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Biomedical subjects

B Boneu

Publications and source records attributed to B Boneu.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1999

Antithrombotic efficacy of the vitamin K antagonist fluindione in a human Ex vivo model of arterial thrombosis : effect of anticoagulation level and combination therapy with aspirin.

Thrombin is a main mediator of arterial thrombus formation, and its inhibition is an important antithrombotic strategy. However, the place of vitamin K antagonists among the different therapeutic strategies for preventing arterial thrombus formation is still debated. We studied the antithrombotic efficacy of the vitamin K antagonist fluindione in a human ex vivo model of arterial thrombosis and determined whether aspirin enhances fluindione efficacy. Ten healthy male volunteers were randomly assigned to receive fluindione, alone or in combination with aspirin (325 mg/d). Fluindione was given at increasing doses to give a stable international normalized ratio (INR) between 1.5 and 2.0 and between 2.1 and 3.0. We induced arterial thrombus formation ex vivo by exposing collagen- or tissue factor (TF)-coated coverslips in a parallel-plate perfusion chamber to native blood for 3 minutes at an arterial wall shear rate of 2600 s(-1). Platelet and fibrin deposition were measured by immunoenzymatic methods. Fluindione inhibited thrombus formation on TF-coated coverslips in a dose-dependent manner by 50% and 80% at INR 1.5 to 2.0 and INR 2.1 to 3.0, respectively (P<0.05). Fluindione in combination with aspirin inhibited TF-induced thrombus formation in a comparable manner. Collagen-induced thrombus formation was not reduced in subjects treated by fluindione. It was reduced by 50% to 60% in those treated with fluindione plus aspirin, regardless of the level of anticoagulation (P<0.05). Thus, the effectiveness of fluindione for preventing arterial thrombosis is dependent on the nature of the thrombogenic trigger. Fluindione is very effective in preventing TF- but not collagen-triggered thrombus formation. Aspirin enhances the antithrombotic effectiveness of fluindione, because combined treatment interrupts both TF- and collagen-induced thrombus formation.

Adolescent↗
PubMed1999

Effects of heparin and related sulfated polysaccharides on tissue factor expression induced by mitogenic and non-mitogenic factors in human vascular smooth muscle cells.

Smooth muscle cells (SMCs) of the intima are generally quiescent and non proliferative. Their proliferation due to different stimulations occurs in myointimal hyperplasia and is regularly present in atherogenesis or after transluminal angioplasty leading to vascular occlusive stenosis. In the course of these pathologies, the Tissue Factor (TF) synthesis was upregulated and rapidly expressed at the membrane of the SMCs. Heparin is known to inhibit SMCs proliferation induced by FCS. We evaluated the inhibitory effect of heparin on the expression of TF induced by various mitogenic (FCS, PDGF-BB and EGF) and non-mitogenic (bacterial LPS) agents. Inhibition by heparin of SMCs proliferation induced by the same agonists was also determined. Quiescent human vascular SMCs from normal adult arteries were treated for 1 h by heparin and related sulfated polysaccharides before stimulation by the agonists. All the agonists up-regulated the expression of TF antigen and activity. TF expression induced by the growth factors was inhibited by heparin (IC 50: 10-30 microg/ml), and other sulfated polysaccharides (IC 50: 1-5 microg/ml). SMCs proliferation, late activation of the extracellular signal-regulated kinases (ERK1/2), and PKC activity were inhibited by heparin (IC 50: 30-50 microg/ml) in SMCs stimulated by FCS but not in SMCs treated by PDGF or EGF. In contrast, heparin had no effect on LPS-induced TF expression nor on LPS-induced PKC activation. These results indicate that, besides its well known effect on SMC proliferation, heparin displays an inhibitory effect on cell mediated blood clotting processes through regulation of the TF expression.

Adult↗
PubMed1999

Further studies on the mechanism for the antithrombotic effects of naroparcil, an orally active thiozyloside compound.

The antithrombotic beta-D-xyloside, naroparcil, has previously been shown to induce a dose-related increase of circulating glycosaminoglycans (GAGs) together with an antithrombin activity (anti-IIa) via heparin cofactor II (HCII) in the rabbit. In order to go further in the mechanisms, the relationship between the antithrombotic activity, the HCII-mediated anti-IIa activity and the plasma GAG content was investigated. We showed that the in vitro specific activity on the inhibition of thrombin by HCII of the plasma GAG extract from naroparcil-treated rabbits was increased by a factor of 60 when compared to controls. In addition, the fractionation of the plasma GAG extract by affinity chromatography on immobilized HCII led to a more potent material whereas the low-affinity fraction was shown to be inactive in thrombin inhibition by HCII. The qualitative analysis of GAGs showed the presence of the deltaDi-4S DS disaccharide, undetectable in control, which accounted for 22% in the unfractionated GAG extract and for 60% in the high affinity fraction. In vitro experiments using immuno-depleted plasma in antithrombin III (ATIII), HCII or both, indicated that the anti-IIa activity of the plasma GAG extract from naroparcil-treated rabbits was mainly due to HCII potentialisation. The unfractionated GAG extract and the high affinity fraction were shown to be antithrombotic in a Wessler-based model in the rat, giving ED80 values of 610 UA/kg and 56 UA/kg respectively whereas the low-affinity fraction was devoid of any antithrombotic activity. These results show that the antithrombotic activity of naroparcil is dependent on modification in the plasma GAG profile which inactivates thrombin via the HCII.

Administration, Oral↗
PubMed1998

A double-blind randomized comparison of combined aspirin and ticlopidine therapy versus aspirin or ticlopidine alone on experimental arterial thrombogenesis in humans.

No randomized study comparing the effect of combined ticlopidine and aspirin therapy versus each drug alone in reducing poststenting thrombotic complications has been performed. To compare these three antiplatelet regimens versus placebo, we conducted a double-blind randomized study using an ex vivo model of thrombosis. Sixteen healthy male volunteers were assigned to receive for 8 days the following four regimens separated by a 1-month period: aspirin 325 mg/d, ticlopidine 500 mg/d, aspirin 325 mg/d + ticlopidine 500 mg/d, and placebo. At the end of each treatment period, native nonanticoagulated blood was drawn directly from an antecubital vein over collagen- or tissue factor (TF)-coated coverslips positioned in a parallel-plate perfusion chamber at an arterial wall shear rate (2, 600 s-1 ) for 3 minutes. Thrombus, which formed on collagen in volunteers treated by placebo, were rich in platelets and poor in fibrin. As compared with placebo, aspirin and ticlopidine alone reduced platelet thrombus formation by only 29% and 15%, respectively (P > .2). In contrast, platelet thrombus formation was blocked by more than 90% in volunteers treated by aspirin + ticlopidine (P < .01 v placebo or each treatment alone). Furthermore, the effect of the drug combination therapy was significantly larger than the sum of the two active treatments (P < .05). Thrombus, which formed on TF-coated coverslips in volunteers treated by placebo, were rich in fibrin and platelets. Neither of the three antiplatelet treatments significantly inhibited fibrin deposition and platelet thrombus formation on this surface (P > .2). Thus, the present study shows that combined aspirin and ticlopidine therapy dramatically potentiates the antithrombotic effect of each drug alone, but that the antithrombotic effect of the combined treatment depends on the nature of the thrombogenic surface.

Adult↗
PubMed1998

Arachidonic acid enhances the tissue factor expression of mononuclear cells by the cyclo-oxygenase-1 pathway: beneficial effect of n-3 fatty acids.

Monocytes express tissue factor (TF) upon stimulation by inflammatory agents. Dietary administration of fish oil rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) results in an impairment of TF expression by monocytes. EPA and DHA are metabolized differently from arachidonic acid (AA), the major fatty acid present in cell membranes. We examined the effects of AA on the TF expression of isolated human PBMC, and we determined whether EPA and DHA modulated this phenomenon differently. Nonstimulated PBMC had a low TF-dependent procoagulant activity. When PBMC were incubated with increasing concentrations of AA, the TF-dependent procoagulant activity increased in a dose-dependent manner to 190% at 7.5 microM. Indomethacin, a cyclo-oxygenase inhibitor, totally abolished the stimulating effect of AA, whereas specific pharmacologic inhibitors of cyclo-oxygenase-2 or of 5-lipoxygenase had no inhibitory effect. A thromboxane (TX)A2/endoperoxides receptor antagonist and a TX synthase inhibitor blocked the potentiating effect of AA. Purified PGG2 and carbocyclic TXA2, a TXA2 agonist, enhanced the procoagulant activity of PBMC in a dose-dependent manner whereas, in contrast, PGE2 inhibited it. Finally, contrary to AA, EPA or DHA did not increase TXB2 production or TF expression by PBMC. The TF-dependent procoagulant activity of isolated PBMC was increased by AA through the production of cyclo-oxygenase-1 metabolites; the combined action of PGG2 and TXA2, which potentiated it, was greater than that of PGE2, which inhibited it. Dietary n-3 fatty acids exert part of their beneficial effect by modulating this procoagulant activity differently from AA.

Arachidonate 5-Lipoxygenase↗
PubMed1998

Haemostatic system activation and prediction of vascular events in patients presenting with stable peripheral arterial disease of moderate severity. Royat Study Group.

This study reports on the predictive value of some haemostatic factors [fibrinogen, factor VII and plasminogen activator inhibitor (PAI)], a marker of endothelial damage (soluble thrombomodulin) and several markers of haemostatic system activation (factor VIIa, prothrombin fragment 1+2, thrombin-antithrombin complexes and D-dimers) on the incidence of vascular events in male, non-diabetic patients with chronic ischaemia of the lower limbs. The patients (n=324) were recruited consecutively in the thermal resort of Royat, France. The low incidence of death from vascular causes during the 2-year survey period (two patients) and the high percentage of former smokers (71%) indicated that this population of patients was affected by an arteriopathy of moderate intensity. After 2 years' follow-up, vascular events had occurred in 51 patients. The clinical and biological profiles did not differ significantly between patients with and without vascular events. However, the risk of vascular events during the 2 years of follow-up was significantly higher in those with high levels of PAI antigen and thrombin-antithrombin complexes. Thus, even in a population of patients with only moderately severe arteriopathy, high levels of thrombin-antithrombin complexes and PAI are predictive of vascular complications.

Adult↗
PubMed1998

A new method for quantifying platelet deposition in flowing native blood in an ex vivo model of human thrombogenesis.

No quantitative, simple and non-radioactive method has been described for measuring the platelet content of experimental thrombi. The aim of the present study was to develop a simple method for quantifying platelets in thrombi formed on thrombogenic surfaces in flowing native human blood. To test the relevance of this new method, the effect of unfractionated heparin on arterial thrombus formation was investigated. Tissue factor (TF)- and collagen-coated coverslips were exposed to non-anticoagulated blood at an arterial wall shear rate (2,600 s(-1)) for 1 to 4 min. Platelet deposition was quantified by measuring the P-selectin (PS) and beta-thromboglobulin (betaTG) content of dissolved plasmin-digested thrombi using immunoenzymoassays; fibrin deposition was determined by measuring the D-dimer levels. These results were compared to those established by morphometrical analysis. Morphometric evaluation showed that fibrin deposition was maximum on TF by 1 min perfusion time. Platelets deposited subsequently and reached a maximum at 3 min. On collagen, platelets deposited directly on the collagen fibrils without detectable fibrin deposit. Platelet deposition increased from 1 to 4 min. Platelet deposition quantified by PS was correlated to the values obtained by morphometry (r = 0.72, r = 0.67, p <0.001, on TF and collagen, respectively). As compared to PS, betaTG measurements gave an underestimation of the size of the thrombus platelet number. Unfractionated heparin infused through a mixing device proximal to the perfusion chamber to obtain plasma concentrations of 0.5, 1 and 3 IU/ml, reduced fibrin deposition on TF-coated coverslips in a dose-dependent manner (77% reduction at 3 IU/ml, p <0.01), but had no significant effect on platelet deposition (33% at 3 IU/ml, p >0.05). In contrast, heparin had no effect on fibrin or platelet deposition on collagen-coated coverslips. Thus, a new quantitative and simple method for measuring platelet deposition in flowing blood has been developed and characterized. Utilizing this system, we have demonstrated that unfractionated heparin did not inhibit arterial thrombus formation either on procoagulant or on proaggregant surface.

Anticoagulants↗
PubMed1998

Pharmacodynamics and tolerance of two nadroparin formulations (10,250 and 20,500 anti Xa IU x ml(-1)) delivered for 10 days at therapeutic dose.

Venous thromboembolism may be efficiently treated by once-a-day (o.d.) administration of a high dose of low molecular weight heparin (LMWH) instead of administration of the same total dose in two injections a day (b.i.d.). To reduce the volume of the subcutaneous (s.c.) injection, a more concentrated form of the drug is advisable. This study was designed to compare the bioavailability of 2 formulations of nadroparin containing 10,250 and 20,500 anti-Xa IU x ml(-1) respectively. This was an open, randomized, cross-over study where 12 healthy volunteers (age 18-35) were enrolled. They received either 90 anti-Xa IU x kg(-1) b.i.d. of the 10,250 IU preparation (treatment A), or 180 anti-Xa IU x kg(-1) o.d. of the 20,500 IU preparation (treatment B) for 10 days. On day 1, the subjects were sampled between 0 and 12 h (treatment A) or between 0 and 24 h (treatment B). On day 10, they were sampled between 0 and 12 h and between 12 and 24 h (treatment A) or between 0 and 24 h (treatment B). Anti-Xa and anti-IIa activities were determined by specific chromogenic assays. The main result of the study was that the bioavailability of the anti-Xa activity of the 2 nadroparin formulations was equivalent, as shown by the comparison of the AUC(0-12 h) plus AUC(12-24 h) (treatment A) and the AUC(0-24 h) (treatment B), calculated on day 10. This study also allowed a number of interesting observations to be made. 1) Between day 1 and day 10, there was an accumulation of the anti-Xa activity for treatment A but not for treatment B (accumulation factors: 1.6 and 1.1 respectively); 2) On day 10, the AUC(0-12 h) were slightly but significantly lower than the AUC(12-24 h) suggesting a circadian effect for anti-Xa and anti-IIa activities; 3) the clearance of the anti-Xa activity was comparable at the 2-dose regimens, while that of the anti-IIa activity was lower in treatment B than in treatment A, indicating a significant dose effect for the pharmacodynamics of the longer heparin chains; 4) On average, the clearance of the anti-IIa activity was twice as high as that of the anti-Xa activity; 5) For treatment B, significant APTT prolongations were noticed at Tmax (prolongation factor: 1.7 +/- 0.25), in relation with the anti-IIa activity (0.3 +/- 0.1 IU x ml(-1)).

Adolescent↗
PubMed1998

Aging and venous thromboembolism influence the pharmacodynamics of the anti-factor Xa and anti-thrombin activities of a low molecular weight heparin (nadroparin).

Venous thromboembolism may be efficiently treated by one single daily administration of a high dose of low molecular weight heparin (LMWH). The present study investigates if the physiological deterioration of renal function associated with normal aging or the presence of an acute venous thromboembolism influences the pharmacodynamic pattern of the anti-factor Xa and anti-thrombin activities. Three groups of 12 subjects were investigated. The first 2 groups were composed of healthy volunteers differing by age (25 +/- 4 and 65 +/- 3 yrs) and creatinine clearance (114 +/- 15 and 62 +/- 6 ml x min(-1)). The third group was composed of patients hospitalized for deep vein thrombosis, having a mean age of 65 +/- 11 yrs and creatinine clearance of 76 +/- 8 ml x min(-1). Nadroparin was administered subcutaneously once daily at the dose of 180 anti-factor Xa IU.kg(-1) for 6 to 10 days. Serial sampling on day 1 and on the last day of administration (day n) allowed the pharmacodynamic parameters of the anti-factor Xa and anti-thrombin activities to be compared at the beginning and at the end of the treatment. The main findings were the following: (1) After repeated administration, a significant accumulation of the anti-factor Xa activity was observed in the healthy elderly and in the patients but not in the healthy young subjects (accumulation factor: 1.3). There was no evidence of accumulation of anti-thrombin activity; (2) There were significant correlations between the clearance of creatinine and the clearance of the anti-factor Xa activity but not with that of the anti-thrombin activity; (3) In the patients, the clearance of the anti-factor Xa and of the anti-thrombin activities were 1.4 and 2 times higher respectively than those calculated in the healthy elderly; (4) The mean ratio of the of anti-factor Xa and anti-thrombin clearances was close to 2 in the healthy subjects but equal to 5.4 in the patients. These results suggest that the mechanisms involved in the clearance of polysaccharide chains which support the anti-thrombin activity are different from those of the anti-factor Xa activity and that the enhanced binding properties of plasma proteins to unfractionated heparin reported in patients presenting an acute venous thromboembolism also exists for LMWH, predominantly for the anti-thrombin activity.

Adult↗
PubMed1997

Efficacy and safety of a low-molecular-weight heparin and standard unfractionated heparin for prophylaxis of postoperative venous thromboembolism: European multicenter trial.

A randomized, double-blind multicenter trial was performed to compare the safety and efficacy of a new low-molecular-weight heparin (LMWH) (LU 47311, Clivarine) and standard unfractionated heparin for the prophylaxis of postoperative venous thromboembolism. Altogether 1351 patients scheduled to undergo abdominal surgery were included. Main outcome measures included the incidence of thromboembolic events (deep vein thrombosis, pulmonary embolism, or both) and bleeding complications, including wound hematoma. A total of 655 patients received 1750 anti-Xa IU of LMWH plus a placebo injection daily; 677 patients received 5000 IU of unfractionated heparin (UFH) twice a day. Both drugs were found to be equally effective, as 4.7% of patients in the LMWH group and 4.3% in the UFH group developed postoperative thromboembolic complications. However, the incidence of bleeding complications was significantly reduced in the LMWH group: 55 (8.3%) patients in the LMWH group and 80 (11.8%) in the UFH group developed bleeding complications, a relative risk (RR) of 0.70 (95% CI 0.51-0.97;p = 0.03); wound hematoma occurred in 29 (4.4%) of the LMWH group compared with 55 (7.7%) in those in the UFH group for an RR of 0.57 (95% CI 0.37-0.88;p = 0.01). This study confirmed that a very low dose of 1750 anti-Xa IU daily of this new LMWH is as effective as 10,000 IU of UFH for preventing postoperative deep vein thrombosis. At this dose its administration is associated with a significant reduction in the risk of bleeding including wound hematoma.

Adult↗
PubMed1997

Long-term persistence of low-molecular-weight material with anti-factor Xa activity contributes to anticoagulant and antithrombotic effects after subcutaneous injection of CY 216 in the rabbit.

This study was done to document further the mechanism of the antithrombotic effect of CY 216 after subcutaneous injection in the rabbit. We first measured the circulating anti-factor Xa and anti-thrombin activities expressed in either International Unit or Standard Independent Unit and from these activities we calculated the above critical length material (ACLM) and below critical length material (BCLM) levels. The clearance of the BCLM was half that of the ACLM. Then we determined the inhibitory effect of CY 216 on thrombin generation (TG) in platelet-poor plasma (PPP) and in whole blood. TG was both inhibited and delayed in whole blood, while it was only inhibited in PPP. The IC50 on TG in PPP and in whole blood were 1.80 +/- 0.16 and 4.33 +/- 1.01 micrograms.ml-1 respectively. After the injection, the inhibition of TG was significant as long as BCLM was detectable. The duration of the antithrombotic effect was essentially correlated to the ACLM level in the Wessler-thromboplastin model and to the BCLM level in the Wessler-serum model. Taken together, these results demonstrate that both ACLM and BCLM components of CY 216 are involved in its anticoagulant effect ex vivo as well as in its antithrombotic activity in vivo, and that the relative contribution of BCLM increases with the time after administration.

Animals↗
PubMed1997

The thrombomodulin/protein C/protein S anticoagulant pathway modulates the thrombogenic properties of the normal resting and stimulated endothelium.

We investigated the role of the thrombomodulin (TM/protein C/protein S anticoagulant pathway in modulating the thrombogenic properties of the endothelium. Endothelial cells (ECs) were placed in parallel-plate flow chambers and exposed to nonanticoagulated human blood at a venous wall shear rate (50 s-1). Fibrin deposition on resting ECs treated with a control IgG1 was negligible. In contrast, a significant amount of fibrin deposited when TM expression was specifically suppressed by > 95% by preincubating ECs with an anti-TM IgG1. Similarly, fibrin deposited on interleukin 1-stimulated ECs, but the fibrin deposition was further increased threefold with anti-TM IgG1. Comparable results were found when ECs were perfused at 650 s-1. When TM surface activity was enhanced by 150% by treating ECs with active phorbol ester (4-phorbol 12-myristate 13-acetate; PMA), the deposition of fibrin was 30% lower than on ECs not pretreated with PMA. Finally, fibrin deposition on stimulated ECs was significantly higher in 11 untreated patients with well-characterized deficiencies of protein C or S or heterozygous factor V Leiden mutation than in 11 healthy individuals, and it was significantly correlated to basal plasma levels of thrombin-antithrombin complexes. Thus, this study underlines the central role of the TM/protein C/protein S pathway in modulating the thrombogenic status of resting and stimulated ECs and indicates that basal coagulation system markers may be helpful in monitoring patients presenting a disorder of this anticoagulant pathway.

Blood Platelets↗
PubMed1997

The activity of unfractionated heparin and low molecular weight heparins in rabbit plasma--the need for using absolute anti-factor Xa and antithrombin activities.

Rabbit being a common animal model to evaluate the antithrombotic effect of heparins, our purpose was to apply the heparin Standard Independent Unit (SIU) approach to rabbit plasma. To take into account the specificities of the enzymes we have measured the decay constants of factor Xa and of thrombin from autologous and heterologous origins, in presence and in absence of heparin. Different heparins or heparin fractions with a mean molecular weight from 1.7 to 10.5 kDa were used. We found that: a) the decay constants varied strongly between species and between enzymes; b) the decay constants of thrombin were always higher than those of factor Xa; c) the specific anti-factor Xa activity of heparins increased with the molecular weight and was 1.33 times higher when determined with bovine factor Xa than with rabbit factor Xa; d) the specific antithrombin activity of heparins also increased with the molecular weight but was similar when determined with rabbit and human thrombin; e) the specific anti-factor Xa activity was always lower than the specific antithrombin activity; f) the calibration of the heparins and heparin fractions against the 4th International Standard of Heparin expressed in International Units (IU) lead to a systematic overestimation of the anti-factor Xa activity and to an under-estimation of the antithrombin activity. These observations indicate that it may be very important to use the SIU approach and to know the accurate activities to better understand the mechanism of the antithrombotic activity of heparins in experimental models.

Animals↗