Elena Dragomir

A Novel Attribute of Enoxaparin: Inhibition of Monocyte Adhesion to Endothelial Cells by a Mechanism Involving Cell Adhesion Molecules

Enoxaparin is a low molecular weight heparin, widely accepted as anticoagulant or antithrombotic drug, and is likely to have a role in acute inflammation. To evaluate the anti-inflammatory potential of enoxaparin, we investigated the direct effect of the drug on the activation of endothelial cells. For this purpose we set up an in vitro system in which cultured valvular endothelial cells (VEC) activated by tumor necrosis factor alpha or lipopolysaccharide were exposed to a monocytic cell line; these conditions induced a significant adhesion of monocytes to VEC. Adhesion assays, ELISA, and flow cytometric analysis revealed that pretreatment with enoxaparin, at a relevant plasma concentration (16 µg/ml), acts upon activation of VEC by inhibition of lipopolysaccharide-induced E-selectin expression and tumor necrosis factor stimulated ICAM-1 expression, thus reducing monocyte adhesion to VEC. These results suggest a novel function of enoxaparin, namely to protect VEC from activation and inhibiting the expression of cell adhesion molecules.

Monocyte Chemoattractant Protein-1 – a major contributor to the inflammatory process associated with diabetes

Abstract There is evidence that strongly suggests that inflammation plays an important role in diabetes and cardiovascular diseases. The high glucose-induced inflammatory process is characterised by the cooperation of a complex network of inflammatory molecules such as cytokines, adhesion molecules, growth factors, and chemokines. Among the chemokine family, monocyte chemoattractant protein (MCP-1) is a potent chemotactic factor, which is upregulated at sites of inflammation being in control of leukocytes trafficking. Here, we review the current knowledge on MCP-1 and its regulation by high glucose level in vascular cells involved in diabetes-induced accelerated atherosclerosis. The signalling pathways involved in MCP-1 modulation by high glucose, the proximal signalling events that stimulate downstream effects and the role of this chemokine in the pathophysiology of diabetes and its complications, are discussed.

High glucose conditions induce upregulation of fractalkine and monocyte chemotactic protein-1 in human smooth muscle cells.

The major complication of diabetes mellitus is accelerated atherosclerosis that entails an inflammatory process, in which fractalkine and monocyte chemotactic protein-1 (MCP-1) play a key role. We investigated the effect of diabetes-associated high glucose (HG) on these chemokines and signalling mechanisms involved in human aortic smooth muscle cells (SMC). Exposure of SMC to HG resulted in an increase of fractalkine and MCP-1 expression and the activated mitogen-activated protein kinase (MAPK) signalling pathway, a process associated with elevated oxidative stress. Transfection with decoy oligodeoxynucleotides identified the involvement of transcription factors activator protein 1 (AP-1) and nuclear factor kappa B (NF-kappaB) in the observed up-regulation of chemokines. The MAPK inhibitors blocked the phosphorylation of IkBalpha and c-jun, indicating the role of MAPK in NF-kappaB and AP-1 activation in SMC under HG conditions. The up-regulation of MCP-1 and fractalkine was associated with increased adhesive interactions between HG-exposed SMC and monocytes. Treatment of HG-exposed SMC with peroxisome proliferator-activated receptors alpha (PPARalpha) activators (fenofibrate and clofibrate) resulted in a reduction of mRNA and protein expression of MCP-1 and fractalkine. In conclusion, HG upregulates the expression of fractalkine and MCP-1 in SMC leading to increased monocyte-SMC adhesive interactions by a mechanism involving activation of MAPK, activator protein-1 (AP-1) and NF-kappaB. The increased expression of these two pro-inflammatory chemokines and the ensuing increased adhesion between SMC and monocytes may trigger the inflammatory process associated with further vascular complications of diabetes.

Similar effects of resistin and high glucose on P-selectin and fractalkine expression and monocyte adhesion in human endothelial cells.

Resistin and high glucose (HG) are concomitantly present at elevated concentration in diabetics plasma; both are pro-inflammatory agents acting on vascular cells by mechanisms that are not fully understood. We questioned whether resistin and HG affect the expression of major adhesion molecules, P-selectin and fractalkine in human endothelial cells (HEC). The results showed that in HEC (i) resistin increased P-selectin expression; (ii) HG up-regulated Fk expression; (iii) P-selectin and fractalkine were functional increasing monocyte adhesion to activated cells. Co-stimulation with resistin and HG increased P-selectin and fractalkine mRNA and protein and induced monocyte adhesion, generated an increase in NADPH oxidase activity and of the intracellular reactive oxygen species and activated the NF-kB and AP-1 transcription factors at similar values as those of each activator. In conclusion in HEC, resistin and HG induce the up-regulation of P-selectin and fractalkine and the ensuing increased monocyte adhesion by a mechanism involving oxidative stress and NF-kB and AP-1 activation.

Binding and uptake of transferrin-bound liposomes targeted to transferrin receptors of endothelial cells

The use of liposomes as carriers for site-specific delivery is an attractive strategy, especially for the vascular endothelium that by position is an accessible target for drug and gene delivery via the blood circulation. The aim of this study was to detect whether liposomes coupled to transferrin (Tf)-bound and are taken up by aortic endothelial cells (EC) following the pathway of Tf interaction with transferrin receptors, reportedly expressed on their cell membrane. To this purpose, small unilamellar liposomes of different compositions, either classical (C) or sterically stabilized (SS), have been prepared, characterized and coupled with transferrin (Tf-liposomes). To assess the binding and uptake, cultured EC were incubated with fluorescently labelled Tf-liposomes for various times intervals (from 5 min to 24 h) at 4 and 37 degrees C, and further investigated by flow cytometry, fluorimetry and fluorescence microscopy. The results showed that: (i) binding of Tf-liposomes to EC was specific; (ii) the EC binding of SS-Tf-liposomes was lower than that of C-Tf-liposomes; and (iii) after 30 min of incubation, both C- and SS-Tf-liposomes appeared localized in the acidic compartments of the cells. Together, the data indicate that transferrin-bound liposomes are specifically taken up by EC by a receptor-mediated mechanism employing the pathway of surface-exposed Tf receptors.

Resistin up-regulates fractalkine expression in human endothelial cells : Lack of additive effect with TNF-α

Resistin is a cytokine and fractalkine (Fk) a cell adhesion molecule and chemokine that contribute to human vascular inflammation by mechanisms not clearly defined. We questioned whether resistin induces Fk expression in human endothelial cells (HEC), compared the effect with that of the pro-inflammatory cytokine, TNF-alpha, and evaluated the consequences of co-stimulating HEC with both activators on Fk induction and on the signalling molecules involved. We found that resistin up-regulated Fk expression at comparable level to that of TNF-alpha by a mechanism involving P38 and JNK MAPK and NF-kappaB. Co-stimulation of cells with resistin and TNF-alpha did not increase Fk expression induced by every single inducer. Moreover resistin reduced the expression induced by TNF-alpha in HEC. The new data uncover Fk as a novel molecular link between resistin and inflammation and show that resistin and TNF-alpha have no additive effect in Fk up-regulation or on the signalling molecules implicated.

Enoxaparin Reduces H2O2-Induced Activation of Human Endothelial Cells by a Mechanism Involving Cell Adhesion Molecules and Nuclear Transcription Factors

There are data that document the anti-inflammatory effect of enoxaparin (EP) and its possible antioxidant potential. This study was designed to search for the antioxidant mechanism(s) of EP directly on endothelial cells exposed to an oxidant stimulus. For this purpose cultured human endothelial cells were exposed to nontoxic concentrations of hydrogen peroxide in the presence or absence of EP, and the adhesion of monocytes, the expression of cell adhesion molecules and transcription factors possibly involved in the process were tested. Adhesion assays, ELISA and Western blot analysis revealed that EP reduced monocyte adhesion, ICAM-1 and P-selectin expression, decreased the nuclear levels of c-Jun and p65 proteins, and diminished the phosphorylation of c-Jun protein, MAPK p38 and JNK. Together, the data demonstrate the antioxidant effect of EP and the involvement of ICAM-1, P-selectin, MAPK p38, JNK and the transcription factors NF-ĸB and AP-1 in the mechanism of action of this drug.