Is raising HDL a futile strategy for atheroprotection. Nat Rev Drug Discov. 2008;7:143-155. [PMID: 18239670 DOI: 10.1038/nrd2489]

The Association between Apolipoprotein A-II and Metabolic Syndrome in Korean Adults: A Comparison Study of Apolipoprotein A-I and Apolipoprotein B

BACKGROUND

Apolipoprotein A-II (apoA-II) is the second-most abundant apolipoprotein in human high-density lipoprotein and its role in cardio metabolic risk is not entirely clear. It has been suggested to have poor anti-atherogenic or even pro-atherogenic properties, but there are few studies on the possible role of apoA-II in Asian populations. The aim of this study is to evaluate the role of apoA-II in metabolic syndrome (MetS) compared with apolipoprotein A-I (apoA-I) and apolipoprotein B (apoB) in Korean adults.

METHODS

We analyzed data from 244 adults who visited the Center for Health Promotion in Pusan National University Yangsan Hospital for routine health examinations.

RESULTS

The mean apoB level was significantly higher, and the mean apoA-I level was significantly lower, in MetS; however, there was no significant difference in apoA-II levels (30.5±4.6 mg/dL vs. 31.2±4.6 mg/dL, P=0.261). ApoA-II levels were more positively correlated with apoA-I levels than apoB levels. ApoA-II levels were less negatively correlated with homocysteine and high sensitivity C-reactive protein levels than apoA-I levels. The differences in MetS prevalence from the lowest to highest quartile of apoA-II were not significant (9.0%, 5.7%, 4.9%, and 6.6%, P=0.279). The relative risk of the highest quartile of apoA-II compared with the lowest quartile also was not significantly different (odds ratio, 0.96; 95% confidence interval, 0.95 to 1.04; P=0.956).

CONCLUSION

Compared with apoA-I (negative association with MetS) and apoB (positive association with MetS) levels, apoA-II levels did not show any association with MetS in this study involving Korean adults. However, apoA-II may have both anti-atherogenic and pro-atherogenic properties.

Adaptive changes in fatty acid profile of erythrocyte membrane in relation to plasma and red cell metabolic changes in chronic alcoholic men

Chronic alcohol consumption is a major reason for several human diseases, and alcoholism has been associated with a variety of societal problems. Changes in fatty acid metabolism in alcoholics and its effects leading to membrane damage are largely unknown. Therefore, we aimed to investigate the fatty acid composition of erythrocyte membrane phospholipids in relation with plasma lipid profile and other plasma metabolites in chronic alcoholics in comparison with controls. We systematically measured the levels of glucose, lactate and pyruvate in the blood and free amino acids, free fatty acids, mucoproteins and glycolipids, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), very-low-density lipoprotein (VLDL) cholesterol and triglycerides (TG) in plasma of chronic alcoholics and controls. Furthermore, we measured fatty acid composition by gas chromatographic analysis. The fatty acid composition clearly revealed certain changes in chronic alcoholic erythrocyte membrane, chiefly increments in C16:0 and a decrease in C22:4 and C22:6 fatty acids besides the presence of unidentified fatty acids, probably C-24 or C-26 fatty acids. In addition, a significant increase in blood lactate, decrease in blood pyruvate and increased levels of free amino acids and free fatty acids, mucoproteins, VLDL cholesterol, TG and HDL-C in chronic alcoholics were observed with no significant change in plasma TC, LDL-C and glycolipids when compared with controls. Alcohol-induced alterations in plasma and erythrocyte membranes of chronic alcoholics in the present study might be an adaptive response to counteract the deleterious effects of alcohol. The implications of our findings warrant further investigation and needs further in-depth study to explore the mechanisms of alcohol-induced membrane changes.

Low levels of serum paraoxonase activities are characteristic of metabolic syndrome and may influence the metabolic-syndrome-related risk of coronary artery disease

Low concentrations of plasma high-density lipoprotein (HDLs) are characteristic in metabolic syndrome (MS). The antioxidant ability of HDLs is, at least in part, attributable to pleiotropic serum paraoxonase (PON1). Different PON1 activities have been assessed in 293 subjects with (n = 88) or without MS (n = 205) and with (n = 195) or without (n = 98) angiographically proven coronary artery disease (CAD). MS subjects had low PON1 activities, with a progressively decreasing trend by increasing the number of MS abnormalities. The activity versus 7-O-diethyl phosphoryl,3-cyano,4-methyl,7-hydroxycoumarin (DEPCyMC), which is considered a surrogate marker of PON1 concentration, showed the most significant association with MS, independently of both HDL and apolipoprotein A-I levels. Subjects with MS and low DEPCyMCase activity had the highest CAD risk (OR 4.34 with 95% CI 1.44–13.10), while no significant increase of risk was found among those with MS but high DEPCyMCase activity (OR 1.45 with 95% CI 0.47–4.46). Our results suggest that low PON1 concentrations are typical in MS and may modulate the MS-related risk of CAD.

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

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

International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B)

The G-protein-coupled receptors GPR81, GPR109A, and GPR109B share significant sequence homology and form a small group of receptors, each of which is encoded by clustered genes. In recent years, endogenous ligands for all three receptors have been described. These endogenous ligands have in common that they are hydroxy-carboxylic acid metabolites, and we therefore have proposed that this receptor family be named hydroxy-carboxylic acid (HCA) receptors. The HCA(1) receptor (GPR81) is activated by 2-hydroxy-propanoic acid (lactate), the HCA(2) receptor (GPR109A) is a receptor for the ketone body 3-hydroxy-butyric acid, and the HCA(3) receptor (GPR109B) is activated by the β-oxidation intermediate 3-hydroxy-octanoic acid. HCA(1) and HCA(2) receptors are found in most mammalian species, whereas the HCA(3) receptor is present only in higher primates. The three receptors have in common that they are expressed in adipocytes and are coupled to G(i)-type G-proteins mediating antilipolytic effects in fat cells. HCA(2) and HCA(3) receptors are also expressed in a variety of immune cells. HCA(2) is a receptor for the antidyslipidemic drug nicotinic acid (niacin) and related compounds, and there is an increasing number of synthetic ligands mainly targeted at HCA(2) and HCA(3) receptors. The aim of this article is to give an overview on the discovery and pharmacological characterization of HCAs, and to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature. We will also discuss open questions regarding this receptor family as well as their physiological role and therapeutic potential.

Nicotinic acid inhibits progression of atherosclerosis in mice through its receptor GPR109A expressed by immune cells

Nicotinic acid (niacin) is a drug used to reduce the progression of atherosclerosis. Its antiatherosclerotic activity is believed to result from lipid-modifying effects, including its ability to decrease LDL cholesterol and increase HDL cholesterol levels in plasma. Here, we report that in a mouse model of atherosclerosis, we found that nicotinic acid inhibited disease progression under conditions that left total cholesterol and HDL cholesterol plasma levels unaffected. The antiatherosclerotic effect was not seen in mice lacking the receptor for nicotinic acid GPR109A. Surprisingly, transplantation of bone marrow from GPR109A-deficient mice into atherosclerosis-prone animals also abrogated the beneficial effect of nicotinic acid. We detected expression of GPR109A in macrophages in atherosclerotic plaques. In macrophages from WT mice, but not from GPR109A-deficient animals, nicotinic acid induced expression of the cholesterol transporter ABCG1 and promoted cholesterol efflux. Furthermore, activation of GPR109A by nicotinic acid inhibited MCP-1-induced recruitment of macrophages into the peritoneal cavity and impaired macrophage recruitment to atherosclerotic plaques. In contrast with current models, our data show that nicotinic acid can reduce the progression of atherosclerosis independently of its lipid-modifying effects through the activation of GPR109A on immune cells. We conclude therefore that GPR109A mediates antiinflammatory effects, which may be useful for treating atherosclerosis and other diseases.

Genetic variant of the scavenger receptor BI in humans

BACKGROUND

In mice, the scavenger receptor class B type I (SR-BI) is essential for the delivery of high-density lipoprotein (HDL) cholesterol to the liver and steroidogenic organs. Paradoxically, elevated HDL cholesterol levels are associated with increased atherosclerosis in SR-BI-knockout mice. It is unclear what role SR-BI plays in human metabolism.

METHODS

We sequenced the gene encoding SR-BI in persons with elevated HDL cholesterol levels and identified a family with a new missense mutation (P297S). The functional effects of the P297S mutation on HDL binding, cellular cholesterol uptake and efflux, atherosclerosis, platelet function, and adrenal function were studied.

RESULTS

Cholesterol uptake from HDL by primary murine hepatocytes that expressed mutant SR-BI was reduced to half of that of hepatocytes expressing wild-type SR-BI. Carriers of the P297S mutation had increased HDL cholesterol levels (70.4 mg per deciliter [1.8 mmol per liter], vs. 53.4 mg per deciliter [1.4 mmol per liter] in noncarriers; P<0.001) and a reduced capacity for efflux of cholesterol from macrophages, but the carotid artery intima-media thickness was similar in carriers and in family noncarriers. Platelets from carriers had increased unesterified cholesterol content and impaired function. In carriers, adrenal steroidogenesis was attenuated, as evidenced by decreased urinary excretion of sterol metabolites, a decreased response to corticotropin stimulation, and symptoms of diminished adrenal function.

CONCLUSIONS

We identified a family with a functional mutation in SR-BI. The mutation carriers had increased HDL cholesterol levels and a reduction in cholesterol efflux from macrophages but no significant increase in atherosclerosis. Reduced SR-BI function was associated with altered platelet function and decreased adrenal steroidogenesis. (Funded by the European Community and others.).

Biological and pharmacological roles of HCA receptors

The hydroxy-carboxylic acid (HCA) receptors HCA(1), HCA(2), and HCA(3) were previously known as GPR81, GPR109A, and GPR109B, respectively, or as the nicotinic acid receptor family. They form a cluster of G protein-coupled receptors with high sequence homology. Recently, intermediates of energy metabolism, all HCAs, have been reported as endogenous ligands for each of these receptors. The HCA receptors are predominantly expressed on adipocytes and mediate the inhibition of lipolysis by coupling to G(i)-type proteins. HCA(1) is activated by lactate, HCA(2) by the ketone body 3-hydroxy-butyrate, and HCA(3) by hydroxylated β-oxidation intermediates, especially 3-hydroxy-octanoic acid. Both HCA(2) and HCA(3) are part of a negative feedback loop which keeps the release of fat stores in check under starvation conditions, whereas HCA(1) plays a role in the antilipolytic (fat-conserving) effect of insulin. HCA(2) was first discovered as the molecular target of the antidyslipidemic drug nicotinic acid (or niacin). Many synthetic agonists have since been designed for HCA(2) and HCA(3), but the development of a new, improved HCA-targeted drug has not been successful so far, despite a number of clinical studies. Recently, it has been shown that the major side effect of nicotinic acid, skin flushing, is mediated by HCA(2) receptors on keratinocytes, as well as on Langerhans cells in the skin. In this chapter, we summarize the latest developments in the field of HCA receptor research, with emphasis on (patho)physiology, receptor pharmacology, major ligand classes, and the therapeutic potential of HCA ligands.

Nanotechnology for synthetic high-density lipoproteins

Atherosclerosis is the disease mechanism responsible for coronary heart disease (CHD), the leading cause of death worldwide. One strategy to combat atherosclerosis is to increase the amount of circulating high-density lipoproteins (HDL), which transport cholesterol from peripheral tissues to the liver for excretion. The process, known as reverse cholesterol transport, is thought to be one of the main reasons for the significant inverse correlation observed between HDL blood levels and the development of CHD. This article highlights the most common strategies for treating atherosclerosis using HDL. We further detail potential treatment opportunities that utilize nanotechnology to increase the amount of HDL in circulation. The synthesis of biomimetic HDL nanostructures that replicate the chemical and physical properties of natural HDL provides novel materials for investigating the structure-function relationships of HDL and for potential new therapeutics to combat CHD.

The versatility of HDL: a crucial anti-inflammatory regulator

BACKGROUND

Low levels of plasma high-density lipoprotein (HDL) represent a major cardiovascular risk factor and therefore raising HDL has been proposed to positively affect patients with atherosclerotic heart disease. However, the current evidence that raising HDL per se will reduce atherosclerosis and thereby cardiovascular events still remains controversial.

AIMS

In this review, we discuss the diverse anti-atherogenic and anti-inflammatory properties of HDL in the light of recent findings indicating that the quality rather than the mere quantity of HDL determines its beneficial effects against atherosclerosis. More specifically, we will focus on the conspicuous anti-inflammatory properties of HDL as this might contribute to the overall beneficial effects of HDL in diseased patients such as modulation of costimulatory/adhesion molecule expression, cytokine production and inhibition of the prototypical proinflammatory transcription factor NF-κB.

RESULTS

A range of clinical disorders share permanent inflammation as a characteristic hallmark including coronary artery disease, chronic kidney disease, diabetes mellitus or rheumatoid arthritis and also display distinct qualitative changes in the HDL compartment. Loss of anti-inflammatory functions of HDL is emerging as an important risk factor for disease progression and survival in these clinical entities.

CONCLUSIONS

It will be important to define the anti-inflammatory effects of HDL at the molecular level and to dissect the manifold functional implications to develop both novel functional assays that enable meaningful outcome studies and foster new therapeutic concepts in patients with altered HDL function.

High density lipoproteins-based therapies for cardiovascular disease

Atherosclerosis is the leading cause of death in developed countries. High density lipoproteins (HDL) cholesterol level correlates inversely with the risk of cardiovascular diseases. Thus, HDL has obtained lots of interest for drug development. In this review, we summarized the mechanisms for the antiatherogenic function of HDL, current HDL-based drugs in clinical use and the future direction for HDL-based therapy development.

Inflammation reduces HDL protection against primary cardiac risk

BACKGROUND

We recently reported high high-density lipoprotein (HDL) cholesterol as a predictor of recurrent risk in a subgroup of postinfarction patients defined by hypercholesterolemia and high C-reactive protein (CRP) levels. We investigated whether a similar high-risk subgroup might exist for incident cardiovascular disease.

MATERIAL AND METHODS

A graphical exploratory data analysis tool was used to identify high-risk subgroups in a male population-based cohort (n = 3405) from the prevention of renal and vascular end-stage disease study by generating 3-dimensional mappings of risk over the HDL-cholesterol/CRP domain with subsequent use of Kaplan-Meier analysis to verify high-risk. Within-subgroup risk was assessed using Cox proportional hazards regression and Kaplan-Meier analysis.

RESULTS

Mappings revealed two high-risk subgroups: a low HDL-cholesterol/high CRP subgroup and a high HDL-cholesterol/high CRP subgroup. The low HDL-cholesterol subgroup demonstrated a pattern of metabolic syndrome dyslipidemia contrasted with a predominantly unremarkable biomarker pattern for the high HDL-cholesterol subgroup. However, in the high HDL-cholesterol subgroup, CRP levels were higher than the low HDL-cholesterol subgroup; and within the high HDL-cholesterol subgroup, CRP predicted risk. Moreover, in the high HDL-cholesterol subgroup, risk was associated with lower triglyceride levels in conjunction with presumptively larger HDL particles.

CONCLUSIONS

High HDL-cholesterol and high CRP levels define a subgroup of men at high-risk for incident cardiovascular disease. High HDL cholesterol-associated risk likely relates to impaired HDL particle remodelling in the setting of inflammation. This approach may facilitate identification of additional inflammation-related mechanisms underlying high HDL cholesterol-associated risk; and potentially influence management of such patients.

Cholesteryl ester transfer protein polymorphism (TaqIB) associates with risk in postinfarction patients with high C-reactive protein and high-density lipoprotein cholesterol levels

OBJECTIVE

To investigate the roles of inflammation and a cholesteryl ester transfer protein (CETP) polymorphism potentially related to recent findings demonstrating coronary risk with increasing high-density lipoprotein cholesterol (HDL-C) level.

METHODS AND RESULTS

A novel graphical exploratory data analysis tool allowed the examination of coronary risk in postinfarction patients relating to HDL-C and C-reactive protein levels. Results demonstrated a high-risk subgroup, defined by high HDL-C and C-reactive protein levels, exhibiting larger HDL particles and lower lipoprotein-associated phospholipaseA(2) levels than lower-risk patients. Subgroup CETP-associated risk was probed using a functional CETP polymorphism (TaqIB, rs708272). In the high-risk subgroup, multivariable modeling revealed greater risk for B2 allele carriers (less CETP activity) versus B1 homozygotes (hazard ratio, 2.41; 95% CI, 1.04 to 5.60; P=0.04). Within the high-risk subgroup, B2 allele carriers had higher serum amyloid A levels than B1 homozygotes. Evidence also demonstrates that CETP genotypic differences in HDL subfraction distributions regarding non-HDL-C and lipoprotein-associated phospholipaseA(2) may potentially relate to impaired HDL remodeling.

CONCLUSIONS

Postinfarction patients with high HDL-C and C-reactive protein levels demonstrate increased risk for recurrent events. Future studies should aim at characterizing altered HDL particles from such patients and at elucidating the mechanistic details related to inflammation and HDL particle remodeling. Such patients should be considered in drug trials involving an increase in HDL-C level.

Cholesterol efflux potential and antiinflammatory properties of high-density lipoprotein after treatment with niacin or anacetrapib

OBJECTIVE

To examine the effects of treatments with niacin or anacetrapib (an inhibitor of cholesteryl ester transfer protein) on the ability of high-density lipoprotein (HDL) to promote net cholesterol efflux and reduce toll-like receptor-mediated inflammation in macrophages.

METHODS AND RESULTS

A total of 18 patients received niacin, 2 g/d, for 4 weeks; 20 patients received anacetrapib, 300 mg/d, for 8 weeks; and 2 groups (n=4 and n=5 patients) received placebo. HDL samples were isolated by polyethylene glycol precipitation or ultracentrifugation, tested for the ability to promote cholesterol efflux in cholesterol-loaded THP-I or mouse peritoneal macrophages, or used to pretreat macrophages, followed by lipopolysaccharide exposure. HDL cholesterol levels were increased by 30% in response to niacin and by approximately 100% in response to anacetrapib. Niacin treatment increased HDL-mediated net cholesterol efflux from foam cells, primarily by increasing HDL concentration, whereas anacetrapib treatment increased cholesterol efflux by both increasing HDL concentration and causing increased efflux at matched HDL concentrations. The increased efflux potential of anacetrapib-HDL was more prominent at higher HDL cholesterol concentrations (>12 microg/mL), which was associated with an increased content of lecithin-cholesterol acyltransferase (LCAT) and apolipoprotein E and completely dependent on the expression of ATP binding cassette transporters (ABCA1 and ABCG1). Potent antiinflammatory effects of HDL were observed at low HDL concentrations (3 to 20 microg/mL) and were partly dependent on the expression of ABCA1 and ABCG1. All HDL preparations showed similar antiinflammatory effects, proportionate to the HDL cholesterol concentration.

CONCLUSIONS

Niacin treatment caused a moderate increase in the ability of HDL to promote net cholesterol efflux, whereas inhibition of cholesteryl ester transfer protein via anacetrapib led to a more dramatic increase in association with enhanced particle functionality at higher HDL concentrations. All HDLs exhibited potent ability to suppress macrophage toll-like receptor 4-mediated inflammatory responses, in a process partly dependent on cholesterol efflux via ABCA1 and ABCG1.

High-density lipoprotein subclasses are a potential intermediary between alcohol intake and reduced risk of cardiovascular disease: the Rancho Bernardo Study

We conducted a cross-sectional study of NMR-derived HDL subclasses and alcohol intake among 2171 community-dwelling older adults with a large proportion of daily or near-daily alcohol consumers (44 %). We aimed to assess whether, in addition to increasing total HDL, alcohol may induce a beneficial shift in HDL particle size distribution. Participants were categorised based on reported alcohol intake (g per week) and on frequency (none, < 3 times/week, 3-4 times/week, ≥ 5 times/week). The association between alcohol intake and lipoprotein fractions was examined using sex-specific linear regression models adjusted for age, BMI, diabetes, current smoking, exercise and hormone therapy in women. There was a stepwise gradient with the highest weekly alcohol consumption associated with the highest total HDL size and greatest number of medium and large HDL particles, as well as higher total HDL concentrations (all P < 0.001); total small HDL did not differ. Alcohol-HDL size associations were similar in both sexes and did not differ by use of hormone replacement therapy in women. In conclusion, regular alcohol consumers had a higher number and percentage of large HDL particles than non-drinkers. These results suggest that one way that alcohol may decrease CVD is through potentially favourable changes in lipoprotein subclass composition.

Anacetrapib: hope for CETP inhibitors?

Inhibition of cholesteryl ester transfer protein (CETP), a key protein involved in reverse cholesterol transport, can lead to increases in high-density lipoprotein cholesterol (HDL-C) levels and thus, is under evaluation as an antiatherogenic strategy. Several CETP inhibitors have been under development including anacetrapib, dalcetrapib, and torcetrapib. To date, anacetrapib demonstrates the greatest HDL-C raising and low-density lipoprotein cholesterol (LDL-C) lowering potential. Phase I and phase II trials with anacetrapib have revealed that anacetrapib is well-tolerated and does not seem to possess the pressor effects associated with torcetrapib. This article will briefly review the HDL-C raising through CETP inhibition as an antiatherogenic strategy with a specific focus on anacetrapib.

Studies on protective effects of human paraoxonases 1 and 3 on atherosclerosis in apolipoprotein E knockout mice

Paraoxonase (PON) possesses antiatherogenic potentials, but the distinct functions of PON members in alleviating atherosclerosis are not yet clear. This study aimed to evaluate the protective effects of hPON1 and hPON3 against atherosclerosis, and thereby exploring their synergistic mechanism in atherosclerosis development. We generated the recombinant adenovirus AdPON1 and AdPON3, which were capable of expressing hPON1 and hPON3. After AdPON1 and AdPON3 were injected intravenously into 5-week-old apolipoprotein E knockout mice, abundant hPON1 and hPON3 mRNA expression levels were detected. However, increase in serum lactonase activity was detected only in AdPON1-treated mice. Serum antioxidation and anti-inflammation capabilities in AdPON1-treated mice, reflected by malondialdehyde, total antioxidant capability and tumor necrosis factor-alpha levels, were greatly enhanced, whereas those in AdPON3-treated mice were not significantly affected. Nevertheless, histological analysis revealed that adenovirus-mediated expression of hPON1, hPON3 or both of them reduced atherosclerotic plaque area to a similar extent. Although no synergistic mechanism was detected in reducing arterial lesion size, hPON1 and hPON3 showed synergistic effects on promoting macrophage cholesterol efflux. In conclusion, hPON1 and hPON3 exhibited similar potentials in reducing arterial lesion size, but they exerted antiatherogenic effects in distinct ways.

Cholesteryl ester transfer protein and mortality in patients undergoing coronary angiography: the Ludwigshafen Risk and Cardiovascular Health study

BACKGROUND

The role of cholesteryl ester transfer protein (CETP) in the development of atherosclerosis is still open to debate. In the Investigation of Lipid Level Management to Understand its Impact in Atherosclerotic Events (ILLUMINATE) trial, inhibition of CETP in patients with high cardiovascular risk was associated with increased high-density lipoprotein levels but increased risk of cardiovascular morbidity and mortality. In this report, we present a prospective observational study of patients referred to coronary angiography in which CETP was examined in relation to morbidity and mortality.

METHODS AND RESULTS

CETP concentration was determined in 3256 participants of the Ludwigshafen Risk and Cardiovascular Health (LURIC) study who were referred to coronary angiography at baseline between 1997 and 2000. Median follow-up time was 7.75 years. Primary and secondary end points were cardiovascular and all-cause mortality, respectively. CETP levels were higher in women and lower in smokers, in diabetic patients, and in patients with unstable coronary artery disease, respectively. In addition, CETP levels were correlated negatively with high-sensitivity C-reactive protein and interleukin-6. After adjustment for age, sex, medication, coronary artery disease status, cardiovascular risk factors, and diabetes mellitus, the hazard ratio for death in the lowest CETP quartile was 1.33 (1.07 to 1.65; P=0.011) compared with patients in the highest CETP quartile. Corresponding hazard ratios for death in the second and third CETP quartiles were 1.17 (0.92 to 1.48; P=0.19) and 1.10 (0.86 to 1.39; P=0.46), respectively.

CONCLUSIONS

We interpret our data to suggest that low endogenous CETP plasma levels per se are associated with increased cardiovascular and all-cause mortality, challenging the rationale of pharmacological CETP inhibition.

Cholesteryl ester transfer protein: at the heart of the action of lipid-modulating therapy with statins, fibrates, niacin, and cholesteryl ester transfer protein inhibitors

Subnormal plasma levels of high-density lipoprotein cholesterol (HDL-C) constitute a major cardiovascular risk factor; raising low HDL-C levels may therefore reduce the residual cardiovascular risk that frequently presents in dyslipidaemic subjects despite statin therapy. Cholesteryl ester transfer protein (CETP), a key modulator not only of the intravascular metabolism of HDL and apolipoprotein (apo) A-I but also of triglyceride (TG)-rich particles and low-density lipoprotein (LDL), mediates the transfer of cholesteryl esters from HDL to pro-atherogenic apoB-lipoproteins, with heterotransfer of TG mainly from very low-density lipoprotein to HDL. Cholesteryl ester transfer protein activity is elevated in the dyslipidaemias of metabolic disease involving insulin resistance and moderate to marked hypertriglyceridaemia, and is intimately associated with premature atherosclerosis and high cardiovascular risk. Cholesteryl ester transfer protein inhibition therefore presents a preferential target for elevation of HDL-C and reduction in atherosclerosis. This review appraises recent evidence for a central role of CETP in the action of current lipid-modulating agents with HDL-raising potential, i.e. statins, fibrates, and niacin, and compares their mechanisms of action with those of pharmacological agents under development which directly inhibit CETP. New CETP inhibitors, such as dalcetrapib and anacetrapib, are targeted to normalize HDL/apoA-I levels and anti-atherogenic activities of HDL particles. Further studies of these CETP inhibitors, in particular in long-term, large-scale outcome trials, will provide essential information on their safety and efficacy in reducing residual cardiovascular risk.

Maturation of high-density lipoproteins

Human high-density lipoproteins (HDLs) are involved in the transport of cholesterol. The mechanism by which HDL assembles and functions is not well understood owing to a lack of structural information on circulating spherical HDL. Here, we report a series of molecular dynamics simulations that describe the maturation of discoidal HDL into spherical HDL upon incorporation of cholesterol ester as well as the resulting atomic level structure of a mature circulating spherical HDL particle. Sixty cholesterol ester molecules were added in a stepwise fashion to a discoidal HDL particle containing two apolipoproteins wrapped around a 160 dipalmitoylphosphatidylcholine lipid bilayer. The resulting matured particle, captured in a coarse-grained description, was then described in a consistent all-atom representation and analysed in chemical detail. The simulations show that maturation results from the formation of a highly dynamic hydrophobic core comprised of cholesterol ester surrounded by phospholipid and protein; the two apolipoprotein strands remain in a belt-like conformation as seen in the discoidal HDL particle, but with flexible N- and C-terminal helices and a central region stabilized by salt bridges. In the otherwise flexible lipoproteins, a less mobile central region provides an ideal location to bind lecithin cholesterol acyltransferase, the key enzyme that converts cholesterol to cholesterol ester during HDL maturation.

Physical Activity, Blood Lipids, and Lipoproteins

Dyslipidemia is a major modifiable cardiovascular disease (CVD) risk factor. While pharmacological treatment has been a focal point of dyslipidemia management for several years, increasing physical activity is a safe, cost-effective treatment option that should also be recommended by health care practitioners. Moderate aerobic exercise consistently increases high-density lipoprotein cholesterol (HDL-C) and reduces triglycerides (TG), independent of changes in body weight. However, reductions in total and low-density lipoprotein cholesterol are reported less often following aerobic exercise. Therefore, clinicians should understand that aerobic exercise is not likely to be an effective treatment option for their management. Recent empirical evidence also indicates that aerobic exercise may be of benefit for treating emerging lipid and lipoprotein risk factors such as lipoprotein particle size and number and triglyceride-rich lipoproteins. Further work is needed to clarify the impact of aerobic exercise on apolipoproteins. Based on current evidence, prescribing aerobic exercise as a means of increasing HDL-C and lowering TG is usually an efficacious strategy for treating these aspects of dyslipidemia. These effects are likely to be accompanied by changes in emerging lipid and lipoprotein risk factors.

Templated spherical high density lipoprotein nanoparticles

We report the synthesis of high density lipoprotein (HDL) biomimetic nanoparticles capable of binding cholesterol. These structures use a gold nanoparticle core to template the assembly of a mixed phospholipid layer and the adsorption of apolipoprotein A-I. These synthesized structures have the general size and surface composition of natural HDL and, importantly, bind free cholesterol (K(d) = 4 nM). The determination of the K(d) for these particles, with respect to cholesterol complexation, provides a key starting and comparison point for measuring and evaluating the properties of subsequently developed synthetic versions of HDL.

Differential stability of high-density lipoprotein subclasses: effects of particle size and protein composition

High-density lipoproteins (HDLs) are complexes of proteins (mainly apoA-I and apoA-II) and lipids that remove cholesterol and prevent atherosclerosis. Understanding the distinct properties of the heterogeneous HDL population may aid the development of new diagnostic tools and therapies for atherosclerosis. Mature human HDLs form two major subclasses differing in particle diameter and metabolic properties, HDL(2) (large) and HDL(3) (small). These subclasses are comprised of HDL(A-I) containing only apoA-I, and HDL(A-I/A-II) containing apoA-I and apoA-II. ApoA-I is strongly cardioprotective, but the function of the smaller, more hydrophobic apoA-II is unclear. ApoA-II is thought to counteract the cardioprotective action of apoA-I by stabilizing HDL particles and inhibiting their remodeling. To test this notion, we performed the first kinetic stability study of human HDL subclasses. The results revealed that the stability of plasma spherical HDL decreases with increasing particle diameter; which may facilitate preferential cholesterol ester uptake from large lipid-loaded HDL(2). Surprisingly, size-matched plasma HDL(A-I/A-II) showed comparable or slightly lower stability than HDL(A-I); this is consistent with the destabilization of model discoidal HDL observed upon increasing the A-II to A-I ratio. These results clarify the roles of the particle size and protein composition in HDL remodeling, and help reconcile conflicting reports regarding the role of apoA-II in this remodeling.

Current and emerging paradigms in the therapeutic management of atherosclerosis

BACKGROUND

The pathogenesis of atherosclerosis lies in abnormalities in lipoprotein metabolism leading to pathological interactions with vessel walls and the release of inflammatory components, which further aggravate the disease condition.

OBJECTIVE

To elucidate current and emerging trends in drug discovery towards the development of new entities regulating lipoprotein metabolism and inflammatory components to combat the progression of atherosclerosis.

METHODS

Research/review articles in the public domain and press releases were employed.

RESULTS/CONCLUSION

With the recent failure of torcetrapib and succinobucol, drug discovery and development efforts towards the treatment of atherosclerosis have received a big jolt and have been slowed down to a certain extent [corrected]. But this could be a starting point for several new mechanisms that are emerging to discover new drugs to combat the disease.

Mass spectrometric determination of apolipoprotein molecular stoichiometry in reconstituted high density lipoprotein particles

Plasma HDL-cholesterol and apolipoprotein A-I (apoA-I) levels are strongly inversely associated with cardiovascular disease. However, the structure and protein composition of HDL particles is complex, as native and synthetic discoidal and spherical HDL particles can have from two to five apoA-I molecules per particle. To fully understand structure-function relationships of HDL, a method is required that is capable of directly determining the number of apolipoprotein molecules in heterogeneous HDL particles. Chemical cross-linking followed by SDS polyacrylamide gradient gel electrophoresis has been previously used to determine apolipoprotein stoichiometry in HDL particles. However, this method yields ambiguous results due to effects of cross-linking on protein conformation and, subsequently, its migration pattern on the gel. Here, we describe a new method based on cross-linking chemistry followed by MALDI mass spectrometry that determines the absolute mass of the cross-linked complex, thereby correctly determining the number of apolipoprotein molecules in a given HDL particle. Using well-defined, homogeneous, reconstituted apoA-I-containing HDL, apoA-IV-containing HDL, as well as apoA-I/apoA-II-containing HDL, we have validated this method. The method has the capability to determine the molecular ratio and molecular composition of apolipoprotein molecules in complex reconstituted HDL particles.

HDL-replacement therapy: mechanism of action, types of agents and potential clinical indications

HDL-replacement therapy is a promising new treatment strategy involving the acute administration of HDL to rapidly stabilize patients at imminent risk for developing a myocardial infarction, such as those with acute coronary syndrome. This review will first focus on the anti-atherogenic mechanisms for HDL, such as the stimulation of the reverse cholesterol transport pathway, and then discuss the other potential beneficial biological effects of HDL on atherosclerosis. The various types of HDL-replacement therapies that are being investigated and developed will be reviewed and ongoing clinical trials and other possible clinical indications for HDL-replacement therapy besides the prevention of myocardial infarction will also be described. Finally, HDL-replacement therapy will be put into perspective by summarizing the current gaps in our knowledge of HDL metabolism and identifying challenges for future research in this area.

Reconstruction and functional analysis of altered molecular pathways in human atherosclerotic arteries

Background

Atherosclerosis affects aorta, coronary, carotid, and iliac arteries most frequently than any other body vessel. There may be common molecular pathways sustaining this process. Plaque presence and diffusion is revealed by circulating factors that can mediate systemic reaction leading to plaque rupture and thrombosis.

Results

We used DNA microarrays and meta-analysis to study how the presence of calcified plaque modifies human coronary and carotid gene expression. We identified a series of potential human atherogenic genes that are integrated in functional networks involved in atherosclerosis. Caveolae and JAK/STAT pathways, and S100A9/S100A8 interacting proteins are certainly involved in the development of vascular disease. We found that the system of caveolae is directly connected with genes that respond to hormone receptors, and indirectly with the apoptosis pathway.

Cytokines, chemokines and growth factors released in the blood flux were investigated in parallel. High levels of RANTES, IL-1ra, MIP-1alpha, MIP-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-17, PDGF-BB, VEGF and IFN-gamma were found in plasma of atherosclerotic patients and might also be integrated in the molecular networks underlying atherosclerotic modifications of these vessels.

Conclusion

The pattern of cytokine and S100A9/S100A8 up-regulation characterizes atherosclerosis as a proinflammatory disorder. Activation of the JAK/STAT pathway is confirmed by the up-regulation of IL-6, STAT1, ISGF3G and IL10RA genes in coronary and carotid plaques. The functional network constructed in our research is an evidence of the central role of STAT protein and the caveolae system to contribute to preserve the plaque. Moreover, Cav-1 is involved in SMC differentiation and dyslipidemia confirming the importance of lipid homeostasis in the atherosclerotic phenotype.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

Metabolomic strategies to identify tissue-specific effects of cardiovascular drugs

BACKGROUND

The number of patients eligible for cardiovascular therapies in general is forecast to increase substantially in the coming decades. However, the current list of potential future cardiovascular blockbuster drugs is alarmingly short. There is thus a clear need for innovative strategies to increase the efficiency of drug development pipelines by establishing new sensitive biomarkers to monitor drug efficacy and safety in the context of complexity of lipoprotein metabolism targeted by the cardiovascular drugs.

METHODS

Metabolomics is a discipline dedicated to the systematic study of small molecules in cells, tissues and biofluids. Since lipids (including cholesterol), as well as other metabolites, are key constituents of lipoprotein particles and are thus part of the complex lipoprotein metabolism that includes exchange of lipids and metabolites with peripheral tissues, cardiovascular drug safety and efficacy needs to be addressed in the context of systemic lipid metabolism.

RESULTS/CONCLUSION

Metabolomics, lipidomics in particular, is expected to make an important impact on the discovery and development of cardiovascular therapies.

Emerging antidyslipidemic drugs

BACKGROUND

Many patients at high risk for coronary heart disease (CHD) fail to reach target lipid levels with currently available medications, and a small but clinically relevant proportion of patients experience adverse effects. Thus, additional pharmaceutical strategies are required to fill these gaps in efficacy and tolerability.

OBJECTIVE

To provide an overview of both current and emerging antidyslipidemic drugs.

METHODS

For the current antidyslipidemic drugs, we focus primarily on statins, bile acid sequestrants, fibrates, ezetimibe, and niacin. Emerging antidyslipidemic drugs herein discussed were identified by searching the Pharmaprojects database for 'hypercholesterolemia drugs' (Phase II or Phase III), 'HDL-based therapies', and 'PCSK9 inhibition'.

RESULTS/CONCLUSIONS

Combinations of currently existing medications are most easily applicable. Meanwhile, strategies to raise HDL-C rely on a deep understanding of the complexity of HDL metabolism. Furthermore, novel approaches to further reduce LDL-C warrant careful evaluation of benefit-risk ratio. Finally, the medical community will have to rely on late-phase CHD outcome studies as the final arbiter of clinical application for any new antidyslipidemia treatment.

The value of HDL genetics

PURPOSE OF REVIEW

To review studies on hereditary disorders of high-density lipoprotein (HDL) metabolism and studies on HDL genetics in mice, which have both provided valuable insight into the pathways of this intriguing lipoprotein and moreover revealed targets to raise HDLc to reduce atherosclerosis.

RECENT FINDINGS

To date, as many as 11 genes are considered key players in the synthesis, maturation, conversion and/or catabolism of HDL. Five of these genes have been identified in humans, APOA1, LCAT, ABCA1, LIPC, and CETP, whereas the other six genes have been identified in mice, SCARB1, ABCG1, ATPB5, PLTP, LIPG and APOM. Genetic association studies are as yet the best line of evidence of the roles of the 'murine genes' in human HDL pathways. In addition to recent genetic association studies, a third section describes exciting news on six newly proposed HDL genes VNN1, GALNT2, MMAB/MVK, CTalpha, BMP-1 and SIRT1.

SUMMARY

This review provides a summary of the current literature on the genetics of HDL. New information from this research area may assist us in obtaining a better understanding of HDL biology and identifying novel pharmacological targets.

HDL metabolism in context: looking on the bright side

PURPOSE OF REVIEW

To review new data concerning HDL metabolism and cardiovascular disease, the concept of HDL 'functionality', and HDL kinetics in the metabolic syndrome.

RECENT FINDINGS

HDL-apoA-I and apoA-II may be better predictors of cardiovascular disease than HDL-cholesterol. Cholesteryl ester transfer protein inhibition with torcetrapib does not benefit cardiovascular disease; whether this is related to 'congestion' of HDL transport or a specific off-target vasopressor effect remains unclear. Accelerated catabolism of HDL particles in metabolic syndrome could be due to increased hepatic secretion of apoB and apoC-III, hepatic steatosis, and low plasma adiponectin. The role of serum amyloid A and homocysteine is uncertain. In metabolic syndrome, therapies that could favourably alter HDL transport include weight loss, fish oils, higher dose statins, and fibrates; 'balancing feedback' may offset reduced catabolism of HDL, fenofibrate being the only agent hitherto shown to increase apoA-I production.

SUMMARY

Elevating HDL-apoA-I and apoA-II may be a more important therapeutic objective than increased HDL-cholesterol. Recent studies underscore the potential value of studying HDL functionality, particularly in the metabolic syndrome. Reverse cholesterol transport can only be reliably probed at present by studying the kinetics of HDL particles or apolipoproteins; new methods are needed for investigating cellular and whole body cholesterol turnover. In metabolic syndrome, HDL-raising therapies have differential impact on HDL kinetics, the optimal endpoint being to increase transport and concentration with unchanged or accelerated catabolism.

The failure of torcetrapib: what have we learned?

The failure of the cholesterol ester transfer protein (CETP) inhibitor, torcetrapib, has led to questions regarding whether the molecule itself or the mechanism of CETP inhibition was responsible for the adverse cardiovascular outcomes. Given the association with increases in blood pressure and plasma aldosterone levels, torcetrapib has been postulated to have adverse 'off-target' effects. In this issue of British Journal of Pharmacology, Forrest and co-workers have elegantly investigated these effects, demonstrating two salient points -- (1) the pressor effect of torcetrapib is independent of CETP inhibition and (2) although associated with hyperaldosteronism, the pressor effect is likely not mediated by hyperaldosteronism. Anacetrapib, by contrast, did not demonstrate any pressor or off-target effects. Despite these findings, it remains to be proven whether the adverse cardiovascular outcomes from torcetrapib were indeed related to the pressor effects and whether CETP inhibition by other agents will result in beneficial clinical outcomes. Yet, the studies of Forrest and co-workers do bring us closer to unravelling the reasons behind the failure of torcetrapib.

Microsomal triglyceride transfer protein inhibition-friend or foe?

This article sets out the clinical context of the research presented by Samaha et al. in an accompanying article in this issue. Hyperlipidemia is a common and important risk factor for cardiovascular disease. Current lipid-lowering therapies, particularly statins, lead to substantial decreases in cardiovascular disease morbidity and mortality, but use has been limited by safety or efficacy issues. The way has, therefore, been paved for the pharmaceutical development and clinical investigation of new lipid-lowering therapies. The clinical trial by Samaha et al. examines the safety and efficacy of microsomal triglyceride transfer protein inhibition for lowering lipids. Joy and Hegele explore the difficulties of translating microsomal triglyceride transfer protein inhibition into clinical practice because of the trade-off between efficacy and potential adverse effects. They also stress the need for outcome studies, rather than biochemical or surrogate studies, as the final arbiter for the clinical use of this new treatment.