Papers by Arnold Von Eckardstein
Cells, Apr 28, 2021
The vascular endothelium serves as a barrier between the intravascular and extravascular compartm... more The vascular endothelium serves as a barrier between the intravascular and extravascular compartments. High-density lipoproteins (HDL) have two kinds of interactions with this barrier. First, bloodborne HDL must pass the endothelium to access extravascular tissues, for example the arterial wall or the brain, to mediate cholesterol efflux from macrophages and other cells or exert other functions. To complete reverse cholesterol transport, HDL must even pass the endothelium a second time to re-enter circulation via the lymphatics. Transendothelial HDL transport is a regulated process involving scavenger receptor SR-BI, endothelial lipase, and ATP binding cassette transporters A1 and G1. Second, HDL helps to maintain the integrity of the endothelial barrier by (i) promoting junction closure as well as (ii) repair by stimulating the proliferation and migration of endothelial cells and their progenitor cells, and by preventing (iii) loss of glycocalix, (iv) apoptosis, as well as (v) transmigration of inflammatory cells. Additional vasoprotective functions of HDL include (vi) the induction of nitric oxide (NO) production and (vii) the inhibition of reactive oxygen species (ROS) production. These vasoprotective functions are exerted by the interactions of HDL particles with SR-BI as well as specific agonists carried by HDL, notably sphingosine-1-phophate (S1P), with their specific cellular counterparts, e.g., S1P receptors. Various diseases modify the protein and lipid composition and thereby the endothelial functionality of HDL. Thorough understanding of the structure-function relationships underlying the multiple interactions of HDL with endothelial cells is expected to elucidate new targets and strategies for the treatment or prevention of various diseases.
International Journal of Molecular Sciences, Aug 22, 2022
High-density lipoprotein (HDL) is a mixture of complex particles mediating reverse cholesterol tr... more High-density lipoprotein (HDL) is a mixture of complex particles mediating reverse cholesterol transport (RCT) and several cytoprotective activities. Despite its relevance for human health, many aspects of HDL-mediated lipid trafficking and cellular signaling remain elusive at the molecular level. During HDL's journey throughout the body, its functions are mediated through interactions with cell surface receptors on different cell types. To characterize and better understand the functional interplay between HDL particles and tissue, we analyzed the surfaceome-residing receptor neighborhoods with which HDL potentially interacts. We applied a combination of chemoproteomic technologies including automated cell surface capturing (auto-CSC) and HATRIC-based ligand-receptor capturing (HATRIC-LRC) on four different cellular model systems mimicking tissues relevant for RCT. The surfaceome analysis of EA.hy926, HEPG2, foam cells, and human aortic endothelial cells (HAECs) revealed the main currently known HDL receptor scavenger receptor B1 (SCRB1), as well as 155 shared cell surface receptors representing potential HDL interaction candidates. Since vascular endothelial growth factor A (VEGF-A) was recently found as a regulatory factor of transendothelial transport of HDL, we next analyzed the VEGF-modulated surfaceome of HAEC using the auto-CSC technology. VEGF-A treatment led to the remodeling of the surfaceome of HAEC cells, including the previously reported higher surfaceome abundance of SCRB1. In total, 165 additional receptors were found on HAEC upon VEGF-A treatment representing SCRB1 co-regulated receptors potentially involved in HDL function. Using the HATRIC-LRC technology on human endothelial cells, we specifically aimed for the identification of other bona fide (co-)receptors of HDL beyond SCRB1. HATRIC-LRC enabled, next to SCRB1, the identification of the receptor tyrosine-protein kinase Mer (MERTK). Through RNA interference, we revealed its contribution to endothelial HDL binding and uptake. Furthermore, subsequent proximity ligation assays (PLAs) demonstrated the spatial vicinity of MERTK and SCRB1 on the endothelial cell surface. The data shown provide direct evidence for a complex and dynamic HDL receptome and that receptor nanoscale organization may influence binding and uptake of HDL.
CardioMetabolic Syndrome Journal
Low plasma levels of high density lipoprotein (HDL) cholesterol (HDL-C) are associated with incre... more Low plasma levels of high density lipoprotein (HDL) cholesterol (HDL-C) are associated with increased risks of several diseases including atherosclerotic cardiovascular disease and diabetes mellitus type 2. In cell culture and animal models, HDL particles exert manifold biological activities that indicate causality. However, results of both randomized controlled trials and genetic Mendelian randomization studies contradicted any causal role and, hence, suitability as a therapeutic target of HDL-C. However, HDL-C does not mirror the structural and functional complexity of HDL particles. Altogether, hundreds of different proteins and lipid species have been identified in HDL. Many of them exert specific functions. This physiological heterogeneity is further increased in inflammatory diseases by the loss or structural modification of typical HDL constituents or by the acquisition of atypical constituents. Moreover, genetic variation in several genes which are important in regulating HDL metabolism or function are associated with risks of diseases but not with differences in HDL-C. Comprehensive knowledge of gene-structure-function-disease relationships of HDL-associated molecules is a pre-requisite to test them for their relative physiological and pathogenic importance and to exploit them for treatment and diagnostics. Hypothesis-freeomics strategies led to the discovery of a series of potentially interesting molecules and modes of action. Their exploitation is hampered by the lack of confidence in HDL and strategies towards validation in preclinical models as well as by epidemiological and clinical studies.
European Heart Journal
Previous interest in high-density lipoproteins (HDLs) focused on their possible protective role i... more Previous interest in high-density lipoproteins (HDLs) focused on their possible protective role in atherosclerotic cardiovascular disease (ASCVD). Evidence from genetic studies and randomized trials, however, questioned that the inverse association of HDL-cholesterol (HDL-C) is causal. This review aims to provide an update on the role of HDL in health and disease, also beyond ASCVD. Through evolution from invertebrates, HDLs are the principal lipoproteins, while apolipoprotein B-containing lipoproteins first developed in vertebrates. HDLs transport cholesterol and other lipids between different cells like a reusable ferry, but serve many other functions including communication with cells and the inactivation of biohazards like bacterial lipopolysaccharides. These functions are exerted by entire HDL particles or distinct proteins or lipids carried by HDL rather than by its cholesterol cargo measured as HDL-C. Neither does HDL-C measurement reflect the efficiency of reverse cholestero...
Circulation Research, 2020
Journal of Lipid Research, 2020
Loss of pancreatic β-cell mass and function as a result of sustained ER stress is a core step in ... more Loss of pancreatic β-cell mass and function as a result of sustained ER stress is a core step in the pathogenesis of diabetes mellitus type 2. The complex control of β-cells and insulin production involves hedgehog (Hh) signaling pathways as well as cholesterol-mediated effects. In fact, data from studies in humans and animal models suggest that HDL protects against the development of diabetes through inhibition of ER stress and β-cell apoptosis. We investigated the mechanism by which HDL inhibits ER stress and apoptosis induced by thapsigargin, a sarco/ER Ca2+-ATPase inhibitor, in β-cells of a rat insulinoma cell line, INS1e. We further explored effects on the Hh signaling receptor Smoothened (SMO) with pharmacologic agonists and inhibitors. Interference with sterol synthesis or efflux enhanced β-cell apoptosis and abrogated the anti-apoptotic activity of HDL. During ER stress, HDL facilitated the efflux of specific oxysterols, including 24-hydroxycholesterol (OHC). Supplementation...
Drugs, 2016
The use of low-density lipoprotein cholesterol (LDL-C)-lowering medications has led to a signific... more The use of low-density lipoprotein cholesterol (LDL-C)-lowering medications has led to a significant reduction of cardiovascular risk in both primary and secondary prevention. Statin therapy, one of the cornerstones for the prevention and treatment of cardiovascular disease (CVD), has been demonstrated to be effective in lowering LDL-C levels and in reducing the risk for CVD and is generally well-tolerated. However, compliance with statins remains suboptimal. One of the main reasons is limitations by adverse events, notably myopathies, which can lead to non-compliance with the prescribed statin regimen. Reducing the burden of elevated LDL-C levels is critical in patients with CVD as well as in patients with very high baseline levels of LDL-C (e.g. patients with familial hypercholesterolaemia), as statin therapy is insufficient for optimally reducing LDL-C below target values. In this review, we discuss alternative treatment options after maximally tolerated doses of statin therapy, including ezetimibe, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors, and cholesteryl ester transfer protein (CETP) inhibitors. Difficult-to-treat patients may benefit from combination therapy with ezetimibe or a PCSK9 inhibitor (evolocumab or alirocumab, which are now available). Updates of treatment guidelines are needed to guide the management of patients who will best benefit from these new treatments. Although statins have proven to be a valuable and efficacious low-density lipoprotein cholesterol (LDL-C)-lowering medication, they may not be sufficient or appropriate for every patient in need. Some patients may benefit from additional or alternative approaches for LDL-C lowering, particularly those with familial hypercholesterolaemia and other patients in whom LDL-C lowering is not sufficient or who are intolerant to statins. Alternative therapies should be considered for patients who do not reach their LDL-C target, for example, ezetimibe or proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors.
Journal of the American Heart Association, 2012
Proceedings of the National Academy of Sciences, 1994
Previous studies have identified lipid-poor high density lipoproteins with electrophoretic pre-be... more Previous studies have identified lipid-poor high density lipoproteins with electrophoretic pre-beta mobility as the initial acceptors of cell-derived cholesterol in human plasma. These lipoproteins contain apolipoprotein A-I (apo A-I) as their sole apolipoprotein. In the present study, incubation of human plasma with [3H]cholesterol-laden skin fibroblasts has led to the identification of another lipoprotein that serves as a potent initial acceptor of cell-derived cholesterol. This lipoprotein, which we term gamma-LpE, exhibits gamma mobility on agarose gel electrophoresis. As determined by nondenaturing PAGE and by electron microscopy, the size of the spherical particle ranges between 12 and 16 nm. SDS/PAGE and subsequent immunoblotting identified apoE as its sole apolipoprotein. Plasma from normal and apoA-I-deficient mice, but not from apoE-deficient mice, released [3H]cholesterol from fibroblasts into a gamma-migrating lipoprotein. Cell culture media from hepatoma cells or mouse ...
Journal of Clinical Investigation, 2011
Therapies that raise levels of HDL, which is thought to exert atheroprotective effects via effect... more 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 (HDL CAD ) does not have endothelial antiinflammatory effects and does not stimulate endothelial repair because it fails to induce endothelial NO production. Mechanistically, this was because HDL CAD 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.
European Heart Journal, 2010
Endocrine Reviews, 2003
A significant and independent association between endogenous testosterone (T) levels and coronary... more A significant and independent association between endogenous testosterone (T) levels and coronary events in men and women has not been confirmed in large prospective studies, although cross-sectional data have suggested coronary heart disease can be associated with low T in men. Hypoandrogenemia in men and hyperandrogenemia in women are associated with visceral obesity; insulin resistance; low highdensity lipoprotein (HDL) cholesterol (HDL-C); and elevated triglycerides, low-density lipoprotein cholesterol, and plasminogen activator type 1. These gender differences and confounders render the precise role of endogenous T in atherosclerosis unclear. Observational studies do not support the hypothesis that dehydroepiandrosterone sulfate deficiency is a risk factor for coronary artery disease. The effects of exogenous T on cardiovascular mortality or morbidity have not been extensively investigated in prospective controlled studies; preliminary data suggest there may be short-term improvements in electrocardiographic changes in men with coronary artery disease. In the majority of animal experiments, exogenous T exerts either neutral or beneficial effects on the development of atherosclerosis. Exogenous androgens induce both apparently beneficial and deleterious effects on cardiovascular risk factors by decreasing serum levels of HDL-C, plasminogen activator type 1 (apparently deleterious), lipoprotein (a), fibrinogen, insulin, leptin, and visceral fat mass (apparently beneficial) in men as well as women. However, androgen-induced declines in circulating HDL-C should not automatically be assumed to be proatherogenic, because these declines may instead reflect accelerated reverse cholesterol transport. Supraphysiological concentrations of T stimulate vasorelaxation; but at physiological concentrations, beneficial, neutral, and detrimental effects on vascular reactivity have been observed. T exerts proatherogenic effects on macrophage function by facilitating the uptake of modified lipoproteins and an antiatherogenic effect by stimulating efflux of cellular cholesterol to HDL. In conclusion, the inconsistent data, which can only be partly explained by differences in dose and source of androgens, militate against a meaningful assessment of the net effect of T on atherosclerosis. Based on current evidence, the therapeutic use of T in men need not be restricted by concerns regarding cardiovascular side effects. Available data also do not justify the uncontrolled use of T or dehydroepiandrosterone for the prevention or treatment of coronary heart disease. (Endocrine Reviews 24: 183-217, 2003) I. Introduction II. The Gender Difference in Coronary Artery Disease III. Relationships between Serum Levels of T and CAD-Observational Studies A. T and CAD in men B. T and CAD in women IV. Relationships between Serum Levels of T and CAD-Interventional Clinical Studies A. Endogenous androgen deprivation B. Androgen excess from anabolic steroid abuse C. Exogenous T treatment in men with CAD D. Exogenous T treatment in women V. Relationships between Serum Levels of T and CAD-Animal Studies VI. Effects of T on Cardiovascular Risk Factors A. Associations between endogenous T and cardiovascular risk factors: role of adipose tissue and insulin B. Effects of puberty on cardiovascular risk factors C. Effects of exogenous T on cardiovascular risk factors VII. Effects of T on Cells of the Arterial Wall and Vascular Function A. Vascular expression of sex hormone receptors and T converting enzymes B. Effects of T on vascular reactivity C. Effects of T on macrophage functions D. Effects of T on arterial smooth muscle functions E. Effects of T on platelet functions VIII. DHEA(S) and CAD in Men and Women IX. Estrogens and Cardiovascular Disease in Men X. Summary and Conclusion XI. Clinical Implications
Diabetes, 2002
Low HDL cholesterol is a frequent cardiovascular risk factor in diabetes. Because of its pivotal ... more Low HDL cholesterol is a frequent cardiovascular risk factor in diabetes. Because of its pivotal role for the regulation of HDL plasma levels, we investigated in vivo and in vitro regulation of the ATP-binding cassette transporter A1 (ABCA1) by insulin and metabolites accumulating in diabetes. Compared with euglycemic control mice, ABCA1 gene expression was severely decreased in the liver and peritoneal macrophages of diabetic mice. Treatment with insulin restored this deficit. Incubation of cultivated HepG2 hepatocytes and RAW264.7 macrophages with unsaturated fatty acids or acetoacetate, but not with insulin, glucose, saturated fatty acids, or hydroxybutyrate, downregulated ABCA1 mRNA and protein. The suppressive effect of unsaturated fatty acids and acetoacetate became most obvious in cells stimulated with oxysterols or retinoic acid but was independent of the expression of the thereby regulated transcription factors liver-X-receptor α (LXRα) and retinoid-X-receptor α (RXRα), res...
Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 1993
ABSTRACT We have recreated and expressed two known natural mutations within the LCAT gene which w... more ABSTRACT We have recreated and expressed two known natural mutations within the LCAT gene which were reported on both alleles in a single case of familial LCAT deficiency. We demonstrate that the Ala-93-->Thr mutation is responsible for the biochemical defect while the Arg-158-->Cys mutation is a co-inherited natural polymorphism of LCAT which results in normal enzyme function.
Atherosclerosis, 2011
Secretion of 27-hydroxycholesterol (27OHC) from macrophages is considered as an alternative to HD... more Secretion of 27-hydroxycholesterol (27OHC) from macrophages is considered as an alternative to HDLmediated reverse transport of excess cholesterol. We investigated 27OHC-concentrations in plasma of humans and mice with monogenic disorders of HDL metabolism. As compared to family controls mutations in the genes for apolipoprotein A-I, ATP binding cassette transporter (ABC) A1 and lecithin:cholesterol acylstransferase (LCAT) were associated with reduced concentrations of both HDLcholesterol and HDL-27OHC whereas mutations in the genes for cholesterylester transfer protein (CETP), scavenger receptor type BI and hepatic lipase were associated with elevated HDL concentrations of either sterol. Compared to family controls and relative to the concentrations of total 27OHC and cholesterol, lower 27OHC-ester but normal cholesterylester levels were found in HDL of heterozygous LCAT mutation carriers and nonHDL of heterozygous CETP mutation carriers. In family controls, LCAT activity and CETP mass were more strongly correlated with 27OHC-ester than cholesterylester concentrations in HDL and nonHDL, respectively. These findings suggest that the formation and transfer of 27OHC-esters are more sensitive to reduced activities of LCAT and CETP, respectively, than the formation and transfer of cholesterylesters. 27OHC plasma levels were also decreased in apoA-I-, ABCA1-or LCAT-knockout mice but increased in SR-BI-knockout mice. Transplantation of ABCA1-and/or ABCG1-deficient bone marrow into LDL receptor deficient mice decreased plasma levels of 27OHC. In conclusion, mutations or absence of HDL genes lead to distinct alterations in the quantity, esterification or lipoprotein distribution of 27OHC. These findings argue against the earlier suggestion that 27OHC-metabolism in plasma occurs independently of HDL.
Handbook of Experimental Pharmacology, 2014
High-density lipoproteins (HDLs) exert many beneficial effects which may help to protect against ... more High-density lipoproteins (HDLs) exert many beneficial effects which may help to protect against the development or progression of atherosclerosis or even facilitate lesion regression. These activities include promoting cellular cholesterol efflux, protecting low-density lipoproteins (LDLs) from modification, preserving endothelial function, as well as anti-inflammatory and antithrombotic effects. However, questions remain about the relative importance of these activities for atheroprotection. Furthermore, the many molecules (both lipids and proteins) associated with HDLs exert both distinct and overlapping activities, which may be compromised by inflammatory conditions, resulting in either loss of function or even gain of dysfunction. This complexity of HDL functionality has so far precluded elucidation of distinct structure-function relationships for HDL or its components. A better understanding of HDL metabolism and structure-function relationships is therefore crucial to exploit HDLs and its associated components and cellular pathways as potential targets for anti-atherosclerotic therapies and diagnostic markers.
Atherosclerosis, 2022
Apolipoprotein D (apoD) is a lipocalin exerting neuroprotective effects. However, the relevance o... more Apolipoprotein D (apoD) is a lipocalin exerting neuroprotective effects. However, the relevance of apoD in respect to cardiovascular risk is largely unexplored. Therefore, this study aimed to evaluate the ability of apoD to predict future all-cause mortality, cardiovascular mortality, and cardiovascular events. Serum apoD levels were measured in a cohort of 531 Caucasian individuals who underwent coronary angiography (356 males, 175 females; mean age 65 ± 10 years). Fatal and non-fatal events were recorded over a median follow-up period of 5.8 years. ApoD concentrations at baseline correlated significantly with age, presence of the metabolic syndrome, body mass index, lipoprotein levels, fasting glucose, and estimated glomerular filtration rate. Kaplan-Meier curve analyses by gender-stratified quartiles of apoD revealed that the cumulative incidence rates of mortality and cardiovascular events become higher with increasing apoD levels. The adjusted hazard ratios for participants in the highest quartile of apoD compared to those in the lowest quartile were 4.00 (95% confidence interval [CI] 1.49-10.74) for overall mortality, 5.47 (95% CI 1.20-25.00) for cardiovascular mortality, and 2.52 (95% CI 1.28-5.00) for cardiovascular events. High circulating levels of apoD are an indicator of poor prognosis in patients with suspected or established coronary artery disease.
Biomolecules, Mar 8, 2023
Biomarkers are important tools to improve the early detection of patients at high risk for develo... more Biomarkers are important tools to improve the early detection of patients at high risk for developing diabetes as well as the stratification of diabetic patients towards risks of complications. In addition to clinical variables, we analyzed 155 metabolic parameters in plasma samples of 51 healthy volunteers and 66 patients with diabetes using nuclear magnetic resonance (NMR) spectrometry. Upon elastic net analysis with lasso regression, we confirmed the independent associations of diabetes with branched-chain amino acids and lactate (both positive) as well as linoleic acid in plasma and HDL diameter (both inverse). In addition, we found the presence of diabetes independently associated with lower concentrations of free cholesterol in plasma but higher concentrations of free cholesterol in small HDL. Compared to plasmas of non-diabetic controls, plasmas of diabetic subjects contained lower absolute and relative concentrations of free cholesterol in all LDL and HDL subclasses except small HDL but higher absolute and relative concentrations of free cholesterol in all VLDL subclasses (except very small VLDL). These disbalances may reflect disturbances in the transfer of free cholesterol from VLDL to HDL during lipolysis and in the transfer of cell-derived cholesterol from small HDL via larger HDL to LDL.
Journal of Biological Chemistry, Feb 1, 2020
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Papers by Arnold Von Eckardstein