High-density lipoprotein stimulates endothelial cell movement by a mechanism distinct from basic fibroblast growth factor

Functional characterization of the dimeric form of PDGF-derived fusion peptide fabricated based on theoretical arguments

A skin wound leads to the loss of skin integrity and the influx of pathogens into the tissue. Platelet-derived growth factors (PDGFs) are cytokines released from alpha granules during wound healing and interact with their cell surface receptors and activate signals involved in chemotaxis, growth, proliferation, and differentiation pathways. Due to the low stability of growth factors (GFs), a new peptide-derived PDGF-BB was designed, expressed in the Shuffle strain of E. coli, and purified by Ni-NTA agarose affinity column chromatography. The effect of fusion peptide was then evaluated on L929 fibroblast cells and animal models with skin lesions. In vitro, studies showed that the peptide led to an increase in the migration of fibroblast cells in the scratch assay. Its positive effect on wound healing was also observed in the skin-injured rats after 3, 7, and 12 days. A significant rise in neutrophils and granular tissue formation, re-epithelialization, angiogenesis, and collagen formation was exhibited on the third day of treatment when compared to the control group. The results showed that, despite reducing PDGF size, the fusion peptide was able to maintain at least some of the known functions attributed to full-length PDGF and showed positive results in wound healing.

Chymase released from hypoxia-activated cardiac mast cells cleaves human apoA-I at Tyr192 and compromises its cardioprotective activity

ApoA-I, the main structural and functional protein of HDL particles, is cardioprotective, but also highly sensitive to proteolytic cleavage. Here, we investigated the effect of cardiac mast cell activation and ensuing chymase secretion on apoA-I degradation using isolated rat hearts in the Langendorff perfusion system. Cardiac mast cells were activated by injection of compound 48/80 into the coronary circulation or by low-flow myocardial ischemia, after which lipid-free apoA-I was injected and collected in the coronary effluent for cleavage analysis. Mast cell activation by 48/80 resulted in apoA-I cleavage at sites Tyr¹⁹² and Phe²²⁹, but hypoxic activation at Tyr¹⁹² only. In vitro, the proteolytic end-product of apoA-I with either rat or human chymase was the Tyr¹⁹²-truncated fragment. This fragment, when compared with intact apoA-I, showed reduced ability to promote migration of cultured human coronary artery endothelial cells in a wound-healing assay. We propose that C-terminal truncation of apoA-I by chymase released from cardiac mast cells during ischemia impairs the ability of apoA-I to heal damaged endothelium in the ischemic myocardium.

Disorders of lipid metabolism in nephrotic syndrome: mechanisms and consequences

Nephrotic syndrome results in hyperlipidemia and profound alterations in lipid and lipoprotein metabolism. Serum cholesterol, triglycerides, apolipoprotein B (apoB)-containing lipoproteins (very low-density lipoprotein [VLDL], immediate-density lipoprotein [IDL], and low-density lipoprotein [LDL]), lipoprotein(a) (Lp[a]), and the total cholesterol/high-density lipoprotein (HDL) cholesterol ratio are increased in nephrotic syndrome. This is accompanied by significant changes in the composition of various lipoproteins including their cholesterol-to-triglyceride, free cholesterol-to-cholesterol ester, and phospholipid-to-protein ratios. These abnormalities are mediated by changes in the expression and activities of the key proteins involved in the biosynthesis, transport, remodeling, and catabolism of lipids and lipoproteins including apoproteins A, B, C, and E; 3-hydroxy-3-methylglutaryl-coenzyme A reductase; fatty acid synthase; LDL receptor; lecithin cholesteryl ester acyltransferase; acyl coenzyme A cholesterol acyltransferase; HDL docking receptor (scavenger receptor class B, type 1 [SR-B1]); HDL endocytic receptor; lipoprotein lipase; and hepatic lipase, among others. The disorders of lipid and lipoprotein metabolism in nephrotic syndrome contribute to the development and progression of cardiovascular and kidney disease. In addition, by limiting delivery of lipid fuel to the muscles for generation of energy and to the adipose tissues for storage of energy, changes in lipid metabolism contribute to the reduction of body mass and impaired exercise capacity. This article provides an overview of the mechanisms, consequences, and treatment of lipid disorders in nephrotic syndrome.

HDL abnormalities in nephrotic syndrome and chronic kidney disease

Normal HDL activity confers cardiovascular and overall protection by mediating reverse cholesterol transport and through its potent anti-inflammatory, antioxidant, and antithrombotic functions. Serum lipid profile, as well as various aspects of HDL metabolism, structure, and function can be profoundly altered in patients with nephrotic range proteinuria or chronic kidney disease (CKD). These abnormalities can, in turn, contribute to the progression of cardiovascular complications and various other comorbidities, such as foam cell formation, atherosclerosis, and/or glomerulosclerosis, in affected patients. The presence and severity of proteinuria and renal insufficiency, as well as dietary and drug regimens, pre-existing genetic disorders of lipid metabolism, and renal replacement therapies (including haemodialysis, peritoneal dialysis, and renal transplantation) determine the natural history of lipid disorders in patients with kidney disease. Despite the adverse effects associated with dysregulated reverse cholesterol transport and advances in our understanding of the underlying mechanisms, safe and effective therapeutic interventions are currently lacking. This Review provides an overview of HDL metabolism under normal conditions, and discusses the features, mechanisms, and consequences of HDL abnormalities in patients with nephrotic syndrome or advanced CKD.

Effect of anti-ApoA-I antibody-coating of stents on neointima formation in a rabbit balloon-injury model

Background and Aims

Since high-density lipoprotein (HDL) has pro-endothelial and anti-thrombotic effects, a HDL recruiting stent may prevent restenosis. In the present study we address the functional characteristics of an apolipoprotein A-I (ApoA-I) antibody coating in vitro. Subsequently, we tested its biological performance applied on stents in vivo in rabbits.

Materials and Methods

The impact of anti ApoA-I- versus apoB-antibody coated stainless steel discs were evaluated in vitro for endothelial cell adhesion, thrombin generation and platelet adhesion. In vivo, response to injury in the iliac artery of New Zealand white rabbits was used as read out comparing apoA-I-coated versus bare metal stents.

Results

ApoA-I antibody coated metal discs showed increased endothelial cell adhesion and proliferation and decreased thrombin generation and platelet adhesion, compared to control discs. In vivo, no difference was observed between ApoA-I and BMS stents in lumen stenosis (23.3±13.8% versus 23.3±11.3%, p=0.77) or intima surface area (0.81±0.62 mm² vs 0.84±0.55 mm², p=0.85). Immunohistochemistry also revealed no differences in cell proliferation, fibrin deposition, inflammation and endothelialization.

Conclusion

ApoA-I antibody coating has potent pro-endothelial and anti-thrombotic effects in vitro, but failed to enhance stent performance in a balloon injury rabbit model in vivo.

Scavenger receptor class B type I regulates cellular cholesterol metabolism and cell signaling associated with breast cancer development

Introduction

Previous studies have identified cholesterol as an important regulator of breast cancer development. High-density lipoprotein (HDL) and its cellular receptor, the scavenger receptor class B type I (SR-BI) have both been implicated in the regulation of cellular cholesterol homeostasis, but their functions in cancer remain to be established.

Methods

In the present study, we have examined the role of HDL and SR-BI in the regulation of cellular signaling pathways in breast cancer cell lines and in the development of tumor in a mouse xenograft model.

Results

Our data show that HDL is capable of stimulating migration and can activate signal transduction pathways in the two human breast cancer cell lines, MDA-MB-231 and MCF7. Furthermore, we also show that knockdown of the HDL receptor, SR-BI, attenuates HDL-induced activation of the phosphatidylinositol 3-kinase (PI3K)/protein Kinase B (Akt) pathway in both cell lines. Additional investigations show that inhibition of the PI3K pathway, but not that of the mitogen-activated protein kinase (MAPK) pathway, could lead to a reduction in cellular proliferation in the absence of SR-BI. Importantly, whereas the knockdown of SR-BI led to decreased proliferation and migration in vitro, it also led to a significant reduction in tumor growth in vivo. Most important, we also show that pharmacological inhibition of SR-BI can attenuate signaling and lead to decreased cellular proliferation in vitro. Taken together, our data indicate that both cholesteryl ester entry via HDL-SR-BI and Akt signaling play an essential role in the regulation of cellular proliferation and migration, and, eventually, tumor growth.

Conclusions

These results identify SR-BI as a potential target for the treatment of breast cancer.

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

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

LXRβ/estrogen receptor-α signaling in lipid rafts preserves endothelial integrity

Liver X receptors (LXR) are stimulated by cholesterol-derived oxysterols and serve as transcription factors to regulate gene expression in response to alterations in cholesterol. In the present study, we investigated the role of LXRs in vascular endothelial cells (ECs) and discovered that LXRβ has nonnuclear function and stimulates EC migration by activating endothelial NOS (eNOS). This process is mediated by estrogen receptor-α (ERα). LXR activation promoted the direct binding of LXRβ to the ligand-binding domain of ERα and initiated an extranuclear signaling cascade that requires ERα Ser118 phosphorylation by PI3K/AKT. Further studies revealed that LXRβ and ERα are colocalized and functionally coupled in EC plasma membrane caveolae/lipid rafts. In isolated aortic rings, LXR activation of NOS caused relaxation, while in mice, LXR activation stimulated carotid artery reendothelialization via LXRβ- and ERα-dependent processes. These studies demonstrate that LXRβ has nonnuclear function in EC caveolae/lipid rafts that entails crosstalk with ERα, which promotes NO production and maintains endothelial monolayer integrity in vivo.

High-density lipoprotein nitration and chlorination catalyzed by myeloperoxidase impair its effect of promoting endothelial repair

High-density lipoprotein (HDL) plays a key role in protecting against atherosclerosis. In cardiovascular disease, HDL can be nitrated and chlorinated by myeloperoxidase (MPO). In this study, we discovered that MPO-oxidized HDL is dysfunctional in promoting endothelial repair compared to normal HDL. Proliferation assay, wound healing, and transwell migration experiments showed that MPO-oxidized HDL was associated with a reduced stimulation of endothelial cell (EC) proliferation and migration. In addition, we found that Akt and ERK1/2 phosphorylation in ECs was significantly lower when ECs were incubated with oxidized HDL compared with normal HDL. To further determine whether oxidized HDL diminished EC migration through the PI3K/Akt and MEK/ERK pathways, we performed experiments with inhibitors of both these pathways. The transwell experiments performed in the presence of these inhibitors showed that the migration capacity was reduced and the differences observed between normal HDL and oxidized HDL were diminished. Furthermore, to study the effects of oxidized HDL on endothelial cells in vivo, we performed a carotid artery electric injury model on nude mice injected with either normal or oxidized HDL. Oxidized HDL inhibited reendothelialization compared to normal HDL in vivo. These findings implicate a key role for MPO-oxidized HDL in the pathogenesis of cardiovascular disease.

Regulation of signal transduction by HDL

High density lipoprotein (HDL) cholesterol has direct effects on numerous cell types that influence cardiovascular and metabolic health. These include endothelial cells, vascular smooth-muscle cells, leukocytes, platelets, adipocytes, skeletal muscle myocytes, and pancreatic β cells. The effects of HDL or apoA-I, its major apolipoprotein, occur through the modulation of intracellular calcium, oxygen-derived free-radical production, numerous kinases, and enzymes, including endothelial nitric-oxide synthase (eNOS). ApoA-I and HDL also influence gene expression, particularly genes encoding mediators of inflammation in vascular cells. In many paradigms, the change in intracellular signaling occurs as a result of cholesterol efflux, with the cholesterol acceptor methyl-β-cyclodextrin often invoking responses identical to HDL or apoA-I. The ABC transporters ABCA1 and ABCG1 and scavenger receptor class B, type I (SR-BI) frequently participate in the cellular responses. Structure-function relationships are emerging for signal initiation by ABCA1 and SR-BI, with plasma membrane cholesterol binding by the C-terminal transmembrane domain of SR-BI uniquely enabling it to serve as a sensor of changes in membrane cholesterol. Further investigation of the processes underlying HDL and apoA-I modulation of intracellular signaling will potentially reveal new prophylactic and therapeutic strategies to optimize both cardiovascular and metabolic health.

Uraemic dyslipidaemia revisited: role of high-density lipoprotein

Chronic kidney disease (CKD) is accompanied by strong cardiovascular risk. In a rather rigid picture of lipoprotein biology, low-density lipoprotein (LDL) is referred to as 'bad cholesterol', while high-density lipoprotein (HDL) is referred to as 'good cholesterol'. However, recent experimental evidence suggests that HDL may be rendered dysfunctional regarding its effects on the vasculature under various clinical conditions such as CKD. Indeed, HDL from the blood of CKD patients has been shown to transform into a particle which promotes endothelial dysfunction, endothelial proinflammatory activation and, thereby, sets the conditions for the development of atherosclerotic disease. Notably, pharmaceutical interventions to raise serum HDL-cholesterol levels have not been proven beneficial so far. Collectively, these findings indicate that HDL cholesterol levels do not represent a valuable marker for indicating the vascular properties of HDL.

Class II phosphoinositide 3-kinases contribute to endothelial cells morphogenesis

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

Novel biological functions of high-density lipoprotein cholesterol

In addition to its role in reverse cholesterol transport, high-density lipoprotein (HDL) cholesterol has direct action on numerous cell types that influence cardiovascular and metabolic health. Cellular responses to HDL entail its capacity to invoke cholesterol efflux that causes signal initiation via scavenger receptor class B, type I, and plasma membrane receptor activation by HDL cargo molecules. In endothelial cells and their progenitors, HDL attenuates apoptosis and stimulates proliferation and migration. HDL also has diverse anti-inflammatory actions in both endothelial cells and leukocytes. In vascular smooth muscles, HDL tempers proinflammatory, promigratory, and degradative processes, and through actions on endothelium and platelets HDL is antithrombotic. There are additional actions of HDL of potential cardiovascular consequence that are indirect, including the capacities to promote pancreatic β-cell insulin secretion, to protect pancreatic β cells from apoptosis, and to enhance glucose uptake by skeletal muscle myocytes. Furthermore, HDL decreases white adipose tissue mass, increases energy expenditure, and promotes the production of adipose-derived cytokine adiponectin that has its own vascular-protective properties. Many of these numerous actions of HDL have been observed not only in cell culture and animal models but also in human studies, and assessments of these functions are now being applied to patient populations to better-elucidate which actions of HDL may contribute to its cardioprotective potential and how they can be quantified and targeted. Further work on the many mechanisms of HDL action promises to reveal new prophylactic and therapeutic strategies to optimize both cardiovascular and metabolic health.

Novel biological functions of high-density lipoprotein cholesterol

In addition to its role in reverse cholesterol transport, high-density lipoprotein (HDL) cholesterol has direct action on numerous cell types that influence cardiovascular and metabolic health. Cellular responses to HDL entail its capacity to invoke cholesterol efflux that causes signal initiation via scavenger receptor class B, type I, and plasma membrane receptor activation by HDL cargo molecules. In endothelial cells and their progenitors, HDL attenuates apoptosis and stimulates proliferation and migration. HDL also has diverse anti-inflammatory actions in both endothelial cells and leukocytes. In vascular smooth muscles, HDL tempers proinflammatory, promigratory, and degradative processes, and through actions on endothelium and platelets HDL is antithrombotic. There are additional actions of HDL of potential cardiovascular consequence that are indirect, including the capacities to promote pancreatic β-cell insulin secretion, to protect pancreatic β cells from apoptosis, and to enhance glucose uptake by skeletal muscle myocytes. Furthermore, HDL decreases white adipose tissue mass, increases energy expenditure, and promotes the production of adipose-derived cytokine adiponectin that has its own vascular-protective properties. Many of these numerous actions of HDL have been observed not only in cell culture and animal models but also in human studies, and assessments of these functions are now being applied to patient populations to better-elucidate which actions of HDL may contribute to its cardioprotective potential and how they can be quantified and targeted. Further work on the many mechanisms of HDL action promises to reveal new prophylactic and therapeutic strategies to optimize both cardiovascular and metabolic health.

Diabetic HDL is dysfunctional in stimulating endothelial cell migration and proliferation due to down regulation of SR-BI expression

BACKGROUND

Diabetic HDL had diminished capacity to stimulate endothelial cell (EC) proliferation, migration, and adhesion to extracellular matrix. The mechanism of such dysfunction is poorly understood and we therefore sought to determine the mechanistic features of diabetic HDL dysfunction.

METHODOLOGY/PRINCIPAL FINDINGS

We found that the dysfunction of diabetic HDL on human umbilical vein endothelial cells (HUVECs) was associated with the down regulation of the HDL receptor protein, SR-BI. Akt-phosphorylation in HUVECs was induced in a biphasic manner by normal HDL. While diabetic HDL induced Akt phosphorylation normally after 20 minutes, the phosphorylation observed 24 hours after diabetic HDL treatment was reduced. To determine the role of SR-BI down regulation on diminished EC responses of diabetic HDL, Mouse aortic endothelial cells (MAECs) were isolated from wild type and SR-BI (-/-) mice, and treated with normal and diabetic HDL. The proliferative and migratory effects of normal HDL on wild type MAECs were greatly diminished in SR-BI (-/-) cells. In contrast, response to diabetic HDL was impaired in both types suggesting diminished effectiveness of diabetic HDL on EC proliferation and migration might be due to the down regulation of SR-BI. Additionally, SR-BI down regulation diminishes diabetic HDL's capacity to activate Akt chronically.

CONCLUSIONS/SIGNIFICANCE

Diabetic HDL was dysfunctional in promoting EC proliferation, migration, and adhesion to matrix which was associated with the down-regulation of SR-BI. Additionally, SR-BI down regulation diminishes diabetic HDL's capacity to activate Akt chronically.

Sumoylation of vimentin354 is associated with PIAS3 inhibition of glioma cell migration

The invasive phenotype of glioblastoma multiforme (GBM) is a hallmark of malignant process, yet the molecular mechanisms that dictate this locally invasive behavior remain poorly understood. Over-expression of PIAS3 effectively changes cell shape and inhibits GBM cell migration. We focused on the molecular target(s) of PIAS3 stimulated sumoylation, which play an important role in the inhibition of GBM cell motility. Here we report, through the immunoprecipitation with SUMO1 antibody, followed by proteomic analysis, the identification of vimentin (vimentin354), a nuclear component in GBM cells, as the main target of sumoylation promoted by PIAS3.

Proteomic analysis of swine serum following highly virulent classical swine fever virus infection

Background

Classical swine fever virus (CSFV) belongs to the genus Pestivirus within the family Flaviviridae. Virulent strains of classical swine fever virus (CSFV) cause severe disease in pigs characterized by immunosuppression, thrombocytopenia and disseminated intravascular coagulation, which causes significant economic losses to the pig industry worldwide.

Methods

To reveal proteomic changes in swine serum during the acute stage of lethal CSFV infection, 5 of 10 pigs were inoculated with the virulent CSFV Shimen strain, the remainder serving as uninfected controls. A serum sample was taken at 3 days post-infection from each swine, at a stage when there were no clinical symptoms other than increased rectal temperatures (≥40°C). The samples were treated to remove serum albumin and immunoglobulin (IgG), and then subjected to two-dimension differential gel electrophoresis.

Results

Quantitative intensity analysis revealed 17 protein spots showing at least 1.5-fold quantitative alteration in expression. Ten spots were successfully identified by MALDI-TOF MS or LTQ MS. Expression of 4 proteins was increased and 6 decreased in CSFV-infected pigs. Functions of these proteins included blood coagulation, anti-inflammatory activity and angiogenesis.

Conclusion

These proteins with altered expression may have important implications in the pathogenesis of classical swine fever and provide a clue for identification of biomarkers for classical swine fever early diagnosis.

Sumoylation of vimentin354 is associated with PIAS3 inhibition of glioma cell migration

The invasive phenotype of glioblastoma multiforme (GBM) is a hallmark of malignant process, yet the molecular mechanisms that dictate this locally invasive behavior remain poorly understood. Over-expression of PIAS3 effectively changes cell shape and inhibits GBM cell migration. We focused on the molecular target(s) of PIAS3 stimulated sumoylation, which play an important role in the inhibition of GBM cell motility. Here we report, through the immunoprecipitation with SUMO1 antibody, followed by proteomic analysis, the identification of vimentin (vimentin354), a nuclear component in GBM cells, as the main target of sumoylation promoted by PIAS3.

Emerging high-density lipoprotein infusion therapies: fulfilling the promise of epidemiology?

High-density lipoprotein (HDL) plays a key role in reverse cholesterol transport but also activates nitric oxide synthase and stimulates prostacyclin release, enhances endothelial repair, inhibits cell adhesion molecule expression on vascular endothelium and monocyte recruitment into the arterial wall, and exerts antithrombotic effects. In experimental animals, infusions of HDL or apolipoprotein A-1 (apoA-1) halt the progression or induce regression of atherosclerosis, with favorable effects on plaque composition. Remarkably, a benefit is observed after a single infusion. In a pilot study, weekly infusions of ETC-216, a formulation of recombinant apoA-1 Milano, were administered at two doses for 5 weeks to patients beginning within 2 weeks of an acute coronary syndrome (ACS). Among the 47 patients completing the study, percent atheroma volume by intracoronary ultrasound was reduced in the combined active treatment groups but not in the placebo group. In a larger trial, the Effect of rHDL on Atherosclerosis-Safety and efficacy (ERASE), 183 post-ACS patients were randomized to 4 weekly infusions of placebo or one of two doses of CSL-111, which consists of apoA-1 derived from human plasma and combined with soybean phosphatidylcholine. The greater dose was discontinued because of a high incidence of hepatic enzyme elevation. Among the 136 patients with evaluable end point data, percent change in atheroma volume, the primary endpoint, improved significantly in the CSL-111 group but not in the placebo group. The secondary end points of plaque characterization indices and quantitative coronary angiographic changes both improved significantly in the CSL-111 group compared with the group receiving placebo. Taken together, this evidence suggests that infusions of HDL or apoA-1 may reduce events, particularly among patients with ACS.

Antioxidant therapy reverses impaired graft healing in hypercholesterolemic rabbits

OBJECTIVE

Limited endothelial cell (EC) coverage and anastomotic intimal hyperplasia contribute to thrombosis and failure of prosthetic grafts. Lipid accumulation and lipid oxidation are associated with decreased EC migration and intimal hyperplasia. The goal of this study was to assess the ability of antioxidants to improve graft healing in hypercholesterolemic animals.

METHODS

Rabbits were placed in one of four groups: chow plus N-acetylcysteine (NAC), chow plus probucol, chow with 1% cholesterol plus NAC, or chow with 1% cholesterol plus probucol. After 2 weeks, expanded polytetrafluoroethylene grafts (12 cm long x 4-mm internal diameter) were implanted in the abdominal aorta. Grafts were removed after 6 weeks and analyzed for cholesterol content, EC coverage, anastomotic intimal thickness, and the cellular composition of the neointima. Plasma samples were obtained to assess systemic oxidative stress. The data were compared with previously reported data from animals fed diets of chow and chow with 1% cholesterol.

RESULTS

Prosthetic grafts from rabbits fed chow with 1% cholesterol had significantly greater anastomotic intimal thickening and lower EC coverage than grafts from rabbits fed a regular chow diet. In hypercholesterolemic rabbits, antioxidant therapy decreased global oxidative stress as evidenced by a 40% decrease in plasma thiobarbituric acid reactive substances. In rabbits fed the chow with 1% cholesterol diet, NAC decreased intimal hyperplasia at the proximal anastomosis by 29% and significantly increased graft EC coverage from 46% to 71% (P = .03). Following a similar pattern, probucol decreased intimal hyperplasia by 43% and increased graft EC coverage to 53% in hypercholesterolemic rabbits.

CONCLUSIONS

Global oxidative stress and anastomotic intimal hyperplasia are increased, and endothelialization of prosthetic grafts is significantly reduced in rabbits fed a high-cholesterol diet. Antioxidant treatment improves EC coverage and decreases intimal hyperplasia. Reducing oxidative stress may promote healing of prosthetic grafts.

Prospective studies on the relationship between high-density lipoprotein cholesterol and cardiovascular risk: a systematic review

Epidemiological studies have extensively evaluated the association between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) risk. The objective of this systematic review was to enumerate the number of original prospective studies that showed a significant association between HDL-C and CVD risk and provided evidence of the consistency of this association across other lipid risk factors. A systematic MEDLINE literature search identified 53 prospective cohort and five nested case-control studies that provided multivariate assessments of the association between HDL-C and CVD risk. Among these 58 prospective studies, 31 studies found a significant inverse association between HDL-C and CVD risk for all CVD outcomes and subpopulations studied, whereas 17 studies found a significant association for some CVD outcomes and/or subpopulations assessed. The ratio of studies that found a significant association out of the total studies identified was similar across all CVD outcomes, although there was less evidence for stroke and atherosclerotic outcomes. Only seven studies tested for the consistency of this association across other lipid risk factors, of which six studies suggested that the association was consistent across other lipid levels. In conclusion, the association between HDL-C and CVD risk is significant and strong, although further evidence may be needed to establish whether this association is consistent across other lipid risk factors. Furthermore, uncertainties remain regarding the mechanism in which HDL-C exerts its effects, suggesting a need for further research focused on new methods for reliable measurement.

Role of High-Density Lipoprotein and Scavenger Receptor B Type I in the Promotion of Endothelial Repair

There is considerable experimental evidence that high-density lipoprotein (HDL) cholesterol and the principal high-affinity HDL receptor scavenger receptor B type I (SR-BI) afford cardiovascular protection. However, the fundamental mechanisms underlying the protection remain complex and not well understood. Recent work in cell culture indicates that the HDL-SR-BI tandem stimulates endothelial cell migration. Further studies have revealed that this entails Src-mediated, phosphatidylinositol 3-kinase-mediated, and mitogen-activated protein kinase-mediated signaling that leads to the activation of Rac guanosine triphosphate hydrolase and the resultant rearrangement of the actin cytoskeleton. Furthermore, assessment of reendothelialization after perivascular electric injury in mice indicates that HDL-SR-BI-mediated stimulation of endothelial migration is operative in vivo. Recent additional work in mice also indicates that HDL activates the recruitment of endothelial progenitor cells into the intimal layer in the setting of endothelial injury. As such, signaling initiated by HDL-SR-BI promotes endothelial repair, and this novel mechanism of action may be critically involved in the impact of the lipoprotein on vascular health and disease.

Molecular mechanisms responsible for the antiinflammatory and protective effect of HDL on the endothelium

In addition to their role in reverse cholesterol transport, high-density lipoproteins (HDL) exert several beneficial effects, including the prevention and correction of endothelial dysfunction. HDL promote endothelium proliferation and diminish endothelial apoptosis; they play a key role in vasorelaxation by increasing the release of nitric oxide and prostacyclin through the induction of the expression and the activity of endothelial nitric oxide synthase and the coupling of cyclooxygenase 2 and prostacyclin synthase. In addition, HDL affect coagulation, fibrynolisis, platelet adhesion, adhesion molecules, and protease expression, and they exert antioxidant activity. These effects are achieved at the gene expression level and are dependent on the activation of several intracellular signaling pathways, including PI3K/Akt, ERK1/2, PKC, and p38MAPK. The complexity of the signaling pathways modulated by HDL reflects the different effects of the components of this class of lipoproteins such as apolipoproteins or lipids on endothelial cell gene expression and the subsequent modulation of endothelial function observed. The in vivo relevance of these findings to endothelial recovery during physiological or pathological conditions remains to be addressed; nevertheless, the results of clinical studies with synthetic HDL, ApoA-I mimetics, and drugs that are becoming available that selectively affect HDL plasma levels and biological functions support the importance of the correction of endothelial function by HDL.

Role of reactive oxygen species in inhibition of endothelial cell migration by oxidized low-density lipoprotein

OBJECTIVE

Endothelial cell migration is inhibited by oxidized low-density lipoprotein (oxLDL) and lysophosphatidylcholine (lysoPC). The purpose of this study was to explore the mechanism of this inhibition, specifically the role of reactive oxygen species.

METHODS

The ability of oxLDL, lysoPC, and known superoxide generators to stimulate endothelial cell production of reactive oxygen species and inhibit endothelial cell migration under the same conditions was assessed. Reactive oxygen species production was assessed with dichlorofluorescein. Migration was studied with a razor scrape assay and measured after 24 hours. In addition, the ability of various antioxidants, added before initiation of the scrape assay, to restore endothelial cell migration in oxLDL was determined.

RESULTS

OxLDL and lysoPC, at concentrations that stimulated reactive oxygen species production, also inhibited endothelial cell migration. Other agents that generated superoxide also inhibited endothelial cell migration, but hydrogen peroxide did not. Of a variety of antioxidants assessed for their ability to preserve endothelial cell migration in the presence of oxLDL, only superoxide dismutase and reduced nicotinamide adenine dinucleotide (phosphate) oxidase inhibitors (diphenyleneiodonium, quinacrine, hydralazine) preserved endothelial cell migration.

CONCLUSIONS

These data suggest that oxLDL inhibits endothelial cell migration through a superoxide-dependent mechanism and that reduced nicotinamide adenine dinucleotide (phosphate) oxidase is the cellular source of the superoxide.

CLINICAL RELEVANCE

OxLDL inhibits endothelial cell migration, and may impair healing of arterial injuries. The mechanism of oxidized LDL inhibition is not known. Our in vitro studies show that the inhibitory properties are related to production of reactive oxygen species. Superoxide dismutase or inhibitors of reduced nicotinamide adenine dinucleotide phosphate oxidase can preserve endothelial migration in the presence of oxLDL. This might improve the healing of endothelial injuries at sites of arterial repair or angioplasty, especially in lipid-laden arterial walls.

High density lipoproteins (HDLs) and atherosclerosis; the unanswered questions

The concentration of high density lipoprotein-cholesterol (HDL-C) has been found consistently to be a powerful negative predictor of premature coronary heart disease (CHD) in human prospective population studies. There is also circumstantial evidence from human intervention studies and direct evidence from animal intervention studies that HDLs protect against the development of atherosclerosis. HDLs have several documented functions, although the precise mechanism by which they prevent atherosclerosis remains uncertain. Nor is it known whether the cardioprotective properties of HDL are specific to one or more of the many HDL subpopulations that comprise the HDL fraction in human plasma. Several lifestyle and pharmacological interventions have the capacity to raise the level of HDL-C, although it is not known whether all are equally protective. Indeed, despite the large body of information identifying HDLs as potential therapeutic targets for the prevention of atherosclerosis, there remain many unanswered questions that must be addressed as a matter of urgency before embarking wholesale on HDL-C-raising therapies as strategies to prevent CHD. This review summarises what is known and highlights what we still need to know.

High density lipoprotein-induced endothelial nitric-oxide synthase activation is mediated by Akt and MAP kinases

High density lipoprotein (HDL) activates endothelial nitric-oxide synthase (eNOS), leading to increased production of the antiatherogenic molecule NO. A variety of stimuli regulate eNOS activity through signaling pathways involving Akt kinase and/or mitogen-activated protein (MAP) kinase. In the present study, we investigated the role of kinase cascades in HDL-induced eNOS stimulation in cultured endothelial cells and COS M6 cells transfected with eNOS and the HDL receptor, scavenger receptor B-I. HDL (10-50 microg/ml, 20 min) caused eNOS phosphorylation at Ser-1179, and dominant negative Akt inhibited both HDL-mediated phosphorylation and activation of the enzyme. Phosphoinositide 3-kinase (PI3 kinase) inhibition or dominant negative PI3 kinase also blocked the phosphorylation and activation of eNOS by HDL. Studies with genistein and PP2 showed that the nonreceptor tyrosine kinase, Src, is an upstream stimulator of the PI3 kinase-Akt pathway in this paradigm. In addition, HDL activated MAP kinase through PI3 kinase, and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibition fully attenuated eNOS stimulation by HDL without affecting Akt or eNOS Ser-1179 phosphorylation. Conversely, dominant negative Akt did not alter HDL-induced MAP kinase activation. These results indicate that HDL stimulates eNOS through common upstream, Src-mediated signaling, which leads to parallel activation of Akt and MAP kinases and their resultant independent modulation of the enzyme.

Detection of oxidized high-density lipoprotein

This paper reviews working procedures for the separation and detection of oxidized high-density lipoproteins (ox-HDL) and their constituents. It begins with an introductory overview of structural alterations of the HDL particle and its constituents generated during oxidation. The main body of the review delineates various procedures for the isolation and detection of ox-HDL as well as the purification and separation of phosphatidylcholine metabolites and denatured apolipoproteins in the particle. The useful methods published more recently are picked up and the utility of the separation techniques is described. The last section covers a clinical evaluation of changes in these factors in ox-HDL as well as future directions of ox-HDL research.

Plasma lipoproteins behave as carriers of extracellular sphingosine 1-phosphate: is this an atherogenic mediator or an anti-atherogenic mediator?

Sphingosine 1-phosphate (S1P) concentration in plasma and serum has been estimated to be within 200-900 nM. Among plasma and serum components, S1P is concentrated in lipoprotein fractions with a rank order of high-density lipoprotein (HDL)>low-density lipoprotein (LDL)>very low-density lipoprotein (VLDL)>lipoprotein-deficient plasma (LPDP) when expressed as the per unit amount of protein. It is well known that LDL, especially oxidized LDL, is closely correlated and HDL is inversely correlated, with the risk of cardiovascular disease, such as atherosclerosis. Evidence was presented that a part of HDL-induced actions previously reported are mediated by the lipoprotein-associated S1P. Furthermore, S1P content in LDL was markedly decreased during its oxidation. This paper will discuss whether S1P is an atherogenic mediator or an anti-atherogenic mediator.

Fibroblast growth factor 2 enhances early stages of in vitro endothelial repair by microfilament bundle reorganization and cell elongation

As endothelial cells convert from quiescent to migrating cells over 8 h along a wound edge, actin microfilaments undergo well-defined sequential changes characterized by an initial random distribution followed by a parallel and then a perpendicular orientation of microfilaments with respect to the wound edge. The latter is associated with subsequent cell migration. We tested the hypothesis that fibroblast growth factor 2 (FGF-2) can enhance the very early stages of wound repair even prior to migration and that FGF-2 enhancement of wound repair is associated with changes in the endothelial actin cytoskeleton. Using an in vitro two-sided wound model, the addition of FGF-2 at the time of wounding enhanced the extent of wound closure over 8 h. Treatment with FGF-2 was associated with significantly longer cells along the wound edge at 4 and 8 h after wounding. When treated with increasing concentrations of neutralizing FGF-2 antibody, the extent of wound closure decreased over 8 h and was associated with a decrease in cell length along the wound edge. Actin microfilaments were localized using rhodamine phalloidin and viewed using laser confocal microscopy. At 4 h after wounding, FGF-2 treatment was associated with significantly more cells along the wound expressing perpendicular microfilaments compared to untreated cells, which suggested a more rapid transition of parallel to perpendicular microfilament distribution. Thus, FGF-2 affects the very early stages of wound repair prior to migration by enhancing wound closure due to the early appearance of perpendicular microfilaments and lengthening of cells along the wound edge.

Effects of growth factors and trefoil peptides on migration and replication in primary oxyntic cultures

Restitution, the lateral migration of cells over an intact basement membrane, maintains mucosal integrity. We studied the regulation of migration and proliferation of enzyme-dispersed canine oxyntic mucosa cells in primary culture. Confluent monolayers were wounded and cultured in serum-free medium, and cells migrating into the wound were counted. [3H]thymidine incorporation into DNA was studied using subconfluent cultures. Considerable migration occurred in untreated monolayers; however, epidermal growth factor (EGF), transforming growth factor (TGF)-alpha, basic fibroblast growth factor (bFGF), insulin-like growth factor I (IGF-I), two trefoil peptides, and interleukin (IL)-1beta further enhanced migration. The specific EGF receptor (EGFR) monoclonal antibody, MAb-528, inhibited both basal and TGF-alpha- or IL-1beta-stimulated migration, but not the response to trefoil peptide, bFGF, or IGF-I. Exogenous TGF-beta inhibited cell proliferation but did not alter migration. Immunoneutralization with anti-TGF-beta blocked the response to exogenous TGF-beta and produced a small enhancement of basal thymidine incorporation but did not attenuate basal or TGF-alpha-stimulated migration. In conclusion, endogenous EGFR ligands regulate proliferation and migration. TGF-beta inhibits mitogenesis; it did not upregulate migration in these cultures. Although bFGF, IGF-I, and IL-1beta enhance gastric epithelial migration, only IL-1beta acted in a TGF-alpha-dependent fashion.

High-density lipoprotein: multipotent effects on cells of the vasculature

The epidemiological evidence showing a strong inverse correlation between the level of plasma high-density lipoprotein (HDL) and the incidence of heart disease suggests that HDL has a protective effect against cardiovascular disease. The mechanism of this protective effect has been the raison d'etre for much research. The ability of HDL to mediate cholesterol efflux from peripheral tissues has been used to explain the cardioprotective effect of HDL. However, there is little direct evidence to suggest that in subjects with low plasma levels of HDL the rate of cholesterol efflux from peripheral tissues is significantly reduced. This observation suggested that HDL may be mediating its protective effect through other mechanisms. This review provides an account of the burgeoning evidence that HDL has many effects on cellular processes, in addition to the effects on cholesterol efflux, and will illustrate the multipotency of this lipoprotein.

Possible role of high susceptibility of high-density lipoprotein to lipid peroxidative modification and oxidized high-density lipoprotein in genesis of coronary artery spasm

Recent study demonstrated high susceptibility of plasma LDL to lipid peroxidative modification in patients with variant angina. Oxidized stress state, especially oxidized LDL, may induce coronary artery spasm by its impairing effect of endothelium-dependent arterial relaxation, but precise mechanisms remain unclear. Study subjects included 93 patients who underwent coronary angiographic examination: 12 patients with coronary artery spasm provoked by ergonovine without organic stenosis (group I), 11 patients who did not demonstrate coronary artery spasm or organic stenosis (group II) and 70 patients with organic coronary artery stenosis (group III). Levels of plasma HDL-cholesterol and apoA-I in group I were similar to those in III but were significantly lower than those in II, although the other plasma lipid parameters were not different among the three groups. The levels of TBARS in plasma and HDL were significantly higher in group I than in II or III (2.94+/-1.56 vs. 1.91+/-0.35 or 2.23+/-0.89 nmol MDA/ml and 1.23+/-1.00 vs. 0.54+/-0.37 or 0.70+/-0.63 nmol MDA/mg protein; P < 0.05), although the levels of TBARS in LDL were not significantly different. In the monitoring curve of diene production during copper-induced lipid peroxidation of HDL, its propagation slope was steeper and levels of maximum diene absorbance was higher in group I as compared with that in II or III, but not found in those of LDL. These results suggested that high susceptibility of HDL to lipid peroxidative modification in group I may contribute to the genesis of coronary artery spasm, and oxidized HDL rather than oxidized LDL is more likely to be related to coronary artery spasm.

Oxidation of low density lipoproteins in the pathogenesis of atherosclerosis

Malondialdehyde (MDA)-modified and oxidized low density lipoproteins (LDL) have been demonstrated in atherosclerotic lesions. Elevated titers of autoimmune antibodies specific for MDA-modified LDL predicted the progression of carotid atherosclerosis and of myocardial infarction. Recently, elevated levels of MDA-modified LDL were detected in the plasma of patients with ischemic heart disease, whereas, elevated levels of oxidized LDL were detected in the plasma of patients with ischemic heart disease and of heart transplant patients with post-transplant cardiovascular disease. Although increased levels of autoimmune antibodies against oxidatively modified LDL and increased levels of oxidized LDL antigen appear to be associated with atherosclerotic cardiovascular disease, there is to date no direct proof of the causal role of oxidized LDL in atherothrombosis. However, the decreased risk of cardiovascular disease associated with the administration of antioxidants (e.g. vitamin E), estrogen supplementation and increased levels of high density lipoproteins (HDL) may, at least partially, be due to the inhibition of oxidation of LDL or to the reversal of the atherothrombotic effects of oxidized LDL.

Arachidonic acid pretreatment enhances smooth muscle cell migration via increased Ca2+ influx

It is well known that vascular smooth muscle cell (SMC) migration is an initial step in atheromatous plaque formation. In the present study, we investigated the effects of arachidonic acid (AA, 20:4 n-6) on bovine carotid artery SMC migration using the modified Boyden chamber technique. SMCs pretreated with 2.5 microg/ml of AA for 2 days, showed an enhanced migration response to fetal bovine serum. AA pretreatment (0.5-5.0 microg/ml) increased fetal bovine serum-induced SMC migration dose-dependently, and maximum stimulation was observed at a concentration of 2.5 microg/ml. However, AA pretreatment did not enhance fetal bovine serum-induced endothelial cell migration. Using lipid analysis, we found that AA was substantially incorporated into cellular phospholipids. When SMC migration was induced by platelet derived growth factor (PDGF)-BB, instead of serum, the stimulative effect of AA pretreatment was retained. SMCs pretreated with AA showed greater mobilization of intracellular Ca2+ in response to PDGF-BB than SMCs without AA pretreatment (controls). Nifedipine, a Ca2+ channel blocker, and glycoletherdiamine-tetraacetic acid (EGTA) had no effect on PDGF-induced migration of controls but both drugs reduced the enhanced PDGE-induced migration of AA-pretreated SMCs to the control level. Baicalein, an inhibitor of 12-lipoxygenase, reduced PDGF-BB-induced migration of both control and AA pretreated SMCs, however the AA-pretreated cells still showed enhanced migration compared to control cells. These findings suggest that AA accelerates SMC migration in the thickening of the intima during atheroma formation, via stimulation of extracellular Ca2+ influx.

Characterization of single-cell migration using a computer-aided fluorescence time-lapse videomicroscopy system

Single-cell assays of cell migration, while yielding dynamic measurements of cell position and morphology, are predominantly limited by the time required for data collection and analysis. Computer-aided fluorescence time-lapse videomicroscopy (CAFTiV) was developed in order to facilitate the tracking and rapid examination of large numbers of motile cells. The system combines time-lapse videomicroscopy with epifluorescence capability, which allows full automation of image capture, sorting, and analysis due to the low background in the fluorescence images. Utilizing the CAFTiV system, data analysis time was reduced from over 125 h to less than 1 labor minute. In addition, fluorescence imaging permits cell tracking in small-volume chambers (<100 microL), which is useful should the addition of expensive reagents be required. It is anticipated that the ability to characterize both biochemical and biophysical properties responsible for cell movement will be enhanced by this methodology.

Role of lysophosphatidylcholine in the inhibition of endothelial cell motility by oxidized low density lipoprotein

Endothelial cell (EC) movement is required for the development and repair of blood vessels. We have previously shown that LDL oxidized by transition metals almost completely suppressed the wound-healing migratory response of vascular EC in vitro. We now report that lysophosphatidylcholine (lysoPC), a lipid component of oxidized LDL, has an important role in the antimigratory activity of the lipoprotein. Purified 1-palmitoyl lysoPC inhibited movement with a half-maximal activity at 12-15 micrometers, and near complete inhibition at 20 micrometers; the inhibitory concentration of lysoPC was consistent with its abundance in oxidized LDL. The inhibition was not due to cytotoxicity since protein synthesis was unaffected and since EC movement was restored after removal of lysoPC. Lysophospholipid activity was dependent on lipid structure. LysoPC's containing 1-position C16 or C18 saturated fatty acids were antimigratory, but those containing C < or = 14 saturated fatty acids or polyunsaturated fatty acids were not. The activity of 1-palmitoyl lysolipids with various head groups was examined. Lysophosphatidylinositol was more antimigratory than lysophosphatidylglycerol and lysophosphatidylcholine, which were more potent than lysophosphatidylserine and lysophosphatidylethanolamine. Monoglyceride was inactive while lysophosphatidate had promigratory activity. These results are consistent with head group size rather than charge as a critical determinant of activity. To show that lysophospholipids within an intact lipoprotein were active, LDL was treated with bee venom phospholipase A2 (PLA2). The modified lipoprotein inhibited EC movement to the same extent as iron-oxidized LDL and antimigratory activity correlated with the amount of lysoPC formed. To determine antimigratory activity of lysoPC present in oxidized LDL, lipid extracts from oxidized LDL were fractionated by normal phase HPLC. The fraction comigrating with lysoPC had nearly the same activity as the total extract confirming that lysoPC (or a co-eluting lipid) was a major antimigratory molecule in oxidized LDL. These studies demonstrate that lysoPC in oxidized LDL limit EC wound healing responses in vitro, and suggest a possible role for lysolipids in limiting endothelial regeneration after a denuding injury in vivo.