Dose-dependent release of endogenous tissue factor pathway inhibitor by different low molecular weight heparins.

Tissue factor pathway inhibitor (TFPI) is released to circulating blood after intravenous and subcutaneous injections of heparins, and may thus contribute to the antithrombotic effect of heparins. A previous study suggested different abilities of various low molecular weight heparins (LMWH) to release endogenous TFPI, but the dose-response relationship was not determined. In the present study, the dose-response relationship for escalating doses of two LMWHs, dalteparin and enoxaparin, on the release of endogenous TFPI was investigated. Six healthy male participants were given 50, 100 and 200 U/kg dalteparin and 0.5, 1.0 and 2.0 mg/kg enoxaparin as a single subcutaneous injection. The study was a randomized, cross-over design with a 1-week wash-out period between each injection. Peak free TFPI antigen and TFPI activity were detected after only 1 h, whereas anti-activated factor X (anti-FXa) and anti-activated factor II (anti-FIIa) activities were detected after 2-6 h. Putative therapeutic equivalent doses of dalteparin and enoxaparin gave similar release of endogenous TFPI, but dissimilar effects on anti-FXa and anti-FIIa activities.     

Erythropoietin-induced thrombosis as a result of increased inflammation and thrombin activatable fibrinolytic inhibitor.

Chronic inflammation is a major cause of morbidity and mortality in end-stage renal disease. The associated anemia in these patients due to renal cortical atrophy and erythropoietin deficiency is treated with recombinant erythropoietin. Recent reports suggest a growing incidence of symptomatic venous thrombosis in cancer patients treated with recombinant erythropoietin. Several investigators have reported on different mechanisms of thrombosis in these patients. We hypothesize that thrombosis in patients with end-stage renal disease due to increased expression of C-reactive protein (CRP) as a result of chronic inflammation promotes the release of thrombin activatable fibrinolytic inhibitor causing fibrinolytic deficit and eventually thrombosis. Furthermore, because endothelial nitric oxide is responsible for the maintenance of the normal vascular function, the decreased levels of nitric oxide in chronic inflammation cause endothelial damage and result in thrombosis. To test this hypothesis, blood samples were collected from 106 patients (49 male and 57 female, aged 59.8+/-15.7 years) with end-stage renal disease undergoing hemodialysis and treated with recombinant erythropoietin at a mean dose of 201.8 U/kg/week. Blood samples were drawn in 5-mL tubes containing 3.2% sodium citrate just before the hemodialysis procedure. These blood samples were immediately centrifuged to obtain platelet-poor plasma, which was aliquoted and frozen at -70 degrees C until further analysis. Erytropoietin antibodies were measured using an anti-EPO enzyme-linked immunosorbent assay (ELISA) method developed in our laboratory. Nitric oxide was measured using a NO analyzer (Sievers 280I, Ionics, Boulder, CO). Plasma CRP levels were measured with a highly sensitive ELISA method IMUNOCLONE CRP ELISA (American Diagnostica, Greenwich, CT). TAFI antigen levels in plasma were analyzed with an IMUCLONE TAFI ELISA kit (American Diagnostica, Greenwich, CT). TAFI functional activity was assayed with an ACTICHROME TAFI activity kit. The measured levels of nitric oxide, CRP, TAFI antigen, and TAFI functional were 37.36+/-36.8 (normal value, 37.49+/-18.96; range, 19.3-102 microM), 12.27+/-10.6 (normal value, < 1 microg/mL), 146.9+/-28.4% NHP (normal, 100% NHP), and 102.55+/-37% NHP (normal range, 22.3-165.7; mean, 89.5% NHP), respectively. The erythropoietin antibody was detected in 9.4% of the patient group. While 20% of the erythropoietin antibody-positive and 27.1% of the erythropoietin antibody-negative patients experienced chest pain, thrombotic events developed in 9.4% of the erythropoietin antibody-negative patients. These data provide the rationale for a novel mechanism of thrombosis through increased activity of CRP, nitric oxide, and TAFI, leading to fibrinolytic deficit and thrombosis in patients treated with erythropoietin.     

Comparative inhibition of LPS-activated human monocyte-induced thrombin generation by unfractionated heparin and low molecular weight heparins

Monocyte tissue factor may play a role in the physiological or pathological triggering of blood coagulation. It is well known that unfractionated heparin and low molecular weight heparins inhibit extrinsic thrombin generation. However, this notion has never been confirmed in a physiological model using tissue factor obtained from stimulated human monocytes. This is the purpose of this study. It was important to obtain a pure preparation of monocytes with no platelet contamination. This was possible by leukapheresis and elutriation. Under sterile and endotoxin-free conditions, the process does not activate tissue factor expression by monocytes. We adapted the technique of thrombin generation on an automatic analyzer and used human monocyte tissue factor to trigger thrombin generation. Our results show that unfractionated and low molecular weight heparins potently inhibit monocytic tissue factor induced thrombin generation. The comparison of low molecular weight heparins suggests that molecules with higher anti-IIa/anti-Xa ratios exert a stronger inhibitory effect. These data may be relevant to explain the therapeutic effects of unfractionated and low molecular weight heparins in cardiovascular disorders such as unstable angina.     

Variability of heparins and heterogeneity of low molecular weight heparins

Chemical and physical characteristics, building blocks, constitutive disaccharides, sulfation degree, and biological activities of heparins (UFHs) and of low molecular weight heparins (LMWHs) obtained by different depolymerization processes are examined comparatively in terms of structure characteristics, content of 1,6-anhydro rings, and other fingerprints. The heterogeneity of different LMWHs depends on different manufacturing processes and on particular specifications of pharmacopoeias. The reported examples prove that the variability among samples of LMWHs manufactured by the same process is quite limited. Most of the variability is derived from the parent UFH. In contrast, fingerprint groups and residues are specific to the depolymerization process and their extent can be roughly controlled through the process parameters.     

The role of thrombin activatable fibrinolysis inhibitor in disturbances of fibrinolytic system in obesity

The aim of the study was to evaluate fibrinolysis in obese women. Study group consisted of 45 obese women (mean age 36,8 +/- 16,6 years, mean BMI 35,7 +/- 4,9), who were allocated to two subgroups: premenopausal (mean age 32,3 +/- 9,9 years, mean BMI 36,9 +/- 5,6) and postmenopausal (mean age 64,8+/-10,1 years, mean BMI 33,3 +/- 2,55). Control group consisted of 45 women (mean age 35,3 +/- 13,9 years) with normal BMI (21,8 +/- 3,09). Global fibrinolytic activity was diminished only in obese women after menopause. Final analysis revealed significant increase of TAFI antigen and activity in the plasma of obese women. The existence of significant correlation in multifactor regression analysis between TAFI plasma content and euglobulin clot lysis time (ECLT) and global fibrinolytic capacity (GFC) as well confirmed negative influence of this inhibitor on fibrinolytic capacity in obese women. The increase of TAFI antigen and activity in the plasma was independent of age, BMI, glucose, cholesterol, triglicerides, insulin and leptin concentration in the plasma. The results of ECLT and GFC may be also influenced by PAI-1 activity particularly in women before menopause, which was significantly elevated in our group of patients. This increase as not dependent with TAFI antigen concentration. In conclusion, the observed increase TAFI antigen and activity in the plasma of obese women may influence the thrombotic risk in this group of patients, especially after menopause.     

Biologic tolerance of two different low molecular weight heparins.

Heparin preparations have been used for prophylaxis and treatment of deep vein thrombosis for many years. Several biologic effects of heparin are known. Since 1978, there have been several reports about reversible elevation in serum values of AST and ALT in patients and healthy volunteers given heparin in small and high doses. Few studies report similar events in patients given LMW heparins. Results of two randomized studies (A and B) comprising 456 patients undergoing THR are presented. Two different compounds of LMW heparin (Logiparin or Enoxaparin) were used for thromboprophylaxis. Significant elevation during the postoperative period of AST and AP in study A, and AST, ALT, AP, LDH, and CK in study B were demonstrated in patients given LMW heparins in both studies. In study A the percentages of patients with normal preoperative values who reached pathologic values were 35% for AST and 15% for AP. In study B the percentages of patients with normal preoperative values who reached pathologic values were 36% for AST, 17% of ALT, 14% for AP, and 36% for LDH. The possible biologic mechanisms and the clinical perspectives are discussed. In all cases the changes in the liver enzymes returned to preoperative levels within 14 days.     

Tissue factor pathway inhibitor and thrombin activatable fibrinolytic inhibitor plasma levels following burn and septic injuries in rats.

Burn and septic injuries induce profound changes in coagulation status. This study examined the changes in plasma tissue factor pathway inhibitor (TFPI) and thrombin activatable fibrinolytic inhibitor (TAFI) levels in a rat model of burn and septic injuries. Rats underwent 30% TBSA cutaneous scald burn injury and septic insult was induced by caecal ligation and puncture (CLP). CLP was superimposed on burn injury to mimic the clinical model of sepsis complicating burn injury. Rats were pretreated with Cprofloxacin orally to colonize their gut with Enterococcus faecalis. TFPI and TAFI plasma levels were measured using functional activity assay kit with a chromogenic method at 24 and 72 hours following the injuries. TFPI levels decreased significantly at 24 hours in burn, CLP, and burn+CLP groups, followed by incomplete rebound recovery at 72 hours in all three groups. On the other hand, TAFI levels increased significantly at 24- and 72-hour time points in all three groups. These results suggest that burn, septic, and their combined injuries perturb coagulation cascade and thrombotic process toward the procoagulant pathway by impairing fibrinolysis.     

Comparative human pharmacology of low molecular weight heparins

The pharmacodynamics of LMW heparins differ consistently from those of normal heparin. The relative bioavailability is greater than 90% and for some LMW heparins more than 100% after subcutaneous administration, as measured by the anti-Factor Xa activity. This indicates release of endothelial bound glycosaminoglycans with anti-Factor Xa-like activities. Direct determination of the LPL and HTGL activities demonstrate higher capacities of two and a lower capacity of three LMW heparins to release these enzymes from their endothelial glycoprotein receptors into the bloodstream. Thus, all LMW heparins are characterized by improved pharmacodynamics compared with normal heparin, but their anti-Xa to APTT and anti-Xa to anti-IIa ratios and half-lives differ among each other. The neutralization of the anticoagulant effects of LMW heparins by protamine are similar in vitro and in vivo at equigravimetric doses. However, unfractionated heparin and LMW heparins are not completely antagonized by protamine on a whole blood clotting test (thrombelastography). This inhibition of Factor Xa of LMW heparins is counteracted not completely by protamine. This may be due to a release of other glucosaminoglycans by LMW heparins. The present overview demonstrates that a comparative human pharmacology gives useful devices for prophylactic and therapeutic regimen for LMW heparins in patients in addition to the data obtained from animal models.     

New-generation anticoagulants: the low molecular weight heparins

Heparin has been the mainstay of acute anticoagulation therapy for decades. Within the past 20 years, several different heparin fractions-collectively known as low molecular weight heparins (LMWHs)-have been evaluated in various medical and surgical settings in which anticoagulation is routinely warranted. The LMWHs are efficacious, safe, cost-effective, and easier to administer and monitor than standard, unfractionated heparin. As LMWH use becomes more widespread, emergency physicians will use these new agents instead of unfractionated heparin for unstable angina, non-Q-wave myocardial infarction, or thromboembolic disease. This review focuses on the pharmacologic properties of unfractionated heparin and LMWH, associated complications, and the use of these agents in acute ischemic coronary syndromes, thromboembolic disease, and other selected clinical situations.     

Impairment of primary haemostasis by low molecular weight heparins in rats

Different low molecular weight (LMW) heparins were tested on primary haemostasis in rats. Four preparations were studied; one was devoid of any effect on the bleeding time, while the other three prolonged the bleeding time to varying extents. As a consequence we studied the effect of these heparins on platelet aggregation. The fractions which prolonged the bleeding time, also inhibited the ex vivo and in vitro platelet aggregation, whereas the one devoid of any effect on the bleeding time did not affect platelet aggregation. Similar results were obtained using both platelet-rich plasma (PRP) and gel-filtered platelets. The in vitro response of platelets to aggregating agents may offer a parameter to detect the presence of 'bleeding factor(s)' in some LMW heparin preparations.     

Issues in the utilization of low molecular weight heparins

Low molecular weight heparins (LMWHs) are parenteral anticoagulants that are widely used for the prevention and treatment of thromboembolic disease. These agents possess several advantages compared to standard heparin, including a more predictable anticoagulant response, better bioavailability allowing for subcutaneous therapy, and a longer half-life. Laboratory monitoring of the LMWHs uses an anti-factor Xa assay, but monitoring is generally not necessary for most patients. However, certain patient populations do benefit from an individualized approach to therapy and, in some cases, therapeutic monitoring, because of an increased bleeding risk and/or relative contraindications to anticoagulant therapy. For example, since LMWHs are cleared by the kidney, they must be used with caution in renal insufficiency. LMWHs are safe and effective during pregnancy but may not be the optimal antithrombotic agent in pregnant women with prosthetic valves. In addition, management around the time of delivery can be difficult because of the bleeding risk, particularly associated with epidural anesthesia. Therapeutic monitoring also may be useful for the morbidly obese, in children, and for patients with malignancy.     

Cost implications of low molecular weight heparins as prophylaxis following total hip and knee replacement

Deep venous thrombosis (DVT) and pulmonary embolism (PE) are serious and costly complications of total hip and knee replacement surgery. The risk of these complications is significantly reduced by prophylaxis. Low molecular weight heparins (LMWH) are being used for this indication with increased frequency. The objective of this study was to assess the cost implications of LMWH for the prevention of symptomatic DVT and PE complications following total hip and knee replacement surgery. The study design was cost analysis based on utilization and the costs of medical resources for prophylaxis and treatment of DVT/PE. A retrospective hospital data set was used to assess symptomatic DVT/PE complication rates and medical resource utilization in patients receiving warfarin, other, and no prophylaxis. The results of a clinical trial were used to estimate relative reductions in risk of symptomatic DVT/PE due to prophylaxis with LMWH. The 7721 total hip and knee replacement patients analyzed were admitted in 1992 in 57 acute-care non-federal hospitals. The measurements were of incremental costs or charges expected to be saved as a result of using LMWH prophylaxis instead of warfarin prophylaxis. Prophylaxis using LMWH rather than warfarin reduces the expected total costs (charges) of treatment by $50 ($193), not including the pharmaceutical costs associated with prophylaxis. The cost reduction in favor of LMWH was sensitive to several factors, including blood monitoring costs and DVT/PE complication rates. Where a reduction of one day in hospital stay could be realized from LMWH's early onset of action, the cost (charges) reduction increased to $226 ($624). In conclusion, LMWH has the potential to offer several short- and long-term cost advantages compared with warfarin, mostly due to lower test costs associated with prophylaxis and reduced complication rates.     

Therapy of unstable angina with the low molecular weight heparins

Unstable angina is in most cases caused by partial or complete coronary artery occlusion due to the disruption of an atherosclerotic plaque and to thrombus formation. An immediate antithrombotic approach is essential to prevent fatal and non-fatal myocardial infarction, and the combination of aspirin and unfractionated heparin has played a pivotal role in the past years. Low molecular weight heparins have improved pharmacokinetic and pharmacodynamic properties over unfractionated heparin that have resulted in greater efficacy and safety in the field of venous thromboembolism. Low molecular weight heparins can be administered by once or twice daily subcutaneous injections at fixed, weight-adjusted doses without the need for monitoring. Because of their potential, many recent clinical trials have evaluated their efficacy and safety in the management of patients with unstable angina. Three low molecular weight heparins have so far been tested: nadroparin, dalteparin and enoxaparin. The results of the published trials confirm that the newer compounds are at least as safe and effective as unfractionated heparin, and offer considerable therapeutic advantages. Nevertheless, the different properties of the three compounds and perhaps the different designs of the clinical trials have led to not entirely comparable findings.     

Practical use of low molecular weight heparins in angiology]

The recent development of low molecular weight heparins (LMWH), obtained by the depolymerization of standard non-fractioned heparin (NFH), considerably simplifies the course of anticoagulant treatments. They now allow effectively and safely dealing with the risks of thrombosis, both in hospital and at the patient's home. Their effectiveness for both the prevention and the treatment of thromboembolic accidents has been proved by many clinical trials. In comparison to standard heparin, the LMWHs still have a high anti-Xa activity, but their anti-IIa action is much reduced, thus preserving their antithrombotic power while reducing the hemorrhagic risks. Owing to their better bioavailability and longer half-life, they allow using in priority the subcutaneous route, reducing the frequency of the injections and simplifying surveillance, without impairing the effectiveness of the treatment. The prevention of thrombosis with LMWHs requires one daily subcutaneous dose. The control of the anti-Xa activity is not necessary for the doses used. Prior to initiating a curative treatment, it is essential to confirm the existence of thrombosis. When the diagnosis is definitive, the three LMWHs currently known are used after reconversion, at a dosage of 100 IU/kg/12 hrs. The anti-Xa activity, in samples taken 3 to 4 hours after the injection, must be maintained between 0.5 and 1 IU anti-Xa/ml. It is prudent to control the platelet level at D5 and D10, although thrombocytopenia is exceptional. The changeover treatment with antivitamins K (AVK), which is essential to prevent the recurrence of venous thrombosis, is initiated very early (2nd or 3rd day).(ABSTRACT TRUNCATED AT 250 WORDS)