Homocysteine alters monocyte-endothelial interaction in vitro.
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To determine whether homocysteine induced endothelial damage through monocyte-endothelial interaction and to characterize both cell types in vitro.Radiomethods were performed on monocyte adhesion to/through endothelium and endothelial damage experiments.Homocysteine-treated endothelial cells increased monocyte adhesion and transmigration. Homocysteine-treated monocytes induced endothelial detachment, but this effect was blocked by catalase. These effects were increased with higher concentrations of homocysteine. Monocyte surface glycoprotein antibodies CD11b/CD18 and CD14 inhibited these processes.Homocysteine alters monocyte-endothelial interaction in vitro, eventually bringing about endothelial damage through release of H(2)O(2). These phenomena are mediated through monocyte surface glycoproteins CD11b/CD18 and CD14. Upregulation of these processes in vivo may contribute to acceleration of atherosclerosis in patients with elevated plasma homocysteine levels.Keywords:
Monocyte
Endothelial Dysfunction
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Background Monocyte adhesion to endothelial cells is a key early event in atherogenesis. Because l -arginine has been shown to reduce atheroma and to decrease monocyte–endothelial cell adhesion in an animal model of atherosclerosis, we studied the effects of l -arginine on human monocyte adhesion to human endothelial cells and endothelial expression of cell adhesion molecules. Methods and Results Human umbilical vein endothelial cells (HUVECs) were grown to confluence, then incubated for 24 hours with arginine-deficient media to which was added saline (control), 100 or 1000 μmol/L l -arginine, 100 μmol/L d -arginine, 100 μmol/L N G -monomethyl- l -arginine (L-NMMA), or 100 μmol/L l -arginine with 100 μmol/L L-NMMA. Human monocytes obtained by elutriation were incubated for 1 hour with HUVECs, and adhesion was measured by light microscopy. Compared with control, monocyte adhesion was reduced by l -arginine (59±10%, P =.01) and increased by L-NMMA (123±20%, P =.01). Surface expression of cell adhesion molecules by HUVECs was assessed by an ELISA under the above conditions with and without stimulation with interleukin-1β. Expression of ICAM-1 was reduced with both concentrations of l -arginine compared with control in both the basal (43±12%, P <.01), and stimulated (46±15%, P <.01) states, which correlated with decreased levels of mRNA. Expression of VCAM-1 was reduced only in the stimulated state and only in the presence of 1000 μmol/L l -arginine (72±24%, P =.02). Conclusions l -Arginine reduces human monocyte adhesion to endothelial cells and decreases expression of certain endothelial cell adhesion molecules.
Monocyte
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The receptors that mediate monocyte adhesion to cytokine-stimulated endothelial monolayers were assessed using a nonstatic (rotating) cell-attachment assay. In this system, leukocyte adhesion molecule-1 (LAM-1) (L-selectin) mediated a major portion (87 +/- 15% at 37 degrees C) of monocyte attachment to activated endothelium. mAb blocking of endothelial leukocyte adhesion molecule-1 (41% inhibition), CD18 (36%), and vascular cell adhesion molecule-1 (25%) function had lesser effects on attachment. These results suggest that LAM-1 may serve an important role in monocyte attachment to endothelium at sites of inflammation.
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E-selectin
Cell–cell interaction
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Upon induction of experimental hyperglycemia (i.e. diabetes) pathological modifications are early detected (∼7 days) at the level of the cardiac valves leading rapidly to the development of valvular atheroma. Monocyte adhesion to the vascular endothelium is one of the initial event at the onset of atherosclerosis. We questioned whether high glucose enhances monocyte adhesion to the valvular endothelial cells (VEC) so as to explain, in part, the accelerated atheroma formation that occur in diabetic conditions. To this purpose we compared the adhesion of monocytes to VEC cultured in 5.5 mM (normal) glucose (NG) or in 33mM (high) glucose (HG) or in high mannitol (HM) (27.5 mM mannitol plus 5.5 mM glucose), a concentration known to simulate the hyperosmolar effect of high glucose. After incubation for 30 min at 37®C, the adhesion of monocyte cell line (U937 cells) to VEC was quantitated by a fluorimetric assay or by direct counting. Statistical data showed a significant increased adhesion of monocytes to VEC grown in HG (up to 4 fold) or in HM (up to 2.7) when compared to normal conditions. Using a battery of specific monoclonal antibodies molecules it was found that the increased adhesion of monocytes to VEC grown in high glucose was specifically inhibited (p< 0.05) by anti-ICAM-1, anti-VCAM-1 and anti-CD 18 monoclonal antibodies. Together, the results indicate that high glucose induces enhanced monocyte adhesion to VEC via a mechanism involving in part an osmotic effect and mainly the cell adhesion molecules: ICAM-1, VCAM-1 and CD 18.
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Objective To determine whether homocysteine induced endothelial damage through monocyte-endothelial interaction and to characterize both cell types in vitro.Methods Radiomethods were performed on monocyte adhesion to/through endothelium and endothelial damage experiments. Results Homocysteine-treated endothelial cells increased monocyte adhesion and transmigration. Homocysteine-treated monocytes induced endothelial detachment, but this effect was blocked by catalase. These effects were increased with higher concentrations of homocysteine. Monocyte surface glycoprotein antibodies CD11b/CD18 and CD14 inhibited these processes.Conclusions Homocysteine alters monocyte-endothelial interaction in vitro, eventually bringing about endothelial damage through release of H2O2. These phenomena are mediated through monocyte surface glycoproteins CD11b/CD18 and CD14. Upregulation of these processes in vivo may contribute to acceleration of atherosclerosis in patients with elevated plasma homocysteine levels.
Monocyte
Endothelial Dysfunction
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To determine whether homocysteine induced endothelial damage through monocyte-endothelial interaction and to characterize both cell types in vitro.Radiomethods were performed on monocyte adhesion to/through endothelium and endothelial damage experiments.Homocysteine-treated endothelial cells increased monocyte adhesion and transmigration. Homocysteine-treated monocytes induced endothelial detachment, but this effect was blocked by catalase. These effects were increased with higher concentrations of homocysteine. Monocyte surface glycoprotein antibodies CD11b/CD18 and CD14 inhibited these processes.Homocysteine alters monocyte-endothelial interaction in vitro, eventually bringing about endothelial damage through release of H(2)O(2). These phenomena are mediated through monocyte surface glycoproteins CD11b/CD18 and CD14. Upregulation of these processes in vivo may contribute to acceleration of atherosclerosis in patients with elevated plasma homocysteine levels.
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Endothelial Dysfunction
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Adhesion of neutrophils to vascular endothelial cells (ECs), mediated by the interaction of CD11/CD18 and intercellular adhesion molecule-1 (ICAM-1), is often required for neutrophil transmigration across endothelium during most inflammatory responses. Induction of intracellular signaling in neutrophils as a result of adhesion has been recognized for many years. Recent studies demonstrated that neutrophil-endothelial adhesion also activates ECs. Examples of neutrophil adherence-induced changes in ECs include increases in intracellular Ca(2+), production of reactive oxygen species, and actin cytoskeleton changes. These changes result, in part, from ligation of EC adhesion molecules. This review article focuses on the signaling events that occur in ECs during neutrophil adhesion and the role of EC adhesion molecules, particularly ICAM-1, in the initiation of these signaling events in ECs. The evidence to date describing the molecular basis of ICAM-1-induced signaling will be summarized. Finally, the potential physiological roles of these signaling events induced by EC adhesion molecules in mediating neutrophil migration will be addressed.
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Elevated plasma homocysteine is an independent risk factor for atherosclerosis. We hypothesized that homocysteine enhances monocyte/human aortic endothelial cell (HAEC) interactions, a pivotal early event in atherogenesis, by upregulating endothelial adhesion molecules. After incubation of cultured HAECs with reduced dl -homocysteine for up to 24 hours, adhesion of human monocytes to homocysteine-stimulated HAECs was significantly upregulated in a time- and dose-dependent fashion. Pretreatment of HAECs with 100 μmol/L homocysteine caused a 4.5-fold increase in the adhesion of normal human monocytes ( P <0.001). Similarly, adhesion of monocytic U937 cells was maximally elevated by 3.5-fold at 100 μmol/L homocysteine ( P <0.001). In support of our hypothesis, vascular cell adhesion molecule (VCAM)-1 mRNA expression increased 5-fold in HAECs after 3 hours of treatment with 100 μ mol/L homocysteine, as assessed by quantitative reverse transcription– polymerase chain reaction. Neutralizing antibody studies confirmed the involvement of VCAM-1 in mediating monocyte adhesion to homocysteine-stimulated HAECs. Coincubation of HAECs with homocysteine and tumor necrosis factor-α synergistically elevated monocyte adhesion as well as VCAM-1 protein expression, with the latter evaluated by flow cytometry. Preincubation of HAECs with cyclooxygenase inhibitors completely abrogated homocysteine-induced monocyte adhesion, whereas scavenging reactive oxygen species and the elevation of NO caused partial inhibition only. These data support the notion that the proinflammatory effects of homocysteine may have important implications in atherogenesis.
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