Oxidized low-density lipoprotein enhances monocyte-endothelial cell binding against shear-stress-induced detachment

HDL and plaque regression in a multiphase model of early atherosclerosis

Atherosclerosis is a chronic disease of the arteries characterised by the accumulation of lipids and lipid-engorged cells in the artery wall. Early plaque growth is aggravated by the deposition of low density lipoproteins (LDL) in the wall and the subsequent immune response. High density lipoproteins (HDL) counterbalance the effects of LDL by accepting cholesterol from macrophages and removing it from the plaque. In this paper, we develop a free boundary multiphase model to investigate the effects of LDL and HDL on early plaque development. We examine how the rates of LDL and HDL deposition affect cholesterol accumulation in macrophages, and how this impacts cell death rates and emigration. We identify a region of LDL-HDL parameter space where plaque growth stabilises for low LDL and high HDL influxes, due to macrophage emigration and HDL clearance that counterbalances the influx of new cells and cholesterol. We explore how the efferocytic uptake of dead cells and the recruitment of new macrophages affect plaque development for a range of LDL and HDL influxes. Finally, we consider how changes in the LDL-HDL profile can change the course of plaque development. We show that changes towards lower LDL and higher HDL can slow plaque growth and even induce regression. We find that these changes have less effect on larger, more established plaques, and that temporary changes will only slow plaque growth in the short term.

Macrophage Anti-inflammatory Behaviour in a Multiphase Model of Atherosclerotic Plaque Development

Atherosclerosis is an inflammatory disease characterised by the formation of plaques, which are deposits of lipids and cholesterol-laden macrophages that form in the artery wall. The inflammation is often non-resolving, due in large part to changes in normal macrophage anti-inflammatory behaviour that are induced by the toxic plaque microenvironment. These changes include higher death rates, defective efferocytic uptake of dead cells, and reduced rates of emigration. We develop a free boundary multiphase model for early atherosclerotic plaques, and we use it to investigate the effects of impaired macrophage anti-inflammatory behaviour on plaque structure and growth. We find that high rates of cell death relative to efferocytic uptake results in a plaque populated mostly by dead cells. We also find that emigration can potentially slow or halt plaque growth by allowing material to exit the plaque, but this is contingent on the availability of live macrophage foam cells in the deep plaque. Finally, we introduce an additional bead species to model macrophage tagging via microspheres, and we use the extended model to explore how high rates of cell death and low rates of efferocytosis and emigration prevent the clearance of macrophages from the plaque.

Malondialdehyde as an Important Key Factor of Molecular Mechanisms of Vascular Wall Damage under Heart Diseases Development

This mini review is devoted to a specific issue: the role of malondialdehyde (MDA)-a secondary product of free radical lipid peroxidation-in the molecular mechanisms of the formation of primary atherosclerotic vascular wall lesions. The principal difference between this review and the available literature is that it discusses in detail the important role in atherogenesis not of "oxidized" LDL (i.e., LDL particles containing lipohydroperoxides), but of LDL particles chemically modified by the natural low-molecular weight dicarbonyl MDA. To confirm this, we consider the data obtained by us earlier, indicating that "atherogenic" are not LDL oxidized as a result of free radical lipoperoxidation and containing lipohydroperoxy derivatives of phospholipids in the outer layer of particles, but LDL whose apoprotein B-100 has been modified due to the chemical reaction of terminal lysine residue amino groups of the apoB-100 with the aldehyde groups of the MDA (Maillard reaction). In addition, we present our original data proving that MDA injures endothelial glycocalyx that suppress the ability of the endothelium to control arterial tone according to changes in wall shear stress. In summary, this mini review for the first time exhaustively discloses the key role of MDA in atherogenesis.

Effects of lipoproteins on endothelial cells and macrophages function and its possible implications on fetal adverse outcomes associated to maternal hypercholesterolemia during pregnancy

Hypercholesterolemia is one of the main risk factors associated with atherosclerosis and cardiovascular disease, the leading cause of death worldwide. During pregnancy, maternal hypercholesterolemia develops, and it can occur in a physiological (MPH) or supraphysiological (MSPH) manner, where MSPH is associated with endothelial dysfunction and early atherosclerotic lesions in the fetoplacental vasculature. In the pathogenesis of atherosclerosis, endothelial activation and endothelial dysfunction, characterized by an imbalance in the bioavailability of nitric oxide, contribute to the early stages of this disease. Macrophages conversion to foam cells, cholesterol efflux from these cells and its differentiation into a pro- or anti-inflammatory phenotype are also important processes that contribute to atherosclerosis. In adults it has been reported that native and modified HDL and LDL play an important role in endothelial and macrophage function. In this review it is proposed that fetal lipoproteins could be also relevant factors involved in the detrimental vascular effects described in MSPH. Changes in the composition and function of neonatal lipoproteins compared to adults has been reported and, although in MSPH pregnancies the fetal lipid profile does not differ from MPH, differences in the lipidomic profiles of umbilical venous blood have been reported, which could have implications in the vascular function. In this review we summarize the available information regarding the effects of lipoproteins on endothelial and macrophage function, emphasizing its possible implications on fetal adverse outcomes associated to maternal hypercholesterolemia during pregnancy.

A Spatially Resolved and Quantitative Model of Early Atherosclerosis

Atherosclerosis is a major burden for all societies, and there is a great need for a deeper understanding of involved key inflammatory, immunological and biomechanical processes. A decisive step for the prevention and medical treatment of atherosclerosis is to predict what conditions determine whether early atherosclerotic plaques continue to grow, stagnate or become regressive. The driving biological and mechanobiological mechanisms that determine the stability of plaques are yet not fully understood. We develop a spatially resolved and quantitative mathematical model of key contributors of early atherosclerosis. The stability of atherosclerotic model plaques is assessed to identify and classify progression-prone and progression-resistant atherosclerotic regions based on measurable or computable in vivo inputs, such as blood cholesterol concentrations and wall shear stresses. The model combines Darcy's law for the transmural flow through vessels walls, the Kedem-Katchalsky equations for endothelial fluxes of lipoproteins, a quantitative model of early plaque formation from a recent publication and a novel submodel for macrophage recruitment. The parameterization and analysis of the model suggest that the advective flux of lipoproteins through the endothelium is decisive, while the influence of the advective transport within the artery wall is negligible. Further, regions in arteries with an approximate wall shear stress exposure below 20% of the average exposure and their surroundings are potential regions where progression-prone atherosclerotic plaques develop.

Atherogenesis: hyperhomocysteinemia interactions with LDL, macrophage function, paraoxonase 1, and exercise

Despite great strides in understanding the atherogenesis process, the mechanisms are not entirely known. In addition to diet, cigarette smoking, genetic predisposition, and hypertension, hyperhomocysteinemia (HHcy), an accumulation of the noncoding sulfur-containing amino acid homocysteine (Hcy), is a significant contributor to atherogenesis. Although exercise decreases HHcy and increases longevity, the complete mechanism is unclear. In light of recent evidence, in this review, we focus on the effects of HHcy on macrophage function, differentiation, and polarization. Though there is need for further evidence, it is most likely that HHcy-mediated alterations in macrophage function are important contributors to atherogenesis, and HHcy-countering strategies, such as nutrition and exercise, should be included in the combinatorial regimens for effective prevention and regression of atherosclerotic plaques. Therefore, we also included a discussion on the effects of exercise on the HHcy-mediated atherogenic process.

Cryptotanshinone inhibits oxidized LDL-induced adhesion molecule expression via ROS dependent NF-κB pathways

Adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin, play important roles in the initial stage of atherosclerosis. Cryptotanshinone (CPT), a natural compound isolated from Salvia miltiorrhiza Bunge, exhibits anti-atherosclerotic activity although the underlying mechanisms remain elusive. In this study, the protective effect of CPT against oxidized low-density lipoprotein (ox-LDL)-induced adhesion molecule expression was investigated in human umbilical vein endothelial cells. Ox-LDL significantly induced ICAM-1, VCAM-1, and E-selectin expression at the mRNA and protein levels but reduced eNOS phosphorylation and NO generation, which were reversed by CPT pretreatment. Sodium nitroprusside, a NO donor, N-acetyl-L-cysteine (NAC), a reactive oxygen species (ROS) scavenger, and BAY117082, a NF-κB inhibitor, inhibited ox-LDL-induced ICAM-1, VCAM-1, and E-selectin expression. Ox-LDL-induced ROS production was significantly inhibited by CPT and NAC. Furthermore, ox-LDL activated the NF-κB signaling pathway by inducing phosphorylation of IKKβ and IκBα, promoting the interaction of IKKβ and IκBα, and increasing p65 nuclear translocation, which were significantly inhibited by CPT. In addition, CPT, NAC, and BAY117082 inhibited ox-LDL-induced membrane expression of ICAM-1, VCAM-1, E-selectin, and endothelial-monocyte adhesion and restored eNOS phosphorylation and NO generation. Results suggested that CPT inhibited ox-LDL-induced adhesion molecule expression by decreasing ROS and inhibiting the NF-κB pathways, which provides new insight into the anti-atherosclerotic mechanism of CPT.

Human scavenger protein AIM increases foam cell formation and CD36-mediated oxLDL uptake

AIM is expressed by macrophages in response to agonists of the nuclear receptors LXR/RXR. In mice, it acts as an atherogenic factor by protecting macrophages from the apoptotic effects of oxidized lipids. In humans, it is detected in atherosclerotic lesions, but no role related to atherosclerosis has been reported. This study aimed to investigate whether the role of hAIM extends beyond inhibiting oxidized lipid-induced apoptosis. To accomplish this goal, functional analysis with human monocytic THP1 cells and macrophages differentiated from peripheral blood monocytes were performed. It was found that hAIM reduced oxLDL-induced macrophage apoptosis and increased macrophage adhesion to endothelial ICAM-1 by enhancing LFA-1 expression. Furthermore, hAIM increased foam cell formation, as shown by Oil Red O and Nile Red staining, as well as quantification of cholesterol content. This was not a result of decreased reverse cholesterol transport, as hAIM did not affect the efflux significantly from [(3)H] Cholesterol-laden macrophages driven by plasma, apoA-I, or HDL2 acceptors. Rather, flow cytometry studies indicated that hAIM increased macrophage endocytosis of fluorescent oxLDL, which correlated with an increase in the expression of the oxLDLR CD36. Moreover, hAIM bound to oxLDL in ELISA and enhanced the capacity of HEK-293 cells expressing CD36 to endocytose oxLDL, as studied using immunofluorescence microscopy, suggesting that hAIM serves to facilitate CD36-mediated uptake of oxLDL. Our data represent the first evidence that hAIM is involved in macrophage survival, adhesion, and foam cell formation and suggest a significant contribution to atherosclerosis-related mechanisms in the macrophage.

Berberine‑attenuated monocyte adhesion to endothelial cells induced by oxidized low‑density lipoprotein via inhibition of adhesion molecule expression

Recruitment of monocytes to endothelial cells is important during early stages of atherosclerosis development. This process is predominantly mediated by cellular adhesion molecules, including vascular cell adhesion molecule‑1 (VCAM‑1) and intercellular adhesion molecule‑1 (ICAM‑1), which are expressed by activated endothelial cells in response to a number of inflammatory stimuli, including oxidized low‑density lipoprotein (oxLDL). Previous studies have demonstrated that berberine, a natural extract from Rhizoma coptidis, prevents oxLDL‑induced endothelial cellular apoptosis. However, its effect on the adhesion of monocytes to endothelial cells and the mechanism associated with this process remains unclear. In the present study, berberine was revealed to markedly reduce oxLDL‑induced monocyte adhesion to human umbilical vein endothelial cells. In addition, the inhibitory mechanism of berberine was associated with suppression of adhesion molecule expression, including VCAM‑1 and ICAM‑1. Results indicate that berberine plays a protective role in the early stages of atherosclerosis.

Endothelial cell activation promotes foam cell formation by monocytes following transendothelial migration in an in vitro model

Foam cells are a pathological feature present at all stages of atherosclerosis. Foam cells develop from monocytes that enter the nascent atheroma and subsequently ingest modified low density lipoproteins (LDL). The regulation of this process has previously been studied in vitro using cultured macrophage fed modified LDL. We used our existing in vitro model of transendothelial migration (TEM) to study this process in a more physiologically relevant setting. In our model, monocytes undergo TEM across a primary endothelial monolayer into an underlying three-dimensional collagen matrix in the presence of 20% human serum. Foam cells were detected by Oil Red O staining for intracellular lipid droplets. We demonstrate that sub-endothelial monocytes can develop into foam cells within 48 h of TEM across TNF-α activated endothelium, in the absence of additional lipids. Our data indicate a role for both monocyte-endothelial interactions and soluble factors in the regulation of foam cell development, including oxidation of LDL in situ from lipid present in culture medium following TNF-α stimulation of the endothelial cells. Our study provides a simple model for investigating foam cell development in vitro that mimics cell migration in vivo, and demonstrates the critical role of inflammation in regulating early atherogenic events.

The effect of oxidized low density lipoprotein (oxLDL)-induced heme oxygenase-1 on LPS-induced inflammation in RAW 264.7 macrophage cells

Macrophages take up oxidized low density lipoprotein (oxLDL) after being exposed to it in the blood vessels. oxLDL transforms macrophages into foam cells, which are a hallmark of atherosclerosis. The effects that oxLDL have on the inflammatory responses of foam cells are not clear. Here, we investigated how oxLDL modulates lipopolysaccharide (LPS)-induced inflammatory mediators in RAW 264.7 murine macrophages. Our results showed that oxLDL dramatically induced HO-1 expression, but did not increase pro-inflammatory mediators such as interleukin-1β, tumor necrosis factor-α, iNOS, and monocyte chemoattractant protein (MCP)-1. In RAW 264.7 macrophages, oxLDL markedly inhibited LPS-induced inflammatory mediators such as inducible nitric oxide synthase (iNOS), IL-1β, IL-6, granulocyte macrophage colony-stimulating factor and stromal cell-derived factor-1. Interestingly, however, the down-regulation of HO-1 by siRNA did not recover the inhibition of LPS-induced expression and/or the secretion of inflammatory mediators. oxLDL blocked LPS-induced NF-κB nuclear translocation by inhibiting inhibitory κB (IκB) degradation. Taken together, our results suggest that oxLDL could modulate LPS-induced inflammatory responses by inhibiting NF-κB signaling independently of HO-1 expression.

Enhanced growth and osteogenic differentiation of human osteoblast-like cells on boron-doped nanocrystalline diamond thin films

Intrinsic nanocrystalline diamond (NCD) films have been proven to be promising substrates for the adhesion, growth and osteogenic differentiation of bone-derived cells. To understand the role of various degrees of doping (semiconducting to metallic-like), the NCD films were deposited on silicon substrates by a microwave plasma-enhanced CVD process and their boron doping was achieved by adding trimethylboron to the CH₄:H₂ gas mixture, the B∶C ratio was 133, 1000 and 6700 ppm. The room temperature electrical resistivity of the films decreased from >10 MΩ (undoped films) to 55 kΩ, 0.6 kΩ, and 0.3 kΩ (doped films with 133, 1000 and 6700 ppm of B, respectively). The increase in the number of human osteoblast-like MG 63 cells in 7-day-old cultures on NCD films was most apparent on the NCD films doped with 133 and 1000 ppm of B (153,000±14,000 and 152,000±10,000 cells/cm², respectively, compared to 113,000±10,000 cells/cm² on undoped NCD films). As measured by ELISA per mg of total protein, the cells on NCD with 133 and 1000 ppm of B also contained the highest concentrations of collagen I and alkaline phosphatase, respectively. On the NCD films with 6700 ppm of B, the cells contained the highest concentration of focal adhesion protein vinculin, and the highest amount of collagen I was adsorbed. The concentration of osteocalcin also increased with increasing level of B doping. The cell viability on all tested NCD films was almost 100%. Measurements of the concentration of ICAM-1, i.e. an immunoglobuline adhesion molecule binding inflammatory cells, suggested that the cells on the NCD films did not undergo significant immune activation. Thus, the potential of NCD films for bone tissue regeneration can be further enhanced and tailored by B doping and that B doping up to metallic-like levels is not detrimental for cells.

Poloxamer 407 increases soluble adhesion molecules, ICAM-1, VCAM-1 and E-selectin, in C57BL/6 mice

Objectives

Soluble shedded forms of cell adhesion molecules (sCAMs) found in plasma are regarded as surrogate markers for the cellular expression of CAMs. The presence of oxidised low-density lipoprotein (ox-LDL) cholesterol and fatty acids in the plasma, hypertriglyceridaemia and reduced plasma concentrations of high-density lipoprotein cholesterol (HDL-C) are all thought to stimulate an increase in the cellular expression of CAMs such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1) and E-selectin. Our objectives were to determine how plasma levels of the soluble CAMs were modulated in a mouse model of dyslipidaemia induced chemically with poloxamer 407, and how these changes might be related to changes in the plasma concentrations of total cholesterol, HDL-C, non-HDL-C and triglycerides.

Methods

C57BL/6 mice were given a single intraperitoneal dose of poloxamer 407 (0.5 g/kg) and plasma concentrations of lipid fractions and sCAMs were measured at predetermined time points thereafter.

Key findings

The plasma concentrations of each sCAM were significantly increased in our mouse model of atherogenic dyslipidaemia compared with control mice administered saline, although the temporal relationship between the plasma sCAM concentration-time profiles and the plasma lipid concentration-time profiles were not coincident.

Conclusions

The atherogenic profile in our mouse model was associated with increases in the plasma concentrations of sICAM-1, sVCAM-1 and sE-selectin. These changes precede the formation of atherosclerotic lesions shown in previous work. This suggests the use of these sCAMs as biomarkers of future atheroma formation in this particular animal model.

Carbamylated Low-Density Lipoprotein Induces Monocyte Adhesion to Endothelial Cells Through Intercellular Adhesion Molecule-1 and Vascular Cell Adhesion Molecule-1

Objective— Carbamylated low-density lipoprotein (LDL), the most abundant modified LDL isoform in human blood, has been recently implicated in causing the atherosclerosis-prone injuries to endothelial cells in vitro and atherosclerosis in humans. This study was aimed at testing the hypothesis that carbamylated LDL acts via inducing monocyte adhesion to endothelial cells and determining the adhesion molecules responsible for the recruitment of monocytes.

Methods and Results— Exposure of human coronary artery endothelial cells with carbamylated LDL but not native LDL caused U937 monocyte adhesion and the induction of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 adhesion molecules as measured by cell enzyme-linked immunosorbent assay. Silencing of intercellular adhesion molecule-1 by siRNA or its inhibition using neutralizing antibody resulted in decreased monocyte adhesion to the endothelial cells. Similar silencing or neutralizing of vascular cell adhesion molecule-1 alone did not have an effect but was shown to contribute to intercellular adhesion molecule-1 when tested simultaneously.

Conclusions— Taken together, these data provide evidence that intercellular adhesion molecule-1 in cooperation with vascular cell adhesion molecule-1 are essential for monocyte adhesion by carbamylated low-density lipoprotein-activated human vascular endothelial cells in vitro.

Activation of Ca2+-activated potassium channels is involved in lysophosphatidylcholine-induced monocyte adhesion to endothelial cells

OBJECTIVE

Ca(2+)-activated K(+)-channels (BK(Ca)) play an important role in lysophosphatidylcholine (LPC)-induced endothelial dysfunction. Aim of our study was to investigate whether LPC-induced activation of BK(Ca) is also involved in monocyte adhesion to endothelial cells (EC).

METHODS AND RESULTS

Measurement of membrane potential (MP) was performed using the fluorescence dye DiBAC. Adhesion of the monocytotic cell line U937 to EC was analysed by (3)[H]-thymidine-adhesion-assay. Expression of ICAM-1 and VCAM-1 were analyzed by FACS. LPC induced a hyperpolarization of EC in a dose-dependent manner with the maximum seen with 2 microM. This was prevented by the BK(Ca)-inhibitor iberiotoxin (IBX, 100nM). Adhesion of U937 cells to EC was increased after stimulation of EC with LPC. This effect was time-dependent with the maximum seen after 4h. LPC-induced adhesion was significantly reduced when EC were co-incubated with IBX, or NAD(P)H oxidase inhibitor diphenyleneiodonium (DPI, 5 microM) and also blocked by addition of 2-aminoethoxydiphenylborate (2-APB, 100 microM) or the calcium-chelator BAPTA (10 microM). Stimulation of U937 cells with LPC did not result in an increased adhesion to unstimulated EC.

CONCLUSION

Activation of the endothelial BK(Ca) plays an important role in monocyte adhesion to endothelial cells.

Postprandial, but not postabsorptive low-density lipoproteins increase the expression of intercellular adhesion molecule-1 in human aortic endothelial cells

The magnitude of postprandial lipemia has been identified as independent risk factor for the development of coronary artery disease. To test the effect of postprandial versus postabsorptive low-density lipoproteins (LDL) on the expression of adhesion molecules, LDL were isolated from healthy subjects before and 4h after ingestion of a standardized fatty test meal. We used flow cytometry and Northern blotting to quantify cell adhesion molecules in human aortic endothelial cells (HAEC). The adherence of leukocytes to HAEC was analyzed using a monocyte adhesion assay. Incubation of HAEC with postprandial, but not postabsorptive LDL induced a two-fold increase in the surface expression of intercellular adhesion molecule-1 (ICAM-1), but not of E-selectin or vascular cell adhesion molecule-1. In addition, increased amounts of ICAM-1 transcripts were found in HAEC treated with postprandial LDL. The adhesion of monocytes to HAEC was enhanced after pretreatment with postprandial, but not with postabsorptive LDL. We conclude that postprandial, but not postabsorptive LDL increase the surface expression of ICAM-1 in HAEC apparently by de novo protein synthesis leading to increased adhesion of monocytes. The upregulation of ICAM-1 by postprandial LDL may explain part of the proatherogenic effect of high postprandial lipemia.

Reduction of oxidative stress and modulation of autoantibodies against modified low-density lipoprotein after rosuvastatin therapy

AIMS

To examine the effect of 24 weeks' rosuvastatin treatment on oxidative stress and changes in immune response to oxidized low-density lipoprotein (LDL).

METHODS

This was an open-label study of patients in Austria receiving 10 or 40 mg rosuvastatin daily alternately during 12 and 24 weeks. Circulating concentrations of antibodies to malondialdehyde-oxidized LDL (MDA-LDL), both IgG and IgM type, to copper-oxidized LDL (Cu-OxLDL-IgG), concentrations of oxidized LDL complexed to IgG (OxLDL-IC) and markers of oxidative stress and systemic inflammation in subjects with plasma LDL cholesterol concentrations between 130 mg dl-1 and 250 mg dl-1 and triglycerides

RESULTS

During statin therapy, plasma endogenous peroxides (POX-ACT) concentrations and peroxidase activity were significantly decreased, associated with a modest increase in total antioxidant capacity (TAC). Antibody titres to MDA-LDL-IgM, Cu-OxLDL-IgG and OxLDL-IC decreased, whereas MDA-LDL-IgG concentrations were increased after therapy. These changes were dose- and LDL-independent. POX-ACT concentrations were significantly positively correlated with inflammation markers before and after therapy and inversely with high-density lipoprotein-cholesterol concentrations after therapy.

CONCLUSION

This study provides in vivo evidence that rosuvastatin significantly reduces oxidative stress and has immunomodulatory properties in a dose- and LDL-independent manner.

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Key Words

• autoantibodies
• oxidative stress
• oxidatively modified low-density lipoprotein
• rosuvastatin

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MESH Headings

• Antioxidants/metabolism
• Autoantibodies/immunology
• Biomarkers/blood
• Copper/metabolism
• Dose-Response Relationship, Drug
• Female
• Fluorobenzenes/therapeutic use
• Humans
• Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use
• Immunoglobulin G/immunology
• Immunoglobulin M/immunology
• Lipoproteins, LDL/metabolism
• Male
• Malondialdehyde/metabolism
• Middle Aged
• Oxidation-Reduction
• Oxidative Stress/drug effects
• Peroxidase/metabolism
• Peroxides/blood
• Pyrimidines/therapeutic use
• Rosuvastatin Calcium
• Sulfonamides/therapeutic use

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Grants Collapse

Affiliation(s)

Ulrike Resch Medical University of Vienna, Wilhelm Auerswald Atherosclerosis Research Group, Vienna, Austria.
Franz Tatzber
Alexandra Budinsky
Helmut Sinzinger

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Oxidized LDL further enhances expression of adhesion molecules in Chlamydophila pneumoniae-infected endothelial cells

Chlamydophila pneumoniae is a common respiratory pathogen that has been shown to be associated with coronary artery disease. Recent studies have shown that one of the possible mechanisms of the atherogenicity of C. pneumoniae is overexpression of cell adhesion molecules (CAMs) in infected endothelial cells. We investigated whether exposure of C. pneumoniae-infected endothelial cells to oxidized LDL (oxLDL) leads to further upregulation of CAMs. Flow cytometry and immunoblot analysis of human aortic endothelial cells (HAECs) was performed for intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. ICAM-1 was expressed in 78.7% of C. pneumoniae-infected HAECs. The addition of oxLDL (100 microg/ml) to infected HAECs increased the proportion of ICAM-1-positive cells to 92%. VCAM-1 was only observed in 9.3% of infected HAECs, and the addition of oxLDL had no further effect on the surface expression of VCAM-1. C. pneumoniae also upregulated the surface expression of E-selectin on 52.2% of the cells, and incubation with oxLDL further increased the proportion of positive cells to 63.64%. In conclusion, C. pneumoniae upregulated the expression of the adhesion molecules ICAM-1, VCAM-1, and E-selectin on HAECs. The addition of oxLDL to the infected cells further enhanced the surface expression of ICAM-1 and E-selectin.

Adhesion molecules, catecholamines and leucocyte redistribution during and following exercise

The circulating blood normally contains no more than 1-2% of the body's population of leucocytes. The numbers and phenotypes of circulating leucocyte subsets can change dramatically during and immediately following exercise. The surface expression of adhesion molecules makes an important contribution to such responses by changing patterns of cell trafficking. Alterations in the surface expression of adhesion molecules could reflect a shedding of molecules, selective apoptosis or differential trafficking of cells with a particular phenotype, effects from mechanical deformation of the cytoplasm, active biochemical processes involving cytokines, catecholamines, glucocorticoids or other hormones, or changes in the induction of adhesion molecules. The expression of adhesion molecules changes with maturation and activation of leucocytes. Typically, mature cells express lower densities of L-selectin (CD62L), the homing receptor for secondary lymphoid organs, and higher densities of LFA-1 (CD11a), the molecule associated with trafficking to non-lymphoid reservoir sites. The neutrophils and natural killer cells that are mobilised during exercise also express high levels of Mac-1 (CD11b), a marker associated with cellular activation. Possibly, exercise demarginates older cells that are awaiting destruction in the spleen. Plasma concentrations of catecholamines rise dramatically with exercise, and there is growing evidence that catecholamines, acting through a cyclic adenosine monophosphate second messenger system, play an important role in modifying the surface expression of adhesion molecules. Analogous changes can be induced by other forms of stress that release catecholamines or by catecholamine infusion, and responses are blocked by beta(2)-blocking agents. Catecholamines also modify adherence and expression of adhesion molecules in vitro. Cell trafficking is modified by genetic deficiencies in the expression of adhesion molecules, but leucocyte responses to exercise and catecholamines are generally unaffected by splenectomy. A number of clinical conditions including atherogenesis and metaplasia are marked by an altered expression of adhesion molecules. The effects of exercise on these molecules could thus have important health implications.

Benefits of gliclazide in the atherosclerotic process: decrease in monocyte adhesion to endothelial cells

Atherosclerotic cardiovascular disease is the leading cause of premature death in patients with diabetes. Atherosclerosis is a chronic immune-mediated disease, the initiation, progression, and destabilization of which is driven and regulated by inflammatory cells. One critical event in the initiation of this vascular inflammatory disease is the adhesion of leukocytes to the activated endothelium and their migration into the vessel wall. These processes are mediated by the upregulation of adhesion molecules on endothelial cells (ECs) and an increased expression in the vascular wall of chemotactic factors to leukocytes. Monocyte binding to ECs is increased in diabetes. One major determinant of this alteration could be oxidative stress. Given the free-radical scavenging activity of gliclazide, we determined the ex vivo and in vitro effects of this drug on human monocyte binding to ECs and the molecular mechanisms involved in this effect. Our results demonstrate that short-term administration of gliclazide to patients with type 2 diabetes normalizes the levels of plasma lipid peroxides and monocyte adhesion in these subjects. Gliclazide (10 microg/mL) also reduces oxidized low-density lipoprotein (oxLDL)- and advanced glycation end product (AGE)-induced monocyte adhesion to ECs in vitro. The inhibitory effect of this drug on AGE-induced monocyte adhesion involves a reduction in EC adhesion molecule expression and inhibition of nuclear factor kappaB (NF-kappaB) activation. In addition, gliclazide inhibits oxLDL-induced monocyte adhesion to cultured human aortic vascular smooth muscle cells (HASMCs) in vitro and reduces the production of monocyte chemotactic protein-1 (MCP-1) by these cells. Taken collectively, these results show that gliclazide, at concentrations in the therapeutic range, inhibits ex vivo and in vitro monocyte adhesiveness to vascular cells. By doing so, this drug could reduce monocyte recruitment into the vessel wall and thereby contribute to attenuating the sustained inflammatory process that occurs in the atherosclerotic plaque. These findings suggest that treatment of diabetic patients with this drug may prevent or retard the development of vasculopathies associated with diabetes.

Antioxidant activity of different dihydropyridines

Lacidipine, a dihydropyridine-based calcium antagonist (DHP), has already been demonstrated to possess antioxidant activity and to reduce the intracellular production of reactive oxygen species (ROS). To verify if this effect is a peculiarity of this molecule, or belongs to other DHPs, the activity of lacidipine was compared with those of amlodipine, lercanidipine, nimodipine, and nifedipine. The DHPs were incorporated in bovine aortic endothelial cells (BAECs). Cu(2+)-oxidized LDL (ox-LDL, 5 microM) was incubated with BAECs for 5 min. 2',7'-Dichlorofluorescein (DCF) as expression of intracellular ROS production was measured by flow cytometry. Ox-LDL induced a strong increase in intracellular ROS formation (p<0.001) that was significantly reduced only with lacidipine and lercanidipine (p from <0.05 to <0.01); the effect of lacidipine, however, resulted in being much more evident than lercanidipine (p<0.01); amlodipine, nimodopine, and nifedipine had no effect on ROS formation. The lowest IC50s, i.e. the concentrations determining the 50% reduction of ROS, were obtained with lacidipine (p<0.01). The inhibitory effect of lacidipine on ox-LDL-induced ROS production in endothelial cells is a peculiarity of this molecule through its antioxidant activity.

Monocyte adhesion in diabetic angiopathy: effects of free-radical scavenging

Increased interaction of monocytes with vascular cells is linked to the development and progression of atherosclerosis in patients with diabetes. One major determinant of increased monocyte binding to vascular cells could be oxidative stress. Given the free-radical scavenging properties of gliclazide, we evaluated the ex vivo and in vitro effects of this drug on human monocyte binding to endothelial cells and smooth muscle cells (SMCs). Short-term administration of gliclazide to patients with type 2 diabetes decreases plasma lipid peroxides and lowers the enhanced adhesion of diabetic monocytes to cultured endothelial cells observed before gliclazide treatment. Gliclazide (10 microg/ml) also reduces oxidized low-density lipoprotein (oxLDL)- and advanced glycation end product (AGE)-induced monocyte adhesion to cultured endothelial cells. The suppressive effect of gliclazide on AGE-induced monocyte adhesion to endothelium involves a reduction of cell adhesion molecule mRNA and protein expression and an inhibition of NF-kappaB activation. Gliclazide also inhibits oxLDL-induced monocyte adhesion to cultured human aortic smooth muscle cells (HASMCs). Furthermore, treatment of HASMCs with gliclazide results in a marked decrease in oxLDL-induced monocyte chemoattractant protein-1 expression, both at the gene and protein levels. These results suggest that gliclazide, at concentrations in the therapeutic range (5-10 microg/ml), by its ability to decrease monocyte-vascular cell interactions could reduce monocyte accumulation in the atherosclerotic plaque and thereby contribute to attenuate the sustained inflammatory process that occurs in the vessel wall. These findings suggest that treatment of diabetic patients with gliclazide may prevent or retard the development of vascular disturbances associated with diabetes.

Oxidized low density lipoprotein-induced LFA-1-dependent adhesion and transendothelial migration of monocytes via the protein kinase C pathway

Inflammatory and immune responses are highly relevant processes in the pathogenesis of atherosclerosis, as illustrated by the central event of monocyte accumulation in atherosclerotic plaques. Integrin LFA-1-mediated adhesion of circulating monocytes to the endothelium is a prerequisite for recruitment of monocytes to these areas. Integrin-mediated adhesion is tightly regulated and integrins are only functional in response to particular monocyte activation stimuli. We investigated the role of oxidized low-density lipoprotein (LDL) in adhesion of resting monocytes prepared by elutriation from endothelium. Our results showed that: (1) oxidized LDL (and MCP-1) induced both LFA-1-mediated adhesion of monocytes to endothelial cells and transendothelial migration of monocytes; (2) oxidized LDL functionally transformed monocyte LFA-1 to an activated form; (3) oxidized LDL induced F-actin polymerization and cytoskeletal rearrangement within seconds; and (4) the LDL-associated antioxidant, alpha-tocopherol, but not beta-tocopherol, inhibited both F-actin polymerization and LFA-1-mediated adhesion of monocytes, which paralleled the effect of protein kinase C (PKC) inhibitors. Our results indicate that oxidized LDL plays a pivotal role in triggering LFA-1 activation and LFA-1-mediated adhesion and transmigration of monocytes to sites of atherosclerotic plaques, via the PKC pathway.

Essential role of ICAM-1 in mediating monocyte adhesion to aortic endothelial cells

Monocyte-endothelial cell interactions have been implicated in the pathogenesis of a number of vascular diseases that target arterial and aortic endothelium, including atherosclerosis. Many different adhesion molecules, such as intercellular adhesion molecule (ICAM)-1, are thought to mediate monocyte binding to endothelial cells during the development of these diseases. However, conflicting results have been reported regarding the specific role of ICAM-1 in these events. In this study, we used a genetic approach to determine the contribution of ICAM-1 in mediating monocyte adhesion to mouse aortic endothelial cells (MAEC) derived from both wild-type and ICAM-1(-/-) mice. Treatment of wild-type MAEC with oxidized low-density lipoprotein significantly induced both WEHI 274.1 and whole blood monocyte adhesion, whereas similarly treated ICAM-1(-/-) MAEC showed a complete inhibition of monocyte binding. Dose-response treatment with tumor necrosis factor-alpha also increased monocyte adhesion to wild-type MAEC, but significant adhesion was only observed at higher doses for ICAM-1(-/-) MAEC. These data demonstrate a crucial role for ICAM-1-mediated monocyte-endothelial cell interactions in response to specific stimuli involved in inflammatory vascular diseases.

Chlamydia pneumoniae-infected monocytes exhibit increased adherence to human aortic endothelial cells

Interactions between monocytes and endothelial cells play an important role in the pathogenesis of atherosclerosis, and monocyte adhesion to arterial endothelium is one of the earliest events in atherogenesis. Work presented in this study examined human monocyte adherence to primary human aortic endothelial cells following monocyte infection with Chlamydia pneumoniae, an intracellular pathogen associated with atherosclerosis by a variety of sero-epidemiological, pathological and functional studies. Infected monocytes exhibited enhanced adhesion to aortic endothelial cells in a time- and dose-dependent manner. Pre-treatment of C. pneumoniae with heat did not effect the organism's capacity to enhance monocyte adhesion, suggesting that heat-stable chlamydial antigens such as chlamydial lipopolysaccharide (cLPS) mediated monocyte adherence. Indeed, treatment of monocytes with cLPS was sufficient to increase monocyte adherence to endothelial cells, and increased adherence of infected or cLPS-treated monocytes could be inhibited by the LPS antagonist lipid X. Moreover, C. pneumoniae-induced adherence could be inhibited by incubating monocytes with a mAb specific to the human beta 2-integrin chain, suggesting that enhanced adherence resulted from increased expression of these adhesion molecules. These data show that C. pneumoniae can enhance the capacity of monocytes to adhere to primary human aortic endothelial cells. The enhanced adherence exhibited by infected monocytes may increase monocyte residence time in vascular sites with reduced wall shear stress and promote entry of infected cells into lesion-prone locations.

The relationship between plasma glucose and insulin responses to oral glucose, LDL oxidation, and soluble intercellular adhesion molecule-1 in healthy volunteers

This study was initiated to describe the relationships between plasma glucose and insulin responses to oral glucose and the concentrations of partially oxidized low density lipoprotein (poxLDL) and soluble intercellular adhesion molecule-1 (sICAM-1) in 23 healthy, non-diabetic volunteers. Results demonstrated that plasma glucose (r=0.65, P<0.002) and insulin (r=0.58, P<0.007) responses to a 75-g oral glucose challenge were highly correlated to poxLDL concentrations. Plasma glucose (r=0.63, P<0.002) and insulin (r=0.68, P<0.001) concentrations also significantly correlated with sICAM-1 concentrations. Furthermore, concentrations of poxLDL and sICAM-1 were significantly related (r=0.55, P<0.001). These relationships remained statistically significant when adjusted for differences in age, gender, body mass index, and lipoprotein concentrations. These results provide further evidence that circulating LDL particles are more highly oxidized in insulin resistant states, and demonstrate the presence of an in vivo relationship between insulin resistance, LDL oxidized state, and sICAM-1 concentrations. These results help explain why soluble forms of adhesion molecules are increased in clinical conditions characterized by insulin resistance, and support the possibility that LDL oxidizability is increased in insulin resistant subjects, and that the increase in sICAM-1 results from stimulation of cellular adhesion molecules by more highly oxidized LDL.

Effect of gliclazide on monocyte-endothelium interactions in diabetes

Enhanced monocyte-endothelial cell interactions have been documented in diabetes. Because adherence of monocytes to the endothelium is one of the earliest events in the development of atherosclerosis, its alteration may represent one of the mechanisms leading to accelerated atherosclerosis in diabetic patients. Previous studies have suggested that lipoprotein oxidation and protein glycation may contribute to the increased monocyte binding to the diabetic vasculature. Based on the recent finding that gliclazide has free-radical scavenging activity, we examined the ex vivo and in vitro effects of this drug on human monocyte binding to endothelial cells. Our results demonstrate that short-term administration of gliclazide to patients with type 2 diabetes lowers the enhanced adhesion of diabetic monocytes observed before gliclazide treatment (163+/-24% over control values, p<0.005) to levels similar to those observed in controls. They also show that gliclazide (10 microg/ml) reduces in vitro by approximately 35% both oxidized low-density lipoprotein (LDL)- and glycated albumin-induced monocyte adhesion to endothelial cells. Based on these results, we next investigated the molecular mechanisms responsible for the inhibitory effect of gliclazide on glycated albumin-induced monocyte adhesion to endothelium. In glycated albumin-treated endothelial cells, we observed induction of cell-associated expression of E-selectin (ELAM-1; 170+/-10% over control values, p<0.005), intercellular cell adhesion molecule-1 (ICAM-1; 131+/-8% over control values, p<0.005) and vascular cell adhesion molecule-1 (VCAM-1; 134+/-8% over control values, p<0.005), augmentation in the levels of the transcripts of these molecules, and an increase in the DNA binding of NF-kappaB in the promoters of these antigens. Gliclazide markedly inhibited the induction of all these parameters. Because the oxidative stress-sensitive transcription factor NF-kappaB is implicated in endothelial cell activation, the observed inhibitory effect of gliclazide on NF-kappaB activation and glycated albumin-induced expression of DNA binding activity for the NF-kappaB site in the ELAM-1, ICAM-1 and VCAM-1 promoters seems to be due to its antioxidant properties. These results suggest that gliclazide, by its ability to reduce endothelial activation, may exert potential beneficial effects in the prevention of atherosclerosis associated with type 2 diabetes.

Oxidized low density lipoprotein (ox-LDL) binding to ox-LDL receptor-1 in endothelial cells induces the activation of NF-kappaB through an increased production of intracellular reactive oxygen species

In this study we examined the effect of oxidized low density lipoprotein (ox-LDL) on the intracellular production of reactive oxygen species (ROS) in bovine aortic endothelial cells (BAECs) and whether this increase occurs through its binding to the endothelial receptor lectin-like ox-LDL receptor-1 (LOX-1). Furthermore, this study also aimed to ascertain whether the binding of ox-LDL to LOX-1 is associated with NF-kappaB activation. ox-LDL induced a significant dose-dependent increase in ROS production after a 30-s incubation with BAECs (p < 0.01). ROS formation was markedly reduced in BAECs incubated with anti-LOX-1 monoclonal antibody (p < 0.001), while control nonimmune IgG produced no effect. ox-LDL induced a time- and dose-dependent significant increase in ROS formation only in CHO-K1 cells stably expressing bovine LOX-1 (p < 0.001), while no increase was present in CHO-K1 cells. The activation of the transcription factor NF-kappaB in BAECs was evident after a 5-min incubation with ox-LDL and was attenuated by anti-LOX-1 monoclonal antibody. The conclusion is that one of the pathophysiological consequences of ox-LDL binding to LOX-1 may be the activation of NF-kappaB through an increased ROS production.

The expression of adhesion molecules on endothelial cells is inhibited by troglitazone through its antioxidant activity

The adhesion of monocytes to endothelium, an early event in atherosclerosis, is mediated by cell adhesion molecules. Signal-transduction pathways for these binding molecules include the translocation of the transcription factor NF-kappaB; moreover, intracellularly generated oxygen-derived free radicals (ODFR) play a major role in this process. This study evaluated the extent to which troglitazone, an oral antidiabetic agent with antioxidant properties, affects the expression of intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin on human umbilical vein endothelial cells (HUVECs), induced by different prooxidant signals such as oxidized LDL and tumor necrosis factor-alpha (TNF-alpha). Furthermore we assessed whether the NF-kappaB activation is modulated by the antioxidative effect of troglitazone. Oxidized LDL not only caused a dose-dependent increase of ICAM-1, VCAM-1 and E-selectin (p<0.001), but also synergically increased their TNF-alpha-induced expression (p<0.001). Troglitazone reduced in a dose-dependent manner the expression of VCAM-1, ICAM-1 and E-selectin induced by different amounts of oxidized LDL (p<0.001). The addition of troglitazone to HUVECs significantly reduced the expression of ICAM-1, VCAM-1 and E-selectin induced by TNF-alpha alone or in combination with oxidized LDL (p<0.001); this reduction was paralleled by a significant fall in NF-kappaB translocation. The results suggest that troglitazone may have prevented NF-kappaB-mediated adhesion molecule expression by exerting its antioxidant effect on ODFR.

Endothelial dysfunction in Type 1 diabetes mellitus: relationship with LDL oxidation and the effects of vitamin E

AIMS

To examine the hypothesis that increased susceptibility of low density lipoproteins (LDL) to oxidation predisposes to endothelial dysfunction in patients with Type 1 diabetes mellitus.

METHODS

A cross-sectional study of 46 non-nephropathic diabetic and 39 control subjects and in the diabetic patients, a 3-month duration, randomized, placebo-controlled double-blind trial of vitamin E 500 U/day. Flow-mediated vasodilatation (FMD) was measured in the forearm by high resolution ultrasound. LDL oxidation by Cu2+ was measured in vitro.

RESULTS

Diabetic patients had greater basal and reactive forearm blood flow (geometric mean (SD%) flow (ml/min) 110.15 (19.19%) vs. 74.99 (23.17%); P=0.045, and 344.35 (20.84%) vs. 205.17 (21.48%); P=0.007), compared with controls, but there was no difference in FMD (median (interquartile range) 0.00 (-0.01-0.02) vs. 0.02 (-0.01-0.02) cm2; P=0.78). Diabetic LDL oxidation lag time correlated with postdilatation brachial artery area (r= 0.32; P=0.05) but not with FMD. Lag-times and total LDL oxidation by Cu2+, lipoprotein and vitamin E concentrations were similar in diabetic and control groups. Antibody titres to oxidized LDL (oxLDL) were higher in non-diabetic than diabetic subjects, and were unrelated to FMD. In diabetic patients, vitamin E increased mean (SD) plasma vitamin E levels (24.0 (6.5) to 47.5 (7.5) gmol/l; P=0.0006) and resulted in increased FMD (delta 0.00 (-0.02-0.01) vs. 0.01 (0.01-0.02)) cm2; P=0.0036), but no changes in LDL Cu2+ oxidation profiles were observed.

CONCLUSIONS

FMD is no different in Type 1 diabetic and non-diabetic subjects and nor are indices of lipid peroxidation and in vitro LDL oxidation although levels of antibody to oxLDL are lower in diabetes. Vitamin E supplementation increases plasma vitamin E levels and may enhance FMD in diabetes but, in the absence of changes in LDL oxidation, this may not be mediated by reduced oxidation of LDL.

Chemokines and atherosclerosis

Chemokines or chemotactic cytokines represent an expanding family of structurally related small molecular weight proteins, recognised as being responsible for leukocyte trafficking and activation. Soon after the discovery of this class of cytokines, about a decade ago, monocyte chemoattractant protein-1 (MCP-1) was found to be highly expressed in human atherosclerotic lesions and postulated to be central in monocyte recruitment into the arterial wall and developing lesions. In this review, we will discuss our present knowledge about MCP-1 and its receptor CCR2 and their role in atherogenesis. Although less well established, other chemokines such as RANTES, MIP-1alpha and MIP-1beta have also been implicated in atherosclerotic lesion formation as are a number of more recently discovered chemokines like MCP-4, ELC and PARC. The role of these chemokines in the progression of atherosclerosis will be discussed as well as the emerging role of IL-8, mostly know for its effects on neutrophils. Particular attention will be given not only to the involvement of chemokines in the inflammatory recruitment of monocytes/macrophages, but also to their role in the related local immune responses and vascular remodelling which occur during the formation of unstable atherosclerotic plaques.

Integrin mediated adhesion of mononuclear cells from patients with familial hypercholesterolemia

BACKGROUND

Low-density lipoproteins (LDL) can induce the adhesion of monocytes to endothelial cells. Monocytes of patients with familial hypercholesterolemia (FH) are exposed to high concentrations of LDL, and it has been reported that adhesiveness of these cells in hypercholesterolemic patients is enhanced. We investigated whether LFA-1 or VLA-4 mediated adhesion is altered in FH patients and whether HMG-CoA reductase inhibitors influence this adhesion.

PATIENTS AND METHODS

LFA-1 and VLA-4 mediated adhesion to ICAM-1 and VCAM-1 coated beads was investigated using freshly isolated monocytes and T-lymphocytes from patients with homozygous FH, heterozygous FH (before and after cholesterol lowering treatment), and from controls. In addition, the expression of beta1- and beta2-integrins on these cells was determined.

RESULTS

Both LFA-1 and VLA-4 mediated adhesion and integrin expression of monocytes and CD3+ cells from patients with homozygous FH and heterozygous FH was similar to that of monocytes from a control population. Treatment with HMG-CoA reductase inhibitors did not affect the adherence to ICAM-1 or VCAM-1, and did not influence the expression of integrins.

CONCLUSIONS

In contrast to studies by others, we demonstrated in the present study that the actual LFA-1 and VLA-4 mediated adhesion of T-lymphocytes and monocytes is not altered in patients with FH.

Effects of oxidized low density lipoprotein, lipid mediators and statins on vascular cell interactions

The integrin heterodimer CDllb/CD18 (alphaMbeta2, Mac-1, CR3) expressed on monocytes or polymorphonuclear leukocytes (PMN) is a receptor for iC3b, fibrinogen, heparin, and for intercellular adhesion molecule (ICAM)-1 on endothelium, crucially contributing to vascular cell interactions in inflammation and atherosclerosis. In this report, we summarize our findings on the effects of lipid mediators and lipid-lowering drugs. Exposure of endothelial cells to oxidized low density lipoprotein (oxLDL) induces upregulation of ICAM-1 and increases adhesion of monocytic cells expressing Mac-1. Inhibition experiments show that monocytes use distinct ligands, i.e. ICAM-1 and heparan sulfate proteoglycans for adhesion to oxLDL-treated endothelium. An albumin-transferable oxLDL activity is inhibited by the antioxidant pyrrolidine dithiocarbamate (PDTC), while 8-epi-prostaglandin F2alpha (8-epi-PGF2alpha) or lysophosphatidylcholine had no effect, implicating yet unidentified radicals. Sequential adhesive and signaling events lead to the firm adhesion of rolling PMN on activated and adherent platelets, which may occupy areas of endothelial denudation. Shear-resistant arrest of PMN on thrombin-stimulated platelets in flow conditions requires distinct regions of Mac-1, involving its interactions with fibrinogen bound to platelet alphallbbeta3, and with other platelet ligands. Both arrest and adhesion strengthening under flow are stimulated by platelet-activating factor and leukotriene B4, but not by the chemokine receptor CXCR2. We tested whether Mac-1-dependent monocyte adhesiveness is affected by inhibitors of hydroxy-methylglutaryl-Coenzyme A reductase (statins) which improve morbidity and survival of patients with coronary heart disease. As compared to controls, adhesion of isolated monocytes to endothelium ex vivo was increased in patients with hypercholesterolemia. Treatment with statins decreased total and low density lipoprotein (LDL) cholesterol plasma levels, surface expression of Mac-1, and resulted in a dramatic reduction of Mac-1-mediated monocyte adhesion to endothelium. The inhibition of monocyte adhesion was reversed by mevalonate but not LDL in vitro, indicating that isoprenoid precursors are crucial for adhesiveness of Mac-1. Such effects may crucially contribute to the clinical benefit of statins, independent of cholesterol-lowering, and may represent a paradigm for novel, anti-inflammatory mechanisms of action by this class of drugs.

Enzymatically modified, nonoxidized LDL induces selective adhesion and transmigration of monocytes and T-lymphocytes through human endothelial cell monolayers

Circulating monocytes and T lymphocytes extravasate through the endothelium at sites of developing atheromatous lesions, where they tend to accumulate and mediate the progression of the disease. We have previously demonstrated the presence of an enzymatically degraded, nonoxidized form of LDL (E-LDL) in early human fatty streaks, which possesses major biological properties of an atherogenic lipoprotein. The effects of E-LDL on human endothelial cells have now been studied with respect to adhesion and transmigration of monocytes and T lymphocytes. E-LDL induced a rapid and dose-dependent selective adhesion of monocytes and T lymphocytes to endothelial cell monolayers within 30 minutes of incubation. Maximal increases in the number of adherent monocytes (8-fold) and of adherent T lymphocytes (4-fold) were observed after treatment with 50 microg/mL E-LDL. E-LDL was more active than oxidized LDL (ox-LDL), whereas native LDL produced only minor adhesive effects. Both E-LDL and ox-LDL enhanced transmigration of monocytes and of T lymphocytes through endothelial monolayers. Again, E-LDL was more potent than ox-LDL, inducing transmigration to a similar extent as N-formyl-Met-Leu-Phe. In endothelial cells, E-LDL stimulated upregulation of intercellular adhesion molecule-1 (ICAM-1), platelet-endothelial cells adhesion molecule-1 (PECAM-1), P-selectin, and E-selectin with distinct kinetics. Analyses with blocking antibodies indicated that ICAM-1 and P-selectin together mediated approximately 70% of cell adhesion, whereas blocking of PECAM-1 had no effect on adhesion but reduced transmigration to less than 50% of controls. E-LDL also upregulated expression of ICAM-1 in human aortic smooth muscle cells, and this correlated with increased adhesion of T lymphocytes. E-LDL is thus able to promote the selective adhesion of monocytes and T lymphocytes to the endothelium, stimulate transmigration of these cells, and foster their retention in the vessel wall by increasing their adherence to smooth muscle cells. These findings underline the potential significance of E-LDL in the pathogenesis of atherosclerosis.

Oxidized low-density lipoprotein increases the production of intracellular reactive oxygen species in endothelial cells: inhibitory effect of lacidipine

OBJECTIVE

The mechanisms by which oxidized low-density lipoprotein (ox-LDL) induces the expression of adhesion molecules on endothelial cells (HUVECs) are still not clear. The signal transduction pathways for these binding molecules include the translocation of the transcription factor NF-kB and the intracellular reactive oxygen species (ROS) are said to play a key role in this process. Aim of this study was (1) to evaluate the effect of ox-LDL on intracellular production of ROS in culture of HUVECs; (2) to evaluate if the intracellular increase of ROS induced by ox-LDL is mediated by the binding to a specific endothelial receptor; (3) to ascertain if lacidipine can decrease ox-LDL-induced ROS production in HUVECs.

METHODS

Five microM Cu2+ ox-LDL were incubated with HUVECs for 5 min. 2',7'-Dichlorofluorescein (DCF) as an expression of intracellular ROS production, was measured by flow cytometry.

RESULTS

ox-LDL induced a significant dose-dependent increase in DCF production (P < 0.001) through the binding to a specific receptor. The preincubation of HUVECs with radical scavengers compounds and lacidipine significantly reduced (P < 0.001) the ox-LDL-induced DCF production.

CONCLUSIONS

ox-LDL increased the intracellular formation of ROS through the ligation to a specific endothelial receptor. Preincubation of HUVECs with lacidipine, a calcium antagonist with antioxidant properties, significantly reduced the intracellular ROS formation induced by ox-LDL. We propose that the effect of lacidipine on adhesion molecule expression and on NF-kB activation can be explained by its effect on intracellular ROS formation.

Monocytic cell adhesion to endothelial cells stimulated by oxidized low density lipoprotein is mediated by distinct endothelial ligands

Treatment of human umbilical vein endothelial cells (HUVEC) with oxidized low density lipoprotein (ox-LDL, 100 microg/ml) for 24 h increased adhesion of human monocytic Mono Mac 6 cells from 4.8 +/- 0.9% to 17.6 +/- 2.5% (P < 0.001). The effect was dose dependent and first evident at 10 microg/ml ox-LDL. In contrast, adhesion of U937 cells was not significantly increased. Mac-1 (CD11b/CD18), a monocytic counter-receptor for intercellular adhesion molecule-1 (ICAM-1), that also binds to heparin, is present on Mono Mac 6 but not on U937 cells, and may thus explain these differences in adhesion. Consistently, ox-LDL induced a 2-fold upregulation of ICAM-1 surface expression on HUVEC. The presence of maltose-1-phosphate or heparin but not monoclonal antibodies (mAbs) to ICAM-1 reduced adhesion of Mono Mac 6 cells to untreated HUVEC. Combinations of mAbs to ICAM-1 with either maltose-1-phosphate or heparin inhibited Mono Mac 6 adhesion to ox-LDL-stimulated HUVEC by more than 50%, while either alone had no effect. This suggests that two distinct endothelial ligands for Mac-1, inducible ICAM-1 and carbohydrate-decorated heparin-like proteoglycan structures mediate monocytic cell interaction with ox-LDL-treated HUVEC. The stimulating activity in ox-LDL could partly be transfered to bovine serum albumin, while lysophosphatidylcholine or 8-epi prostaglandin F2alpha produced no stimulatory effects. The inhibition of ox-LDL effects with the antioxidant PDTC indicates radicals as possible mediators. In conclusion, we show that oxidatively modified LDL induces adhesion of monocytic cells, which utilize at least two distinct adhesive receptors on endothelium, one being identified as ICAM-1.

Lacidipine inhibits the activation of the transcription factor NF-kappaB and the expression of adhesion molecules induced by pro-oxidant signals on endothelial cells

OBJECTIVE

The adhesion of monocytes to endothelium, an early event in atherosclerosis is mediated by cell adhesion molecules. Signal-transduction pathways for these binding molecules include the translocation of the transcription factor NF-kappaB; moreover, intracellularly generated oxygen-derived free radicals play a major role in this process. In this study we evaluated the extent to which lacidipine, a calcium antagonist with antioxidant properties, affects the expression of intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin on human umbilical vein endothelial cells, induced by different pro-oxidant signals such as oxidized low density lipoprotein (LDL) and tumor necrosis factor-alpha (TNF-alpha).

METHODS

We incubated 5 micromol/l Cu2+-oxidized LDL and TNF-alpha (2 ng/ml) with human umbilical vein endothelial cells for 48 and 6 h, respectively. ICAM-1, VCAM-1 and E-selectin were measured by flow cytometry. NF-kappaB was evaluated by electrophoretic mobility shift assay.

RESULTS

The incubation of 5 micromol/l Cu2+-oxidized LDL not only caused a dose-dependent increase in ICAM-1, VCAM-1 and E-selectin (P < 0.001), but also synergically increased their TNF-alpha-induced expression (P < 0.001). The addition of lacidipine to human umbilical vein endothelial cells significantly reduced the expression of ICAM-1, VCAM-1 and E-selectin induced by TNF-alpha alone or with oxidized LDL (P < 0.001). The reduction in adhesion molecule expression caused by lacidipine was paralleled by a significant fall in NF-kappaB translocation.

CONCLUSIONS

The results suggest that lacidipine may have prevented NF-kappaB-mediated adhesion molecule expression by exerting its effects on oxygen-derived free radicals. The results support previous observations that lacidipine may have therapeutic effects in atherosclerosis.

Cellular effects of hypercholesterolemia in modulation of cancer growth and metastasis: a review of the evidence

Hypercholesterolemia and increased cancer risk have been associated, particularly with the high fat diets characteristic of Western societies. We were interested in the possible association between preexisting hypercholesterolemia and the rapidity and extent of tumor metastases in these patients. To date there has been only a few studies that have suggested and explored this determinant of cancer metastases although it may play a role in a subset of patients who develop cancers. This article will review the literature on the effects of LDL-cholesterol on cell proliferation and differentiation and speculate on mechanisms of involvement of a hypercholesterolemic milieu on cancer progression and enhancement of metastatic potential.

Native and gamma radiolysis-oxidized lipoprotein(a) increase the adhesiveness of rabbit aortic endothelium

Accumulation of monocyte-derived foam cells in the arterial intima is a major event in the development of atherogenesis. We have examined whether native and oxidized lipoprotein(a) (Lp(a)) can induce adhesion of monocytic cells to aortic endothelium. The extensive oxidation of paired samples of Lp(a) and low-density lipoprotein (LDL) was achieved by O2.-/OH. free radicals produced by gamma radiolysis of water, leading to similar values for the formation of peroxidation markers (conjugated dienes, TBARS, 8-epi-PGF2alpha) for both Lp(a) and LDL. Rabbit aortic segments were incubated for 5 h in the presence of equimolar concentrations of native and oxidized preparations of Lp(a) and LDL (125 micromol cholesterol/l, corresponding to 40 and 30 mg protein/l for Lp(a) and LDL, respectively). The aortic segments were incubated with rhodamin-isothiocyanate labeled U937 monocytic cells for 30 min and cell adhesion was quantified by fluorescent microscopy. Native Lp(a), and to a larger extent oxidized Lp(a), significantly increased U937 cell adhesion by 2.3 and 2.7 fold compared to controls (P < 0.005 and P < 0.001, respectively). Monocytic cell adhesion was also increased by native LDL (1.6 fold, P < 0.005), and to a greater extent by oxidized LDL (2.3 fold, P < 0.001). Thus native Lp(a) enhances the adhesive properties of the arterial endothelium which may account for its proatherogenic action. Furthermore, our results show that oxidized Lp(a), as well as oxidized LDL, are potent stimuli of monocyte adhesion to endothelial cells.

Oxidative modifications of apoB-100 by exposure of low density lipoproteins to HOCL in vitro

Although the products of oxidation of the lipid components of LDL have been studied extensively, much less is known about the specific products of oxidative modification of the apoprotein. We reacted native LDL and LDL that had been treated with HOCl with 2,4-dinitrophenylhydrazine (DNPH), delipidated and trypsinized the protein, and analyzed the products by HPLC. Although tryptic digests of native LDL and LDL oxidized by limited quantities of HOCl showed similar patterns by HPLC with detection at 220 nm, oxidized LDL showed several discrete peaks at 365 nm, which is characteristic of hydrazones formed with aldehydes and ketones, commonly termed protein carbonyls. Native LDl showed no peaks in the chromatograms at 365 nm. Peptides absorbing at 365 nm were isolated by HPLC and characterized. In most cases, the probable sites of modification on the peptides could be implied by failure of an anticipated amino acid to appear in the expected sequence. Of the 14 peptides isolated and characterized to date, eight peptides contained Cys residues. In other peptides, Lys, Trp, and Met were identified as amino acid residues apparently modified by HOCl treatment of LDL. Thirteen of the peptides identified are from trypsin-releasable peptides located on the surface of unoxidized native LDL. Our studies suggest a selective process of modification of apoB-100 by HOCl and the approaches used in the present studies should be useful for the characterization of the mechanisms of oxidation of this and other proteins.

Antioxidants inhibit the expression of intercellular cell adhesion molecule-1 and vascular cell adhesion molecule-1 induced by oxidized LDL on human umbilical vein endothelial cells

The oxidative modification of low density lipoprotein (LDL) and the endothelial expression of adhesion molecules are key events in the pathogenesis of atherosclerosis. In this study we evaluated the effect of oxidized LDL on the expression of intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin on human umbilical vein endothelial cells (HUVECs). The hypothesis that oxidized LDL functions as a prooxidant signal was also evaluated, by studying the effect of different radical-scavenging antioxidants on expression of adhesion molecules. LDL was oxidized by using Cu2+, HUVECs or phospholipase A2 (PLA2)/ soybean lipoxygenase (SLO), the degree of oxidation being measured as thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (CD). Exposure of 200 micrograms/ml of native LDL to 1 microns Cu2+, HUVECs and to PLA2/ SLO resulted in four- to fivefold higher levels of TBARS and CD than in native LDL. Cu(2+)-(1 microM), HUVEC-, and PLA2/SLO-oxidized LDL caused a dose-dependent, significant increase of ICAM-1 and VCAM-1 (p < .01). The expression of E-selectin did not change. LDL oxidized with a 2.5 and 5 microM Cu2+ did not increase ICAM-1 and VCAM-1 significantly. Both the Cu(2+)- and HUVEC-oxidized LDL, subjected to dialysis and ultrafiltration, induced ICAM-1 and VCAM-1 expression. After incubation with the ultrafiltrate, the expression of ICAM-1 and VCAM-1 was not significantly different from that obtained with native LDL. LDL pretreated with different antioxidants (vitamin E and probucol) and subjected to oxidation by Cu2+ and HUVECs induced a significantly lower expression of ICAM-1 and VCAM-1 than nonloaded LDL (p < .01). The pretreatment of HUVECs with vitamin E and probucol significantly reduced the expression of VCAM-1 on HUVECs induced by oxidized LDL (p < .01); the effect on ICAM-1 was much less evident. In conclusion, oxidized LDL can induce the expression of different adhesion molecules on HUVECs; this induction can be prevented by pretreating either the LDL or the cells with radical-scavenging antioxidant.

Modified lipoproteins, cytokines and macrovascular disease in non-insulin-dependent diabetes mellitus

The processes of glycation and oxidation play a significant role in the acceleration of atherosclerosis in diabetes mellitus. Glycation is thought not only to increase the susceptibility of low-density lipoprotein (LDL) to oxidation but also to enhance the propensity of vessel wall structural proteins to bind extravasated plasma proteins, including LDL, and thus to contribute to a more marked oxidative modification of LDL. Glycated and oxidized lipoproteins induce cholesteryl ester accumulation in human macrophages and may promote platelet and endothelial cell dysfunction. Furthermore, these modified lipoproteins have the ability to trigger an autoimmune response that leads to the formation of autoantibodies and subsequently to the formation of immune complexes containing LDL. Both the modified lipoproteins and the immune complexes formed with autoantibodies reactive with modified lipoproteins may be responsible for several alternative and not mutually exclusive pathways leading to foam cell formation, macrophage activation and endothelial cell damage and may thus be of potential significance in initiating and/or contributing to the acceleration of the development of atherosclerosis. In this review we discuss how modified LDL affects lipoprotein metabolism, how immune complexes containing LDL induce the transformation of macrophages into foam cells and promote macrophage activation leading to the release of cytokines and thus initiating a sequence of events leading to endothelial cell damage and to the recruitment and activation of leucocytes. We also summarize our work showing that macrophage activation by LDL containing immune complexes leads to a paradoxical increase in LDL-receptor expression thus further impairing cholesterol homeostasis and enhancing the development of atheromatous lesions.

Induction of heat shock protein in monocytic cells by oxidized low density lipoprotein

The atherosclerotic lesion may be characterized as a chronic inflammatory process, and oxidized LDL is believed to be a key event in the development of atherosclerosis, though the mechanisms by which oxidized LDL exerts its proatherogenic properties are largely unknown. Heat shock proteins (hsp) are a group of proteins with a highly conserved structure and of these, hsp60 has been suggested to play a role in autoimmunity due to T lymphocyte crossreactivity between bacterial and human hsp60. The present study was designed to investigate the effects of oxidized LDL on the expression of hsp60 using the monocytic cell lines U937 and HL60 as models. The expression of hsp60 was determined by using monoclonal antibodies to hsp60 in FACScan, Western blot, and a sandwich ELISA. The results show that hsp60 is induced in both cell types after 2 h exposure to oxidized LDL, with a maximal effect at 20 micrograms/ml for U937 cells and 5 micrograms/ml for HL60 cells. A close to 3-fold increase in the expression of hsp60 was seen after culturing oxidized LDL (20 micrograms/ml) treated U937 cells for a period of 24 h. Interleukin 1-beta had similar effects on hsp60 expression to oxidized LDL. The results indicate that expression of hsp60 by monocytes in the vascular wall may be enhanced by oxidized LDL. It is thus possible that the chronic inflammatory process characterizing atherosclerosis is perpetuated by autoreactive T cells, which recognize hsp60 expressed by monocytes, induced by oxidized LDL.

Neovascular expression of E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 in human atherosclerosis and their relation to intimal leukocyte content

BACKGROUND

Leukocyte recruitment is an early event in atherogenesis, and the leukocyte adhesion molecules E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) recently have been detected in human atherosclerosis. However, no previous study has evaluated either the distribution of these three molecules at different sites within the arterial intima or their relation to plaque leukocyte content.

METHODS AND RESULTS

Immunohistochemistry was performed on 99 coronary artery segments (34 controls and 65 with atherosclerotic plaque) to identify E-selectin, ICAM-1, VCAM-1, macrophages, smooth muscle cells, and T lymphocytes. For each segment, the presence or absence of adhesion molecule was determined at the arterial lumen, on intimal neovasculature, and on intimal nonendothelial cells. Each segment was scored for intimal macrophage and T-lymphocyte densities on a semiquantitative scale of 0 to 3. In atherosclerotic plaques, the prevalences of E-selectin, ICAM-1, and VCAM-1 on plaque neovasculature were twofold higher than their prevalences on arterial luminal endothelium. E-selectin was the only adhesion molecule for which expression on arterial luminal endothelial cells was more prevalent in plaques than in control segments. Increased plaque intimal macrophage density was associated with expression of VCAM-1 on neovasculature (P < .01) and on nonendothelial cells (P < .01). Increased plaque intimal T-lymphocyte density was associated with the presence of both ICAM-1 and VCAM-1 on neovasculature (both P < .01) and on nonendothelial cells (both P < .01).

CONCLUSIONS

In atherosclerotic plaques, the expression of all three leukocyte adhesion molecules was more prevalent on intimal neovasculature than on arterial luminal endothelium. Further, the presence on neovasculature and nonendothelial cells of VCAM-1 and ICAM-1 was strongly associated with increased intimal leukocyte accumulation. These findings suggest that leukocyte recruitment through and/or activation of intimal neovasculature may play important roles in the pathogenesis of human atherosclerosis.

Isolation and characterization of human antioxidized LDL autoantibodies

Autoantibodies to oxidized LDL have been reported in normal subjects and in patients with arteriosclerosis, but their possible pathogenic role is not yet well defined. One important problem is the existence of contradictory data reported by different groups concerning the associations between antioxidized LDL autoantibodies and the presence or progression of arteriosclerotic lesions. Such contradictions led us to decide to isolate and characterize antioxidized LDL antibodies by affinity chromatography with the use of oxidized LDL cross-linked to Sepharose. Antioxidized LDL antibodies were isolated from selected serum samples obtained from eight subjects. Seven of them (six patients and one control subject) had high levels of antioxidized LDL antibody during screening. The other subject, a healthy volunteer, had a low level of antibody. All purified antibodies contained IgG (of subclasses 1 and 3) as the predominant isotype and were primarily specific for oxidized LDL but showed some cross-reactivity with malondialdehyde-modified LDL and native LDL. Two of the purified antibodies cross-reacted with cardiolipin. We determined average dissociation constants for the antioxidized LDL antibodies purified from five individuals, which varied between 2.4 x 10(-7) and 7.5 x 10(-7) mol/L, whereas the average dissociation constant of rabbit hyperimmune anti-LDL antibody was determined to be 2.7 x 10(-8) mol/L. In conclusion, we have purified human autoantibodies reactive with oxidized LDL that appear to be predominantly of moderate-to-low affinity and of variable cross-reactivity. The predominance of IgG1 and IgG3 antibodies is significant from the standpoint of potential pathogenicity, since these two subclasses activate the classic complement pathway system and have the highest binding affinities for Fc gamma receptors on phagocytic cells.