HDL action on the vascular wall: is the answer NO?

HDL Composition, Heart Failure, and Its Comorbidities

Although research on high-density lipoprotein (HDL) has historically focused on atherosclerotic coronary disease, there exists untapped potential of HDL biology for the treatment of heart failure. Anti-oxidant, anti-inflammatory, and endothelial protective properties of HDL could impact heart failure pathogenesis. HDL-associated proteins such as apolipoprotein A-I and M may have significant therapeutic effects on the myocardium, in part by modulating signal transduction pathways and sphingosine-1-phosphate biology. Furthermore, because heart failure is a complex syndrome characterized by multiple comorbidities, there are complex interactions between heart failure, its comorbidities, and lipoprotein homeostatic mechanisms. In this review, we will discuss the effects of heart failure and associated comorbidities on HDL, explore potential cardioprotective properties of HDL, and review novel HDL therapeutic targets in heart failure.

Relationship Between HDL Functional Characteristics and Cardiovascular Health and Potential Impact of Dietary Patterns: A Narrative Review

Cardiovascular disease is a leading cause of death around the world. Overall diet quality and dietary behaviors are core contributors to metabolic health. While therapeutic targets have traditionally focused on levels of lipoprotein cholesterol when evaluating cardiovascular risk, current perspectives on high-density lipoprotein (HDL) have shifted to evaluating the functionality of this lipoprotein particle. Effects of diet on cardiovascular health are mediated through multiple pathways, but the impact on HDL composition and function deserves greater attention. Potential areas of investigation involve changes in particle characteristics, distribution, microRNA cargo, and other functional changes such as improvements to cholesterol efflux capacity. Various dietary patterns like the Mediterranean diet and Dietary Approaches to Stop Hypertension (DASH) diet have beneficial effects on cardiovascular health and may prevent cardiovascular events. These healthful dietary patterns tend to be rich in plant-based foods, with cardiovascular benefits likely resulting from synergistic effects of the individual dietary components. The purpose of this review is to summarize current perspectives on selected functions of HDL particles and how various dietary patterns affect cardiovascular health biomarkers, with a focus on HDL functionality.

ALDH2 gene G487A polymorphism and coronary artery disease: a meta-analysis including 5644 participants

Several studies indicate the mitochondrial Aldehyde Dehydrogenase-2 (ALDH2) gene G487A polymorphism may be correlated with coronary artery disease (CAD) susceptibility, but a clear consensus has yet to be reached. To elucidate the relationship between the ALDH2 gene G487A polymorphism and CAD within the Chinese population, a meta-analysis of 5644 subjects from nine individual studies was performed. Pooled odds ratios (ORs) and their corresponding 95% confidence intervals were assessed using random or fixed-effect models depending the heterogeneity existence or not. Our meta-analysis found a significant association between ALDH2 gene G487A polymorphism and CAD in the Chinese population under allele (OR: 1.830, 95% CI: 1.560-2.140, P = 1.36 × 10^-13 ), recessive (OR: 1.920, 95% CI: 1.530-2.390, P = 1.20 × 10^-8 ), dominant (OR: 1.593, 95% CI: 1.336-1.900, P = 2.22 × 10^-7 ), homozygous (OR: 2.280, 95% CI: 1.810-2.870, P = 3.17 × 10^-12 ) and heterozygous genetic models (OR: 3.330, 95% CI: 2.070-5.370, P = 7.81 × 10^-7 ). The positive correlation between the ALDH2 gene G487A polymorphism and CAD makes the mutation a strong candidate as a genetic risk marker for CAD. Through further analysis, we also found that A allele carriers of ALDH2 gene G487A polymorphism may be particularly susceptible to CAD.

Inducing apolipoprotein A-I synthesis to reduce cardiovascular risk: from ASSERT to SUSTAIN and beyond

Increasing attention has focused on efforts to promote the biological activities of high-density lipoproteins (HDL) in order to reduce cardiovascular risk. Targeting apolipoprotein A-I (apoA-I), the major protein carried on HDL particles, represents an attractive approach to promoting HDL by virtue of its ability to increase endogenous synthesis of functional HDL particles. A number of pharmacological strategies that target apoA-I, including upregulation of its production with the bromodomain and extraterminal (BET) protein inhibitor RVX-208, development of short peptide sequences that mimic its action, and administration as a component of reconstituted HDL particles, have undergone clinical development. The impact of these approaches on cardiovascular biomarkers will be reviewed.

A Novel Anti-Inflammatory Effect for High Density Lipoprotein

High density lipoprotein has anti-inflammatory effects in addition to mediating reverse cholesterol transport. While many of the chronic anti-inflammatory effects of high density lipoprotein (HDL) are attributed to changes in cell adhesion molecules, little is known about acute signal transduction events elicited by HDL in endothelial cells. We now show that high density lipoprotein decreases endothelial cell exocytosis, the first step in leukocyte trafficking. ApoA-I, a major apolipoprotein of HDL, mediates inhibition of endothelial cell exocytosis by interacting with endothelial scavenger receptor-BI which triggers an intracellular protective signaling cascade involving protein kinase C (PKC). Other apolipoproteins within the HDL particle have only modest effects upon endothelial exocytosis. Using a human primary culture of endothelial cells and murine apo-AI knockout mice, we show that apo-AI prevents endothelial cell exocytosis which limits leukocyte recruitment. These data suggest that high density lipoprotein may inhibit diseases associated with vascular inflammation in part by blocking endothelial exocytosis.

MiR-135b-5p and MiR-499a-3p Promote Cell Proliferation and Migration in Atherosclerosis by Directly Targeting MEF2C

Proliferation and migration of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are critical processes involved in atherosclerosis. Recent studies have revealed that microRNAs (miRNAs) can be detected in circulating blood with a stable form and the expression profiles differ in many cellular processes associated with coronary artery disease (CAD). However, little is known about their role, especially serum-derived miRNAs, in ECs and VSMCs phenotype modulation during atherosclerosis. We compared the miRNA expressions in serum samples from 13 atherosclerotic CAD patients and 5 healthy control subjects and identified 36 differentially expressed miRNAs. The expression of selected miRNAs (miR-135b-5p and miR-499a-3p) was further validated in 137 serum samples. Interestingly, miR-135b-5p and miR-499a-3p directly regulated a common target gene: myocyte enhancer factor 2C (MEF2C) which plays an important role in modulating cell phenotype of cardiovascular systems. Furthermore, our results indicated that the 2 elevated miRNAs could jointly promote ECs and VSMCs proliferation and migration by repressing MEF2C expression. Together, our findings demonstrated a serum-based miRNA expression profile for atherosclerotic CAD patients, potentially revealing a previously undocumented mechanism for cell proliferation and migration mediated by miR-135b-5p and miR-499a-3p, and might provide novel insights into the role of circulating miRNAs in atherosclerosis pathogenesis.

17β-Estradiol regulates scavenger receptor class BI gene expression via protein kinase C in vascular endothelial cells

High-density lipoprotein (HDL) mediates reverse cholesterol transport. In this process, the human homolog of the B class, type I scavenger receptor (SR-BI), CD36, and LIMPII analogous-1 (hSR-BI/CLA-1) facilitates the cellular uptake of cholesterol from HDL. In endothelial cells, HDL activates endothelial nitric oxide synthase (eNOS) via hSR-BI/CLA-1, and 17β-estradiol (E2) modulates nitric oxide (NO) synthesis. In this study, we elucidated the effect of E2 on hSR-BI/CLA-1 expression in human umbilical vein endothelial cells (HUVECs). HSR-BI/CLA-1 expression was examined by real-time PCR, western blot analysis and reporter gene assay in HUVECs incubated with E2. eNOS activity was assessed by detection of phosphorylation (Ser 1179) of eNOS. We investigated the effect of the constitutively active form or dominant negative form of protein kinase C on hSR-BI/CLA-1 promoter activity. Our results showed that E2 increased the endogenous expression of hSR-BI/CLA-1. E2 also enhanced the activity of the hSR-BI/CLA-1 promoter and the expression of its mRNA. However, bisindolylmaleimide I, an inhibitor of protein kinase C, blocked the stimulatory effect of E2 on hSR-BI/CLA-1 promoter activity. Moreover, constitutively active PKC increased the activity of the hSR-BI/CLA-1 promoter, and a dominant-negative mutant of PKC prevented E2 from stimulating promoter activity. In cells treated with E2, HDL stimulated the phosphorylation of serine 1179 of eNOS in HUVECs. These results suggested that E2 upregulates the expression of the endothelial hSR-BI/CLA-1 via the PKC pathway, which may be a novel mechanism of the anti-atherosclerotic potential of E2 in vascular endothelial cells.

High-density lipoprotein cholesterol efflux, nitration of apolipoprotein A-I, and endothelial function in obese women

Subjects at risk of atherosclerosis might have dysfunctional high-density lipoprotein (HDL) despite normal cholesterol content in the plasma. We considered whether the efflux of excess cellular cholesterol to HDL from obese subjects is associated with impaired arterial endothelial function, a biomarker of cardiovascular risk. A total of 54 overweight (body mass index [BMI] 25 to 29.9 kg/m(2)) or obese (BMI ≥30 kg/m(2)) women, aged 46 ± 11 years, were enrolled in a worksite wellness program. The HDL cholesterol averaged 57 ± 17 mg/dl and was inversely associated with the BMI (r = -0.419, p = 0.002). Endothelial function was assessed using brachial artery flow-mediated dilation. Cholesterol efflux from (3)H-cholesterol-labeled baby hamster kidney cells transfected with the adenosine triphosphate-binding cassette transporter 1 showed 8.2% to 22.5% cholesterol efflux within 18 hours when incubated with 1% serum and was positively correlated with brachial artery flow-mediated dilation (p <0.05), especially in the 34 subjects with BMI ≥30 kg/m(2) (r = 0.482, p = 0.004). This relation was independent of age, HDL or low-density lipoprotein cholesterol concentrations in plasma, blood pressure, or insulin resistance on stepwise multiple regression analysis (β = 0.31, R(2) = 0.21, p = 0.007). Nitration of apolipoprotein A-I tyrosine residues (using sandwich enzyme-linked immunosorbent assay) was significantly greater in women with a BMI ≥30 kg/m(2) and the lowest cholesterol efflux than in women with a BMI of 25 to 29.9 kg/m(2) and the greatest cholesterol efflux (p = 0.01). In conclusion, we have shown that decreased cholesterol efflux by way of the adenosine triphosphate-binding cassette transporter 1 is associated with increased nitration of apolipoprotein A-I in HDL and is an independent predictor of impaired endothelial function in women with a BMI of ≥30 kg/m(2). This finding suggests that the functional measures of HDL might be better markers for cardiovascular risk than the HDL cholesterol levels in this population.

Apo a-I modulating therapies

The substantial residual risk of cardiovascular events despite the implementation of effective lowering of low-density lipoprotein cholesterol highlights the need to develop additional cardioprotective therapies. Evidence from population and animal studies suggests that high-density lipoproteins (HDLs), the protective lipid particles, may represent a target for therapeutic modification. As a result intensive efforts are in progress to develop new agents that promote HDL activity. Among these different approaches, a range of strategies that target apolipoprotein A-I, the major protein carried on HDL, are being evaluated.

Endothelial expression of human ABCA1 in mice increases plasma HDL cholesterol and reduces diet-induced atherosclerosis

The role of endothelial ABCA1 expression in reverse cholesterol transport (RCT) was examined in transgenic mice, using the endothelial-specific Tie2 promoter. Human ABCA1 (hABCA1) was significantly expressed in endothelial cells (EC) of most tissues except the liver. Increased expression of ABCA1 was not observed in resident peritoneal macrophages. ApoA-I-mediated cholesterol efflux from aortic EC was 2.6-fold higher (P < 0.0001) for cells from transgenic versus control mice. On normal chow diet, Tie2 hABCA1 transgenic mice had a 25% (P < 0.0001) increase in HDL-cholesterol (HDL-C) and more than a 2-fold increase of eNOS mRNA in the aorta (P < 0.04). After 6 months on a high-fat, high-cholesterol (HFHC) diet, transgenic mice compared with controls had a 40% increase in plasma HDL-C (P < 0.003) and close to 40% decrease in aortic lesions (P < 0.02). Aortas from HFHC-fed transgenic mice also showed gene expression changes consistent with decreased inflammation and apoptosis. Beneficial effects of the ABCA1 transgene on HDL-C levels or on atherosclerosis were absent when the transgene was transferred onto ApoE or Abca1 knockout mice. In summary, expression of hABCA1 in EC appears to play a role in decreasing diet-induced atherosclerosis in mice and is associated with increased plasma HDL-C levels and beneficial gene expression changes in EC.

Mechanisms underlying adverse effects of HDL on eNOS-activating pathways in patients with coronary artery disease

Therapies that raise levels of HDL, which is thought to exert atheroprotective effects via effects on endothelium, are being examined for the treatment or prevention of coronary artery disease (CAD). However, the endothelial effects of HDL are highly heterogeneous, and the impact of HDL of patients with CAD on the activation of endothelial eNOS and eNOS-dependent pathways is unknown. Here we have demonstrated that, in contrast to HDL from healthy subjects, HDL from patients with stable CAD or an acute coronary syndrome (HDLCAD) does not have endothelial antiinflammatory effects and does not stimulate endothelial repair because it fails to induce endothelial NO production. Mechanistically, this was because HDLCAD activated endothelial lectin-like oxidized LDL receptor 1 (LOX-1), triggering endothelial PKCβII activation, which in turn inhibited eNOS-activating pathways and eNOS-dependent NO production. We then identified reduced HDL-associated paraoxonase 1 (PON1) activity as one molecular mechanism leading to the generation of HDL with endothelial PKCβII-activating properties, at least in part due to increased formation of malondialdehyde in HDL. Taken together, our data indicate that in patients with CAD, HDL gains endothelial LOX-1- and thereby PKCβII-activating properties due to reduced HDL-associated PON1 activity, and that this leads to inhibition of eNOS-activation and the subsequent loss of the endothelial antiinflammatory and endothelial repair-stimulating effects of HDL.

High-density lipoprotein hydrolysis by endothelial lipase activates PPARalpha: a candidate mechanism for high-density lipoprotein-mediated repression of leukocyte adhesion

Although high-density lipoprotein (HDL) is known to inhibit endothelial adhesion molecule expression, the mechanism for this anti-inflammatory effect remains obscure. Surprisingly, we observed that HDL no longer decreased adhesion of U937 monocytoid cells to tumor necrosis factor (TNF)alpha-stimulated human endothelial cells (EC) in the presence of the general lipase inhibitor tetrahydrolipstatin. In considering endothelial mechanisms responsible for this effect, we found that endothelial lipase (EL) overexpression in both EC and non-EL-expressing NIH/3T3 mouse embryonic fibroblasts cells significantly decreased TNFalpha-induced VCAM1 expression and promoter activity in a manner dependent on HDL concentration and intact EL activity. Given recent evidence for lipolytic activation of peroxisome proliferator-activated receptors (PPARs)-nuclear receptors implicated in metabolism, atherosclerosis, and inflammation-we hypothesized HDL hydrolysis by EL is an endogenous endothelial mechanism for PPAR activation. In both EL-transfected NIH cells and bovine EC, HDL significantly increased PPAR ligand binding domain activation in the order PPAR-alpha> >-gamma>-delta. Moreover, HDL stimulation induced expression of the canonical PPARalpha-target gene acyl-CoA-oxidase (ACO) in a PPARalpha-dependent manner in ECs. Conditioned media from EL-adenovirus transfected cells but not control media exposed to HDL also activated PPARalpha. PPARalpha activation by EL was most potent with HDL as a substrate, with lesser effects on LDL and VLDL. Finally, HDL inhibited leukocyte adhesion to TNFalpha-stimulated ECs isolated from wild-type but not PPARalpha-deficient mice. This data establishes HDL hydrolysis by EL as a novel, distinct natural pathway for PPARalpha activation and identifies a potential mechanism for HDL-mediated repression of VCAM1 expression, with significant implications for both EL and PPARs in inflammation and vascular biology.