Diffuse severe digestive angiodysplasia in Bernard-Soulier syndrome. Improvement of bleeding by oestroprogestative therapy.
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Angiodysplasia↗
Biomedical subjects
G Tobelem
Publications and source records attributed to G Tobelem.
Thrombin induces endothelial cell growth via both a proteolytic and a non-proteolytic pathway.
Binding of 125I-thrombin to human umbilical vein endothelial cells (HUVECs) was specifically displaced by the synthetic tetradecapeptide SFLLRNPNDKYEPF, named thrombin receptor agonist peptide (TRAP), which has recently been described as a peptide mimicking the new N-terminus created by cleavage of the thrombin receptor, and F-14, a tetradecapeptide representing residues 365-378 of the human alpha-thrombin B chain. Binding of 125I-TRAP to HUVECs was time-dependent, reversible and saturable, showing high affinity (KD = 1.5 +/- 0.4 microM) and high binding capacity (Bmax. = 7.1 +/- 0.6 x 10(6) sites/cell) (n = 3). Unlabelled thrombin and TRAP competitively and selectively inhibited the specific binding of 125I-TRAP with IC50 values of 5.8 +/- 0.7 nM and 2.8 +/- 0.4 microM respectively, whereas F-14 remained ineffective at displacing 125I-TRAP from its binding sites, suggesting the presence of at least two different types of thrombin-binding sites on HUVECs. TRAP was a potent mitogen for HUVECs in culture. Both TRAP and alpha-thrombin stimulated the proliferation of HUVECs with half-maximum mitogenic responses between 1 and 10 nM. F-14 also promoted HUVEC growth. The mitogenic effects of F-14 and TRAP were additive. N alpha-(2-Naphthylsulphonylglycyl)-DL-p-amidinophenylalanylpiper idine (NAPAP) and hirudin (two specific inhibitors of the enzyme activity of thrombin) specifically inhibited thrombin-induced HUVEC growth (IC50 values 400 +/- 60 and 52 +/- 8 nM respectively) but remained without effect on the mitogenic effect of TRAP or F-14. This demonstrated that the mitogenic effect of alpha-thrombin for HUVECs was intimately linked to its esterolytic activity but also showed that thrombin can stimulate HUVEC growth via another non-enzymic pathway. This hypothesis was further reinforced by the fact that F-14-induced proliferation of HUVECs remained unaltered by two antibodies directed against TRAP or the cleavage site on the extracellular portion of the thrombin receptor, which both strongly reduced thrombin-induced proliferation of HUVECs. Thrombin-, TRAP- or F-14-induced HUVEC proliferation was strongly inhibited by a neutralizing monoclonal antibody directed against basic fibroblast growth factor (bFGF), suggesting that thrombin regulates the autocrine release of bFGF in HUVECs.
Amino Acid Sequence↗
Phosphorylation of Rap1GAP during the cell cycle.
Rap1GAP (for Rap1 GTPase Activating Protein) is an 89 kD protein that highly stimulates the intrinsic GTPase activity of the small GTP binding protein Rap1. It has been shown that Rap1GAP is phosphorylated in vitro by purified p34cdc2 kinase, which regulates the G2/M transition of the cell cycle. In this work, we have studied the phosphorylation of Rap1GAP during the cell cycle and showed that Rap1GAP is phosphorylated in vivo in interphasic and mitotic Hela cells; the electrophoretic mobility of Rap1GAP from mitotic cells is reduced compared with that from interphasic cells, suggesting that the mitotic form of the protein is hyperphosphorylated. As the cdc2 kinase is specifically active during mitosis, we sought to investigate whether it actually phosphorylates Rap1GAP during this phase of the cell cycle. We show that p34cdc2 co-immunoprecipitated from mitotic Hela cell lysates with an anti human cyclin B1 antibody, but not from interphasic cell lysates, is able to phosphorylate efficiently wild-type Rap1GAP, but not a mutant in which the putative consensus site for phosphorylation by the cdc2 kinase (serine 484) has been altered. Moreover, depletion of p34cdc2 from mitotic extracts abolishes the phosphorylation of Rap1GAP by such lysates. These results therefore strongly suggest that Rap1GAP is indeed a substrate of the cdc2 kinase during mitosis. This phosphorylation does not affect the stimulation of the GTPase activity of Rap1 by Rap1GAP but may play a role in regulating the interaction of Rap1GAP with other proteins involved in the cellular functions regulated by Rap1 and Rap1GAP.
Amino Acid Sequence↗
Evidence for Rap1 in vascular smooth muscle cells. Regulation of their expression by platelet-derived growth factor BB.
The effect of platelet-derived growth factor (PDGF) on Rap1 expression was investigated in rat vascular smooth muscle cells (SMC). First, evidence for Rap1 proteins was shown by their: (i) detection in membranes using a specific anti-Rap1 antibody, (ii) typical shift in electrophoretic mobility as a consequence of reduction, and (iii) cAMP-induced phosphorylation and immunoprecipitation. Then, the mitogenic activity of 10 ng/ml PDGF AA and BB for 48 h, resulting in a 2- and 5-fold increase in [3H]thymidine incorporation, was correlated with that of total Rap1 protein expression which was found to be 99% +/- 36% and 260% +/- 70%, respectively. Further time-course studies established that this up-regulation of Rap1 proteins was only observed after 48 h of PDGF BB treatment. Lastly, comparative RT-PCR of both rap1a and rap1b mRNAs showed that PDGF BB also up-regulated the rap1a mRNA species, which was 1.5-fold increased in contrast with the rap1b mRNA species. It is concluded that the PDGF BB-induced SMC proliferation is associated with an up-regulation of Rap1a protein.
Animals↗
Increased mitogenic activity of scleroderma serum: inhibitory effect of human recombinant interferon-gamma.
OBJECTIVES: To investigate the role of platelet activation in the development of systemic sclerosis and the role of interferon-gamma (IFN gamma) in the inhibition of mitogenic activity induced by whole blood serum of patients with systemic sclerosis. METHODS: The mitogenic activity of whole blood serum in the absence or presence of different concentrations of IFN gamma (a potent inhibitor of induced collagen synthesis in dermal fibroblasts) and platelet-poor plasma derived serum were tested on human dermal fibroblasts by measuring incorporation of [3H]thymidine. Platelet activation was determined by quantification of plasma beta-thromboglobulin (beta-TG) using a beta-TG radioimmunoassay kit. RESULTS: The mitogenic activity was significantly increased in whole blood serum and in platelet-poor plasma derived serum of the patients compared with controls. In contrast, no significant increase in beta-TG concentration was observed in scleroderma platelet-poor plasma compared with control. Recombinant human IFN gamma had a greater inhibitory effect on the mitogenic activity induced by whole blood serum of patients than on that produced with control sera, at any concentration of IFN gamma tested. CONCLUSIONS: Our results suggest that mitogenic activity observed in the plasma of sclerodermic patients could originate from cells other than platelets and could be involved in the development of fibrosis. The potent inhibitory effect of IFN gamma on this proliferative activity may account for the beneficial effect of this cytokine in the treatment of progressive systemic sclerosis.
Adult↗
Ex vivo inhibition of platelet aggregation in patients with severe limb arteriopathy treated with BAY U3405, a specific TX A2 receptor antagonist.
A double-blind, placebo-controlled randomized study with BAY U3405, a specific thromboxane A2 (TX A2) receptor blocker, was performed in patients suffering from severe stade II limb arteriopathy. BAY U3405 or placebo was administered in 16 patients at 20 mg four times a day (from day 1 to day 3). Hemostatic studies were done before therapy, and on day 2 and day 3 under therapy. On day 3, BAY U3405 was shown to induce a highly statistically significant decrease of the velocity and the intensity of the aggregations mediated by arachidonic acid (56 +/- 37% for the velocity, 58 +/- 26% for the intensity) or by U46619 endoperoxide analogue (36 +/- 35% for the velocity, 37 +/- 27% for the intensity). Similar results were already observed on day 2. By contrast, such a decrease was not noticed with ADP mediated platelet aggregation. Furthermore, plasma levels of betathromboglobulin and platelet factor 4 remained unchanged. Peripheral hemodynamic parameters were also studied. The peripheral blood flow was measured using a Doppler ultrasound; the pain free walking distance and the total walking ability distance were determined under standardized conditions on a treadmill. These last two parameters show a trend to improvement which nevertheless was not statistically significant. All together these results encourage further in vivo studies using BAY U3405 or related compounds on a long-term administration.
Adult↗
Tumour angiogenesis.
The progressive emergence of a close relationship between the formation of blood vessels in the vicinity of tumour cells and the development and spreading of tumours, strongly suggests that angiogenesis might be a prerequisite for tumour development. Angiogenesis starts and develops in response to two sets of extracellular signals: soluble angiogenic factors and extracellular matrix. Different experimental models have been used to study angiogenesis in vivo, but they have numerous limitations. Three-dimensional culture systems reconstitute normal interactions between endothelial cells and the surrounding extracellular matrix. Numerous parameters including angiogenic growth factors and cytokines, cell-to-cell interactions and cell-to-extracellular matrix adhesion influence the growth and differentiation of endothelial cells in vitro as well as in vivo. Angiogenesis plays a major role not only in tumour growth but also in metastasis development. Mechanisms of switching to angiogenic phenotype have been recently described and onset of angiogenic activity is now recognized as another discrete step in tumorigenesis. Tumour cells can induce b-FGF expression and exportation, VEGF and VEGF receptor expression and inactivation of the cancer suppressor gene encoding for a fragment of thrombospondin. A controlled net proteolytic balance produced by tumour cells or endothelial cells is required to favour migration and invasion of endothelial cells and angiogenesis. The hypothesis that assessment of tumour angiogenesis might predict tumour aggressiveness in human cancer has recently gained support from several clinical studies. This has been shown for cutaneous melanoma, breast carcinoma, and non-small-cell lung cancer by quantitation of microvessels in human biopsies using von Willebrand factor or CD3 antigen labelling with specific antibodies. However, more specific and sensitive markers are needed to improve this approach for predicting tumour aggressiveness. Folkman proposed twenty years ago that inhibition of angiogenesis might represent a suitable complementary strategy for the treatment of various forms of cancer. Since then numerous angiostatic compounds have been identified but very few of them fit the required criteria of a potential drug. Fumagillin and particularly its synthetic analogue AGM 1470 might be developed for use in humans in the near future.
Amino Acid Sequence↗
[Immunoglobulins in Hematology. Immunologic thrombopenic purpura].
Immunologic thrombopenic purpura refers to several diseases including the most frequent, autoimmune thrombopenic purpura (AITP). Immunologic thrombopenia is related to anti-platelet autoantibodies, usually IgGs. In 15 to 20% of the cases, no auto-antibody can be detected. The severity of the cutaneomucosal manifestations is not always correlated with the degree of thrombopenia but only occurs for platelet counts less than 50 x 10(9)/L. The clinical course includes acute episodes of AITP and complete remissions in 80% of the cases in the episodes of AITP and complete remissions in 80% of the cases in the very young child. Inversely, in the adult, treatment of AITP has been highly debated because chronicity is frequent. Two therapeutic approaches, corticotherapy and splenectomy, have been widely used. Corticoids given at a dose of 0.5 to 1 mg/kg/day leads to remission in 15 to 30% of the cases. Splenectomy, a second intention therapy, leads to platelet counts above 100 x 10(9)/L in 60 to 70% of the patients. In 1981, intravenous polyvalent immunoglobulins were first employed for 13 children in a study reported by Imbach et al. The results have been confirmed in children and in adults. There are few side effects with this method and the dose of 1 g/kg over 2 days is effective. Response is rapid (platelet counts above 50 x 10(9)/L in 1 to 5 days) but often temporary (relapse to former levels in 5 to 45 days). The high cost of this intravenous polyvalent immunoglobulins has led to much debate over their use.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Pharmacokinetics of a low molecular weight heparin [Fragmin] in young and elderly subjects.
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Adult↗
Procoagulant activity of endotoxin or tumor necrosis factor activated monocytes is enhanced by IgG from patients with lupus anticoagulant.
The effect of lupus anticoagulant (LA) positive plasma on the expression of human monocyte procoagulant activity (PCA) was studied. LA positive plasma were able to enhance the endotoxin or TNF alpha induced monocyte associated PCA. The monocyte PCA had the characteristic of tissue factor activity (factor VII, factor X dependence). The enhancement of monocyte PCA could be confirmed using purified LA positive IgG. The stimulating effect was supported by the F(ab')2 fragments.
Adult↗
Transforming growth factor-beta 1 inhibitory effect of platelet-derived growth factor-induced signal transduction on human bone marrow fibroblasts: possible involvement of protein phosphatases.
Transforming growth factor-beta 1 (TGF-beta 1) is a potent growth inhibitor for many cell types. On fibroblasts, TGF-beta 1 has been shown to inhibit human platelet-derived growth factor (PDGF)-induced mitogenicity. The mechanism implicated in this growth inhibition is unknown. In this work, we show on human bone marrow fibroblasts that TGF-beta 1, which inhibited PDGF-BB mitogenicity, was able to block PDGF-BB-induced early events such as polyphosphoinositide (PtdIns 4,5-P2, PtdIns 4-P, and PtdIns) breakdown and Ins 1,4,5-P3 formation. No significant modification by TGF-beta 1 of PDGF-BB binding (n1 = 200,000 vs. n2 = 195,000 sites per cell with TGF-beta 1; Kd1 = Kd2 = 0.5 x 10(-9) M) and of internalization kinetics was observed. In addition, TGF-beta 1 was shown to inhibit PDGF-BB receptor autophosphorylation either in intact cells or in partially isolated membranes and to partially inhibit PDGF-R tyrosine kinase activity. Since a dephosphorylation mechanism through protein phosphatases could be implicated, we used okadaic acid, a potent inhibitor of type 1 and 2A serine/threonine phosphatases and showed that okadaic acid restored PDGF-receptor autophosphorylation on tyrosine residues. Based on these data, we suggest that an alternative regulatory mechanism of PDGF tyrosine phosphorylation seems to involve serine/threonine phosphatase activation.
Bone Marrow↗
Inhibition of platelet-derived growth factor-induced mitogenesis and tyrosine kinase activity in cultured bone marrow fibroblasts by tyrphostins.
Tyrphostins, which block protein tyrosine kinase activity, were studied for their inhibitory action on platelet-derived growth factor (PDGF)-induced proliferation of human bone marrow fibroblasts. Of the seven tryphostins examined, tyrphostin AG370 was found to be the most potent blocker against PDGF-induced mitogenesis (IC50 = 20 microM). This PTK blocker also blocks mitogenesis induced by epidermal growth factor (IC50 = 50 microM) and human serum (IC50 = 50 microM), but with lower efficacy. In digitonin-permeabilized fibroblasts as well as in intact fibroblasts, tyrphostin AG370 inhibits PDGF receptor autophosphorylation and the tyrosine phosphorylation of intracellular protein substrates (pp120, pp85, and pp75) which coprecipitate with the PDGF receptor. In comparison to AG370, AG18, a potent EGF receptor blocker, was less efficient in inhibiting PDGF-induced proliferation of fibroblasts and phosphorylation of the intracellular protein substrates. Under the conditions in which AG370 inhibits PDGF-induced mitogenesis and phosphorylation, it does not affect [125I]PDGF internalization and enhance [125I]PDGF binding. These findings suggest that AG370, which is an indole tyrphostin, may serve as a model for developing analogues with a therapeutic potential for treatment of diseases which involve abnormal cellular proliferation induced by PDGF.
Blotting, Western↗
[Kaposi's sarcoma in multiple myeloma].
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Aged↗
[Thrombopenia. Diagnostic orientation].
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Humans↗
Platelet thrombospondin and glycoprotein IV abnormalities in patients with essential thrombocythemia: effect of alpha-interferon treatment.
Platelet aggregability and some biochemical parameters were evaluated in seven patients with essential thrombocythemia (ET) compared with seven patients with secondary thrombocytosis (ST). Defective platelet aggregation with one or more agonists was seen in five patients with ET whereas aggregation was increased in two other patients. In addition, three patients with ET demonstrated spontaneous platelet aggregation in citrated plasma. This was associated with increased level of thrombospondin (TSP) in the plasma membrane. Interestingly, the presence of a proteolyzed 160 kDa form of TSP was detected in all patients with ET, whereas it was never found in patients with ST. Furthermore, three patients with ET demonstrated increased levels of platelet surface glycoprotein IV (GP IV), the putative receptor for TSP in the plasma membrane. In two of these patients, this correlated with increased surface expression of TSP and spontaneous platelet aggregation. The results suggest a possible link between the increased number of plasma membrane GP IV molecules, the spontaneous expression of TSP on the platelet surface and platelet hyperaggregability in some ET patients. The levels of plasma membrane GP IV and platelet surface-associated TSP tended to be normalized during alpha-interferon treatment, whereas the presence of an altered form of TSP persisted. This last parameter might be of practical usefulness in the characterization of the disease, permitting a clear distinction from ST.
Aged↗
Interaction of vasculotropin/vascular endothelial cell growth factor with human umbilical vein endothelial cells: binding, internalization, degradation, and biological effects.
Vasculotropin/vascular endothelial cell growth factor (VAS/VEGF) is a newly purified growth factor with a unique specificity for vascular endothelial cells. We have investigated the interactions of VAS/VEGF with human umbilical vein endothelial cells (HUVE cells). 125I-VAS/VEGF was found to HUVE cells in a saturable manner with a half-maximum binding at 2.8 ng/ml. Scatchard analysis did show two classes of high-affinity binding sites. The first class displayed a dissociation constant of 9 pM with 500 sites/cell. The dissociation constant and the number of binding sites of the second binding class were variable for different HUVE cell cultures (KD = 179 +/- 101 pM, 5,850 +/- 2,950 sites/cell). Half-maximal inhibition of 125I-VAS/VEGF occurred with a threefold excess of unlabeled ligand. Basic fibroblast growth factor (bFGF) and heparin did not compete with 125I-VAS/VEGF binding. In contrast, suramin and protamin sulfate completely displaced 125I-VAS/VEGF binding from HUVE cells. VAS/VEGF was shown to be internalized in HUVE cells. Maximum internalization (55% of total cell-associated radioactivity) was observed after 30 min. 125I-VAS/VEGF was completely degraded 2-3 hr after binding. At 3 hr, the trichloroacetic acid (TCA)-soluble radioactivity accumulated in the medium was 60% of the total radioactivity released by HUVE cells. No degradation fragment of 125I-VAS/VEGF was observed. Chloroquine completely inhibited degradation. VAS/VEGF was able to induce angiogenesis in vitro in HUVE cells. However, it did not significantly modulate urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1), and tissue factor (TF). Prostacyclin production was only stimulated at very high VAS/VEGF concentrations. Taken together, these results indicate that VAS/VEGF might be a potent inducer of neovascularization resulting from a direct interaction with endothelial cells. The angiogenic activity seems to be independent of the plasminogen activator or inhibitor system.
Cells, Cultured↗
Modulation of allogenic reaction by ticlopidine treatment.
Ability of response in proliferation and cytotoxicity of lymphocytes, after in vitro allogeneic reaction was tested in three independent series of experiments, before and after seven days of ticlopidine treatment (500 mg daily) taken by normal adult individuals. In the third experiment, blood samples were taken twice before treatment and twice during the treatment. In two of the three series of experiments the ability of proliferation of responding cells in a mixed lymphocyte reaction was decreased (P less than 0.01). Cytotoxicity was reduced in the three series of experiments when the combination effector/target cells after treatment was compared with the combination before treatment (P less than 0.01 - 0.001), at various effector to target cells ratios for one target (50:1 and 100:1).
Adjuvants, Immunologic↗
Phenotypic modulations of human umbilical vein endothelial cells and human dermal fibroblasts using two angiogenic assays.
Different angiogenic assays in vitro have helped to define various events underlying angiogenesis. In this report we have compared the phenotypic modifications of human umbilical vein endothelial cells (HUVE cells) and human dermal fibroblasts using Matrigel and collagen gels. Both HUVE cells and human dermal fibroblasts form a network of anastomosing cords that apparently resemble blood capillaries when grown on Matrigel. The whole network was formed by several cellular aggregates joined to each other by cellular cords. Lumen formation was not observed in this angiogenic system. In opposite, considerable differences between HUVE cells and human dermal fibroblasts were observed in the three-dimensional angiogenic assay on collagen gels described by Montesano et al [14]. These results indicate that data obtained with angiogenic systems using Matrigel must be interpreted with caution and that the assay described by Montesano et al [14], is more reliable to describe angiogenesis.
Cells, Cultured↗