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Biomedical subjects

B Boneu

Publications and source records attributed to B Boneu.

At least 109 records · Page 6Linked to original sources
PubMed1991

An acquired antithrombin autoantibody directed toward the catalytic center of the enzyme.

Antibody inhibitors against human thrombin are rare and have remained poorly characterized. We report the case of a 40-yr-old patient who developed a potent thrombin inhibitor revealed by mild bleeding symptoms and marked prolongation of most laboratory clotting times. After two years of evolution, he died from cerebral hemorrhage. The inhibitor, a polyclonal IgG, was associated with hematological and immunological criteria of autoimmune disorder. Antithrombin IgG was isolated from the patient's plasma by protein A- and thrombin-affinity chromatography. Fab fragments inhibited amidolytic activity of alpha thrombin, and thrombin-thrombomodulin catalyzed protein C activation with a Ki of approximately 10(-8) M in a noncompetitive manner. Alpha to gamma conversion of thrombin resulted in a moderate loss of affinity for the inhibitor. Upon complex formation of thrombin with staphylocoagulase or alpha 2-macroglobulin (alpha 2M), inhibition was decreased by two orders of magnitude and acquired an apparent competitive character. In Western blot experiments, the antibody reacted with active alpha-thrombin, did not react with chloromethylketone-inhibited thrombin and reacted with a lower affinity with iPr2P-thrombin. The inhibitor did not block thrombin binding to benzamidine-, heparin-, or fibrin-Sepharose, but displaced proflavin from its complex with thrombin. Taken together, these results indicate that the patient's autoantibody recognized a conformational structure which includes, at least in part, the apolar binding site adjacent to the catalytic site of thrombin.

Adult↗
PubMed1991

Limitations of the chronometric assays to determine plasma antifactor Xa activity during low molecular weight heparin therapy.

The most convenient way to estimate low molecular weight heparin (LMWH) concentration in the plasma is to determine its antifactor Xa activity. This is usually performed with specific chromogenic assays. Chronometric methods, easy to perform, have recently been introduced in clinical laboratories. This study provides evidence that these chronometric assays, are unsuitable for measuring the antifactor Xa activity in the plasma of patients receiving such heparins, because they are also sensitive to the residual antithrombin activity of LMWHs. The clearance of the antithrombin activity of a LMWH is higher than that of the antifactor Xa activity. Therefore the antifactor Xa/antifactor IIa ratio of an HBPM continuously increases after parenteral injection. It results in a significant under estimation of the antifactor Xa activity when assayed with a chronometric method because the in vitro antifactor Xa/antifactor IIa ratio of a given LMWH used to construct the calibration curve is lower than that observed ex vivo after its parenteral administration.

Artifacts↗
PubMed1991

Determination of plasma dermatan sulfate at relevant pharmacological concentrations.

1. Routine clotting assays and tests used for monitoring heparin therapy are not suitable for measuring plasma DS in most clinical conditions. 2. Sensitive and specific assays have been developed recently for this purpose. They are based on different biological properties of DS. 3. As DS is heterogeneous, significant differences between the results obtained with different assays are expected. 4. Ex vivo measurements of DS do not reflect an actual concentration because, due to complex pharmacokinetics, the spectrum of molecular species found in a patient's plasma may be different from that present in the material administered. 5. DSs from different sources may exhibit wide variations in structure and biological properties. Ex vivo assays must be calibrated with the DS preparation administered to the patient. Information obtained with one DS is not reliable for other DSs. 6. The relationship between ex vivo activities of DS and antithrombotic effects in man is unknown. Simultaneous assessment of DS concentration and of activation of coagulation in models such as hemodialysis will be very welcome.

Animals↗
PubMed1990

Pharmacokinetics of heparin and low molecular weight heparin.

After parenteral injection, heparin is removed from the blood via two mechanisms, saturable and non-saturable. The saturable mechanism represents clearance by the reticuloendothelial system and endothelial cells, to which heparin binds with a high affinity. The non-saturable mechanism is represented by renal excretion. The contribution of the two mechanisms to the clearance of heparin varies according to the dose delivered and the molecular weight of the heparin preparation. At low doses, unfractionated heparin (UH) is removed mainly via the saturable mechanism, while at higher doses the contribution of the non-saturable mechanism to its clearance becomes pre-eminent. This model accounts for the major pharmacokinetic properties of UH. After bolus intravenous injection of low doses, UH disappears from the blood exponentially with a dose-dependent half-life; at higher doses, UH disappears with a concave-convex pattern. Under continuous intravenous infusion there is a non-linear relationship between the dose of UH injected and the steady-state plasma concentration. After subcutaneous injection, the bioavailability of the anti-factor Xa activity increases with the dose delivered and tends toward 100% at high doses. In contrast, low molecular weight heparins (LMWH) are mainly removed by non-saturable renal excretion. This explains the dose independence of the pharmacokinetic parameters of LMWH, the excellent bioavailability of the subcutaneous route at any dose, and the prolongation of LMWH half-life in cases of chronic renal insufficiency. However, the model does not explain the large interindividual variability of the pharmacokinetic parameters of both UH and LMWH.

Animals↗
PubMed1990

Antithrombotic potencies of heparins in relation to their antifactor Xa and antithrombin activities: an experimental study in two models of thrombosis in the rabbit.

Our purpose was to determine the relative contribution of the antifactor Xa and antithrombin activities of heparin to its antithrombotic potency. The antithrombotic activities of unfractionated heparin (UH), two low molecular weight heparins (LMWH, CY 216 and CY 222) with increasing anti-factor Xa/antithrombin ratio and a synthetic pentasaccharide (PS) with high affinity to antithrombin III and no antithrombin activity were evaluated. In the Wessler-thromboplastin model, the most potent antithrombotic agent, on a weight basis, was UH followed by CY 216, CY 222 and the PS which was 40 times less potent than UH. On an antithrombin unit basis, the antithrombotic potencies of UH, CY 216 and of CY 222 were equivalent. Thus, in this model, the antithrombotic effect results from the catalytic action of UH or LMWH on thrombin inhibition. In the Wessler-serum model, on a weight basis, the antithrombotic effectiveness of UH was unchanged, those of CY 216 and CY 222 were doubled, and that of the PS was increased 10 times. On an anti-factor Xa unit basis, CY 216 was as effective as UH, and PS as effective as CY 222. On an antithrombin unit basis, CY 216 and CY 222 were equivalent and more potent than UH. Thus, in this model, the antifactor Xa activity of heparin becomes important for its antithrombotic property. After a single subcutaneous injection of 1000 antifactor Xa U/kg, the antithrombotic effects of UH were maintained for more than 14 h in the two models. After injection of the same dose of CY 216 significant antithrombotic effects were observed only for 9 h, in the Wessler-thromboplastin model but for 18 h in the Wessler-serum model. At that time, no detectable antithrombin activity was measurable in the plasma while 0.11 units of antifactor Xa activity/ml was detected. Thus, the relative contribution of the anti-factor Xa and antithrombin activities to the antithrombotic effect of a LMWH differs according to the nature of the thrombogenic stimulus.

Animals↗
PubMed1990

Pharmacodynamics of CY 216 in healthy volunteers: inter-individual variations.

The pharmacodynamic parameters of a low molecular weight heparin (LMWH, CY 216) and their inter-individual variations were investigated. In a cross over study 100 anti-factor Xa IC U/kg were injected, one week apart, to 12 healthy volunteers by intravenous (IV) or subcutaneous (SC) route. The pharmacological effects were followed by performing activated partial thromboplastin time (APTT), thrombin clotting time (TCT) and a chromogenic anti-factor Xa assay. The main pharmacodynamic parameters were calculated from the anti-factor Xa activity disappearance curves. Five to ten min after IV injection, the APTT ranged between 56 and 98 sec (baseline 40 sec), the TCT between 28 and 99 sec (baseline 19 sec) and the anti-factor Xa activity between 1.58 and 2.28 IC U/ml. The anti-factor Xa activity half-life ranged between 1.5 and 2.9 h. After SC injection, there were no detectable APTT and TCT prolongations; the maximum anti-factor Xa activity ranged between 0.36 and 0.88 IC U/ml and the half life between 1.5 and 6.4 h. These results indicate that, as for standard heparin, there are large inter-individual variations in the anticoagulant responses to a given dose of CY 216 an observation which may have clinical implications.

Adult↗
PubMed1990

Distribution of 16 hemostatic laboratory variables assayed in 100 blood donors.

The aim of the present study was to establish the normal range of 16 hemostatic variables routinely assayed in our laboratory. We therefore measured the activated partial thromboplastin time, the prothrombin time, and the plasma levels of fibrinogen (Fg), factors II, V, VII + X, VIII, IX, XI, XII, von Willebrand factor-antigen (vWf), protein C (PC), total (tPS) and free (fPS) protein S-antigen, C4b binding protein (C4bBP) and fibrin degradation products (FDP), in 100 unselected adult blood donors (58 males, 42 females). We further examined the influence of age and sex on these variables. Age was shown to affect the plasma level of free PS: in comparison with a normal reference plasma, the levels of measured fPS in subjects less than or equal to 40 years (n = 67) and greater than 40 years (n = 33) were 86% (normal range: 52-143%) and 99% (60-162%), respectively (P = 0.01). The plasma levels of factors VIII, vWf, C4bBP and PS were significantly influenced by sex. This finding was particularly marked for fPS: in males (n = 31) and females (n = 36) less than or equal to 40 years, plasma levels of fPS were 94% (59-150%) and 80% (49-132%), respectively (P = 0.008). Finally, we studied the relationships existing between these factors. We found that plasma levels of most coagulation factors were interrelated. In addition, FDP values were positively correlated with plasma level of Fg (r = 0.26); P = 0.008).

Adult↗
PubMed1990

Pharmacologic properties of a low molecular weight dermatan sulfate: comparison with unfractionated dermatan sulfate.

The anticoagulant, pharmacodynamic, and antithrombotic properties of a low molecular weight dermatan sulfate (molecular weight range 1600 to 8000, peak 4000) were compared with those of unfractionated dermatan sulfate (molecular weight range 12,000 to 45,000, peak 25,000). Anticoagulant activities were evaluated as the ability of the compounds to catalyze the inhibition of thrombin in the presence of heparin cofactor II in a purified system and to prolong the activated partial thromboplastin time or the thrombin clotting time of human and rabbit plasmas. On the basis of weight, low molecular weight dermatan sulfate was two times less potent than unfractionated dermatan sulfate. After bolus intravenous injection into rabbits, the volume of distribution of low molecular weight dermatan sulfate was 10 times larger than that of unfractionated compound, and the half-life of disappearance was two to four times longer despite a 1.4 to 2.3 times higher total clearance. The bioavailability of low molecular weight dermatan sulfate from its subcutaneous depot was 100%; it was absorbed faster from that depot than unfractionated dermatan sulfate. The antithrombotic activities of unfractionated and of low molecular weight dermatan sulfate were also examined with a Wessler-type model with tissue factor as the thrombogenic stimulus. When evaluated 3 minutes after a bolus intravenous injection, unfractionated dermatan sulfate was twice as active as low molecular weight dermatan sulfate on the basis of weight. With subcutaneous injection, 10 mg/kg of low molecular weight dermatan sulfate generated an activity in plasma equivalent to 5.6 micrograms/ml 1 hour later. This concentration was associated with a significant antithrombotic effect that lasted for less than 6 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[Prospective study of HIV infection in a group of 30 young hemophiliacs].

In order to investigate the progression to AIDS, we studied 39 patients with hemophilia ranging presently in age from 8 to 20 years, who had been positive for HIV antibodies for a mean of 36 months. Every 3 to 6 months a clinical and laboratory examination was performed. The number of patients with AIDS increased from 2 to 6 and 2 patients died from opportunistic infections. The percentage of patients with less than 500 T4 cells increased from 28% to 41%. Increase in serum IgA concentrations above 2.5 gl/l ranged from 23% to 38% of patients. Seven subjects were found to be positive for HIV antigen and 11 of 15 had a loss of p24 antibody. Patients' distribution into two groups according to the results of T4 cells count at the beginning of the study have shown a significant difference on the basis of clinical and biological progression. The present investigation confirms the progression in this population and the importance of some markers.

Acquired Immunodeficiency Syndrome↗
PubMed1989

[Role of platelets in atherosclerosis and arterial thrombosis].

A thrombus is an abnormal manifestation of normal haemostasis occurring on the internal surface of the blood vessels. Endothelial injury is the first event which ultimately may result in arterial thrombosis. Platelets stick to subendothelial components, are activated and release a number of mediators which aggregate new platelets. Simultaneously, thrombin is generated on the platelet surface and enhances these phenomenons. Due to the high blood flow which avoids local thrombin accumulation, arterial thrombosis is mainly composed of platelets with a poor fibrin content. A mural arterial thrombosis may embolize, be incorporated in the vessel wall, or occlude the lumen of the artery. Platelets are involved in the development of atherosclerosis: severe thrombocytopenia or von Willebrand disease protect efficiently against experimental atherosclerosis; several clinical conditions known to increase cardiovascular diseases are also associated with an increased platelet aggregability; in contrast, polyunsaturated fatty acids decrease platelets aggregability and protect against vascular diseases.

Arteriosclerosis↗
PubMed1989

Unfractionated heparin and CY 216: pharmacokinetics and bioavailabilities of the antifactor Xa and IIa effects after intravenous and subcutaneous injection in the rabbit.

This report compares the pharmacokinetics and the bioavailabilities of the antifactor Xa and of the antifactor IIa activities generated by intravenous (IV) and subcutaneous (SC) injections of increasing doses of unfractionated heparin (UH) and of a low molecular weight heparin (CY 216). Rabbits were injected with 500, 1,000, 2,500, and 5,000 antifactor Xa u/kg of both heparins and their biological activities were followed at various time intervals. After IV injection the clearance of the antifactor Xa activities was independent of the dose and the clearance of UH was significantly higher than that of CY 216; after SC injection the bioavailability estimated from the antifactor Xa effect was consistently over 100% for CY 216 while that of UH increased from 27% at the lowest dose to 93% at the highest dose. The pharmacokinetic parameters estimated by the antifactor IIa activity of UH were superimposable to those calculated with the antifactor Xa activity. For CY 216 no direct comparison between the two activities was made since the dose injected expressed in antifactor IIa units was 3.4 times lower. UH and CY 216 were therefore injected intravenously to other animals at equivalent and increasing doses expressed in antifactor IIa units (50-5,000 u/kg). The pharmacokinetic parameters calculated from the curves of the antifactor IIa activities were basically identical except at the two lower doses (50 and 100 u/kg) for which UH was cleared faster than CY 216.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Neutralization of dermatan sulfate in vitro and in vivo by protamine sulfate and polybrene.

The neutralization of the anticoagulant, anti-thrombin, and bleeding effects of dermatan sulfate (DS), a potential antithrombotic agent, was investigated. Protamine sulfate (PS) and hexadimethrine bromide (Polybrene), which reverse the anticoagulant effect of heparin, also neutralized DS in vitro. In human plasma, polybrene was approximately 3 times more active on a weight basis than PS for neutralizing DS (1.5 micrograms polybrene inhibits 1 microgram DS). Intravenous administration of polybrene to rabbits pretreated with DS in a 1:1 weight ratio immediately neutralized 90% of DS and this effect was stable with time. In contrast, PS in a weight ratio of 6:1 (PS to DS) only neutralized 50% of DS injected. When plasma DS concentrations were maintained by continuous infusion between 3 and 15 micrograms/ml, a bolus of polybrene 0.25 mg/kg induced an immediate drop of about 4 micrograms/ml but initial values of DS were recovered within 20 min. PS was again much less effective than polybrene for neutralizing DS. The bleeding effect of DS and its correction by polybrene was studied by using the rat tail transection model. Very large doses of DS (greater than 10 mg/kg) were required to get a modest prolongation of bleeding time. The injection of equivalent doses of polybrene in animals pretreated by DS induced a strong bleeding effect associated with a drop in platelet and leukocyte counts. Animal models are thus inappropriate for investigating the correction of DS-induced bleeding, because high doses of both DS and neutralizing agents are required in these models. Our results indicate that, provided the doses of neutralizing agents remain below their established levels of toxicity in man, DS could if necessary be neutralized completely by polybrene and partially by PS.

Animals↗
PubMed1989

Plasminogen activator inhibitor in plasma is related to testosterone in men.

Low plasma testosterone and high levels of the rapid inhibitor of plasminogen activator (PA-I) have been proposed as risk factors for myocardial infarction. In this study, the relationship between testosterone and PA-I activity levels in middle-aged men without thrombotic antecedent was investigated. In 54 normogonadic men (testosterone, 7.3 to 29.1 nmol/L), PA-I was related positively to body mass index (BMI) and triglycerides and negatively to testosterone. When these variables were controlled, the relation between PA-I and testosterone remained significant (P less than .01). In the 41 normogonadic men with BMI less than 25, testosterone was the only variable to influence PA-I. Fibrinolytic activity was evaluated by the euglobulin lysis plate method and the specific measurement of functional tissue plasminogen activator. The basal fibrinolytic activity and the response to venous occlusion were essentially controlled by PA-I but were not significantly related to testosterone. In 17 men with severe hypogonadotrophinic hypogonadism (testosterone less than 3 nmol/L), PA-I was significantly increased (18.5 +/- 1.8 AU/mL, mean +/- SE) compared with 9.5 +/- 0.8 AU/mL in 41 normogonadic men of normal weight (P less than .001). However, 14 hypogonadic men had a hypertriglyceridemia or a BMI greater than 25, which could explain high PA-I levels. This study shows that the level of the inhibitor of plasminogen activator is partly dependent on hormonal status in men and provides a link between independently established epidemiologic data.

Adult↗
PubMed1989

Pharmacokinetics of heparin and related polysaccharides.

The pharmacodynamic profile of standard heparin (SH), a low molecular weight derivative (CY 216) and of dermatan sulfate (DS), a new potential antithrombotic drug, was investigated in the rabbit over a large range of doses. After bolus i.v. injection of low doses, the biological activity of SH disappeared exponentially; however, its half-life was prolonged when the dose injected increased, and over 158 micrograms/kg (100 anti-factor Xa U/kg) the biological activity disappeared as a concave-convex curve. CY 216 disappeared more slowly than SH at low doses but faster than SH at higher doses. More than 90% of the DS biological activity present 1 minute after the i.v. injection disappeared exponentially without dose-dependent effects. Increasing doses of the three drugs were then delivered for 5 h under continuous infusions. Below 500 micrograms/kg/h the DS and CY 216 plateau concentrations were higher than that of SH while above this dose the SH concentration was higher than that of DS and CY 216. These observations may be explained by the results of pharmacokinetics experiments where 125I-labeled compounds were delivered by bolus i.v. injection in association with increasing doses of their unlabeled counterparts. For SH there was a 10-fold difference between the half-life of the lower dose (32 micrograms/kg or 5 anti-factor Xa U/kg) and that of the higher dose (3200 micrograms/kg); it was demonstrated that the half-life of SH continuously shortened as its plasma concentration decreased. In contrast the CY 216 and DS half-lives were very close, independent of the dose delivered, and therefore longer than that of SH at low doses and shorter than that of SH at higher doses. The renal contribution to the clearance of SH, CY 216, and DS was also investigated by injecting a low dose (150-200 micrograms/kg) and a 10 times higher dose to sham-operated or binephrectomized animals: renal function is critical for the elimination of the three compounds from the blood except for SH at low doses. These observations are promising for the development of DS and may have clinical implications.

Animals↗
PubMed1989

Pharmacological properties of dermatan sulfate, of a low molecular weight dermatan sulfate and of two oversulfated derivatives.

The pharmacological properties of unfractionated dermatan sulfate (U-DS, mean MW 25 kd, range 12-45 kd) of a low molecular weight fraction (LMW-DS, mean MW 4 kd range 1.6-8 kd), and of 2 oversulfated derivatives (S-DS1 and S-DS2, 2 and 3.8 sulfate groups per disaccharide units) were investigated. In a purified system, LMW-DS, S-DS1 and S-DS2 were respectively 0.5, 10 and 17 times more potent than U-DS to catalyse thrombin inhibition by heparin cofactor II. Identical differences were observed for the respective anticoagulant activities (activated partial thromboplastin time and thrombin clotting time). After bolus IV injection of increasing doses the pharmacokinetic parameters of U-DS were slightly dose dependent, and the total clearance of LMW-DS was, on the average, 2 times higher. The patterns of disappearance of S-DS1 and S-DS2 were strongly dose dependent and became concave-convex, suggesting different mechanisms of clearance. After SC injection, the bioavailability was less than 50% for U-DS and at least 100% for LMW-DS. The antithrombotic activity (Wessler-thromboplastin model) of LMW-DS was 2 timer lower than that of U-DS. In contrast to their in vitro (and ex vivo) enhanced anticoagulant activities, the antithrombotic potency of S-DS1 was identical to that of U-DS, while, at the same doses S-DS2 was devoid of any activity.

Animals↗
PubMed1989

[Alpha 2-adrenergic receptors and arterial pressure].

The aim of this work was to investigate the influence of blood pressure levels on human platelet alpha 2-adrenergic receptivity. The study was carried out on 12 mild essential hypertensive patients and 7 normotensive parkinsonians with orthostatic hypotension. Alpha 2-adrenoceptors number and affinity were determined by 3H-yohimbine binding, plasma catecholamines were measured by HPLC and adrenaline-induced platelet aggregation by turbidimetry. Results obtained were compared with those of two groups of 12 normotensive control subjects. In hypertensive patients, both platelet alpha 2-adrenoceptors (139 +/- 6 vs 176 +/- 18 fmol/mg protein) and velocity of adrenaline-induced platelet aggregation were decreased whereas plasma adrenaline and noradrenaline remained unchanged. In patients with orthostatic hypotension, there was an increased number of platelet alpha 2-adrenoceptors (313 +/- 52 vs 168 +/- 8 fmol/mg protein) associated with a significant decrease in plasma noradrenaline (62 +/- 11 vs 190 +/- 25 pg/ml). In none of the two groups of patients there was any change in receptor affinity for 3H-yohimbine. These results indicate that human platelet alpha 2-adrenoceptors levels are related to blood pressure values. Moreover, up-regulation in orthostatic hypotension and lack of down-regulation in essential hypertension suggest that only sustained abnormal plasma noradrenaline levels could allow the development of alpha 2-adrenoceptors regulatory mechanisms. These variations can represent tentative compensatory mechanisms for normalization of blood pressure levels.

Aged↗