptotic, and anti-oxidant functions. In addition, HDL are able at i) binding LPS, preventing the activating of TLR4, and ii) inducing the expression of ATF3 (Activating transcription factor 3), a negative regulator of the TLR signalling pathways, contributing at justifying their capacity to hamper infection-based illnesses. Therefore, reconstituted HDL (rHDL), constituted by apolipoprotein A-I/apolipoprotein A-IMilano complexed with phospholipids, may be considered as a new therapeutic tool for the management of sepsis.

Sphingolipids and Atherosclerosis: The Dual Role of Ceramide and Sphingosine-1-Phosphate

Sphingolipids are bioactive molecules that play either pro- and anti-atherogenic roles in the formation and maturation of atherosclerotic plaques. Among SLs, ceramide and sphingosine-1-phosphate showed antithetic properties in regulating various molecular mechanisms and have emerged as novel potential targets for regulating the development of atherosclerosis. In particular, maintaining the balance of the so-called ceramide/S1P rheostat is important to prevent the occurrence of endothelial dysfunction, which is the trigger for the entire atherosclerotic process and is strongly associated with increased oxidative stress. In addition, these two sphingolipids, together with many other sphingolipid mediators, are directly involved in the progression of atherogenesis and the formation of atherosclerotic plaques by promoting the oxidation of low-density lipoproteins (LDL) and influencing the vascular smooth muscle cell phenotype. The modulation of ceramide and S1P levels may therefore allow the development of new antioxidant therapies that can prevent or at least impair the onset of atherogenesis, which would ultimately improve the quality of life of patients with coronary artery disease and significantly reduce their mortality.

Expression of SR-B1 receptor in breast cancer cell lines, MDAMB-468 and MCF-7: Effect on cell proliferation and apoptosis

OBJECTIVES

High-density lipoprotein (HDL) is necessary for proliferation of several cells. The growth of many kinds of cells, such as breast cancer cells (BCC) is motivated by HDL. Cellular uptake of cholesterol from HDL which increases cell growth is facilitated by scavenger receptors of the B class (SR-BI). The proliferative effect of HDL might be mediated by this receptor. It is also believed that HDL has an anti-apoptotic effect on various cell types and promotes cell growth. This study was designed to investigate SR-BI expression, proliferation and apoptotic effect of HDL on human BCC lines, MCF-7 and MDA-MB-468.

MATERIALS AND METHODS

Real-time-PCR method was used to evaluate expression of SR-BI, and cholesterol concentration was measured using a cholesterol assay kits (Pars AZ moon, Karaj, Iran). Cell viability was assessed using the MTT test. To identify cell apoptosis, the annexin V-FITC staining test and caspase-9 activity assay were applied.

RESULTS

Treatment of both cell lines (MCF-7, MDA-MB-468) with HDL results in augmentation of SR-BI mRNA expression and also elevation of the intracellular cholesterol (P<0.01). HDL induced cell proliferation, cell cycle progression, and prevented activation of caspase-9 (P<0.05). We also demonstrated that inhibition of SR-B1 by BLT-1 could reduce cell proliferation, and induction of SR-B1 receptor by quercetin increased HDL-induced proliferation in both cell lines (P<0.05).

CONCLUSION

It can be concluded that alteration in HDL levels by SR-B1 activator (Quercetin) or inhibitor (BLT-1) may affect BCC growth and apoptosis induction.

Lipoprotein receptor signalling in atherosclerosis

The founding member of the lipoprotein receptor family, low-density lipoprotein receptor (LDLR) plays a major role in the atherogenesis through the receptor-mediated endocytosis of LDL particles and regulation of cholesterol homeostasis. Since the discovery of the LDLR, many other structurally and functionally related receptors have been identified, which include low-density lipoprotein receptor-related protein (LRP)1, LRP5, LRP6, very low-density lipoprotein receptor, and apolipoprotein E receptor 2. The scavenger receptor family members, on the other hand, constitute a family of pattern recognition proteins that are structurally diverse and recognize a wide array of ligands, including oxidized LDL. Among these are cluster of differentiation 36, scavenger receptor class B type I and lectin-like oxidized low-density lipoprotein receptor-1. In addition to the initially assigned role as a mediator of the uptake of macromolecules into the cell, a large number of studies in cultured cells and in in vivo animal models have revealed that these lipoprotein receptors participate in signal transduction to modulate cellular functions. This review highlights the signalling pathways by which these receptors influence the process of atherosclerosis development, focusing on their roles in the vascular cells, such as macrophages, endothelial cells, smooth muscle cells, and platelets. Human genetics of the receptors is also discussed to further provide the relevance to cardiovascular disease risks in humans. Further knowledge of the vascular biology of the lipoprotein receptors and their ligands will potentially enhance our ability to harness the mechanism to develop novel prophylactic and therapeutic strategies against cardiovascular diseases.

Obesity-Related Changes in High-Density Lipoprotein Metabolism and Function

In obese individuals, atherogenic dyslipidemia is a very common and important factor in the increased risk of cardiovascular disease. Adiposity-associated dyslipidemia is characterized by low high-density lipoprotein cholesterol (HDL-C) levels and an increase in triglyceride-rich lipoproteins. Several factors and mechanisms are involved in lowering HDL-C levels in the obese state and HDL quantity and quality is closely related to adiponectin levels and the bioactive lipid sphingosine-1-phosphate. Recent studies have shown that obesity profoundly alters HDL metabolism, resulting in altered HDL subclass distribution, composition, and function. Importantly, weight loss through gastric bypass surgery and Mediterranean diet, especially when enriched with virgin olive oil, is associated with increased HDL-C levels and significantly improved metrics of HDL function. A thorough understanding of the underlying mechanisms is crucial for a better understanding of the impact of obesity on lipoprotein metabolism and for the development of appropriate therapeutic approaches. The objective of this review article was to summarize the newly identified changes in the metabolism, composition, and function of HDL in obesity and to discuss possible pathophysiological consequences.

Lipid Profile Alterations during Fingolimod Treatment in Multiple Sclerosis Patients

Fingolimod reduces inflammatory activity in multiple sclerosis (MS) by acting as a functional antagonist of sphingosine 1-phosphate (S1P) receptors. It has been suggested that S1P might also contribute to the antiatherogenic effect of high-density lipoprotein (HDL). We conducted a retrospective observational study using data of 72 MS patients from two Finnish hospital districts to find out whether lipid profiles change during treatment with fingolimod. A mixed-effects model with patient as a random effect was used to analyze lipid profile alterations. We found a statistically significant elevation in both total cholesterol (0.12 mmol/L per year) and HDL (0.04 mmol/L per year) during a median follow-up of 12 months, while low-density lipoprotein (LDL) and triglycerides remained unchanged. Since the mean elevation observed in both lipid values seems to be modest, we suggest that routine lipid profile monitoring is unnecessary during fingolimod treatment in MS patients without pre-existing cardiovascular comorbidities. Graphical abstract.

Lyso-diacylglyceryltrimethylhomoserine (lyso-DGTS) isolated from Nannochloropsis microalgae improves high-density lipoprotein (HDL) functions

Many population studies have shown that blood concentrations of high-density lipoprotein (HDL) cholesterol are inversely correlated with risk of cardiovascular disease (CVD). However, in recent studies, increasing blood HDL cholesterol concentrations failed to reduce CVD events. On the other hand, studies suggest that improving HDL quality can be a more efficient tool for assessing atherosclerotic risk than simply measuring blood HDL cholesterol concentration. Thus, improving HDL activity using natural substances might be a useful therapeutic approach to reducing CVD risk. We previously isolated a novel active compound from Nannochloropsis microalgae termed lyso-diacylglyceryltrimethylhomoserine (lyso-DGTS), which increased activity of paraoxonase 1, the main antioxidant enzyme associated with HDL. Here we examined the effect of lyso-DGTS on HDL quality and function. Tryptophan-fluorescence-quenching assay showed that lyso-DGTS interacts spontaneously with the entire HDL lipoprotein and with apolipoprotein A1 (ApoA1), the major structural and functional HDL protein, with high affinity (K_a = 2.17 × 10⁴  M^-1 at 37°C). Lyso-DGTS added to HDL and to ApoA1 increased cholesterol efflux from macrophage cells, the main antiatherogenic function of HDL, dose-dependently, and significantly increased HDL's ability to induce nitric oxide production from endothelial cells. In-vivo supplementation of lyso-DGTS to the circulation of mice fed a high-fat diet via osmotic mini-pumps implanted subcutaneously enhanced HDL anti-inflammatory effect significantly as compared to controls. Our findings suggest that lyso-DGTS may have a beneficial effect in decreasing atherosclerosis risk by interacting with HDL particles and improving their quality and antiatherogenic functions.

Role of Sphingosylphosphorylcholine in Tumor and Tumor Microenvironment

Sphingosylphosphorylcholine (SPC) is a unique type of lysosphingolipid found in some diseases, and has been studied in cardiovascular, neurological, and inflammatory phenomena. In particular, SPC’s studies on cancer have been conducted mainly in terms of effects on cancer cells, and relatively little consideration has been given to aspects of tumor microenvironment. This review summarizes the effects of SPC on cancer and tumor microenvironment, and presents the results and prospects of modulators that regulate the various actions of SPC.

Lipoproteins in Atherosclerosis Process

BACKGROUND

Dyslipidaemias is a recognized risk factor for atherosclerosis, however, new evidence brought to light by trials investigating therapies to enhance HDLcholesterol have suggested an increased atherosclerotic risk when HDL-C is high.

RESULTS

Several studies highlight the central role in atherosclerotic disease of dysfunctional lipoproteins; oxidised LDL-cholesterol is an important feature, according to "oxidation hypothesis", of atherosclerotic lesion, however, there is today a growing interest for dysfunctional HDL-cholesterol. The target of our paper is to review the functions of modified and dysfunctional lipoproteins in atherogenesis.

CONCLUSION

Taking into account the central role recognized to dysfunctional lipoproteins, measurements of functional features of lipoproteins, instead of conventional routine serum evaluation of lipoproteins, could offer a valid contribution in experimental studies as in clinical practice to stratify atherosclerotic risk.

Lyso-DGTS lipid isolated from microalgae enhances PON1 activities in vitro and in vivo, increases PON1 penetration into macrophages and decreases cellular lipid accumulation

High-density lipoprotein (HDL) plays an important role in preventing atherosclerosis. The antioxidant effect of HDL is mostly associated with paraoxonase 1 (PON1) activity. Increasing PON1 activity using nutrients might improve HDL function and quality and thus, decrease atherosclerotic risk. We previously isolated and identified a novel active compound, lyso-DGTS (C20:5,0) from Nannochloropsis sp. ethanol extract. In the present study, its effect on PON1 activities was examined and the mechanism by which the compound affects PON1 activity was explored. Lyso-DGTS elevated recombinant PON1 (rePON1) lactonase and esterase activities in a dose- and time-responsive manner, and further stabilized and preserved rePON1 lactonase activity. Incubation of lyso-DGTS with human serum for 4 h at 37 °C also increased PON1 lactonase activity in a dose-responsive manner. Using tryptophan-fluorescence-quenching assay, lyso-DGTS was found to interact with rePON1 spontaneously with negative free energy (ΔG = -22.87 kJ mol^-1 at 25 °C). Thermodynamic parameters and molecular modeling calculations showed that the main interaction of lyso-DGTS with the enzyme is through a hydrogen bond with supporting van der Waals interactions. Furthermore, lyso-DGTS significantly increased rePON1 influx into macrophages and prevented lipid accumulation in macrophages stimulated with oxidized low-density lipid dose-dependently. In vivo supplementation of lyso-DGTS to the circulation of mice fed a high-fat diet via osmotic mini-pumps implanted subcutaneously significantly increased serum PON1 lactonase activity and decreased serum glucose concentrations to the level of mice fed a normal diet. Our findings suggest a beneficial effect of lyso-DGTS on increasing PON1 activity and thus, improving HDL quality and atherosclerotic risk factors. © 2018 BioFactors, 44(3):299-310, 2018.

The role of HDL in plaque stabilization and regression: basic mechanisms and clinical implications

On the basis of studies that extend back to the early 1900s, regression and stabilization of atherosclerosis in humans has progressed from being a concept to one that is achievable. Successful attempts at regression generally applied robust measures to improve plasma lipoprotein profiles. Possible mechanisms responsible for lesion shrinkage include decreased retention of atherogenic apolipoprotein B within the arterial wall, efflux of cholesterol and other toxic lipids from plaques, emigration of lesional foam cells out of the arterial wall, and influx of healthy phagocytes that remove necrotic debris as well as other components of the plaque. Currently available clinical agents, however, still fail to stop most cardiovascular events. For years, HDL has been considered the 'good cholesterol.' Clinical intervention studies to causally link plasma HDL-C levels to decreased progression or to the regression of atherosclerotic plaques are relatively few because of the lack of therapeutic agents that can selectively and potently increase HDL-C. The negative results of studies that were carried out have led to uncertainty as to the role that HDL plays in atherosclerosis. It is becoming clearer, however, that HDL function rather than quantity is most crucial and, therefore, discovery of agents that enhance the quality of HDL should be the goal.

S1P in HDL promotes interaction between SR-BI and S1PR1 and activates S1PR1-mediated biological functions: calcium flux and S1PR1 internalization

HDL normally transports about 50-70% of plasma sphingosine 1-phosphate (S1P), and the S1P in HDL reportedly mediates several HDL-associated biological effects and signaling pathways. The HDL receptor, SR-BI, as well as the cell surface receptors for S1P (S1PRs) may be involved partially and/or completely in these HDL-induced processes. Here we investigate the nature of the HDL-stimulated interaction between the HDL receptor, SR-BI, and S1PR1 using a protein-fragment complementation assay and confocal microscopy. In both primary rat aortic vascular smooth muscle cells and HEK293 cells, the S1P content in HDL particles increased intracellular calcium concentration, which was mediated by S1PR1. Mechanistic studies performed in HEK293 cells showed that incubation of cells with HDL led to an increase in the physical interaction between the SR-BI and S1PR1 receptors that mainly occurred on the plasma membrane. Model recombinant HDL (rHDL) particles formed in vitro with S1P incorporated into the particle initiated the internalization of S1PR1, whereas rHDL without supplemented S1P did not, suggesting that S1P transported in HDL can selectively activate S1PR1. In conclusion, these data suggest that S1P in HDL stimulates the transient interaction between SR-BI and S1PRs that can activate S1PRs and induce an elevation in intracellular calcium concentration.

Human carotid atherosclerotic plaque protein(s) change HDL protein(s) composition and impair HDL anti-oxidant activity

High density lipoprotein (HDL) anti-atherogenic functions are closely associated with cardiovascular disease risk factor, and are dictated by its composition, which is often affected by environmental factors. The present study investigates the effects of the human carotid plaque constituents on HDL composition and biological functions. To this end, human carotid plaques were homogenized and incubated with HDL. Results showed that after incubation, most of the apolipoprotein A1 (Apo A1) protein was released from the HDL, and HDL diameter increased by an average of approximately 2 nm. In parallel, HDL antioxidant activity was impaired. In response to homogenate treatment HDL could not prevent the accelerated oxidation of LDL caused by the homogenate. Boiling of the homogenate prior to its incubation with HDL abolished its effects on HDL composition changes. Moreover, tryptophan fluorescence quenching assay revealed an interaction between plaque component(s) and HDL, an interaction that was reduced by 50% upon using pre-boiled homogenate. These results led to hypothesize that plaque protein(s) interacted with HDL-associated Apo A1 and altered the HDL composition. Immuno-precipitation of Apo A1 that was released from the HDL after its incubation with the homogenate revealed a co-precipitation of three isomers of actin. However, beta-actin alone did not significantly affect the HDL composition, and yet the active protein within the plaque was elusive. In conclusion then, protein(s) in the homogenate interact with HDL protein(s), leading to release of Apo A1 from the HDL particle, a process that was associated with an increase in HDL diameter and with impaired HDL anti-oxidant activity.

Therapeutic applications of reconstituted HDL: When structure meets function

Reconstituted forms of HDL (rHDL) are under development for infusion as a therapeutic approach to attenuate atherosclerotic vascular disease and to reduce cardiovascular risk following acute coronary syndrome and ischemic stroke. Currently available rHDL formulations developed for clinical use contain apolipoprotein A-I (apoA-I) and one of the major lipid components of HDL, either phosphatidylcholine or sphingomyelin. Recent data have established that quantitatively minor molecular constituents of HDL particles can strongly influence their anti-atherogenic functionality. Novel rHDL formulations displaying enhanced biological activities, including cellular cholesterol efflux, may therefore offer promising prospects for the development of HDL-based, anti-atherosclerotic therapies. Indeed, recent structural and functional data identify phosphatidylserine as a bioactive component of HDL; the content of phosphatidylserine in HDL particles displays positive correlations with all metrics of their functionality. This review summarizes current knowledge of structure-function relationships in rHDL formulations, with a focus on phosphatidylserine and other negatively-charged phospholipids. Mechanisms potentially underlying the atheroprotective role of these lipids are discussed and their potential for the development of HDL-based therapies highlighted.

Network-Based Analysis on Orthogonal Separation of Human Plasma Uncovers Distinct High Density Lipoprotein Complexes

High density lipoprotein (HDL) particles are blood-borne complexes whose plasma levels have been associated with protection from cardiovascular disease (CVD). Recent studies have demonstrated the existence of distinct HDL subspecies; however, these have been difficult to isolate and characterize biochemically. Here, we present the first report that employs a network-based approach to systematically infer HDL subspecies. Healthy human plasma was separated into 58 fractions using our previously published three orthogonal chromatography techniques. Similar local migration patterns among HDL proteins were captured with a novel similarity score, and individual comigration networks were constructed for each fraction. By employing a graph mining algorithm, we identified 183 overlapped cliques, among which 38 were further selected as candidate HDL subparticles. Each of these 38 subparticles had at least two literature supports. In addition, GO function enrichment analysis showed that they were enriched with fundamental biological and CVD protective functions. Furthermore, gene knockout experiments in mouse model supported the validity of these subparticles related to three apolipoproteins. Finally, analysis of an apoA-I deficient human patient's plasma provided additional support for apoA-I related complexes. Further biochemical characterization of these putative subspecies may facilitate the mechanistic research of CVD and guide targeted therapeutics aimed at its mitigation.

Dietary Njavara rice bran oil reduces experimentally induced hypercholesterolaemia by regulating genes involved in lipid metabolism

The present study was carried out to evaluate the anti-atherogenic effect of Njavara rice bran oil (NjRBO) on atherosclerosis by modulating enzymes and genes involved in lipid metabolism in rats fed a high-cholesterol diet (HCD). Adult male rats (Sprague–Dawley strain, weighing 100–120 g) were divided into three groups of nine animals each. Group I served as the control, group II were fed a HCD and group III were fed a HCD and NjRBO (100 mg/kg body weight). The study duration was 60 d. Serum and tissue lipid profile, atherogenic index, enzymes of lipid metabolism, plasma C-reactive protein levels, serum paraoxonase and arylesterase activities, thiobarbituric acid-reactive substances, gene and protein expression of paraoxonase 1 (PON1), PPARα, ATP-binding cassette transporter A1 (ABCA1), apoB and apoA1 in the liver were quantified. Total cholesterol, TAG, phospholipid, NEFA, LDL-cholesterol concentrations in the serum and liver, lipogenic enzyme activities, hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity and atherogenic index were significantly increased in HCD-fed rats, but they decreased after treatment with NjRBO. HDL-cholesterol level and lecithin cholesterol acyl transferase activity were increased in the NjRBO-treated group, but decreased in the HCD-fed group. The expression levels of ABCA1, apoA1, PON1 and PPARα were found to be significantly increased in NjRBO-treated group compared with the HCD-fed group; however, the expression level of apoB was found to be higher in HCD-fed group and lower in the NjRBO-treated group. These data suggest that NjRBO possesses an anti-atherogenic property by modulating lipid metabolism and up-regulating genes involved in reverse cholesterol transport and antioxidative defence mechanism through the induction of the gene expressionPON1.

HDL particle subpopulations: Focus on biological function

Low levels of high-density lipoprotein-cholesterol (HDL-C) constitute an independent biomarker of cardiovascular morbi-mortality. However, recent advances have drastically modified the classical and limited view of HDL as a carrier of 'good cholesterol', and have revealed unexpected levels of complexity in the circulating HDL particle pool. HDL particles are indeed highly heterogeneous in structure, intravascular metabolism and biological activity. This review describes recent progress in our understanding of HDL subpopulations and their biological activities, and focuses on relationships between the structural, compositional and functional heterogeneity of HDL particles.

Loss of sex difference in high-density lipoprotein cholesterol in diabetic women during acute stress

CONTEXT

The gender gap in high-density lipoprotein cholesterol (HDL-C) is well documented in health and also maintained in diverse chronic conditions, including menopause and diabetes. The mechanism for this difference in HDL-C and its regulation is not well understood. We evaluated whether this gender gap is maintained during acute stress.

SETTING AND DESIGN

Diabetic patients with metabolic decompensation (n=179) were studied in the fasting state within 24 hours of admission to hospital, and again at outpatient follow-up. Fasting lipids and measures of glycemic control were evaluated on both occasions. The population was predominately minority, 78% Hispanic or African American.

RESULTS

During admission, fasting lipid concentrations were not different in women (W) (n = 88) and men (M) (n = 91); serum total cholesterol (total-C), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and HDL-C were similar. Glycemic control was also similar; hemoglobin A1c (A1C) and serum glucose at presentation to hospital were not different in men and women. Compared with a subset of patients with pre-admission data (W, 35; M, 24), a decline of HDL-C was observed, greater in women (P = .005). At outpatient follow-up after admission, median duration approximately 4 months in each group (P = .39), changes in TG, LDL-C, and total-C from baseline admission were not different in men and women. In contrast, whereas HDL-C increased in both groups, the increase (median [interquartile range]) was significantly greater in women, 11 (4, 23) vs 6 (-1, 15) mg/dL (P < .003). This larger increase restored the gender gap in fasting HDL-C, 48 (39, 61) and 41 (36, 49) mg/dL in women and men at follow-up (P < .002). A1C improved similarly in each group.

CONCLUSIONS

The sex difference in HDL-C levels is lost at time of admission to hospital in patients with diabetes, and returns when acute stress has resolved. These results raise the possibility that recurrent episodes of acute stress may lead to cumulative loss of the HDL-C advantage in women.

High-density lipoprotein subfractions: current views and clinical practice applications

High-density lipoprotein (HDL) is astonishingly complex, but the de facto standard for its measurement has been remarkably simple: total cholesterol content. It is time to prioritize higher-resolution HDL measurement techniques that capture better the biologically and clinically important characteristics of HDL. Scientific advances have ushered in a new era in which we view HDL in terms of its subfractions, particle structure, metabolism, and functional integration of its proteome and lipidome. HDL subfractions appear to be associated with function. In general, smaller, denser HDL3 is more tightly linked to favorable atheroprotective functions and clinical outcomes. Techniques to measure the cholesterol content or particle concentrations of HDL subfractions are available clinically. In the future, we anticipate subfractionating HDL based on its functional properties.

Small, dense high-density lipoprotein-3 particles are enriched in negatively charged phospholipids: relevance to cellular cholesterol efflux, antioxidative, antithrombotic, anti-inflammatory, and antiapoptotic functionalities

OBJECTIVE

High-density lipoprotein (HDL) displays multiple atheroprotective activities and is highly heterogeneous in structure, composition, and function; the molecular determinants of atheroprotective functions of HDL are incompletely understood. Because phospholipids represent a major bioactive lipid component of HDL, we characterized the phosphosphingolipidome of major normolipidemic HDL subpopulations and related it to HDL functionality.

APPROACH AND RESULTS

Using an original liquid chromatography-mass spectrometry/mass spectrometry methodology for phospholipid and sphingolipid profiling, 162 individual molecular lipid species were quantified across the 9 lipid subclasses, in the order of decreasing abundance, phosphatidylcholine>sphingomyelin>lysophosphatidylcholine>phosphatidylethanolamine>phosphatidylinositol>ceramide>phosphatidylserine>phosphatidylglycerol>phosphatidic acid. When data were expressed relative to total lipid, the contents of lysophosphatidylcholine and of negatively charged phosphatidylserine and phosphatidic acid increased progressively with increase in hydrated density of HDL, whereas the proportions of sphingomyelin and ceramide decreased. Key biological activities of HDL subpopulations, notably cholesterol efflux capacity from human THP-1 macrophages, antioxidative activity toward low-density lipoprotein oxidation, antithrombotic activity in human platelets, cell-free anti-inflammatory activity, and antiapoptotic activity in endothelial cells, were predominantly associated with small, dense, protein-rich HDL3. The biological activities of HDL particles were strongly intercorrelated, exhibiting significant correlations with multiple components of the HDL phosphosphingolipidome. Specifically, the content of phosphatidylserine revealed positive correlations with all metrics of HDL functionality, reflecting enrichment of phosphatidylserine in small, dense HDL3.

CONCLUSIONS

Our structure-function analysis thereby reveals that the HDL lipidome may strongly affect atheroprotective functionality.

HDL-C: clinical equipoise and vascular endothelial function

Serum levels of HDL cholesterol represent a strong, and coherent cardiovascular risk marker seen across all populations, with higher levels of HDL cholesterol being associated with decreased incidence of coronary artery disease. The cardiovascular protective effects of HDL particles are attributed, in great part, to the ability of HDL particles to promote cellular cholesterol efflux from lipid-laden macrophages within the atherosclerotic plaque. HDL also has pleiotropic effects that protect the vascular wall, at least in vitro. These effects include potent anti-inflammatory and antioxidant properties and the modulation of vascular endothelial function. The mechanisms by which HDL exert their function on the vascular endothelium is dependent on HDL particle size, protein (proteome) and lipid (lipidome). The cooperative binding of HDL via SR-BI and G-coupled S1PR1-5 receptors mediates phosphorylation of endothelial nitric oxide synthase at residue 1177 through AKT signaling, preventing uncoupling of NADPH oxidation and nitric oxide synthesis and increasing endothelial nitric oxide synthase abundance. Furthermore, HDL can modulate the activation of NF-κB and the expression of cell adhesion molecules, an early step in endothelial dysfunction. In the present review the authors will focus on the controversies surrounding HDL, clinical treatments and vascular endothelial functions of HDL.

Unraveling the complexities of the HDL lipidome

Plasma high density lipoproteins (HDL) are small, dense, protein-rich particles compared with other lipoprotein classes; roughly half of total HDL mass is accounted for by lipid components. Phospholipids predominate in the HDL lipidome, accounting for 40-60% of total lipid, with lesser proportions of cholesteryl esters (30-40%), triglycerides (5-12%), and free cholesterol (5-10%). Lipidomic approaches have provided initial insights into the HDL lipidome with identification of over 200 individual molecular lipids species in normolipidemic HDL. Plasma HDL particles, however, reveal high levels of structural, compositional, and functional heterogeneity. Establishing direct relationships between HDL structure, composition, and atheroprotective functions bears the potential to identify clinically relevant HDL subpopulations. Furthermore, development of HDL-based therapies designed to target beneficial subspecies within the circulating HDL pool can be facilitated using this approach. HDL lipidomics can equally contribute to the identification of biomarkers of both normal and deficient HDL functionality, which may prove useful as biomarkers of cardiovascular risk. However, numerous technical issues remain to be addressed in order to make such developments possible. With all technical questions resolved, quantitative analysis of the molecular components of the HDL lipidome will contribute to expand our knowledge of cardiovascular and metabolic diseases.

Class II phosphoinositide 3-kinases contribute to endothelial cells morphogenesis

The question of whether the distinct isoforms of the family of enzymes phosphoinositide 3-kinases (PI3Ks) play redundant roles within a cell or whether they control distinct cellular processes or distinct steps within the same cellular process has gained considerable importance in the recent years due to the development of inhibitors able to selectively target individual isoforms. It is important to understand whether inhibition of one PI3K can result in compensatory effect from other isoform(s) and therefore whether strategies aimed at simultaneously blocking more than one PI3K may be needed. In this study we investigated the relative contribution of distinct PI3K isoforms to endothelial cells (EC) functions specifically regulated by the sphingolipid sphingosine-1-phosphate (S1P) and by high density lipoproteins (HDL), the major carrier of S1P in human plasma. Here we show that a co-ordinated action of different PI3Ks is required to tightly regulate remodelling of EC on Matrigel, a process dependent on cell proliferation, apoptosis and migration. The contribution of each isoform to this process appears to be distinct, with the class II enzyme PI3K-C2β and the class IB isoform p110γ mainly regulating the S1P- and HDL-dependent EC migration and PI3K-C2α primarily controlling EC survival. Data further indicate that PI3K-C2β and p110γ control distinct steps involved in cell migration supporting the hypothesis that different PI3Ks regulate distinct cellular processes.

Immunomodulatory type II natural killer T lymphocytes in health and disease

Natural killer T (NKT) lymphocytes are αβ T cells activated by lipid-based ligands presented on the non-polymorphic CD1d-molecule. Type I NKT cells that carry an invariant Vα14 (in the mouse) or Vα24 (in humans) T cell receptor α-chain rearrangement have received significant attention for their involvement in a diversity of immune reactions. Their sister population, CD1d-restricted type II NKT cells, has been more difficult to study because of the lack of molecular markers that specify these cells. In the last few years, however, significant progress has been made, demonstrating that type II NKT cells have unique functions in immune responses to tumours and infections, in autoimmunity, obesity and graft-versus-host disease. Type II NKT cells appear more frequent than type I NKT cells in humans and accumulate in certain diseases such as ulcerative colitis, hepatitis and multiple myeloma. Recently, novel type II NKT cell ligands have been identified, and it is becoming clear that the type II NKT cell population may be oligoclonal. Here, we review the recent progress in the study of type II NKT cells, supporting the view that type II NKT cells may be attractive targets for immunotherapy.

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.

Fenofibrate increases high-density lipoprotein and sphingosine 1 phosphate concentrations limiting abdominal aortic aneurysm progression in a mouse model

There are currently no acceptable treatments to limit progression of abdominal aortic aneurysm (AAA). Increased serum concentrations of high-density lipoprotein (HDL) are associated with reduced risk of developing an AAA. The present study aimed to assess the effects of fenofibrate on aortic dilatation in a mouse model of AAA. Male low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice were maintained on a high-fat diet for 3 weeks followed by 6 weeks of oral administration of vehicle or fenofibrate. From 14 to 18 weeks of age, all mice were infused with angiotensin II (AngII). At 18 weeks of age, blood and aortas were collected for assessment of serum lipoproteins, aortic pathology, aortic Akt1 and endothelial nitric oxide synthase (eNOS) activities, immune cell infiltration, eNOS and inducible NOS (iNOS) expression, sphingosine 1 phosphate (S1P) receptor status, and apoptosis. Mice receiving fenofibrate had reduced suprarenal aortic diameter, reduced aortic arch Sudan IV staining, higher serum HDL levels, increased serum S1P concentrations, and increased aortic Akt1 and eNOS activities compared with control mice. Macrophages, T lymphocytes, and apoptotic cells were less evident and eNOS, iNOS, and S1P receptors 1 and 3 were up-regulated in aortas from mice receiving fenofibrate. The present findings suggest that fenofibrate antagonizes AngII-induced AAA and atherosclerosis by up-regulating serum HDL and S1P levels, with associated activation of NO-producing enzymes and reduction of aortic inflammation.

Effect of sphingosine 1-phosphate (S1P) receptor agonists FTY720 and CYM5442 on atherosclerosis development in LDL receptor deficient (LDL-R⁻/⁻) mice

OBJECTIVES

Sphingosine 1-phosphate (S1P)--a lysosphingolipid present in HDL--exerts atheroprotective effects in vitro, while FTY720, a non-selective S1P mimetic inhibits atherosclerosis in LDL receptor-deficient (LDL-R⁻/⁻) mice under conditions of severe hypercholesterolemia. We here examined the effect of FTY720 and a selective S1P receptor type 1 agonist CYM5442 on atherosclerosis in moderately hypercholesterolemic LDL-R⁻/⁻ mice.

METHODS AND RESULTS

LDL-R⁻/⁻ mice fed Western diet (0.25% cholesterol) were given FTY720 (0.4 mg/kg/day) or CYM5442 (2.0 mg/kg/day) for 18 weeks. FTY720 but not CYM5422 persistently lowered blood lymphocytes, depleted CD4⁺ and CD8⁺ T cells in spleen and lymph nodes, and reduced splenocyte IL-2 secretion. However, both compounds reduced the activity of splenic and peritoneal macrophages as inferred from the down-regulated CD68 and MHC-II expression in CD11b⁺ cells and the reduced IL-6 secretion in response to LPS, respectively. CYM5442 and FTY720 reduced weight gain, white adipose tissue depots and fasting glucose suggesting improvement of metabolic control, but failed to influence atherosclerosis in LDL-R⁻/⁻ mice.

CONCLUSION

Despite down-regulating macrophage function and--in case of FTY720--altering lymphocyte distribution CYM5442 and FTY720 fail to affect atherosclerosis in moderately hypercholesterolemic LDL-R⁻/⁻ mice. We hypothesize that S1P mimetics exert atheroprotective effects only under conditions of increased cholesterol burden exacerbating vascular inflammation.

Plasma levels of sphingosine-1-phosphate and apolipoprotein M in patients with monogenic disorders of HDL metabolism

BACKGROUND

Apolipoprotein M (apoM) has been identified as a specific sphingosine-1-phosphate (S1P) binding protein of HDL.

OBJECTIVES AND METHODS

To investigate the in vivo effects of disturbed apoM or HDL metabolism we quantified S1P and apoM in plasmas of wild-type, apoM-knock-out, and apoM transgenic mice as well as 50 patients with seven different monogenic disorders of HDL metabolism and their 51 unaffected relatives.

RESULTS

Compared to wild type mice, S1P plasma levels in apoM knock-out and apoM transgenic mice were decreased by 30% and increased by 270%, respectively. Compared to family controls, S1P and apoM levels in apoB-depleted plasma were significantly decreased by in average 34% and 12%, respectively, in heterozygous carriers of mutations in APOA1, LCAT or ABCA1, and by 70% and 48%, respectively, in carriers of two defective alleles in LCAT or ABCA1. Heterozygous mutations in CETP, SCARB1, LIPC, or LIPG did not significantly affect S1P or apoM concentrations. Albumin-corrected molar S1P-to-apoM ratios varied from 0.12 to 0.8 (median 0.3) and were not affected by any mutation. S1P levels in apoB-depleted plasma correlated significantly with HDL-cholesterol and less so with apoM both if apoA-I plasma concentrations were below the median.

CONCLUSION

In the context of previous data, our findings can be explained by the existence of a specific apoM and S1P containing HDL subclass which contains a considerable molar excess of apoM over S1P and is critically determined by apoA-I up to a threshold concentration around the median found in a Caucasian population.

Biological activities of HDL subpopulations and their relevance to cardiovascular disease

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

HDL and sphingosine-1-phosphate activate stat3 in prostate cancer DU145 cells via ERK1/2 and S1P receptors, and promote cell migration and invasion

BACKGROUND

Androgen deprivation therapy in men with prostate cancer leads to a significant increase of high density lipoprotein (HDL), but the effect of HDL on prostate cancer is unknown. Recently, HDL, which transports sphingosine-1-phosphate (S1P), was reported to activate signal transducer and activator of transcription 3 (Stat3) in cardiomyocytes. In this study, we examined the effect of HDL and S1P on Stat3 activation in prostate cancer cells and the involvement of S1P receptors in this process in three prostate cancer cell lines (PC-3, LNCaP, and DU145).

METHODS

Discordial reconstituted(r) HDL containing POPC, apoA-1, and S1P were prepared by the cholate dialysis method. The phosphorylations of Stat3, ERK1/2, and Akt were detected by Western blotting. Cell migration and invasion were determined by wound-healing assay and matrigel invasion chamber assay.

RESULTS

HDL increased serine 727 phosphorylation of Stat3, but not tyrosine 705 only in DU145 cells. S1P and rHDL-S1P also induced the phosphorylation, but not rHDL without S1P. They also induced DU145 cells migration and invasion. PD98059, a MEK inhibitor, and pertussis toxin, a Gi inhibitor, attenuated HDL-, S1P-, and rHDL-S1P-induced Stat3 phosphorylation, whereas LY294002, a PI3K inhibitor, had no effect. Concerning S1P receptors, S1P1 expression was much lower than S1P2 and S1P3 in DU145 cells. Both JTE013, a S1P2 antagonist, and VPC23019, a S1P1/S1P3 antagonist, attenuated HDL-, S1P-, and rHDL-S1P-induced Stat3 phosphorylations and cell migrations.

CONCLUSIONS

These results suggest that the change in HDL plasma levels by androgen deprivation therapy may alter prostate cancer growth and metastasis.

Intravenous sphingosylphosphorylcholine protects ischemic and postischemic myocardial tissue in a mouse model of myocardial ischemia/reperfusion injury

HDL, through sphingosine-1-phosphate (S1P), exerts direct cardioprotective effects on ischemic myocardium. It remains unclear whether other HDL-associated sphingophospholipids have similar effects. We therefore examined if HDL-associated sphingosylphosphorylcholine (SPC) reduces infarct size in a mouse model of transient myocardial ischemia/reperfusion. Intravenously administered SPC dose-dependently reduced infarct size after 30 minutes of myocardial ischemia and 24 hours reperfusion compared to controls. Infarct size was also reduced by postischemic, therapeutical administration of SPC. Immunohistochemistry revealed reduced polymorphonuclear neutrophil recruitment to the infarcted area after SPC treatment, and apoptosis was attenuated as measured by TUNEL. In vitro, SPC inhibited leukocyte adhesion to TNFα-activated endothelial cells and protected rat neonatal cardiomyocytes from apoptosis. S1P₃ was identified as the lysophospholipid receptor mediating the cardioprotection by SPC, since its effect was completely absent in S1P₃-deficient mice. We conclude that HDL-associated SPC directly protects against myocardial reperfusion injury in vivo via the S1P₃ receptor.

Adipose tissue and ceramide biosynthesis in the pathogenesis of obesity

Although obesity is a complex metabolic disorder often associated with insulin resistance, hyperinsulinemia and Type 2 diabetes, as well as with accelerated atherosclerosis, the molecular changes in obesity that promote these disorders are not completely understood. Several mechanisms have been proposed to explain how increased adipose tissue mass affects whole body insulin resistance and cardiovascular risk. One theory is that increased adipose derived inflammatory cytokines induces a chronic inflammatory state that not only increases cardiovascular risk, but also antagonizes insulin signaling and mitochondrial function and thereby impair glucose hemostasis. Another suggests that lipid accumulation in nonadipose tissues not suited for fat storage leads to the buildup of bioactive lipids that inhibit insulin signaling and metabolism. Recent evidence demonstrates that sphingolipid metabolism is dysregulated in obesity and specific sphingolipids may provide a common pathway that link excess nutrients and inflammation to increased metabolic and cardiovascular risk. This chapter will focus primarily on the expression and regulation of adipose and plasma ceramide biosynthesis in obesity and, its potential contribution to the pathogenesis of obesity and the metabolic syndrome.

Pharmacomodulation of high-density lipoprotein metabolism as a therapeutic intervention for atherosclerotic disease

The high-density lipoproteins (HDLs) are produced by the liver and small intestine as well as on the surface of lipid-enriched macrophages in the subendothelial space of arterial walls. Unlike the apo B100-containing lipoproteins, the HDLs are uniquely antiatherogenic. Based on prospective observational studies performed throughout the world, there is a consistent inverse relationship between serum levels of HDLs and risk for cardiovascular events: low levels of high-density lipoprotein-cholesterol (HDL-C) are associated with increased risk, whereas high levels are usually associated with reduced risk for myocardial infarction, ischemic stroke, and cardiovascular mortality. Post hoc analyses of a number of studies using statins and fibrates have shown that raising serum HDL-C correlates with a reduction in risk for cardiovascular morbidity and mortality. Given these observations, enormous resources are being committed to the development of novel means by which to pharmacologically increase rates of HDL biosynthesis, modulate the functionality of HDL, and to promote reverse cholesterol transport with intravenous infusions of HDL particles.

Role of sphingosine 1-phosphate in anti-atherogenic actions of high-density lipoprotein

The reverse cholesterol transport mediated by high-density lipoprotein (HDL) is an important mechanism for maintaining body cholesterol, and hence, the crucial anti-atherogenic action of the lipoprotein. Recent studies, however, have shown that HDL exerts a variety of anti-inflammatory and anti-atherogenic actions independently of cholesterol metabolism. The present review provides an overview of the roles of sphingosine 1-phosphate (S1P)/S1P receptor and apolipoprotein A-I/scavenger receptor class B type I systems in the anti-atherogenic HDL actions. In addition, the physiological significance of the existence of S1P in the HDL particles is discussed.

Sphingosine-1-phosphate receptor-2 deficiency leads to inhibition of macrophage proinflammatory activities and atherosclerosis in apoE-deficient mice

Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid that has pleiotropic effects in a variety of cell types including ECs, SMCs, and macrophages, all of which are central to the development of atherosclerosis. It may therefore exert stimulatory and inhibitory effects on atherosclerosis. Here, we investigated the role of the S1P receptor S1PR2 in atherosclerosis by analyzing S1pr2-/- mice with an Apoe-/- background. S1PR2 was expressed in macrophages, ECs, and SMCs in atherosclerotic aortas. In S1pr2-/-Apoe-/- mice fed a high-cholesterol diet for 4 months, the area of the atherosclerotic plaque was markedly decreased, with reduced macrophage density, increased SMC density, increased eNOS phosphorylation, and downregulation of proinflammatory cytokines compared with S1pr2+/+Apoe-/- mice. Bone marrow chimera experiments indicated a major role for macrophage S1PR2 in atherogenesis. S1pr2-/-Apoe-/- macrophages showed diminished Rho/Rho kinase/NF-κB (ROCK/NF-κB) activity. Consequently, they also displayed reduced cytokine expression, reduced oxidized LDL uptake, and stimulated cholesterol efflux associated with decreased scavenger receptor expression and increased cholesterol efflux transporter expression. S1pr2-/-Apoe-/- ECs also showed reduced ROCK and NF-κB activities, with decreased MCP-1 expression and elevated eNOS phosphorylation. Pharmacologic S1PR2 blockade in S1pr2+/+Apoe-/- mice diminished the atherosclerotic plaque area in aortas and modified LDL accumulation in macrophages. We conclude therefore that S1PR2 plays a critical role in atherogenesis and may serve as a novel therapeutic target for atherosclerosis.

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.

High-density lipoprotein induces proliferation and migration of human prostate androgen-independent cancer cells by an ABCA1-dependent mechanism

Androgen deprivation therapy for prostate cancer leads to a significant increase of high-density lipoprotein (HDL), which is generally viewed as beneficial, particularly for cardiovascular disease, but the effect of HDL on prostate cancer is unknown. In this study, we investigated the effect of HDL on prostate cancer cell proliferation, migration, intracellular cholesterol levels, and the role of cholesterol transporters, namely ABCA1, ABCG1, and SR-BI in these processes. HDL induced cell proliferation and migration of the androgen-independent PC-3 and DU145 cells by a mechanism involving extracellular signal-regulated kinase (ERK) 1/2 and Akt, but had no effect on the androgen-dependent LNCaP cell, which did not express ABCA1 unlike the other cell lines. Treatment with HDL did not significantly alter the cholesterol content of the cell lines. Knockdown of ABCA1 but not ABCG1 or SR-BI by small interfering RNA (siRNA) inhibited HDL-induced cell proliferation, migration, and ERK1/2 and Akt signal transduction in PC-3 cells. Moreover, after treatment of LNCaP cells with charcoal-stripped fetal bovine serum, ABCA1 was induced ∼10-fold, enabling HDL to induce ERK1/2 activation, whereas small interfering RNA knockdown of ABCA1 inhibited HDL-induced ERK1/2 activation. Simvastatin, which inhibited ABCA1 expression in PC-3 and DU145 cells, attenuated HDL-induced PC-3 and DU145 cell proliferation, migration, and ERK1/2 and Akt phosphorylation. In human prostate biopsy samples, ABCA1 mRNA expression was ∼2-fold higher in the androgen deprivation therapy group than in subjects with benign prostatic hyperplasia or pretreatment prostate cancer groups. In summary, these results suggest that HDL by an ABCA1-dependent mechanism can mediate signal transduction, leading to increased proliferation and migration of prostate cancer cells.

Native and reconstituted HDL protect cardiomyocytes from doxorubicin-induced apoptosis

AIMS

We analysed the impact of native and reconstituted HDL on doxorubicin-induced cardiomyocyte apoptosis. While it is an effective anti-cancer agent, doxorubicin has serious cardiotoxic side effects. HDL has been shown to protect cardiomyocytes, notably against oxidative stress.

METHODS AND RESULTS

Cultured neonatal rat ventricular cardiomyocytes were subjected to doxorubicin-induced stress, monitored as caspase3 activation, apoptotic DNA fragmentation and cell viability. The protective effects of HDL and sphingosine-1-phosphate (S1P) were investigated using native HDL, reconstituted HDL of varied composition and agonists and antagonists of S1P receptors. Anti-apoptotic signalling pathways were identified with specific inhibitors. Native and reconstituted HDL significantly decreased doxorubicin-induced cardiomyocyte apoptosis, essentially due to the S1P component of HDL. The latter was mediated by the S1P2 receptor, but not the S1P1 or S1P3 receptors. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) signalling pathway was required for the anti-apoptotic effects of HDL and S1P. The transcription factor Stat3 also played an important role, as inhibition of its activity compromised the protective effects of HDL and S1P on doxorubicin-induced apoptosis.

CONCLUSION

HDL and its sphingosine-1-phosphate component can protect cardiomyocytes against doxorubicin toxicity and may offer one means of reducing cardiotoxic side effects during doxorubicin therapy. The study identified anti-apoptotic pathways that could be exploited to improve cardiomyocyte survival.

Multiple tissue-specific isoforms of sulfatide activate CD1d-restricted type II NKT cells

The glycosphingolipid sulfatide (SO(3)-3Galbeta1Cer) is a demonstrated ligand for a subset of CD1d-restricted NKT cells, which could regulate experimental autoimmune encephalomyelitis, a murine model for multiple sclerosis, as well as tumor immunity and experimental hepatitis. Native sulfatide is a mixture of sulfatide isoforms, i.e. sulfatide molecules with different long-chain bases and fatty acid chain lengths and saturation. Here, we demonstrate that sulfatide-specific CD1d-restricted murine NKT hybridomas recognized several different sulfatide isoforms. These included the physiologically relevant isoforms C24:1 and C24:0, major constituents of the myelin sheet of the nervous system, and C16:0, prominent in the pancreatic islet beta-cells. The most potent sulfatide isoform was lysosulfatide (lacking a fatty acid). Shortened fatty acid chain length (C24:1 versus C18:1), or saturation of the long fatty acid (C24:0), resulted in reduced stimulatory capacity, and fatty acid hydroxylation abolished the response. Moreover, sulfatide was not responsible for the natural autoreactivity toward splenocytes by XV19 T hybridoma cells. Our results reveal a promiscuity in the recognition of sulfatide isoforms by a CD1d-restricted NKT-cell clone, and suggest that sulfatide, a major component of the myelin sheet and pancreatic beta-cells, is one of several natural ligands for type II CD1d-restricted NKT cells.

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.

Lipids as targets for novel anti-inflammatory therapies

Lipids serve important functions as membrane constituents and also as energy storing molecules. Besides these functions certain lipid species have now been recognized as signalling molecules that regulate a multitude of cellular responses including cell growth and death, and also inflammatory reactions. Bioactive lipids are generated by hydrolysis from membrane lipids mainly by phospholipases giving rise to fatty acids and lysophospholipids that either directly exert their function or are further converted to active mediators. This review will summarize the present knowledge about bioactive lipids that either promote or attenuate inflammatory reactions. These lipids include polyunsaturated fatty acids (PUFA), eicosanoids including the epoxyeicosatrienoic acids (EET), peroxisome proliferation activating receptor (PPAR) activators, cannabinoids and the sphingolipids ceramide, sphingosine 1-phosphate and sphingosylphosphorylcholine.

A Translational Medicine perspective of the development of torcetrapib: Does the failure of torcetrapib development cast a shadow on future development of lipid modifying agents, HDL elevation strategies or CETP as a viable molecular target for atherosclerosis? A case study of the use of biomarkers and Translational Medicine in atherosclerosis drug discovery and development

Although the relationship between HDL (high density lipoprotein) function and cardiovascular (CV) risk has been extensively explored, the premise that HDL elevation is linked to reduced CV risks and that high HDL cholesterol (HDL-C) might be a potential surrogate biomarker for reduced CV risk remains controversial. Substantial genetic, molecular, biochemical and preclinical evidence have raised the hope that HDL-C elevation via CETP inhibition might generate clinical benefits. However, four large-scale clinical trials with the CETP inhibitor torcetrapib failed to demonstrate benefits on CV clinical outcomes. Likewise, biomarkers that were supposed to predict vascular risk reduction provided disappointing results. The sad tale of torcetrapib development emphasizes the need for a paradigm shift from the conventional drug development mode to a biomarker-based Translational Medicine (TMed) strategy. Emergence of further CETP inhibitors encourage continued development of such compounds for cardiovascular risk management. However, there is a need to adopt biomarker-driven TMed strategies in target validation, target-compound interaction, pharmacodynamic activities, disease modification and patient selection to guide future drug development efforts. This commentary analyzes the issues surrounding the demise of torcetrapib and proposes a TMed-based road map towards successful development of new CETP inhibitors.

In vivo macrophage-specific RCT and antioxidant and antiinflammatory HDL activity measurements: New tools for predicting HDL atheroprotection

The beneficial therapeutic effects of raising HDL cholesterol are proving difficult to confirm in humans. The evaluation of antiatherogenic functions of HDL is an important area of research which includes the role of HDL in reverse cholesterol transport (RCT), especially macrophage-specific RCT, and its antioxidant and antiinflammatory roles. The antioxidant and antiinflammatory functions of HDL can be assessed using cell-free and cell-based assays. Also, a new approach was developed to measure RCT from labeled-cholesterol macrophages to liver and feces of mice. Studies in genetically engineered animals indicate that these major HDL antiatherogenic functions are better predictors of atherosclerosis susceptibility than HDL cholesterol or total RCT. Thus, functional testing of the antiatherogenic functions of HDL in experimental animal models may facilitate the development of new strategies for the prevention and treatment of atherosclerosis.

Small, dense HDL 3 particles attenuate apoptosis in endothelial cells: pivotal role of apolipoprotein A-I

Plasma high-density lipoproteins (HDLs) protect endothelial cells against apoptosis induced by oxidized low-density lipoprotein (oxLDL). The specific component(s) of HDLs implicated in such cytoprotection remain(s) to be identified. Human microvascular endothelial cells (HMEC-1) were incubated with mildly oxLDL in the presence or absence of each of five physicochemically distinct HDL subpopulations fractionated from normolipidemic human plasma (n= 7) by isopycnic density gradient ultracentrifugation. All HDL subfractions protected HMEC-1 against oxLDL-induced primary apoptosis as revealed by nucleic acid staining, annexin V binding, quantitative DNA fragmentation, inhibition of caspase-3 activity and reduction of cytoplasmic release of cytochrome c and apoptosis-inducing factor. Small, dense HDL 3c displayed twofold superior intrinsic cytoprotective activity (as determined by mitochondrial dehydrogenase activity) relative to large, light HDL 2b on a per particle basis (P < 0.05). Equally, all HDL subfractions attenuated intracellular generation of reactive oxygen species (ROS); such anti-oxidative activity diminished from HDL 3c to HDL 2b. The HDL protein moiety, in which apolipoprotein A-I (apoA-I) predominated, accounted for ∼70% of HDL anti-apoptotic activity. Furthermore, HDL reconstituted with apoA-I, cholesterol and phospholipid potently protected HMEC-1 from apoptosis. By contrast, modification of the content of sphingosine-1-phosphate in HDL did not significantly alter cytoprotection. We conclude that small, dense, lipid-poor HDL 3 potently protects endothelial cells from primary apoptosis and intracellular ROS generation induced by mildly oxLDL, and that apoA-I is pivotal to such protection.

Native and reconstituted HDL activate Stat3 in ventricular cardiomyocytes via ERK1/2: role of sphingosine-1-phosphate

AIMS

High-density lipoprotein (HDL) has been reported to have cardioprotective properties independent from its cholesterol transport activity. The influence of native HDL and reconstituted HDL (rHDL) on Stat3, the transcription factor playing an important role in myocardium adaptation to stress, was analysed in neonatal rat ventricular cardiomyocytes. We have investigated modulating the composition of rHDL as a means of expanding its function and potential cardioprotective effects.

METHODS AND RESULTS

Stat3 phosphorylation and activation were determined by western blotting and electrophoretic mobility shift assay (EMSA). In ventricular cardiomyocytes, HDL and the HDL constituent sphingosine-1-phosphate (S1P) induce a concentration- and time-dependent increase in Stat3 activation. They also enhance extracellular signal-regulated kinases (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) phosphorylation. U0126, a specific inhibitor of MEK1/2, the upstream activator of ERK1/2, abolishes HDL- and S1P-induced Stat3 activation, whereas the p38 MAPK blocker SB203580 has no significant effect. Inhibition of the tyrosine kinase family Src (Src) caused a significant reduction of Stat3 activation, whereas inhibition of phosphatidylinositol 3-kinase (PI3K) had no effect. S1P and rHDL containing S1P have a similar strong stimulatory action on Stat3, ERK1/2, and p38 MAPK comparable to native HDL. S1P-free rHDL has a much weaker effect. Experiments with agonists and antagonists of the S1P receptor subtypes indicate that HDL and S1P activate Stat3 mainly through the S1P2 receptor.

CONCLUSION

In ventricular cardiomyocytes, addition of S1P to rHDL enhances its therapeutic potential by improving its capacity to activate Stat3. Activation of Stat3 occurs mainly via the S1P constituent and the lipid receptor S1P2 requiring stimulation of ERK1/2 and Src but not p38 MAPK or PI3K. The study underlines the therapeutic potential of tailoring rHDL to confront particular clinical situations.

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.

The role of sphingosine kinase and sphingosine-1-phosphate in the regulation of endothelial cell biology

Sphingolipids, in particular sphingosine kinase (SphK) and its product sphingosine-1-phosphate (S1P), are now recognized to play an important role in regulating many critical processes in endothelial cells. Activation of SphK1 is essential in mediating the endothelial proinflammatory effects of inflammatory cytokines such as tumor necrosis factor (TNF). In addition, S1P regulates the survival and proliferation of endothelial cells, as well as their ability to undergo cell migration, all essential components of angiogenesis. Thus the inflammatory and angiogenic potential of the endothelium is in part regulated by intracellular components including the activity of SphK1 and levels of S1P. Herein a review of the sphingomyelin pathway with a particular focus on its relevance to endothelial cell biology is presented.