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We previously reported that platelet-activating factor (PAF) enhances the angiogenic activity of certain polypeptide mediators such as tumor necrosis factor and hepatocyte growth factor by promoting endothelial cell motility. The purpose of the present study was to evaluate whether the synthesis of PAF induced by vascular endothelial growth factor (VEGF) might affect endothelial cell motility, microvascular permeability, and angiogenesis. The neoangiogenesis and synthesis of PAF induced by VEGF were studied in vivo in a murine Matrigel model. Dermal permeability was studied in mice by injection of (125)I-albumin. The synthesis of PAF, cell motility, and the increased (125)I-albumin transfer across endothelial monolayers were studied in vitro by using cultures of human umbilical cord vein-derived endothelial cells (HUVECs). The results obtained demonstrate that the neoangiogenesis induced by VEGF in vivo was associated with a local synthesis of PAF and was inhibited by WEB2170 and CV3988, 2 chemically unrelated, specific PAF-receptor antagonists. In contrast, WEB2170 did not inhibit VEGF-enhanced dermal permeability, suggesting that the latter was independent of the synthesis of PAF. In vitro, it was found that VEGF induced the synthesis of PAF by HUVECs in a dose- and time-dependent manner. The cell motility induced by VEGF was inhibited by PAF-receptor antagonists. In contrast, VEGF-induced proliferation of HUVECs and albumin transfer through HUVEC monolayer were unaffected by PAF-receptor antagonists. These results suggest that the synthesis of PAF induced by VEGF enhances endothelial cell migration and contributes to the angiogenic effect of VEGF in the in vivo Matrigel model.

Background: The adhesion of leukocytes to the endothelium and the edema of vessel wall may cause vascular reocclusion after thrombolytic therapy. The aim of this study was to evaluate the role of platelet activating factor (PAF) and P-selectin on the adherence of polymorphonuclear neutrophils (PMN) to the endothelium and of PAF on the increased vascular permeability induced by tissue-type plasminogen activator, streptokinase, and plasmin., Methods and Results: We studied (1) the adhesion of 111Inlabeled PMN to human umbilical cord vein-derived cultured endothelial cells (HUVEC), (2) the transfer of 125I-labeled albumin across HUVEC monolayers, and (3) the adhesion of PMN to isolated bovine coronary arteries under flow conditions. It was found that the adhesion of PMN, induced by tissue-type plasminogen activator, streptokinase, and plasmin, correlated with the synthesis of PAF by HUVEC and was inhibited by WEB 2170, a PAF receptor antagonist. The adhesion of PMN was also inhibited by the treatment of HUVEC with anti-P-selectin antibodies or of PMN with soluble P-selectin or with anti-CD18 monoclonal antibodies. Plasmin also increased the permeability of HUVEC monolayers, an effect that was partially prevented by WEB 2170. Moreover, plasmin promoted the synthesis of PAF from isolated bovine coronary arteries and the adherence of PMN to the endothelium under flow conditions. The pretreatment of PMN with WEB 2170 or with soluble P-selectin prevented adhesion., Conclusions: The synthesis of PAF by endothelial cells at the site of plasmin generation and the endothelial expression of P-selectin may render the endothelial cell surface proadhesive for neutrophils and may favor a local increase in vascular permeability.

The aim of this review is to summarize the current concepts concerning the active role of the endothelium in the pathogenesis of atherosclerosis. Activated endothelium may promote the adhesion of monocytes and their transmigration into the intima. The coordinated expression of adhesion molecules of the selectin, integrin or immunoglobulin superfamily on the surface of endothelial cells and of monocytes modulates these events. The role of lipoproteins and their oxidative derivatives as well as that of selected cytokines and platelet activated factor in initiating changes on the endothelial cell surface has been investigated: these events are associated with an increased endothelial permeability to lipids and lipoproteins with their accumulation in the subendothelium. Once migrated into the intima, monocytes undergo morphological and functional modifications leading to the generation of a polypeptide mediator network which is instrumental in the migration, differentiation and proliferation of smooth muscle cells. Mediators produced by macrophages infiltrating the atherosclerotic plaque and by the endothelium may render the surface of the endothelial cells thrombogenic thus favoring thrombotic occlusion. In conclusion, the most recent studies suggest that the endothelium plays an active role in the pathogenesis of atherosclerosis.

Background: Reocclusion of a successfully recanalized infarct-related artery may account for failure of thrombolytic therapy. Evidence suggests that the intravascular activation of platelets may limit the response to this treatment. The aim of the present study was to investigate whether platelet-activating factor (PAF), an ether lipid mediator with multiple potent biological activities, is synthesized during therapy with thrombolytic agents. Two sets of experiments were performed: (1) we extracted and quantified PAF in blood of patients with acute myocardial infarction treated or untreated with streptokinase (SK), and (2) since the endothelium/platelet interaction is thought to be at the basis of vascular reocclusion, we studied whether cultured human endothelial cells synthesize PAF after stimulation with SK or plasmin., Methods and Results: PAF was extracted from blood samples immediately after acidification to destroy the acid-labile PAF-acetylhydrolase in 25 patients with acute myocardial infarction treated (group A, n = 14) and untreated (group B, n = 11) with intravenous infusion of SK. PAF was detected in 10 of 14 patients of group A and none of group B. PAF began to be detectable 60 to 90 minutes after SK infusion and disappeared from the circulation within 120 to 180 minutes. Percent variation of platelet count over basal values correlated negatively with the amount of PAF present in the circulation at 90 minutes (r = -.719; P < .001) and at 120 minutes (r = -.652; P < .001). Cultured human umbilical cord vein-derived endothelial cells (ECs) synthesized PAF in a dose-dependent manner in response to SK and plasmin, with a synthesis that peaked at 15 minutes and persisted up to 30 minutes for SK and 2 hours for plasmin. PAF extracted from blood samples or from ECs was quantified by bioassay performed after purification by thin-layer chromatography and high-performance liquid chromatography (HPLC). PAF-bioactive material was characterized as PAF with physicochemical and enzymatic treatments, HPLC-tandem mass spectrometry, and specific PAF-receptor antagonists., Conclusions: The observation that PAF was detectable in the blood of patients of group A only after treatment with SK and was not detectable in patients with a comparable infarct not treated with SK (group B) suggested that SK stimulates the synthesis of this mediator either directly or via plasmin generation. Indeed, cultured human ECs synthesize PAF after stimulation with both SK and plasmin. PAF production by ECs may promote platelet activation and interaction of these cells as well as of circulating leukocytes with endothelium. These events may limit the beneficial effects of thrombolytic therapy.

Umbilical vein endothelial cells are known to be able to produce interleukins and colony stimulating factors. In the present work supernatant of human umbilical vein endothelial cell culture have been administered to neoplastic patients treated with chemotherapy to reduce the iatrogenic inhibition of hemopoiesis. While no undesired effect could be observed, neutrophil count was favourably influenced by endothelial cell supernatant administration. Such data can be considered useful in order to reduce collateral effect of antineoplastic therapy.

The prostaglandin system is impaired in cholestasis; bile salts, which are a specific biochemical feature of this condition, have been shown to affect functional properties of cells and tissues, and, in some cases, their action is mediated through an alteration of prostaglandin pathway. Endothelium is a privileged site for the production and the action of arachidonate metabolites-prostacyclin in particular. To determine the effects of bile salts on the properties of vascular endothelium, cultured human endothelial cells were studied. Cholic acid sodium salt was seen to induce a direct injury on endothelial cells, as was demonstrated by a massive dismission of the intracellular radiolabel chromium 51. In the absence of detectable toxic effect, sodium taurocholate caused a significant depression of prostacyclin constitutive production from human endothelial cells. The action of sodium taurocholate was related to its concentration and to the time of exposure, and the alteration of prostacyclin production was found to be reversible. Conversely, the generation of thromboxane A2 was not influenced by this bile salt, which may suggest a specific action of sodium taurocholate on arachidonic acid metabolism. These findings indicate that bile salts may directly alter some functional properties of cultured human endothelial cells and may provide a basis for explaining some generalized manifestations that are observed in pathologic conditions characterized by cholemia.