Induction of vascular cell adhesion molecule-1 by low-density lipoprotein

Aronia berry extract inhibits TNF-α-induced vascular endothelial inflammation through the regulation of STAT3

Background

Inflammation in endothelial cells induces production of inflammatory cytokines and monocytes adhesion, which are crucial events in the initiation of atherosclerosis. Aronia berry (Aronia meranocalpa), also called black chokeberry, contains abundant anthocyanins that have received considerable interest for their possible relations to vascular health.

Objective

The aim of this study was to investigate whether an anthocyanin-rich extract obtained from aronia berry can attenuate inflammatory responses in vascular endothelial cells.

Methods

As a model of vascular endothelial inflammation, human umbilical vein endothelial cells (HUVECs) pretreated with aronia berry extract were stimulated with tumor necrosis factor-alpha (TNF-α). The expression levels of cytokines and adhesion molecules were analyzed. To investigate the effects of aronia berry extract on the adhesion of THP-1 monocytic cell, the static adhesion assay was carried out. The possible molecular mechanisms by which aronia berry extract regulated vascular inflammatory responses were explored.

Results

The mRNA expressions of interleukins (IL-1β, IL-6, and IL-8) and monocyte chemoattractant protein-1 (MCP-1) upregulated by TNF-α were significantly suppressed by pretreatment with aronia berry extract. Aronia berry extract decreased TNF-α-induced monocyte/endothelial adhesion and suppressed vascular cell adhesion molecule-1 (VCAM-1) expression, but did not affect intercellular adhesion molecule-1 (ICAM-1) expression. Moreover, aronia berry extract decreased the phosphorylation of signal transducer and activator of transcription 3 (STAT3) and the nuclear levels of STAT3 and interferon regulatory transcription factor-1 (IRF1). The nuclear translocation of nuclear factor-kappa B (NF-κB) was not inhibited by aronia berry extract.

Conclusion

Aronia berry extract could exert anti-atherosclerotic effects on TNF-α-induced inflammation through inhibition of STAT3/IRF1 pathway in vascular endothelial cells.

The Role of (Modified) Lipoproteins in Vascular Function: A Duet Between Monocytes and the Endothelium

Over the last century, many studies have demonstrated that low-density lipoprotein (LDL) is a key risk factor of cardiovascular diseases (CVD) related to atherosclerosis. Thus, for these CVD patients, LDL lowering agents are commonly used in the clinic to reduce the risk for CVD. LDL, upon modification, will develop distinct inflammatory and proatherogenic potential, leading to impaired endothelial integrity, influx of immune cells and subsequent increased foam cell formation. LDL can also directly affect peripheral monocyte composition, rendering them in a more favorable position to migrate and accumulate in the subendothelial space. It has become apparent that other lipoprotein particles, such as triglyceride- rich lipoproteins or remnants (TRL) and lipoprotein(a) [Lp(a)] may also impact on atherogenic pathways. Evidence is accumulating that Lp(a) can promote peripheral monocyte activation, eventually leading to increased transmigration through the endothelium. Similarly, remnant cholesterol has been identified to play a key role in endothelial dysfunction and monocyte behavior. In this review, we will discuss recent developments in understanding the role of different lipoproteins in the context of inflammation at both the level of the monocyte and the endothelium.

Native low density lipoprotein increases the production of both nitric oxide and reactive oxygen species in the human umbilical vein endothelial cells

BACKGROUND

Nitric oxide synthases (NOSs) are a unique family of enzymes that catalyze the production of nitric oxide (NO) from L-arginine. Atherogenic action of oxidized low-density lipoproteins (oxLDL) may be mediated partly by the formation of NO in endothelial cells.

OBJECTIVE

The objective of this study was to identify sources of reactive oxygen species (ROS) causing native LDL (nLDL)-induced senescence of cultured human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were treated with nLDL and NO production was assessed using Griess reagent as substrate and spectrophotometry in the absence or presence of specific inhibitors of endothelial NOS (eNOS) and inducible NOS (iNOS). In addition, expression levels of eNOS and iNOS were measured with ELISA and western blotting, and ROS was evaluated using 2',7'-dichlorofluorescin diacetate (DCF-DA) and a fluorescence microplate reader.

RESULTS

NO formation in nLDL-treated HUVECs was significantly increased. Long-term treatment with nLDL up-regulated both eNOS and iNOS proteins. Such increase of NO production in HUVECs induced by nLDL was significantly suppressed by treatment with iNOS-selective inhibitor 1400 W, but not by the eNOS-selective inhibitor L-NIO. Native LDL treatment uncoupled Hsp90, the regulatory binding protein of eNOS, from the enzyme in HUVECs. Native LDL also significantly increased ROS production in HUVECs.

CONCLUSION

These findings suggest that oxidative stress originated from induction of iNOS and eNOS could be a causative factor for nLDL-induced senescence of HUVECs.

Long-Term Treatment of Native LDL Induces Senescence of Cultured Human Endothelial Cells

The study aimed to evaluate whether the treatment of primary cultured human endothelial cells with native low-density lipoprotein (nLDL) could induce their senescence and to uncover some of the putative mechanisms involved. For this purpose, human umbilical vein endothelial cells (HUVECs) were subcultured and/or continuously cultured with nLDL (0, 2, 5, and 10 μg protein/mL), for up to 9 days. The results indicated that nLDL inhibited the proliferation of HUVECs by arresting the cell cycle at G1 phase. The G1-arrested cells showed increase in cytosolic senescence-associated-β-galactosidase (SA-β-Gal) activity, a biomarker of cellular senescence. The causative factor of the cellular senescence was nLDL itself and not oxidized LDL (oxLDL), since blocking LDL receptor (LDLR) with the anti-LDLR antibody opposed the nLDL-induced increase of SA-β-Gal activity and decrease of cellular proliferation. In addition, nLDL-induced cellular senescence by inhibiting the phosphorylation of pRb (G1 arrest) via p53 as well as p16 signal transduction pathways. G1 phase arrest of the senescent cells was not overcome by nLDL removal from the culture medium. Moreover, the nLDL-treated cells produced reactive oxygen species (ROS) dose- and time-dependently. These results suggested, for the first time, that long-term treatment of nLDL could induce the premature senescence of endothelial cells.

Myocardial Structural and Biological Anomalies Induced by High Fat Diet in Psammomys obesus Gerbils

Background

Psammomys obesus gerbils are particularly prone to develop diabetes and obesity after brief period of abundant food intake. A hypercaloric high fat diet has been shown to affect cardiac function. Here, we sought to determine whether a short period of high fat feeding might alter myocardial structure and expression of calcium handling proteins in this particular strain of gerbils.

Methods

Twenty Psammomys obesus gerbils were randomly assigned to receive a normal plant diet (controls) or a high fat diet. At baseline and 16-week later, body weight, plasma biochemical parameters (including lipid and carbohydrate levels) were evaluated. Myocardial samples were collected for pathobiological evaluation.

Results

Sixteen-week high fat dieting resulted in body weight gain and hyperlipidemia, while levels of carbohydrates remained unchanged. At myocardial level, high fat diet induced structural disorganization, including cardiomyocyte hypertrophy, lipid accumulation, interstitial and perivascular fibrosis and increased number of infiltrating neutrophils. Myocardial expressions of pro-apoptotic Bax-to-Bcl-2 ratio, pro-inflammatory cytokines [interleukin (IL)-1β and tumor necrosis factor (TNF)-α], intercellular (ICAM1) and vascular adhesion molecules (VCAM1) increased, while gene encoding cardiac muscle protein, the alpha myosin heavy polypeptide (MYH6), was downregulated. Myocardial expressions of sarco(endo)plasmic calcium-ATPase (SERCA2) and voltage-dependent calcium channel (Cacna1c) decreased, while protein kinase A (PKA) and calcium-calmodulin-dependent protein kinase (CaMK2D) expressions increased. Myocardial expressions of ryanodine receptor, phospholamban and sodium/calcium exchanger (Slc8a1) did not change.

Conclusions

We conclude that a relative short period of high fat diet in Psammomys obesus results in severe alterations of cardiac structure, activation of inflammatory and apoptotic processes, and altered expression of calcium-cycling determinants.

Protective effects of monomethyl fumarate at the inflamed blood-brain barrier

BACKGROUND

Reactive oxygen species play a key role in the pathogenesis of multiple sclerosis as they induce blood-brain barrier disruption and enhance transendothelial leukocyte migration. Thus, therapeutic compounds with antioxidant and anti-inflammatory potential could have clinical value in multiple sclerosis. The aim of the current study was to elucidate the therapeutic effects of monomethyl fumarate on inflammatory-mediated changes in blood-brain barrier function and gain insight into the underlying mechanism.

METHODS

The effects of monomethyl fumarate on monocyte transendothelial migration across and adhesion to inflamed human brain endothelial cells (hCMEC/D3) were quantified using standardized in vitro migration and adhesion assays. Flow cytometry analysis and qPCR were used to measure the concomitant effects of monomethyl fumarate treatment on protein expression of cell adhesion molecules. Furthermore, the effects of monomethyl fumarate on the expression and nuclear localization of proteins involved in the activation of antioxidant and inflammatory pathways in human brain endothelial cells were elucidated using nuclear fractionation and Western blotting. Statistical analysis was performed using one-way ANOVA followed by the Bonferroni post-hoc test.

RESULTS

Our results show that monomethyl fumarate induced nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 and concomitant production of the antioxidant enzymes heme oxygenase-1 and NADPH:quinone oxidoreductase-1 in brain endothelial cells. Importantly, monomethyl fumarate treatment markedly decreased monocyte transendothelial migration across and adhesion to inflamed human brain endothelial cells. Treatment of brain endothelial cells with monomethyl fumarate resulted in a striking reduction of vascular cell adhesion molecule expression. Surprisingly, monomethyl fumarate did not affect nuclear translocation of nuclear factor-кB suggesting that monomethyl fumarate potentially affects activity of nuclear factor-ĸB downstream of nuclear translocation.

CONCLUSIONS

Taken together, we show that monomethyl fumarate, the primary metabolite of dimethyl fumarate, which is currently used in the clinics for the treatment of relapsing-remitting multiple sclerosis, demonstrates beneficial therapeutic effects at the inflamed blood-brain barrier.

Ginseng Berry Extract Prevents Atherogenesis via Anti-Inflammatory Action by Upregulating Phase II Gene Expression

Ginseng berry possesses higher ginsenoside content than its root, which has been traditionally used in herbal medicine for many human diseases, including atherosclerosis. We here examined the antiatherogenic effects of the Korean ginseng berry extract (KGBE) and investigated its underlying mechanism of action in vitro and in vivo. Administration of KGBE decreased atherosclerotic lesions, which was inversely correlated with the expression levels of phase II genes to include heme oxygenase-1 (HO-1) and glutamine-cysteine ligase (GCL). Furthermore, KGBE administration suppressed NF-κB-mediated expression of atherogenic inflammatory genes (TNF-α, IL-1β, iNOS, COX-2, ICAM-1, and VCAM-1), without altering serum cholesterol levels, in ApoE^−/− mice fed a high fat-diet. Treatment with KGBE increased phase II gene expression and suppressed lipopolysaccharide-induced reactive oxygen species production, NF-κB activation, and inflammatory gene expression in primary macrophages. Importantly, these cellular events were blocked by selective inhibitors of HO-1 and GCL. In addition, these inhibitors reversed the suppressive effect of KGBE on TNF-α-mediated induction of ICAM-1 and VCAM-1, resulting in decreased interaction between endothelial cells and monocytes. These results suggest that KGBE ameliorates atherosclerosis by inhibiting NF-κB-mediated expression of atherogenic genes via upregulation of phase II enzymes and thus has therapeutic or preventive potential for atherosclerosis.

Tanshinone IIA inhibits TNF-α-mediated induction of VCAM-1 but not ICAM-1 through the regulation of GATA-6 and IRF-1

The goal of this study was to investigate the differential effect of tanshinone IIA on the induction of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by TNF-α and the possible molecular mechanisms by which it regulates ICAM-1 and VCAM-1 expression differentially. Stimulation of human umbilical vein endothelial cells (HUVEC) with TNF-α increased ICAM-1 and VCAM-1 expressions, and the pretreatment with tanshinone IIA concentration dependently inhibited VCAM-1 expression but not ICAM-1 expression. In previous study, PI3K/Akt, PKC and Jak/STAT-3 pathways were involved in the TNF-α-mediated induction of VCAM-1 but not ICAM-1. Thus, we examined the effect of tanshinone IIA on TNF-α-mediated activations of PI3K/Akt, PKC and Jak/STAT-3 pathways. Tanshinone IIA efficiently inhibited the phosphorylations of Akt, PKC and STAT-3 by TNF-α. Moreover, we determined the effect of tanshinone IIA on IRF-1 or GATAs induction and binding activity to VCAM-1 promoter since the upstream promoter region of VCAM-1 but not ICAM-1 contains IRF-1 and GATA binding motifs. Western blot analysis and ChIP assay showed that tanshinone IIA efficiently inhibited TNF-α-increased nuclear level of IRF-1 and GATA-6 and their binding affinity to VCAM-1 promoter region. Taken together, tanshinone IIA selectively inhibits TNF-α-mediated expression of VCAM-1 but not ICAM-1 through modulation of PI3/Akt, PKC and Jak/STAT-3 pathway as well as IRF-1 and GATA-6 binding activity.

Deficiency of the NR4A orphan nuclear receptor NOR1 decreases monocyte adhesion and atherosclerosis

RATIONALE

The orphan nuclear receptor NOR1 is a member of the evolutionary highly conserved and ligand-independent NR4A subfamily of the nuclear hormone receptor superfamily. Members of this subfamily have been characterized as early response genes regulating essential biological processes including inflammation and proliferation; however, the role of NOR1 in atherosclerosis remains unknown.

OBJECTIVE

The goal of the present study was to determine the causal contribution of NOR1 to atherosclerosis development and to identify the mechanism by which this nuclear receptor participates in the disease process.

METHODS AND RESULTS

In the present study, we demonstrate expression of NOR1 in endothelial cells of human atherosclerotic lesions. In response to inflammatory stimuli, NOR1 expression is rapidly induced in endothelial cells through a nuclear factor kappaB-dependent transactivation of the NOR1 promoter. Overexpression of NOR1 in human endothelial cells increased the expression of vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule-1, whereas NOR1 deficiency altered adhesion molecule expression in response to inflammatory stimuli. Transient transfection experiments and chromatin immunoprecipitation assays revealed that NOR1 induces VCAM-1 promoter activity by binding to a canonical response element for NR4A receptors in the VCAM-1 promoter. Further functional studies confirmed that NOR1 mediates monocyte adhesion by inducing VCAM-1 and intercellular adhesion molecule-1 expression in endothelial cells. Finally, we demonstrate that NOR1 deficiency reduces hypercholesterolemia-induced atherosclerosis formation in apoE(-/-) mice by decreasing the macrophage content of the lesion.

CONCLUSIONS

In concert, these studies identify a novel pathway underlying monocyte adhesion and establish that NOR1 serves a previously unrecognized atherogenic role in mice by positively regulating monocyte recruitment to the vascular wall.

Anthocyanins from black soybean seed coats preferentially inhibit TNF-alpha-mediated induction of VCAM-1 over ICAM-1 through the regulation of GATAs and IRF-1

Adhesion molecules have a key role in pathological inflammation. Thus, we investigated the effect of anthocyanins on the induction of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by TNF-alpha and the possible molecular mechanisms by which anthocyanins differentially regulate ICAM-1 and VCAM-1 expression. Stimulation of cells with TNF-alpha increased ICAM-1 and VCAM-1 expression, and pretreatment with anthocyanins inhibited VCAM-1 expression, but not ICAM-1 expression. We found that IRF-1 and GATAs, especially GATA-4 and -6, were involved in the TNF-alpha-mediated expression of VCAM-1 but not ICAM-1, and anthocyanins decreased nuclear levels of GATA-4 and GATA-6 as well as IRF-1. Moreover, pretreatment with a Jak/STAT inhibitor decreased TNF-alpha-induced VCAM-1 expression and nuclear GATA-4, GATA-6, and IRF-1 levels. Furthermore, anthocyanins efficiently inhibited the phosphorylation of STAT-3. This suggests that anthocyanins differentially regulate TNF-alpha-mediated expression of VCAM-1 and ICAM-1 through modulation of the GATA and IRF-1 binding activity via Jak/STAT-3 activation.

Critical role for GATA3 in mediating Tie2 expression and function in large vessel endothelial cells

Endothelial phenotypes are highly regulated in space and time by both transcriptional and post-transcriptional mechanisms. There is increasing evidence that the GATA family of transcription factors function as signal transducers, coupling changes in the extracellular environment to changes in downstream target gene expression. Here we show that human primary endothelial cells derived from large blood vessels express GATA2, -3, and -6. Of these factors, GATA3 was expressed at the highest levels. In DNA microarrays of human umbilical vein endothelial cells (HUVEC), small interfering RNA-mediated knockdown of GATA3 resulted in reduced expression of genes associated with angiogenesis, including Tie2. At a functional level, GATA3 knockdown inhibited angiopoietin (Ang)-1-mediated but not vascular endothelial cell growth factor (VEGF)-mediated AKT signaling, cell migration, survival, and tube formation. In electrophoretic gel mobility shift assays and chromatin immunoprecipitation, GATA3 was shown to bind to regulatory regions within the 5'-untranslated region of the Tie2 gene. In co-immunoprecipitation and co-transfection assays, GATA3 and the Ets transcription factor, ELF1, physically interacted and synergized to transactivate the Tie2 promoter. GATA3 knockdown blocked the ability of Ang-1 to attenuate vascular endothelial cell growth factor stimulation of vascular cell adhesion molecule-1 expression and monocytic cell adhesion. Moreover, exposure of human umbilical vein endothelial cells to tumor necrosis factor-alpha resulted in marked down-regulation of GATA3 expression and reduction in Tie2 expression. Together, these findings suggest that GATA3 is indispensable for Ang-1-Tie2-mediated signaling in large vessel endothelial cells.

In vivo low-density lipoprotein exposure induces intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 correlated with activator protein-1 expression

OBJECTIVE

We tested the hypothesis that direct native low-density lipoprotein (LDL) injection into LDL receptor-deficient (LDLR(-/-)) mice would induce the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in their aortic endothelial cells, and that transcriptional regulation of this pathway involved activator protein-1 (AP-1) but not nuclear factor kappaB (NF-kappaB).

METHODS AND RESULTS

Using tail vein injection of LDL into LDLR(-/-) mice, we were able to maintain atherogenic LDL blood levels, which induced ICAM-1 and VCAM-1 expression in their aortic endothelial cells after 24 hours. We were able to visualize and quantify this expression using immunohistochemistry and confocal microscopy. Under conditions in which ICAM-1 and VCAM-1 were expressed, the regulatory AP-1 proteins c-Fos and c-Jun were also highly expressed in the endothelial cell cytoplasm and observed within the cell nucleus. The NF-kappaB protein P65, although expressed in the endothelial cell cytoplasm after LDL injection, was not observed within the cell nucleus.

CONCLUSIONS

Elevated LDL blood levels, maintained in vivo, increased the expression of the adhesion molecules ICAM-1 and VCAM-1 in aortic endothelial cells. This effect appeared to correlate with AP-1 but not NF-kappaB.

Molecular aspects of atherogenesis: new insights and unsolved questions

The development of atherosclerotic disease results from the interaction between environment and genetic make up. A key factor in atherogenesis is the oxidative modification of lipids, which is involved in the recruitment of mononuclear leukocytes to the arterial intima--a process regulated by several groups of adhesion molecules and cytokines. Activated leukocytes, as well as endothelial mitochondria, can produce reactive oxygen species (ROS) that are associated with endothelial dysfunction, a cause of reduced nitric oxide (NO) bioactivity and further ROS production. Peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) are nuclear receptors significantly involved in the control of lipid metabolism, inflammation and insulin sensitivity. Also, an emerging role has been suggested for G protein coupled receptors and for the small Ras and Rho GTPases in the regulation of the expression of endothelial NO synthase (eNOS) and of tissue factor, which are involved in thrombus formation and modulation of vascular tone. Further, the interactions among eNOS, cholesterol, oxidated LDL and caveola membranes are probably involved in some molecular changes observed in vascular diseases. Despite the relevance of oxidative processes in atherogenesis, anti-oxidants have failed to significantly improve atherosclerosis (ATS) prevention, while statins have proved to be the most successful drugs.

Anionic Peptide Factor/Phosphatidylcholine Particles Promote the Inhibition of Vascular Cell Adhesion Molecule-1 in Human Umbilical Vein Endothelial Cells

OBJECTIVE

High-density lipoproteins (HDLs) have significant cardiovascular benefits by retarding the progression of atherosclerosis. One of the mechanisms is the inhibition by HDLs of the vascular cell adhesion molecule-1 (VCAM-1) expression in endothelial cells. Our objective was to test the effect on VCAM-1 expression by the human umbilical vein endothelial cells (HUVEC) of a minor HDL2 and HDL3 apolipoprotein, the anionic peptide factor (APF). The peptide has previously been found to develop some beneficial effects against atherosclerosis, i.e. by promoting the cholesterol efflux from endothelial cells.

METHODS

We examined the effects of two HDL apolipoproteins A-I and APF, either in presence or absence of phosphatidylcholines (PCs), or free PCs, on the expression of VCAM-1 by HUVEC. The cells were stimulated with either the tumor necrosis factor-alpha (TNFalpha, 500 pg/ml) or the calcium bound to heparin (10 microg Ca2+/ml, 50 microg heparin/ml).

RESULTS

In the presence of TNFalpha, only the free PCs (0.25 and 1 mM) developed an inhibitory effect (up to 50%). In the absence of TNFalpha and in the presence of calcium bound to heparin, either the lipid-free APF (3.5 microM) or the APF/PC complexes (1:57 molar ratio) or the free PCs (0.25 mM) exhibited a substantial inhibitory effect (72, 71 and 42%, respectively).

CONCLUSION

Our present findings suggest for the first time that one of the mechanisms of the antiatherogenic action of APF involves the inhibition of VCAM-1 expression by HUVEC. The peptide, through its phospholipid-binding and its calcium antagonist abilities, appears to confer on the HDLs a protective effect against the early cellular event of the inflammatory process.

Irbesartan inhibits human T-lymphocyte activation through downregulation of activator protein-1

1 Irbesartan is a promising antihypertensive drug with beneficial effects on atherosclerotic processes. In the progression of atherosclerosis, human T-lymphocytes play an important role, but it is not yet known how irbesartan modulates human T-lymphocytes activation. To gain insight into the mechanisms by which irbesartan acts, we investigated its effects on human T-lymphocytes. 2 Primary human T-lymphocytes were isolated from whole blood. Cytokines were determined by ELISA. Activator protein-1 (AP-1) and related protein activities were determined by electrophoretic mobility shift assays, kinase assays, Western blotting and transfection assays. 3 Irbesartan inhibited the production of both tumor necrosis factor-alpha and interferon-gamma by activated T-cells, especially at therapeutic concentrations. Further investigation at the molecular level indicated that the inhibition of activated human T-lymphocytes specifically correlated with the downregulation of AP-1 DNA-binding activity. In the Jurkat T-cell line, irbesartan also inhibited AP-1 transcriptional activity. Finally, we revealed that irbesartan is unique in its ability to inhibit the activation of both c-Jun NH2-terminal protein kinase and p38 MAPK. 4 Our studies show that irbesartan may modulate inflammation-based atherosclerotic diseases through a cell-mediated mechanism involving suppression of human T-lymphocytes activation via downregulation of AP-1 activity.

Acetylsalicylic Acid Inhibits Monocyte Adhesion to Endothelial Cells by an Antioxidative Mechanism

The adhesion of monocytes to vascular endothelium increases in the presence of high levels of low density lipoprotein (LDL). LDL changes oxidative status of endothelial cells leading to an increased expression of cell adhesion molecules. Acetylsalicylic acid (ASA) has been shown to exert antioxidant effects in high and very high concentrations. This study was designed to demonstrate the influence of acetylsalicylic acid and its major metabolite, salicylic acid (SA), on the adhesion of monocytes to LDL-stimulated endothelial cells. Monocyte adhesion to endothelial cells was concentration-dependently inhibited by both salicylates upon stimulation of endothelial cells with TNF-alpha, oxidized LDL (oxLDL), and native LDL (nLDL). The inhibitory effect of ASA was more potent than that of SA, whereas the cyclooxygenase inhibitor ibuprofen had no effect. F2-isoprostane release from LDL-stimulated endothelial cells was reduced by simultaneous incubation with ASA or SA, whereas ibuprofen had no effect. LDL-induced activation of the transcription factor NF-kappaB was inhibited by ASA, and ferritin protein was increased when endothelial cells were incubated with this drug. These results show that acetylsalicylic acid and-less potently-salicylic acid inhibit monocyte adhesion to LDL-stimulated endothelial cells by antioxidative effects. For ASA, the observed inhibition of monocyte adhesion was accomplished with concentrations that can be reached after single oral doses of 500 mg of ASA.

Identification of two serine residues important for p53 DNA binding and protein stability

The p53 core DNA binding domain has been implied in Mdm2-mediated protein degradation. Here we show that the substitution of the serine residues 116 and 127 with alanine residues (S116/127A) has no effect on p53 DNA binding and protein stability. However, the substitution of the serine residues with the aspartic acid (S116/127D) abolished p53 DNA binding and led to protein stabilization. Importantly, we have shown that S116/127D exhibits a structural mutant conformation that results in a loss of p53-dependent transcription and Mdm2-mediated protein degradation.

Signal transduction pathways in mast cell granule-mediated endothelial cell activation

BACKGROUND

We have previously shown that incubation of human endothelial cells with mast cell granules results in potentiation of lipopolysaccharide-induced production of interleukin-6 and interleukin-8.

AIMS

The objective of the present study was to identify candidate molecules and signal transduction pathways involved in the synergy between mast cell granules and lipopolysaccharide on endothelial cell activation.

METHODS

Human umbilical vein endothelial cells were incubated with rat mast cell granules in the presence and absence of lipopolysaccharide, and IL-6 production was quantified. The status of c-Jun amino-terminal kinase and extracellular signal-regulated kinase 1/2 activation, nuclear factor-kappaB translocation and intracellular calcium levels were determined to identify the mechanism of synergy between mast cell granules and lipopolysaccaride.

RESULTS

Mast cell granules induced low levels of interleukin-6 production by endothelial cells, and this effect was markedly enhanced by lipopolysaccharide. The results revealed that both serine proteases and histamine present in mast cell granules were involved in this activation process. Mast cell granules increased intracellular calcium, and activated c-Jun amino-terminal kinase and extracellular signal-regulated kinase 1/2. The combination of lipopolysaccharide and mast cell granules prolonged c-Jun amino-terminal kinase activity beyond the duration of induction by either stimulant alone and was entirely due to active proteases. However, both proteases and histamine contributed to calcium mobilization and extracellular signal-regulated kinase 1/2 activation. The nuclear translocation of nuclear factor-kappaB proteins was of greater magnitude in endothelial cells treated with the combination of mast cell granules and lipopolysaccharide.

CONCLUSIONS

Mast cell granule serine proteases and histamine can amplify lipopolysaccharide-induced endothelial cell activation, which involves calcium mobilization, mitogen-activated protein kinase activation and nuclear factor-kappaB translocation.

Expression of interleukin-1 beta and interleukin-1 receptor antagonist in oxLDL-treated human aortic smooth muscle cells and in the neointima of cholesterol-fed endothelia-denuded rabbits

The migration of vascular smooth muscle cells (VSMCs) from the media to the intima and the proliferation of intimal VSMCs are key events in restenotic lesion development. These events, which are preceded and accompanied by inflammation, are modulated by the proinflammatory cytokine, interleukin-1 beta (IL-1 beta), which induces vascular smooth muscle cells to express adhesion molecules and to proliferate. IL-1 beta action is complex and regulated, in part, by its naturally occurring inhibitor, the IL-1 receptor antagonist (IL-1ra). Whether there was a temporal and spatial correlation between IL-1 beta and IL-1ra expression in, and release by, oxidized low density lipoproteins (oxLDL)-stimulated human aortic smooth muscle cells (HASMCs) was determined by using ELISA and Western blot. In addition, IL-1 beta and IL-1ra expression was detected in the neointima of endothelia-denuded cholesterol-fed New Zealand white rabbits by immunohistochemistry and Western blot. In HASMCs, oxLDL induced IL-beta and IL-1ra expression and release in a dose- and time-dependent manner. Treatment with 20 microg/ml oxLDL resulted in increased IL-1 beta release after 6 h, which peaked at 24 h, and in increased IL-1ra release, first seen after 12 h, but continuing to increase for at least 48 h. In the cells, IL-beta expression showed a similar pattern to release, whereas IL-1ra expression was seen in unstimulated cells and was not increased by oxLDL treatment. Confocal microscopy showed colocalization of IL-beta and IL-1ra expression in oxLDL-stimulated HASMCs. oxLDL caused significant induction of nuclear factor kappa B and activator protein-1 DNA binding activity in HASMCs (6.6- and 3.3-fold, respectively). In cholesterol-fed endothelia-denuded rabbits, the notably thickened intima showed significant IL-1 beta and IL-1ra expression. These results provide further support for the role of IL-1 system in the pathogenesis of restenosis. This is the first demonstration of IL-1 beta and IL-1ra expression and secretion of oxLDL-treated HASMCs and their expression in the rabbit neointima, suggesting that the smooth muscle cells of the intima are an important source of these factors.

Circulating endothelial cells: tea leaves for renal disease

Fully differentiated endothelial cells and their precursors circulate in the bloodstream. Since their initial description more than 30 years ago, circulating endothelial cells have been quantified in a number of different clinical conditions that affect the endothelium. Only recently, however, have investigators begun to examine the protein expression and functionality of these cells. Because a number of diseases prevalent in the field of nephrology affect endothelial cells, the study of circulating endothelial cells may allow the direct examination of the state of the endothelium in these conditions. This review will discuss the endothelium and renal disease, the methods to quantify these circulating endothelial cells, their origins, and their therapeutic potential.

Malondialdehyde binding to proteins dramatically alters fibroblast functions

The regulation of cell metabolism by the surrounding environment is deeply altered by the posttranslational nonenzymatic modifications of extracellular proteins that occur throughout lifespan in vivo and modify their structural and functional properties. Among them are protein adducts formed by components generated from oxidative processes, such as malondialdehyde (MDA). We have investigated here the effects of MDA-binding to proteins on cultured fibroblast functions. Type I collagen and/or serum proteins were incubated with 0-100 mM MDA for 3 h before use in fibroblast cultures. In tridimensional lattice cultures, MDA-treated collagen inhibited the contracting activity of fibroblasts. A similar inhibition of lattice contraction was reproduced by the addition of MDA-treated serum to the culture medium. In monolayer cultures, the addition of MDA-modified serum proteins completely inhibited fibroblast multiplication without effect on initial adhesion steps. MDA-modified proteins decreased the proliferative capacities of cells, strongly altered cell cycle progression by blocking passage to G2/M phases, and induced apoptotic features in fibroblasts. Our results show, for the first time, that MDA-modified proteins are potentially as deleterious as free MDA, and could be involved in aging as well as in degenerative complications of diseases with increased oxidative stress such as diabetes mellitus or atherosclerosis.

Small-sized low-density lipoproteins of subclass B from patients with end-stage renal disease effectively augment tumor necrosis factor-alpha-induced adhesive properties in human endothelial cells

Increased prevalence of small-sized low-density lipoprotein (LDL) subclass B (diameter < 25.5 nm) possibly is involved in the multifactorial process of cardiovascular disease in patients with end-stage renal disease. Given these epidemiological observations, mechanisms underlying the combined effect of a proinflammatory insult and LDL of different subclasses (subclass A, diameter > 25.5 nm, and subclass B) in a cellular model were investigated. For this, human umbilical vein endothelial cells were preexposed to LDL, then stimulated with tumor necrosis factor-alpha (TNF-alpha). Modulatory effects of LDL phenotypes on the activation of adhesion molecules, monocyte adherence, and transcriptional activity of nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) were investigated. Our data show that subclass B LDLs were metabolized through nonspecific scavenger receptors and specific LDL-receptor pathways in endothelial cells. Furthermore, LDL subclass B in comparison to subclass A more effectively enhanced monocyte recruitment and adhesive properties of endothelial cells in response to TNF-alpha. These effects appeared not to be mediated by oxidative stress-responsive NF-kappaB because modulation of this transcription factor by LDL was moderate and similar for both LDL phenotypes. Conversely, effects of LDL subclass B were considered to be caused by augmented AP-1 binding activity. In conclusion, the present model provides new clues in atherogenic mechanisms of small-sized LDLs, which sensitize vascular cells to inflammatory signals more effectively than normal-sized LDLs.

Cholesterol enrichment upregulates intercellular adhesion molecule-1 in human vascular endothelial cells

Hypercholesterolemia is a major risk factor for atherosclerosis, but the mechanism by which cholesterol activates the endothelium remains undocumented. The present investigation was undertaken to investigate the role of cholesterol, one of the bioactive moieties of the low-density lipoprotein (LDL) particle, in initiating of intracellular signaling in endothelial cells (ECs) and culminating in increased abundance of the intercellular adhesion molecule-1 (ICAM-1). Cholesterol was delivered to human umbilical vein ECs (HUVECs) via cholesterol-enriched liposomes. In HUVECs, the cellular cholesterol:phospholipid ratio increased after 1 h of exposure to cholesterol. The level of ICAM-1 increased in both mRNA and protein after 24 h of cholesterol exposure. ICAM-1 mRNA half-life was not affected by cholesterol exposure. Promoter studies showed greater than two-fold activation of the ICAM-1 gene expression after cholesterol exposure. Electrophoretic mobility shift assay showed that activator protein-1 (AP-1) activity substantially increased after 2 h of exposure to cholesterol. In contrast, cholesterol did not affect nuclear factor-kappaB (NF-kappaB) activity. Results of trans-reporting assay revealed 2.5-fold increased expression of the AP-1-dependent reporter gene after cholesterol exposure whereas NF-kappaB-dependent expression was not affected. The AP-1/Ets (-891 to -908) site, one of the three AP-1-like sites in the ICAM-1 promoter, was most responsive to cholesterol. These data demonstrate for the first time that cholesterol enrichment phenotypically modulates ECs by transcriptionally upregulating ICAM-1 expression.

Adenovirus-mediated overexpression of dominant-negative mutant of c-Jun prevents intercellular adhesion molecule-1 induction by LDL: a critical role for activator protein-1 in endothelial activation

Low density lipoprotein (LDL) induces intercellular adhesion molecule-1 (ICAM-1) gene expression and leads to endothelial cell (EC) leukocyte adhesion. However, the transcriptional mechanism for LDL-induced EC perturbation remains to be fully explained. Activator protein-1 (AP-1) is induced after the exposure of ECs to LDL. In the present study, a regulated adenovirus expressing a dominant-negative mutant of c-Jun (TAM-67) was used to examine the role of AP-1 in the LDL-induced ICAM-1 activation. Overexpression of TAM-67 specifically inhibited AP-1 activation and prevented the LDL-activated surface expression of ICAM-1 protein in human umbilical vein ECs and human coronary artery ECs. Northern analyses and promoter transactivation assays indicated that this effect of TAM-67 was likely mediated through a suppression of the transcriptional regulation of the ICAM-1 gene. Functionally, TAM-67 attenuated leukocyte adherence to ECs in response to LDL. Furthermore, electrophoresis mobility shift assays and site-directed mutagenesis suggested that an AP-1-like motif in the promoter region of the human ICAM-1 gene was a critical cis element for LDL induction. These results, for the first time, provide evidence suggesting that AP-1 is a major regulatory mechanism leading to endothelial activation.

LDL-activated p38 in endothelial cells is mediated by Ras

Endothelial dysfunction is a major atherogenic proinflammatory event. LDL causes the activation and phenotypic changes of cultured vascular endothelial cells (ECs). We previously reported that LDL activates c-Jun and AP-1 in ECs. In this study, we demonstrated that p38-ATF-2 is activated by LDL in human ECs and that this activation is mediated by Ras. When ECs are incubated with LDL in pathophysiological concentrations, the p38-mediated ATF-2 phosphorylation and ATF-2 transactivation are increased in a time- and dose-dependent manner. To elucidate the upstream mechanism in LDL-activated p38 in ECs, we demonstrate that LDL increases Ras translocation from the cytoplasm to the cellular membrane, with concurrent increases in Ras binding activity to GST-Raf-1. Overexpression of RasN17, a dominant negative mutant of Ras, attenuates the LDL-induced increases in (1) phosphorylation of ATF-2, (2) phosphorylation of c-Jun, (3) AP-1 binding, and (4) AP-1-driven luciferase activity. To study the effect of p38 in the regulation of an LDL targeting gene, we show that a specific p38 inhibitor attenuates LDL-induced E-selectin at the mRNA level. Thus, LDL activates both p38 and JNK signaling pathways through Ras activation, and furthermore, these events may play an important role in LDL-induced endothelial activation.

Function of GATA transcription factors in induction of endothelial vascular cell adhesion molecule-1 by tumor necrosis factor-alpha

Endothelial vascular cell adhesion molecule-1 (VCAM-1) is expressed in response to cytokine stimulation and plays a critical role in inflammatory reactions. Previously, we developed a novel VCAM-1 inhibitor that acts through a mechanism independent of nuclear factor-kappaB activity. It suppresses the binding activity of GATA proteins in cytokine-stimulated endothelial cells, which may be related to the anti-VCAM-1 induction effect of this drug. In this study, we investigated the role of GATA proteins in the induction of VCAM-1 by tumor necrosis factor-alpha (TNF-alpha) in human endothelial cells. The mRNA expression of GATA-6 was increased, whereas GATA-3 mRNA was decreased by TNF-alpha stimulation. Electrophoretic mobility shift assay showed that TNF-alpha stimulation increased the DNA binding of GATA-6 but decreased that of GATA-3. Experiments using protein overexpression or antisense oligonucleotides revealed that GATA-6 potently acts as a positive regulator of VCAM-1 gene transcription. In contrast, overexpression of GATA-3 was able to suppress TNF-alpha-induced VCAM-1 expression. Our results provide evidence of the importance of GATA proteins in the induction of VCAM-1 by TNF-alpha in vascular endothelial cells. The switch from GATA-3 to GATA-6 is taken to be an important transcriptional control event in TNF-alpha induction of VCAM-1.

LDL downregulates CYP51 in porcine vascular endothelial cells and in the arterial wall through a sterol regulatory element binding protein-2-dependent mechanism

Hypercholesterolemia is associated with endothelial dysfunction and atherosclerotic lesion formation. By mRNA-differential display analysis, we have identified lanosterol 14alpha-demethylase (CYP51) as a gene highly regulated by native LDLs (nLDLs) in endothelial cells. CYP51 is a cytochrome P-450 enzyme involved in the postsqualene phases of cholesterol biosynthesis. CYP51 mRNA levels decrease in nLDL-treated cells in a dose- and time-dependent manner (9-fold after 24 hours with 180 mg of LDL cholesterol per deciliter), an effect that is blocked by cycloheximide. In parallel, sterol regulatory element (SRE) binding protein-2 (SREBP-2) expression falls (10-fold), without alteration in SREBP-1 level. N:-Acetyl-leucyl-leucyl-norleucinal, which inhibits catabolism of the active form of SREBPs, abolished the effect of high concentrations of nLDL on CYP51 expression. Gel-shift assays performed with the SRE of the cyp51 gene (cyp51-SRE) revealed a diminished SREBP-SRE interaction in LDL-treated cells. Moreover, nLDLs downregulate CYP51 promoter activity in transfection assays. Thus, atherogenic levels of nLDL downregulate endothelial CYP51 mRNA levels through a reduction in SRE-SREBP-2 interaction. Additionally, SREBP-2 and CYP51 mRNA levels are decreased in the arterial wall of hypercholesterolemic pigs. In summary, we have described for the first time, both in in vivo and in vitro systems, that CYP51 is expressed in the vascular wall and that it is downregulated together with SREBP-2 by high levels of nLDL. Because this transcription factor controls multiple cell lipid metabolism pathways, its regulation by nLDL could play a key role in lipid-mediated endothelial dysfunction.

The smooth muscle cell membrane during atherogenesis: a potential target for amlodipine in atheroprotection

BACKGROUND

Atherosclerotic disease has been present in the human population apparently from the beginning of time. However, it has only been in the 20th century that improvements in the control of infectious diseases have allowed the average life span to increase to the point where atherosclerosis has been able to affect the general population. By the middle of the 20th century, atherosclerosis had reached epidemic levels, and it is currently pandemic and increasing worldwide. Despite its growing significance to health care, we still know relatively little about the cellular basis for plaque genesis in the vessel wall. Current thinking holds that atherosclerosis is caused by an unchecked chronic inflammatory process involving the cells of the arterial wall and their interaction with LDL and various inflammatory cells. Considerable evidence suggests that the principal insults underlying atherogenesis are serum dyslipidemias and oxidative stress mediated primarily by oxidized LDL. However, just how these insults alter the cell biology of vascular cells and lead to the atherosclerotic phenotype is still under intense investigation. Moreover, recent clinical trials have provided evidence that certain classes of drugs, including newer calcium channel blockers (CCBs), can remodel the arterial smooth muscle cell (SMC) membrane and inhibit the progression of atherosclerotic disease.

METHODS

This review summarizes our current thinking on atherogenesis in the arterial SMC and considers recent developments regarding alterations in the SMC membrane during the very early period of atherogenesis. We also discuss how certain CCBs might operate to produce atheroprotection.

RESULTS

The SMC membrane becomes enriched in unesterified cholesterol soon after the development of serum hypercholesterolemia. With excess membrane cholesterol, the membrane becomes thicker and develops distinct cholesterol domains. These alterations in the membrane increase the permeability of SMC to calcium and induce a variety of alterations in SMC function that contribute to cellular atherogenic processes during plaque genesis. Amlodipine, a third-generation CCB, markedly inhibits the progression of lesions. The explanation of this novel action may lie in the effects of this drug on various potential cellular targets.

CONCLUSIONS

Evidence is accumulating that excess membrane cholesterol may contribute to the cellular defects responsible for the transformation of the SMC to the atherosclerotic phenotype. Amlodipine, which has membrane-remodeling properties, is emerging as an important atheroprotective drug.

De novo expression of macrophage migration inhibitory factor in atherogenesis in rabbits

Macrophage migration inhibitory factor (MIF) has been shown to play an important role in macrophage-mediated diseases. We investigate the potential role of MIF in atherogenesis using a hypercholesterolemic rabbit model. New Zealand White rabbits fed with a 2% cholesterol diet developed hypercholesterolemia and early fatty streaks at 1 month. The lesions became advanced at 3 months and were associated with de novo MIF expression by vascular endothelial cells (VECs) and smooth muscle cells (SMCs), as demonstrated by immunohistochemistry, reverse transcriptase-polymerase chain reaction, and in situ hybridization. By contrast, there was no increase in MIF levels in rabbits fed a normal diet. In early atherogenesis, marked upregulation of MIF mRNA and protein by VECs and some intimal cells were closely associated with CD68(+) monocyte adhesion onto and subsequent migration into subendothelial space. Of significance, the accumulation of macrophages was exclusively localized to areas of strong MIF expression, which may be associated with the macrophage-rich fatty streak lesion formation. Upregulation of MIF by SMCs is transient during atherogenesis. Importantly, strong MIF expression by activated macrophages may be responsible for the development of foam cell-rich lesions. Finally, the ability of MIF to induce intercellular adhesion molecule-1 expression by VECs implicates its pathogenic role in atherogenesis. In conclusion, the present study provides the first demonstration that MIF is markedly upregulated during atherogenesis. Upregulation of MIF by VECs and SMCs may play a role in macrophage adhesion, transendothelial migration, accumulation, and, importantly, transformation into foam cells. Furthermore, strong MIF expression by macrophages may both initiate and amplify the atherogenesis process.

Selective activation of endothelial cells by the antioxidant pyrrolidine dithiocarbamate: involvement of C-jun N-terminal kinase and AP-1 activation

The antioxidant agent pyrrolidine dithiocarbamate (PDTC) has been shown to protect endothelial cells (EC) from pro-inflammatory-induced and pro-oxidant-induced NF-kappaB activation. It also perturbs EC by altering activator protein-1 (AP-1) status and inducing ICAM-1. Experiments were performed to investigate the upstream mechanism by which PDTC produces these effects. We have demonstrated that PDTC not only induced AP-1 binding and ICAM-1 expression by itself, but it also augmented AP-1 activation and ICAM-1 induction in low-dose IL-1alpha treated cells. To dissect the mechanism of these effects, we measured c-Jun and c-Fos expression, and the activity of c-Jun NH2-terminal kinase (JNK) and extracellular signal regulated kinase (ERK) in human umbilical vein endothelial cells (HUVEC). We detected an increase in JNK activity in PDTC-treated HUVEC. Following cotransfection with JNK[K-M], a kinase-deficient JNK1, the PDTC-increased AP-1-driven-luciferase activity was attenuated. Utilizing a specific trans-reporting system we confirmed c-Jun activation by upstream signaling mechanisms. The results show that c-Jun activity was increased 9-fold after PDTC treatment. In addition, PDTC promoted more transient activation in ERK-c-fos. In contrast, PDTC produced sustained JNK-c-Jun activation, which translated into long-lasting ICAM-1 production. These results suggest that an antioxidant may contribute to chronic vascular endothelial activation.

Endothelial cell activation, injury, damage and dysfunction: separate entities or mutual terms?

The loss of well-regulated endothelial cell functioning is followed by adverse changes in a variety of physiological systems, such as the expression of adhesion molecules, maintenance of adequate blood vessel tone and haemostasis. Therefore, a full understanding of endothelial cell biology is essential if the losses of normal function of these systems are to be avoided. The viewpoint presented in this paper suggests that a spectrum between endothelial cell health and disease can be drawn: midway between these two extremes is immunological activation (by, for example, cytokines), which is reversible. Endothelial cell damage or injury (which may be the result of chronic inflammatory activation, hypercholesterolaemia, and/or smoking) are invariably associated with clinical conditions such as hypertension and oedema (and, ultimately, thrombosis and infarction), and are more difficult to reverse. A better understanding of the events, including apoptosis, that lead to vascular dysfunction may be useful in developing our understanding of vascular biology.

A novel cell adhesion inhibitor, K-7174, reduces the endothelial VCAM-1 induction by inflammatory cytokines, acting through the regulation of GATA

A novel inhibitor for the adhesion of monocytes to cytokine-stimulated endothelial cells, K-7174, was selected by an assay system using the cultured human monocytic cells and human endothelial cells. K-7174 inhibited the expression of vascular cell adhesion molecule-1 (VCAM-1) induced by either tumor necrosis factor alpha or interleukin-1beta, without affecting the induction of intercellular adhesion molecule-1 or E-selectin. K-7174 had no effect on the stability of VCAM-1 mRNA. Electrophoretic mobility shift assay revealed that its inhibitory effect on VCAM-1 induction was mediated by an effect on the binding to the GATA motifs in the VCAM-1 gene promoter region. K-7174 did not influence the binding to any of the following binding motifs: octamer binding protein, AP-1, SP-1, ets, NFkappaB, or interferon regulatory factor. These results suggest that the regulation of GATA binding may become a new target for anti-inflammatory drug development, acting through a mechanism independent from NFkappaB activity.

Mildly oxidized LDL induces expression of group IIa secretory phospholipase A(2) in human monocyte-derived macrophages

Phospholipase A(2)s (PLA(2)s) constitute a family of enzymes that hydrolyze fatty acids of membrane phospholipids, thus initiating the synthesis of proinflammatory mediators. Various PLA(2)s have been detected in human atherosclerotic arteries (advanced lesions); however, only the secretory group of PLA(2) has been shown to specifically hydrolyze low density lipoprotein (LDL)-associated phospholipids and, as such, may play a potential role in atherogenesis. In the present study, we investigated the expression pattern of group IIa, IV, and V PLA(2)s in human macrophages, which are the key cells involved in the onset and perpetuation of atherosclerosis. Immunohistochemical staining by double labeling showed that the secretory nonpancreatic PLA(2) (snpPLA(2)) is detectable in macrophages in the intima of early atherosclerotic lesions. Reverse transcription-polymerase chain reaction analysis of RNA extracted from human monocytes clearly showed that expression of group IV PLA(2) was enhanced during differentiation into macrophages, with an onset of induction at days 2 to 3 of differentiation. Group V snpPLA(2) was constitutively expressed on differentiation, whereas the detection of group IIa snpPLA(2) was dependent on both differentiation and subsequent stimulation of macrophages. Indeed, the transcription of group IIa snpPLA(2) in macrophages was induced by treatment with minimally modified or mildly oxidized LDL, whereas native, extensively oxidized, or acetylated LDL had no effect. To our knowledge, this is the first report describing induction of group IIa snpPLA(2) expression in human monocyte-derived macrophages. The mRNA levels of cytosolic PLA(2) group IV and snpPLA(2) group V remained unchanged on LDL treatment. Thus, our results show that the expression of distinct PLA(2) enzymes is regulated not only during differentiation of monocytes into macrophages but also on exposure of macrophages to distinct LDL species. Consequently, our results indicate a potential role for both cytosolic and secretory PLA(2) enzymes in inflammation and in macrophage functions related to atherosclerosis, with a specific role for group IIa snpPLA2 in LDL scavenging.

Small oxidative changes in atherogenic LDL concentrations irreversibly regulate adhesiveness of human endothelial cells: effect of the lazaroid U74500A

The adherence of monocytes to the endothelium is an early event in atherogenesis which is modulated by low density lipoproteins (LDL). We analyzed the effect of atherogenic LDL levels (180 mg cholesterol/dl, for 24 h) with minimal oxidative modifications (thiobarbituric-acid-reactive-substances (TBARS) concentration between 1.2+/-0.1 and 2.5+/-0.3 nmol of malonaldehyde bis-diethyl acetal (MDA) per mg protein) on human umbilical vein endothelial cell (HUVEC) adhesive properties. We used native LDL (n-LDL), and LDL exposed to spontaneous oxidation without antioxidants (mox-LDL) or with 20 micromol/l of the antioxidant butylated hydroxytoluene (BHT-LDL) or 10 micromol/l U74500A (U74500A-LDL), a scavenger of free radicals. Thiobarbituric-acid-reactive-substances (TBARS) levels were significantly higher in mox-LDL (2.5+/-0.3 nmol MDA/mg protein) than in BHT-LDL (1.6+/-0.2), U74500A-LDL (1.2+/-0.1) or in n-LDL (1.3+/-0.1). mox-LDL induced the greatest adhesion of U937 cells to HUVEC (103+/-9% over controls) followed by BHT-LDL (75+/-10%), U74500A-LDL (36+/-9%) and n-LDL (35+/-3%). The lazaroid U74500A efficiently protected U74500A-LDL against oxidative damage and prevented endothelial adhesiveness associated with this LDL modification, inducing adhesion effects similar to those of n-LDL. However, U74500A could not reverse the adhesion induced by previously oxidized LDL (mox-LDL). LDL did not induce the expression of the intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) or E-selectin, but it produced a downregulation of endothelial nitric oxide synthase (NOS III) mRNA levels. Thus, adhesiveness of human endothelial cells (EC) exposed to atherogenic concentrations of LDL is closely modulated by minimal changes in LDL oxidative state, and could be related to a downregulation of NOS III.

Inhibitory effects of vitamin E on endothelial-dependent adhesive interactions with leukocytes induced by oxidized low density lipoprotein

Leukocyte-endothelial cell interactions, which are mediated by various adhesion molecules, are a crucial event in inflammatory reactions including atherosclerosis. Alpha-tocopherol (alpha-Toc) has been used for protection and therapy of vascular diseases because of its antioxidant activity. The objective of the present study was to determine effect of alpha-Toc on endothelial-dependent adhesive interactions with leukocytes elicited by oxidized low density lipoprotein (oxLDL). Incubation of HUVEC with oxLDL (100 microg/mL) increased expression of proteins and messenger RNA of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on enzyme immunoassay and northern blotting assay; pretreatment with alpha-Toc reduced in a dose dependent manner. Adherence of polymorphonuclear leukocytes (PMN) or mononuclear leukocytes (MNC) to oxLDL-activated HUVEC was much increased compared with that to unstimulated HUVEC. Treatment of HUVEC with alpha-Toc, monoclonal antibody to ICAM-1 or VCAM-1 inhibited adherence of PMN or MNC in a dose dependent manner. These results suggest that alpha-Toc works as anti-atherogenic agent through inhibiting endothelial-dependent adhesive interactions with leukocytes induced by oxLDL.

Oxidative stress as a regulator of gene expression in the vasculature

Oxidative stress and the production of intracellular reactive oxygen species (ROS) have been implicated in the pathogenesis of a variety of diseases. In excess, ROS and their byproducts that are capable of causing oxidative damage may be cytotoxic to cells. However, it is now well established that moderate amounts of ROS play a role in signal transduction processes such as cell growth and posttranslational modification of proteins. Oxidants, antioxidants, and other determinants of the intracellular reduction-oxidation (redox) state play an important role in the regulation of gene expression. Recent insights into the etiology and pathogenesis of atherosclerosis suggest that this disease may be viewed as an inflammatory disease linked to an abnormality in oxidation-mediated signals in the vasculature. In this review, we summarize the evidence supporting the notion that oxidative stress and the production of ROS function as physiological regulators of vascular gene expression mediated via specific redox-sensitive signal transduction pathways and transcriptional regulatory networks. Elucidating, at the molecular level, the regulatory processes involved in redox-sensitive vascular gene expression represents a foundation not only for understanding the pathogenesis of atherosclerosis and other inflammatory diseases but also for the development of novel therapeutic treatment strategies.

Intimal deposition of functional von Willebrand factor in atherogenesis

During the formation of intimal thickening in normocholesterolemic rabbits, von Willebrand factor (vWF) is increased in the endothelial cells (ECs) and deposited in the intima. We investigated whether this also occurs during cholesterol-induced plaque formation, whether the synthesis of vWF increases, and whether this influences platelet adhesion. Rabbits were fed a cholesterol-rich (0.3%) diet for 26 weeks. Thereafter, half of the animals received a normal diet for another 26 weeks (cholesterol withdrawal). To induce intimal thickening in normocholesterolemic rabbits, collars were positioned around the carotid artery. Arterial segments were studied using immunohistochemistry, reverse transcription-polymerase chain reaction, electron microscopy, and platelet adhesion tests. Cholesterol treatment induced plaque formation in the aorta. The ECs had a cuboidal aspect, showed a dense immunoreactivity for vWF, a pronounced rough endoplasmic reticulum, and numerous Weibel-Palade bodies. There were subendothelial vWF deposits in the plaques and vWF mRNA was significantly increased as compared with controls. Similar changes were seen after collar-induced intimal thickening. After cholesterol withdrawal, both vWF mRNA and the ultrastructural morphology of the ECs normalized, and the vWF deposits disappeared from the plaque. Perfusion studies with anticoagulated rabbit blood over cross-sections of atherosclerotic aortas revealed increased vWF-mediated platelet adhesion in the subendothelial plaque region. Whereas rabbit platelets perfused through the lumen adhered to the same extent to de-endothelialized aortas of normocholesterolemic and atherosclerotic rabbits, vWF mediated platelet adhesion to endothelium was observed in atherosclerotic but not in normal aortas. Our results show an increased synthesis and (sub)endothelial presence of vWF after vascular injury, with functional consequences for platelet deposition on the vessel wall.

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.

Low-density lipoprotein augments interleukin-1-induced vascular adhesion molecule expression in human endothelial cells

In this study, the effect of low density lipoproteins (LDL) on the ability of the vascular endothelium to respond to vascular cell adhesion molecule 1 (VCAM-1) activation by a cytokine was investigated. After a 4-day pre-exposure to 240 mg/dl of LDL, human umbilical vein endothelial cells (HUVECs) were hyperresponsive to minute amounts of interleukin 1 alpha (IL-1 alpha) as demonstrated by an augmentation of VCAM-1 gene expression. Furthermore, in response to LDL exposure, endothelial recruitment of monocytes induced by minute amounts of IL-1 alpha was increased. This enhancing effect was blocked by an anti-VCAM antibody. The increased response appears not to be due to changes in IL-1 binding affinity or induction of endogenous IL-1 alpha. Transient transfection of HUVECs with a reporter driven by the VCAM promoter showed that LDL increased cellular response to IL-1 alpha by 46%. LDL itself does not increase NF-kappa B binding in endothelial cells (ECs). However, after a 2-day LDL incubation, NF-kappa B binding could be induced by over 63% with a very low dose of IL-1 alpha. IL-1 alpha at this dose (which activates NF-kappa B, but not AP-1) also enhanced LDL-activated AP-1 binding. This cross-enhanced effect may be an important intracellular signaling mechanism for EC activation. The results from this study provide new clues to understanding the mechanisms governing combined risk factors for atherosclerosis.

Focal increases in vascular cell adhesion molecule-1 and intimal macrophages at atherosclerosis-susceptible sites in the rabbit aorta after short-term cholesterol feeding

We tested the hypotheses that vascular cell adhesion molecule-1 (VCAM-1) expression on endothelium at lesion-prone sites in the rabbit aorta correlates with exposure to plasma cholesterol and that macrophage accumulation is associated with endothelial cells expressing VCAM-1. After rabbits were fed 0.25% cholesterol for 2 weeks, VCAM-1 expression was selectively increased at the distal and lateral portions of the major abdominal branches. In the arch and the celiac, superior mesenteric, and renal artery branches, VCAM-1 expression was positively correlated with the plasma cholesterol integrated over the duration of the experiments. After 2 weeks of cholesterol feeding, more macrophages were present around distal and lateral portions of the intercostal arteries and major abdominal branches relative to nonbranch regions. In the arch and around the intercostals and major abdominal branches, macrophage densities were positively correlated with the integrated plasma cholesterol. VCAM-1 and macrophage levels were correlated in lesion-prone regions. In normocholesterolemic rabbits, 23+/-4% (mean+/-SEM) of the macrophages were directly associated with VCAM-1-positive endothelium. After 2 weeks of 0.25% cholesterol feeding, the association increased to 37+/-4% (P<0.015). Associations were highest around the lateral and distal regions of the major abdominal branches. These results suggest that (1) VCAM-1 expression and intimal macrophage densities are influenced by plasma cholesterol and regional factors such as arterial fluid dynamics and (2) VCAM-1 plays a significant role in the localization of macrophages.

Low-density lipoprotein activates Jun N-terminal kinase (JNK) in human endothelial cells

We have reported previously that native low-density lipoprotein (LDL) activates c-Jun and transcription factor AP-1 in human umbilical vein endothelial cells (HUVEC). The aim of this study was to elucidate the upstream signaling mechanisms mediating LDL activation of c-Jun/AP-1. Using a c-Jun NH2-terminal kinase (JNK) activity assay, we have detected an increase in JNK activity in LDL-exposed HUVEC, which started at 15 min and reached maximum activity after 1-2 h. This JNK activity, increased by LDL, occurred in a dose-dependent fashion starting at a concentration of 80 mg/dl of LDL and reaching maximum activation at a concentration of 160-240 mg/dl. Following cotransfection, the increase of AP-1 driven luciferase activity by LDL was attenuated 54% by a kinase-deficient JNK1. Furthermore, a specific trans-reporting system was utilized to confirm c-Jun activation by upstream signal mechanisms. The results show c-Jun activity increased by 3-fold after LDL exposure when compared with respective controls. In contrast, LDL exposure did not affect the activation of extracellular signal regulated kinase 1 and 2 (ERK1/2), even though phorbol 12-myristate 13-acetate treatment remarkably increased the activity of these kinases. Thus, this study demonstrates, for the first time, that JNK mediates LDL-induced endothelial cell activation.

Small low-density lipoproteins and vascular cell adhesion molecule-1 are increased in association with hyperlipidemia in preeclampsia

The pregnancy disorder preeclampsia is characterized by endothelial cell dysfunction that may be promoted by abnormal increases in circulating lipids, particularly triglycerides and free fatty acids. Serum triglyceride concentration is a major regulatory determinant of low-density lipoprotein (LDL) size and density distribution. Smaller, denser LDL particles have several intrinsic properties capable of inducing endothelial dysfunction. The present nested, case-control study of gestationally matched preeclamptic and normal pregnant women tested the hypothesis that hypertriglyceridemia in preeclampsia is accompanied by decreases in LDL peak particle diameter (predominant LDL size). Plasma LDL peak particle diameter was determined by nondenaturing 2% to 16% polyacrylamide gel electrophoresis. Correlations of LDL diameter with the concentration of serum triglycerides, free fatty acids, total cholesterol, LDL-cholesterol, and apolipoprotein B (apo B) were determined. In the same individuals, we measured serum concentrations of a marker of vascular dysfunction previously reported to be increased in preeclampsia, soluble vascular cell adhesion molecule-1 (VCAM-1), and examined the association of VCAM-1 with LDL diameter and serum lipids. LDL peak particle diameter was decreased in preeclampsia relative to normal pregnancy (P < .01). The LDL-cholesterol:apo B ratio, which frequently decreases with decreasing LDL diameter, was also decreased (P < .04). Triglyceride concentrations were increased in preeclampsia (P < .0002), and there was a significant inverse relationship between LDL peak particle diameter and triglycerides (r = -.55, P < .02). Serum soluble VCAM-1 concentrations were markedly increased in preeclampsia (P < .0003). Apo B (P < .004), free fatty acids (P < .01), total cholesterol (P < .01), and LDL-cholesterol (P < .02) were also increased. VCAM-1 correlated with apo B (r = .50, P < .03) and LDL-cholesterol (r = .50, P < .03), but showed no relationship with the LDL diameter, LDL-cholesterol:apo B ratio, or other lipids. We conclude that the predominance of smaller, denser LDL, a potential contributor to endothelial cell dysfunction, is a feature of preeclampsia. However, the serum VCAM-1 level, one indicator of endothelial involvement, may be influenced more by quantitative lipoprotein changes (serum apo B or LDL-cholesterol) than by LDL particle size.

LDL induces transcription factor activator protein-1 in human endothelial cells

Low density lipoprotein (LDL) has been shown to perturb endothelial cells, with manifestations ranging from alterations in free radicals and arachidonate metabolism to stress fiber formation and monocyte recruitment. Some of these changes are regulated by LDL at the transcriptional level. Using mobility shift assays with consensus sequences for various transcription factors, we have detected an increase in activator protein 1 (AP-1), but not nuclear factor-kappaB (NF-kappaB), binding in human umbilical vein endothelial cells exposed to LDL. Following transfection, AP-1-driven chloramphenicol acetyltransferase and AP-1-driven-luciferase are upregulated by LDL. In contrast, there is no effect on NF-kappaB-driven chloramphenicol acetyltransferase. AP-1 increases in a biphasic fashion, with the first peak occurring 6 hours after and the second 48 hours after exposure to LDL. This AP-1 binding increase involves c-Jun, but not c-Fos, as shown by gel supershift, Northern hybridization, and Western blotting analyses. c-Jun mRNA levels are elevated by 9 hours after and remain so until at least 24 hours after exposure to LDL. c-Jun protein levels increase at 12 hours and continue to rise for 24 hours after exposure to LDL. Moreover, this LDL-increased AP-1 binding is suppressed by several protein kinase (PK) inhibitors: the PKC inhibitor calphostin C, the cAMP-dependent PK inhibitor H89, and the tyrosine PK inhibitors genistein and lavendustin A. This study demonstrates that (1) LDL is an endothelial agonist distinct from other cell stimulators, such as cytokines, endotoxin, and phorbol 12-myristate 13-acetate, because LDL appears to activate human umbilical vein endothelial cells predominantly through the transcription factor AP-1 and not NF-kappaB; and (2) LDL increases AP-1 via mechanisms involving multiple kinase activities and c-Jun transcription.