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Biomedical subjects

B Boneu

Publications and source records attributed to B Boneu.

At least 19 recordsLinked to original sources
PubMed2004

Enhancement of enzymatic fibrinolysis with 2-MHz ultrasound and microbubbles.

BACKGROUND: Microbubbles used for echo-contrast agents accelerate enzymatic fibrinolysis of clots exposed to low-frequency ultrasound (US). It is not known whether microbubbles are also effective in enhancing high-frequency US-driven enzymatic fibrinolysis. METHODS AND RESULTS: Calibrated whole blood clots were exposed to US, or US and galactose-based microbubbles (Levovist), with or without recombinant tissue plasminogen activator (rt-PA) in an in-vitro flow system. We used low-intensity, 2-MHz, pulsed wave US. Relative weight reduction of clot +/- SD was 30.7 +/- 9.5% after exposure to microbubbles, rt-PA and US, 13.1 +/- 2.6% after exposure to rt-PA and US, 10.9 +/- 3.6% after exposure to microbubbles and US, and 6.1 +/- 1.9% after exposure to US alone. anova demonstrated a significant effect of rt-PA (P =0.001), microbubbles (P = 0.012), and interaction of both (P = 0.022). CONCLUSIONS: The application of galactose-based microbubbles (Levovist) strongly accelerates lysis of clots exposed to 2 MHz, low-intensity US in vitro both with and without rt-PA. The findings suggest a synergy between microbubbles and rt-PA. These methods routinely used for transcranial diagnostic applications have the potential to improve the efficacy of intravenous rt-PA in acute ischemic stroke.

Blood Coagulation↗
PubMed2002

[Oral anticoagulant treatment: practical aspects and significance of anticoagulant clinics].

Vitamin K antagonists (VKA) decrease the synthesis of the active forms of four coagulation factors (factors II, VII, IX, X) and three inhibitors (proteins C, S, Z). There are VKA having a short half life (Sintrom, Pindione) and VKA having a long half life (Apegmone, Previscan, Coumadine). The treatment is monitored by the INR which in the majority of the indications must range between two and three. The first INR is usually performed 36 to 72 h after starting the treatment. There are a number of drug interactions. The rate of major bleedings range from 1.1 to 4.9 for 100 patient-year according to the published studies. Since around 600,000 patients are treated by VKA in our country, the absolute number of serious bleeding is high (> or = 17,000 per year). Anticoagulant clinics are structures aimed to instruct the patient and to advise the general practitioner to monitor the treatment, using computer assisted methods. It has been reported that these structures reduce the incidence of bleeding and of thrombotic events by 3 to 4 times.

Acenocoumarol↗
PubMed2001

Role of 4 platelet membrane glycoprotein polymorphisms on experimental arterial thrombus formation in men.

This study investigates whether the polymorphisms of 3 important platelet receptors affected experimental thrombus formation in men. Forty healthy male volunteers randomly recruited were genotyped for the variable number of tandem repeat (VNTR) of GPIbalpha, the -5T/C polymorphism in the Kozak sequence of GPIbalpha, the 807C/T polymorphism of GPIa, and the PI(A1)/PI(A2) polymorphism of GPIIb/IIIa. Platelet thrombus formation was induced ex vivo by exposing a collagen-coated coverslip in a parallel plate perfusion chamber to native blood for 4 minutes. The shear rates at the collagen surface were 650 and 2600 x s(-1). At 2600 x s(-1) platelet thrombus formation was significantly related only to the 807C/T polymorphism. In contrast, at 650 x s(-1) thrombus formation was significantly altered only by the Kozak sequence polymorphism. The VNTR and the PI(A1)/PI(A2) polymorphisms did not influence thrombus formation. Thus, platelet thrombus formation is significantly influenced by genetic variations of the GPIbalpha and GPIa receptors. The effect of these polymorphisms was dependent on the blood flow rate.

Adult↗
PubMed2001

Anti-thrombotic and haemorrhagic effects of active site-inhibited factor VIIa in rats.

Active site-inhibited factor VIIa (FFR-rFVIIa) competes with factor VIIa (FVIIa) for binding to tissue factor (TF) and exerts an anti-thrombotic effect. We report an evaluation of the anti-thrombotic properties of FFR-rFVIIa in a model of thrombosis involving two thrombogenic surfaces. Uncoated glass capillaries or glass capillaries coated with TF were incorporated into an arterioarterial shunt in the rat and the occlusion time (OT) of the shunt was determined. An anti-thrombotic activity of FFR-rFVIIa was shown only on the TF-coated surface: the OT of the shunt was significantly prolonged, from 167 +/- 34 s in control animals to 312 +/- 42 s after i.v. bolus administration of 4 mg/kg FFR-rFVIIa. This OT was similar to those observed with the uncoated shunts in untreated animals (353 +/- 84 s). In vitro preincubation of the TF-coated shunt with FFR-rFVIIa significantly prolonged the OT to 245 +/- 45 s in the absence of detectable amounts of FFR-rFVIIa in the plasma. rFFR-rFVIIa weakly prolonged the tail template bleeding time by a factor of 1.5. This effect was more pronounced in animals pretreated with heparin. The anti-thrombotic and prohaemorrhagic effects of FFR-rFVIIa were totally reversed by administration of an equidose of rFVIIa. These results provide new information on the pharmacological properties of FFR-rFVIIa that will be useful for its clinical development.

Animals↗
PubMed2001

How and when to monitor a patient treated with low molecular weight heparin.

Low molecular weight heparins (LMWHs) are as efficient as unfractionated heparin (UFH) for prevention and treatment of thromboembolism. There is no evidence that monitoring the dose improves the clinical efficacy. In contrast, any overdosage increases the risk of hemorrhage. Because renal function plays a significant role in the elimination of LMWH, curative treatment should be monitored with an anti-factor Xa assay in patients presenting renal insufficiency, in the elderly, and in patients presenting an increased hemorrhagic risk. It is advisable to sample the patient at peak activity (3 to 5 hours after the subcutaneous [sc] administration) and to target the mean anti-factor Xa activity that was found efficient and safe in the clinical trial. This target is different for each LMWH and each dose regimen.

Anticoagulants↗
PubMed2001

Essential role of TGF-beta in the natural resistance to experimental allergic encephalomyelitis in rats.

Experimental allergic encephalomyelitis (EAE) is a T cell-mediated autoimmune disease induced in susceptible rat strains by a single immunization with myelin basic protein (MBP). The Lewis (LEW) strain is susceptible to disease induction while the Brown Norway (BN) strain is resistant. This resistance involves non-MHC genes since congenic BN-1L rats, with LEW MHC on a BN-derived background, are also resistant. In the present study we show that, upon immunization with MBP, the non-MHC-encoded resistance to develop clinical EAE in BN-1L rats is associated with a decreased production of IFN-gamma. This may be due to a difference between LEW and BN-1L rats in their ability to produce regulatory cytokines such as IL-4, IL-10 and TGF-beta. In comparison to LEW rats, immune lymph node cells from BN-1L rats express an increased amount of IL-4 mRNA but produce less IL-10. Furthermore, the sera from BN-1L rats contain higher amounts of active TGF-beta1. Therefore, we have investigated the involvement of IL-4 and TGF-beta in the resistance of BN-1L rats to develop EAE using neutralizing mAb. Neutralization of TGF-beta, but not IL-4, renders BN-1L rats susceptible to clinical EAE without affecting the proliferation or the cytokine repertoire of immune lymph node cells. With respect to the origin of the endogenous TGF-beta production, we excluded the involvement of CD8 T cells and discuss a possible role of platelets and of CD4 T cells exhibiting the CD45RC(low) phenotype.

Animals↗
PubMed2001

The effect of platelet PlA polymorphism on experimental thrombus formation in man depends on blood flow and thrombogenic substrate.

A number of studies have reported conflicting data on the association of the PlA1/PlA2 polymorphism of the GPIIIa gene and coronary syndromes. We have investigated the effect of this polymorphism on experimental platelet thrombus formation in man. Forty healthy male volunteers were genotyped for the PlA1/PlA2 polymorphism. Thrombus formation was induced ex vivo by exposing a tissue factor (TF) or a collagen-coated coverslip in a parallel plate perfusion chamber to native blood for 2 and 4 min. The shear rates at these surfaces were 650 and 2,600 s(-1). Platelet and fibrin deposition was quantified by immunoenzymatic methods. The frequencies of PlA1/PlA1 and PlA1/PlA2 genotypes were 52.5% and 47.5%, respectively. Ex vivo deposition of fibrin on TF was not affected by the PlA1/PlA2 polymorphism. However, the ex vivo platelet deposition at 650 s(-1) was higher in blood from PlA1/PlA1 individuals than in PlA1/PlA2 individuals (P= 0.008 at 4 min). On collagen, neither fibrin nor platelet deposition was significantly affected by the PlA1/PlA2 polymorphism. Platelet thrombus formation is significantly influenced by genetic variations in the GPIIIa platelet receptor. This effect depends on the blood flow properties and the nature of the thrombogenic stimulus.

Adult↗
PubMed2001

[Genetic predisposition to arterial and venous thrombosis].

Thrombosis is a multifactorial pathology. In addition to the environmental factors, there are genetic components which either predispose or protect against its occurrence. Some are common to only a small number of subjects: these are the high risk families to thrombotic disease. Others are present in a larger percentage of the general population: this is called polymorphism and its clinical expression is usually modest. The role of these genetic factors in the development of thrombosis is not easy to demonstrate, especially as there are many gene-gene and gene-environment interactions. Nevertheless, the genetic basis of venous thrombosis is well established and the value of this knowledge in the management of these patients is becoming recognised. On the other hand, there are many genetic factors in arterial pathology and the role of each taken in isolation is small. Well-targeted large scale trials are required to determine their effects.

Anticoagulants↗
PubMed2000

Low molecular weight heparins: are they superior to unfractionated heparins to prevent and to treat deep vein thrombosis?

In many countries, low molecular weight heparins (LMWHs) have replaced unfractionated heparin (UH) for prevention and treatment of venous thromboembolism. The present paper reviews the possible advantages of LMWHs over UH. In spite of their lower molecular weight distribution, LMWHs are functionally more heterogeneous than UH. Their anti-Xa/anti-IIa ratio varies significantly, and the injection of the same dose generates different anti-Xa activities and activated partial thromboplastin time (APTT) prolongations. Their pharmacodynamic properties account for their more convenient use in comparison with UH; however, there is a risk of accumulation in case of renal insufficiency. Even if they are less anticoagulant on the basis of the APTT prolongation, they are not less prohemorrhagic than UH. LMWHs are probably less immunogenic and probably induce less osteoporosis. Several meta-analyses published between 1992 and 1999 indicate that LMWHs are as efficient as UH in preventing postoperative deep vein thrombosis (DVT) in general surgery and more efficient than UH in preventing DVT in orthopedic surgery and treating established DVT.

Anticoagulants↗
PubMed2000

Early potent antithrombotic effect with combined aspirin and a loading dose of clopidogrel on experimental arterial thrombogenesis in humans.

BACKGROUND: We conducted a double-blind, randomized, crossover study to assess the antithrombotic effects of the combination of aspirin (acetylsalicylic acid, ASA) and clopidogrel, with or without a loading dose, versus ASA alone in a model of arterial thrombosis in humans. METHODS AND RESULTS: Eighteen male volunteers received the following 3 regimens for 10 days separated by a 1-month period: (1) 325 mg ASA daily, (2) 325 mg ASA+75 mg clopidogrel daily, (3) 325 mg ASA daily+300-mg clopidogrel loading dose on day 1 and +75 mg clopidogrel per day on days 2 to 10. The antithrombotic effect was measured 1.5, 6, and 24 hours after drug intake on day 1 and 6 hours after drug intake on day 10. Arterial thrombus formation was induced ex vivo by exposing a collagen-coated coverslip in a parallel-plate perfusion chamber to native blood for 3 minutes at an arterial wall shear rate. Without a loading dose, clopidogrel+ASA developed an antithrombotic effect within 6 hours after the first intake. It was superior to that produced by ASA, but it was moderate (P</=0.03). However, with the loading dose, the antithrombotic effect of clopidogrel+ASA appeared within 90 minutes, and after 6 hours it was comparable to that on day 10. On day 10, clopidogrel+ASA decreased platelet thrombus formation by approximately 70%, and the effect was significantly more potent than that produced by ASA alone (P<0.001). CONCLUSIONS: This study confirms the synergistic antithrombotic effects of a combined ASA and clopidogrel therapy and shows the early benefit obtained with a loading dose of clopidogrel.

Adult↗
PubMed2000

Polymorphonuclear leukocytes modulate tissue factor production by mononuclear cells: role of reactive oxygen species.

To determine whether polymorphonuclear leukocytes (PMN) modulate the production of tissue factor (TF) by monocytes, PBMC were incubated with increasing concentrations of PMN. PMN did not express any procoagulant activity. After 20-h cocultures, PMN enhanced or inhibited the TF production of PBMC, and this effect depended on the PMN/PBMC ratio. When the ratio increased from 1/1000 to 1/5, without or with LPS, the TF activity of PBMC increased to peak at 2.5-fold the baseline value (p < 0.01). The TF Ag and TF mRNA also increased. This potentiating effect was mediated by reactive oxygen species (ROS) released by PMN during the coculture; it did not require direct cell contact between PMN and PBMC, it was enhanced when PMN were stimulated by fMLP (a chemotactic peptide), and it was inhibited by two antioxidants, N-acetyl cysteine and pyrrolidine dithiocarbamate. In contrast, when the PMN/PBMC ratio was further increased from 1/2 to 2/1, the PBMC TF activity, Ag, and mRNA decreased and were inhibited compared with those of PBMC cultured alone (p < 0.01). This inhibitory effect required direct cell contact between PMN and PBMC, and it was not due to a PMN-mediated cytotoxicity. To confirm the role of ROS, H2O2 enhanced then inhibited the TF activity of PBMC in a dose-dependent manner, similarly to PMN. Thus, PMN may play an important role in the pathogenesis of thrombosis and atherosclerosis by exerting concentration-dependent regulatory effects on the TF production by PBMC via the release of ROS.

Adult↗
PubMed2000

Pharmacodynamic study of low molecular weight dermatan sulphate (Desmin) after a single subcutaneous administration in patients with renal insufficiency.

The pharmacodynamic pattern of low molecular weight dermatan sulphate (CAS 24967-94-0, Desmin-LMWDS) was studied in patients presenting chronic renal insufficiency. Three groups of six patients were defined according to their creatinine clearance: group 1, more than 50 ml/min, group 2 between 10 and 50 ml/min and group 3 lower than 10 ml/min (haemodialized patients). Desmin-LMWDS concentrations were determined with the Heptest assay and the chromogenic specific heparin cofactor II dependent anti IIa assay. In patients of group 1 affected by moderate renal insufficiency, the pharmacodynamic profiles were roughly comparable to those obtained in normal subjects. In the two other groups, the profiles were markedly modified by the renal insufficiency. The maximal concentrations were doubled and the areas under the time-activity curve were 4-fold higher in haemodialyzed (group 3) and severe renal insufficient patients (group 2) than in patients of group 1. The clearance of the anti IIa activity were 13.98 +/- 6.25 l/h; 4.12 +/- 2.64 l/h and 2.94 +/- 1.53 l/h and the half-lives were 2.79 +/- 2.60 h, 6.15 +/- 4.02 h and 11.51 +/- 6.54 h in groups 1 to 3, respectively (p < 0.05). The Desmin-LMWDS clearance was directly correlated to the creatinine clearance (r = 0.8244, n = 18, p < 0.001). Thus, as for low molecular weight heparin, renal function plays a major role in the elimination of low molecular weight dermatan sulphate.

Adult↗
PubMed2000

Inhibition of tissue factor synthesis by disruption of ERK kinases and PKC signaling pathways in human vascular SMCs.

Tissue Factor (TF), the receptor for plasma VII/VIIa and the initiator of blood coagulation, is inducible in vascular smooth muscle cells (SMCs) by growth factors and bacterial lysopolysaccharides (LPS) and is expressed in vivo after vascular injury. As TF expression is a determinant of the thrombogenicity of vascular lesions, we investigated the signal pathways involved in this process. Human vascular SMCs were obtained from normal arteries and made quiescent by serum deprivation. Baseline TF antigen and activity were up-regulated by various agonists: fetal calf serum (FCS), LPS, and platelet derived growth factor (PDGF) being the most effective but with different kinetics. TF expression induced by LPS was transient with a maximum 6 h after stimulation and returned to baseline levels after 24 h whereas TF expression induced by serum or PDGF was sustained for at least 24 h. Rapid and transient activation of Extracellular signal-Regulated Kinase (ERK) was observed after stimulation by PDGF and FCS, but not by LPS. The role of ERK, Ras and protein kinase C activities were investigated using specific inhibitors, PD 98059, manumycin A and calphostin C respectively. For TF induction by LPS, PKC activity was required and the ERK/Ras pathway was not involved. In contrast, the effect of PDGF was strictly ERK and Ras dependent, but partially prevented by PKC inhibitors. TF induction by FCS was ERK dependent but partially Ras and PKC dependent. In conclusion, TF expression appears to be a non-specific response of SMCs to numerous stimuli through multiple signal pathways which differ according to the inducing agent.

Adult↗
PubMed1999

[Anticoagulants in clinical practice].

Four classes of anticoagulants are now available: vitamin K antagonists, heparin, Orgaran and hirudin. For each of these classes the mechanism of the anticoagulant effect, the usual doses and biological monitoring are described. Each low molecular weight heparin must be considered as an original product. Orgaran and hirudin are new antithrombotic agents allowing to solve the dramatic problems raised by heparin-induced thrombocytopenia.

Anticoagulants↗
PubMed1999

Effects of lysophosphatidic acid on proliferation and cytosolic Ca++ of human adult vascular smooth muscle cells in culture.

Lysophosphatidic acid (LPA) is a lipid mediator generated by activated platelets and having various effects on numerous cell types. We investigated some effects of 1-oleyl LPA on vascular smooth muscle cells cultured from adult human normal arteries. At micromolar concentrations, LPA induced a mitogenic effect ([3H]-thymidine incorporation and cell proliferation) on quiescent cells, without an additional growth factor being required. This effect was equipotent to that of 10% fetal calf serum, and it was accompanied by early (5 minutes) and late (1-3 hours) phosphorylation of mitogenactivated protein kinase. LPA inhibited cell migration through collagen coated membranes, with or without platelet-derived growth factor BB as chemoattractant. LPA induced a typical biphasic Ca2+ signal response made up of a rapid first phase due to Ca2+ release from intracellular stores followed by a second wave due to external Ca2+ influx. These findings support the proposal that LPA released from activated platelets is a mediator for smooth muscle cell response at the site of vessel injury in humans.

Adult↗
PubMed1999

Nonfractionated heparin fails to inhibit arterial thrombosis in a human ex vivo thrombosis model.

The effect of nonfractionated heparin on the formation and composition of arterial thrombus is unclear. The purpose of this study in a human ex vivo model was to analyze fibrinoplatelet thrombi and test the inhibitory effect of nonfractionated heparin on arterial thrombus formation. Experiments were carried out in Sakariassen perfusion chambers. Strips coated with either tissue factor (TF) or collagen were exposed to human blood collected from healthy volunteers at an arterial shear stress rate of 2600 s-1 for 1 to 4 min. Platelet deposition was determined using immunoenzymatic techniques to quantify P-selectine, a platelet membrane receptor, in thrombi. Fibrin deposition was determined by quantifying fibrin degradation products released after application of plasmin (D-dimers). Heparin was injected into the blood flow through a blender port system located between the venous puncture site and perfusion chamber. The results of the study showed that in a human ex vivo model, formation of arterial thrombus on two thrombogenic surfaces (tissue factor and collagen) is not inhibited by nonfractionated heparin.

Anticoagulants↗
PubMed1999

Comparison of the antithrombotic effect of PEG-hirudin and heparin in a human ex vivo model of arterial thrombosis.

Polyethylene glycol (PEG)-hirudin is a derivative of hirudin with a long plasma half-life. We have compared the efficacy of PEG-hirudin with unfractionated heparin (UH) in preventing arterial thrombosis. Arterial thrombus formation was induced ex vivo in 12 healthy human volunteers by exposing a tissue factor-coated coverslip positioned in a parallel-plate perfusion chamber to flowing nonanticoagulated human blood drawn directly from an antecubital vein at an arterial wall shear rate of 2600 s-1 for 3.5 minutes. PEG-hirudin, UH, or saline (as control) were administered ex vivo through a heparin-coated mixing device positioned proximal to the perfusion chamber. Platelet and fibrin deposition was quantified by immunoenzymatic measure of the P-selectin and D-dimer content of dissolved plasmin-digested thrombi, respectively. UH was administered to a plasma concentration of 0.35 IU/mL. This concentration prolonged the activated partial thromboplastin time from 32+/-1 seconds to 79+/-4 seconds (P<0.01). UH did not significantly prevent platelet deposition. However, fibrin deposition was reduced by 39% (P<0.05). PEG-hirudin in plasma concentrations of 0.5, 2.5, and 5 microg/mL prolonged the activated partial thromboplastin time to 48+/-2, 87+/-4, and 118+/-4 seconds, respectively. In contrast to UH, PEG-hirudin prevented both platelet and fibrin deposition in a dose-dependent manner with a >80% reduction at 5 microg/mL (P<0.01). Furthermore, the plasma level of PEG-hirudin required to significantly prevent fibrin deposition (0.5 microg/mL) corresponded to a much shorter prolongation of activated partial thromboplastin time (48+/-2 seconds) than that needed for UH (79+/-4 seconds). Thus, our results are compatible with the view that thrombin is greatly involved in recruitment of platelets in evolving thrombi, and that PEG-hirudin is an effective agent for preventing arterial thrombosis in a human ex vivo experimental model.

Antithrombin III↗