Low molecular weight heparin(s)

Application of low molecular weight heparins in umbilical artery thrombosis: A case series and review of the literature

RATIONALE

Low molecular weight heparins are widely used in various thrombotic diseases and exert a preventive effect on thrombosis in high-risk patients. Umbilical artery thrombosis (UAT) is a rare occurrence that is difficult to detect during routine prenatal visits but can lead to adverse perinatal outcomes.

PATIENT CONCERNS

The aim of this study was to elucidate the therapeutic effect of low molecular weight heparins on UAT and to provide a new treatment option for the timing of delivery timing.

DIAGNOSES AND INTERVENTIONS

A retrospective study was conducted on cases involving thrombosis of the umbilical cord enrolled from July 2017 to July 2022. Data were acquired and analyzed from medical records and the final diagnosis was confirmed by histopathology. All included patients received LWMHs therapy after initial diagnosis of UAT.

OUTCOMES

The mean age of the 10 pregnant women recruited into this study was 27.9 ± 4.0 year-of-age; 1 (10%) was elderly. The gestational age at diagnosis was 29.9 ± 3.7 weeks, the gestational age at termination was 36.3 ± 2.5 weeks and the mean gestational age of extension was 6.4 ± 4.2 weeks. Low molecular weight heparin sodium was administered after umbilical artery embolism was detected on ultrasound. The LWMHs treatment received by the included patients in this study was subcutaneous injection. The specific usage varies due to the types of LWMHs. Of the 10 cases, 5 (50%) had fetal distress but all fetuses were born alive without neonatal asphyxia. With regards to delivery mode, 9 pregnancies were terminated by cesarean section.

LESSON

Early anticoagulant treatment with LWMHs may improve pregnancy outcomes. The timing and mode of termination of pregnancy should be determined according to the condition of the mother and the fetus along with the gestational age.

A Nanoscale Tool for Photoacoustic-Based Measurements of Clotting Time and Therapeutic Drug Monitoring of Heparin

Heparin anticoagulation therapy is an indispensable feature of clinical care yet has a narrow therapeutic window and is the second most common intensive care unit (ICU) medication error. The active partial thromboplastin time (aPTT) monitors heparin but suffers from long turnaround times, a variable reference range, limited utility with low molecular weight heparin, and poor correlation to dose. Here, we describe a photoacoustic imaging technique to monitor heparin concentration using methylene blue as a simple and Federal Drug Administration-approved contrast agent. We found a strong correlation between heparin concentration and photoacoustic signal measured in phosphate buffered saline (PBS) and blood. Clinically relevant heparin concentrations were detected in blood in 32 s with a detection limit of 0.28 U/mL. We validated this imaging approach by correlation to the aPTT (Pearson's r = 0.86; p < 0.05) as well as with protamine sulfate treatment. This technique also has good utility with low molecular weight heparin (enoxaparin) including a blood detection limit of 72 μg/mL. We then used these findings to create a nanoparticle-based hybrid material that can immobilize methylene blue for potential applications as a wearable/implantable heparin sensor to maintain drug levels in the therapeutic window. To the best of our knowledge, this is the first use of photoacoustics to image anticoagulation therapy with significant potential implications to the cardiovascular and surgical community.

Heparan sulfate proteoglycans and heparin regulate melanoma cell functions

BACKGROUND

The solid melanoma tumor consists of transformed melanoma cells, and the associated stromal cells including fibroblasts, endothelial cells, immune cells, as well as, soluble macro- and micro-molecules of the extracellular matrix (ECM) forming the complex network of the tumor microenvironment. Heparan sulfate proteoglycans (HSPGs) are an important component of the melanoma tumor ECM. Importantly, there appears to be both a quantitative and a qualitative shift in the content of HSPGs, in parallel to the nevi-radial growth phase-vertical growth phase melanoma progression. Moreover, these changes in HSPG expression are correlated to modulations of key melanoma cell functions.

SCOPE OF REVIEW

This review will critically discuss the roles of HSPGs/heparin in melanoma development and progression.

MAJOR CONCLUSIONS

We have correlated HSPGs' expression and distribution with melanoma cell signaling and functions as well as angiogenesis.

GENERAL SIGNIFICANCE

The current knowledge of HSPGs/heparin biology in melanoma provides a foundation we can utilize in the ongoing search for new approaches in designing anti-tumor therapy. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Anticoagulants: A Review of the Pharmacology, Dosing, and Complications

Anticoagulants remain the primary strategy for the prevention and treatment of thrombosis. Unfractionated heparin, low molecular weight heparin, fondaparinux, and warfarin have been studied and employed extensively with direct thrombin inhibitors typically reserved for patients with complications or those requiring intervention. Novel oral anticoagulants have emerged from clinical development and are expected to replace older agents with their ease of use and more favorable pharmacodynamic profiles. Hemorrhage is the main concerning adverse event with all anticoagulants. With their ubiquitous use, it becomes important for clinicians to have a sound understanding of anticoagulant pharmacology, dosing, and toxicity.

In silico discovery of a compound with nanomolar affinity to antithrombin causing partial activation and increased heparin affinity

The medical and socioeconomic relevance of thromboembolic disorders promotes an ongoing effort to develop new anticoagulants. Heparin is widely used as activator of antithrombin but incurs side effects. We screened a large database in silico to find alternative molecules and predicted d-myo-inositol 3,4,5,6-tetrakisphosphate (TMI) to strongly interact with antithrombin. Isothermal titration calorimetry confirmed a TMI affinity of 45 nM, higher than the heparin affinity (273 nM). Functional studies, fluorescence analysis, and citrullination experiments revealed that TMI induced a partial activation of antithrombin that facilitated the interaction with heparin and low affinity heparins. TMI improved antithrombin inhibitory function of plasma from homozygous patients with antithrombin deficiency with a heparin binding defect and also in a model with endothelial cells. Our in silico screen identified a new, non-polysaccharide scaffold able to interact with the heparin binding domain of antithrombin. The functional consequences of this interaction were experimentally characterized and suggest potential anticoagulant therapeutic applications.

History of heparin

The history of heparin is described from its initial discovery in 1916 to recent developments in knowledge of its mechanism of action and clinical use. Commercial production started soon after its discovery, in the 1920s, and improved purification methods led to animal studies and the first clinical trials in the 1930s. Research into heparin's chemical structure proved difficult, with uncertainty about the uronic acid moiety and the N-acetyl content, but the structure of the basic disaccharide unit was established by the 1960s, though knowledge of the heterogeneity and fine structure of heparin chains continued to accumulate over the next 20 years. In 1976, it was found that only one third of heparin chains bound with high affinity to antithrombin, and subsequent studies identified a unique pentasaccharide sequence, which was essential for antithrombin binding and anticoagulant activity - this pentasaccharide was synthesised in 1983. Clinical usage of heparin continued to increase and two major developments were the use of low- dose heparin for prevention of deep vein thrombosis and pulmonary embolism, and the development of low-molecular-weight heparin as a separate drug.

Heparin characterization: challenges and solutions

Although heparin is an important and widely prescribed pharmaceutical anticoagulant, its high degree of sequence microheterogeneity and size polydispersity make molecular-level characterization challenging. Unlike nucleic acids and proteins that are biosynthesized through template-driven assembly processes, heparin and the related glycosaminoglycan heparan sulfate are actively remodeled during biosynthesis through a series of enzymatic reactions that lead to variable levels of O- and N-sulfonation and uronic acid epimers. As summarized in this review, heparin sequence information is determined through a bottom-up approach that relies on depolymerization reactions, size- and charge-based separations, and sensitive mass spectrometric and nuclear magnetic resonance experiments to determine the structural identity of component oligosaccharides. The structure-elucidation process, along with its challenges and opportunities for future analytical improvements, is reviewed and illustrated for a heparin-derived hexasaccharide.

Analysis and characterization of heparin impurities

This review discusses recent developments in analytical methods available for the sensitive separation, detection and structural characterization of heparin contaminants. The adulteration of raw heparin with oversulfated chondroitin sulfate (OSCS) in 2007–2008 spawned a global crisis resulting in extensive revisions to the pharmacopeia monographs on heparin and prompting the FDA to recommend the development of additional physicochemical methods for the analysis of heparin purity. The analytical chemistry community quickly responded to this challenge, developing a wide variety of innovative approaches, several of which are reported in this special issue. This review provides an overview of methods of heparin isolation and digestion, discusses known heparin contaminants, including OSCS, and summarizes recent publications on heparin impurity analysis using sensors, near-IR, Raman, and NMR spectroscopy, as well as electrophoretic and chromatographic separations.

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An assessment of polydispersed species in unfractionated and low molecular weight heparins by diffusion ordered nuclear magnetic resonance spectroscopy method

The primary goal of this project is to extend a (1)H NMR based method, which combines elements of separation on the basis of molecular size with the information specific to (1)H-1D NMR, to the assessment of the heparin contaminant oversulfated chondroitin sulfate (OSCS) and process related impurity dermatan sulfate (DS), and their polydisperse degradation products in samples of unfractionated heparins (UFHs) and low molecular weight heparins (LMWHs) used as the active pharmaceutical ingredients (APIs) in finished pharmaceutical products. The method has been briefly introduced by us in a recent contribution (vide infra). We propose a labelling of the N-acetyl peaks in the (1)H NMR spectra of the UFHs and LMWHs with the parameter D(i), the translational diffusion coefficient available from DOSY NMR. It is shown how DOSY can be applied for screening lots of unfractionated and depolymerised heparins for obtaining molecular size information for heparins and any impurities when using (1)H NMR. The evidence has been presented that title method can be applied as a routine means for assessment of the OSCS and DS contaminants and the polydisperse chemical entities present in the UFHs and LMWHs used as the APIs in heparin pharmaceuticals.

Lessons learned from the contamination of heparin

Heparin is unique as one of the oldest drugs currently still in widespread clinical use as an anticoagulant, a natural product, one of the first biopolymeric drugs, and one of the few carbohydrate drugs. Recently, certain batches of heparin have been associated with anaphylactoid-type reactions, some leading to hypotension and death. These reactions were traced to contamination with a semi-synthetic oversulfated chondroitin sulfate (OSCS). This Highlight reviews the heparin contamination crisis, its resolution, and the lessons learned. Pharmaceutical scientists now must consider dozens of natural and synthetic heparinoids as potential heparin contaminants. Effective assays, which can detect both known and unknown contaminants, are required to monitor the quality of heparin. Safer and better-regulated processes are needed for heparin production.

Oversulfated chondroitin sulfate: impact of a heparin impurity, associated with adverse clinical events, on low-molecular-weight heparin preparation

Heparin, a widely used anticoagulant, is being rapidly displaced by low-molecular-weight heparins. Recently, certain lots of heparin have been associated with anaphylactoid-type reactions resulting from contamination with oversulfated chondroitin sulfate. This impurity has also contaminated low-molecular-weight heparins obtained by chemical and enzymatic depolymerization of heparin. The sensitivity of oversulfated chondroitin sulfate to five different depolymerization processes similar to ones used in preparing low-molecular-weight heparins is reported.

Low molecular weight heparins: a developmental perspective

Low molecular weight heparins (LMWHs) are now universally accepted as drugs of choice for post-surgical prophylaxis of deep vein thrombosis (DVT). Currently these agents are also being developed for the treatment of thrombosis and various cardiovascular indications. Due to manufacturing differences, each of the LMWHs exhibits a distinct pharmacological and biochemical profile. The specific activity of these agents in the anticoagulant assays ranges from 35 - 45 anti-IIa U/mg, whereas the specific activity in terms of anti-Xa units is designated as 80 - 145 anti-Xa U/mg. These LMWHs are capable of producing product-specific dose- and time-dependent antithrombotic effects in animal models of thrombosis. While the ex vivo effects are initially present at doses that are antithrombotic, these agents have been found to produce sustained antithrombotic effects without any detectable ex vivo anticoagulant actions. In experimental animal models and in various clinical trials, these agents have also been found to release tissue factor pathway inhibitor (TFPI) after both iv. and sc. administration. Repeated administration of LMWHs produces progressively stronger antithrombotic effects; however, the haemorrhagic responses vary and are largely dependent on the product used. The release of TFPI following iv. and sc. administration in a primate model also demonstrates product individuality and the relevance of this inhibitor to the actions of LMWHs. Furthermore, repeated administration, mimicking the post-surgical prophylaxis of DVT, leads to product-based augmentation of the antithrombotic or haemorrhagic effects. Antithrombotic and haemorrhagic studies are discussed, comparing the pharmacological profile of some of the available LMWHs. Product individuality, in terms of relative potency in different assays and the failure of standardisation protocols to provide any guidelines for product substitution and prediction of the clinical effects, is also addressed.

Activity of a synthetic hexadecasaccharide (SanOrg123781A) in a pig model of arterial thrombosis

The activity of SanOrg123781A, a new synthetic antithrombotic drug inhibiting both factor Xa and thrombin through antithrombin (AT), was compared to that of unfractionated heparin (UFH) and of the synthetic pentasaccharide (fondaparinux, SP) in an ex vivo arterial thrombosis model in the pig. Six groups of four pigs were administered intravenously with SanOrg123781A (1, 3, 10 and 30 nmol kg(-1)), UFH (30 nmol kg(-1)) or SP (30 nmol kg(-1)). In this arterial model in which platelet thrombus was formed on a thrombogenic surface under a constant high shear rate, UFH and SP had moderate antithrombotic effects while SanOrg123781A exhibited a strong, dose-dependent inhibitory activity on platelet adhesion and platelet thrombus formation. In contrast to UFH, SanOrg123781A did not modify the activated partial thromboplastin time (aPTT) even at 30 nmol kg(-1), but strongly inhibited thrombin generation. At the same dose, despite a lower antithrombotic activity than SanOrg123781A, UFH significantly affected all the coagulation parameters. Taken together, these results show that SanOrg123781A, due to its potent and selective antifactor Xa and antifactor IIa activities is a promising new antithrombotic agent even in arterial setting.

Molecular and biochemical profiling of a heparin-derived oligosaccharide, C3

This study was designed to characterize a heparin-derived oligosaccharide (HDO), C3, using chemical and biochemical methods. Although previous studies have suggested C3 as a promising compound in the treatment of Alzheimer's disease (AD), its molecular and biochemical properties are still unknown. In this study, the molecular profiles and anticoagulant effects of C3 were investigated. To characterize the molecular and biochemical properties of C3, gel permeation chromatography (GPC), polyacrylmide gel electrophoresis (PAGE), radiolabeling and anticoagulant assays, such as activated partial thromboplastin time (APTT), Heptest, and anti-factor Xa assay, were used. The GPC profile revealed that C3 was an ultra-low-molecular-weight (MW) heparin mixture. The multiple components in C3 were studied with PAGE analysis. Tritium-labeled C3 exhibited similar biological properties as nonlabeled materials. The biological assays showed that C3 and its components exhibited weak anticoagulant effect. These results demonstrated the applicability of the combination of GPC, PAGE, and coagulation assays to characterize the molecular and biochemical profile of HDO. In addition, the low anticoagulant effect of C3 suggests that this compound could be a relatively low-risk adjunct in the treatment of AD.

A 3.0-kDa low molecular weight heparin promotes gastric ulcer healing in rats

BACKGROUND

Previous studies have shown that intragastric administration of unfractionated heparin enhances gastric ulcer healing in rats. As the large molecule of heparin may be partially degraded in the upper gastrointestinal tract, it is likely that fragments of heparin, derived from the unfractionated parent compound, are involved in the anti-ulcer action in the stomach. Therefore, it is possible that low molecular weight heparin may have a similar ulcer healing effect.

METHODS

Male Sprague-Dawley rats with acetic acid-induced gastric ulcers were given a 3.0-kDa low molecular weight heparin (0.6-6.0 mg/kg) intravenously or intragastrically once daily for 4 days. Ulcer healing, mucosal histological changes, angiogenesis and gastric mucus production both in vivo and in vitro were determined. The bleeding time was measured to indicate the anticoagulation activity.

RESULTS

Both intravenous and intragastric low molecular weight heparin dose dependently accelerated gastric ulcer healing, which was accompanied by a significant increase in mucosal regeneration and proliferation, angiogenesis and mucus content in the stomach. The drug also stimulated the mucus production in MKN-28 cells. Drug administration by either route did not alter the bleeding time in rats.

CONCLUSIONS

A 3.0-kDa low molecular weight heparin possesses an ulcer healing effect similar to that of unfractionated heparin in the stomach of the rat. This smaller molecular drug is superior to the unfractionated form, does not affect the coagulation activity and may show better absorption in the gastrointestinal tract.

Enzymatic preparation of heparin disaccharides as building blocks in glycosaminoglycan synthesis

Pharmaceutical heparin and heparan sulfate, isolated from a side-stream of a commercial heparin manufacturing process, have been enzymatically depolymerzed with heparin lyases obtained from Flavobacterium heparinun. Heparin afforded a trisulfated disaccharide product that was recovered from the reaction mixture using gel permeation chromatography. Heparan sulfate afforded unsulfated disaccharide that was conveniently recovered from the product mixture by ion exchange chromatography. Both disaccharides were obtained in gram amounts at 90% or higher purity. Both enzymatically prepared disaccharides were chemically protected to prepare building blocks required for the future chemical synthesis of therapeutically valuable heparin oligosaccharides.

Immobilization of recombinant heparinase I fused to cellulose-binding domain

Immobilization of biologically active proteins is of great importance to research and industry. Cellulose is an attractive matrix and cellulose-binding domain (CBD) an excellent affinity tag protein for the purification and immobilization of many of these proteins. We constructed two vectors to enable the cloning and expression of proteins fused to the N- or C-terminus of CBD. Their usefulness was demonstrated by fusing the heparin-degrading protein heparinase I to CBD (CBD-HepI and HepI-CBD). The fusion proteins were over-expressed in Escherichia coli under the control of a T7 promoter and found to accumulate in inclusion bodies. The inclusion bodies were recovered by centrifugation, the proteins were refolded and recovered on a cellulose column. The bifunctional fusion protein retained its abilities to bind to cellulose and degrade heparin. C-terminal fusion of heparinase I to CBD was somewhat superior to N-terminal fusion: Although specific activities in solution were comparable, the latter exhibited impaired binding capacity to cellulose. CBD-HepI-cellulose bioreactor was operated continuously and degraded heparin for over 40 h without any significant loss of activity. By varying the flow rate, the mean molecular weight of the heparin oligosaccharide produced could be controlled. The molecular weight distribution profiles, obtained from heparin depolymerization by free heparinase I, free CBD-HepI, and cellulose-immobilized CBD-HepI, were compared. The profiles obtained by free heparinase I and CBD-HepI were indistinguishable, however, immobilized CBD-HepI produced much lower molecular weight fragments at the same percentage of depolymerization. Thus, CBD can be used for the efficient production of bioreactors, combining purification and immobilization into essentially a single step.

Low molecular weight heparins: differences and similarities in approved preparations in the United States

There is adequate preclinical data to support the differential biochemical and pharmacological behavior of the currently approved low molecular weight heparins (LMWHs) in the United States. Initial studies on the anti-Xa, anti-IIa, and U.S. Pharmacopoeial (USP) potencies have clearly demonstrated differences among these products. Furthermore, the ratios between the anti-X and anti-IIa activities vary from one product to another. This is primarily due to the composition of each product manufactured by using different patented methods. Studies in pharmacologic animal models, using gravimetric dosages or adjusted anti-Xa dosages of the LMWHs, produce product-specific results. The pharmacokinetics and pharmacodynamics of each product also vary markedly and are not predictable on the basis of any pharmacopoeial potency designation. These agents are capable of releasing tissue factor pathway inhibitor (TFPI), an inhibitor of the coagulation process. Its release is also dependent on the type of LMWH. In the United States enoxaprin, dalteparin, and ardeparin have been approved for DVT prophylaxis. Only enoxaparin and dalteparin have been approved for the acute coronary syndrome. Recently the clinical differentiation among these LMWHs has been demonstrated in the treatment of acute coronary syndrome. Similarly, when these drugs are used at high dosages, they are expected to produce product-specific pharmacodynamic effects. It must be noted that while these drugs may be interchangeable at clinically optimized/approved dosages, these drugs are not interchangeable at equivalent anti-Xa dosages. Even at optimized dosages, the clinical provile of each drug may be different. Thus, each of the LMWHs should be considered a distinct entity and their use in a given clinical situation should be validated in proper clinical trials.

Low molecular weight heparin (dalteparin) as adjuvant treatment of thrombolysis in acute myocardial infarction--a pilot study: biochemical markers in acute coronary syndromes (BIOMACS II)

OBJECTIVES

This randomized, double blind, placebo-controlled pilot trial evaluated the effect of dalteparin as an adjuvant to thrombolysis in patients with acute myocardial infarction regarding early reperfusion, recurrent ischemia and patency at 24 h.

BACKGROUND

Low-molecular-weight heparin, given subcutaneously twice daily without monitoring, might be an attractive alternative to conventional intravenous heparin in the treatment of acute myocardial infarction.

METHODS

In 101 patients dalteparin/placebo 100 IU/kg was given just before streptokinase and a second injection 120 IU/kg after 12 h. Monitoring with continuous vector-ECG was done to obtain signs of early reperfusion and later ischemic episodes. Blood samples for myoglobin were obtained at start and after 90 min to evaluate signs of reperfusion. Coronary angiography was performed after 20-28 h to evaluate TIMI-flow in the infarct-related artery.

RESULTS

Dalteparin added to streptokinase tended to provide a higher rate of TIMI grade 3 flow in infarct-related artery compared to placebo, 68% versus 51% (p = 0.10). Dalteparin had no effects on noninvasive signs of early reperfusion. In patients with signs of early reperfusion, there seemed to be a higher rate of TIMI grade 3 flow, 74% versus 46% (myoglobin) (p = 0.04) and 73% versus 52% (vector-ECG) (p = 0.11). Ischemic episodes 6-24 h. after start of treatment were fewer in the dalteparin group, 16% versus 38% (p = 0.04).

CONCLUSIONS

When dalteparin was added as an adjuvant to streptokinase and aspirin, there were tendencies for less ECG monitoring evidence of recurrent ischemia and better patency at 24 h, warranting further study.

Current Clinical Practice: Low-Molecular-Weight Heparins in The Prophylaxis and Treatment of Thrombo-Embolic Disease

Low-Molecular-Weight Heparin (LMWH) fractions are prepared from standard unfractionated heparin (UFH) and are thus similar to it in many aspects. The major advantages of LMWH are improved efficacy and safety, longer half-life and reduced need for laboratory monitoring. In addition, the dangers of UFH administered by continuous infusion in the hospital setting are often not fully appreciated and the necessary monitoring and dosage adjustment poorly carried out resulting in inadequate doses being given. LMWHs are the drug of choice in many clinical situations. Four LMWHs are now licensed in the UK for prophylaxis of venous thrombo-embolism during or after surgery (Certoparin, Dalteparin [Fragmin], Enoxaparin [Lovenox/Clexane] and Tinzaparin [Inno-hep]; a fifth is licensed but not currently available in the UK. Dalteparin, Enoxaparin and Tinzaparin are licensed for the treatment of Deep Vein Thrombosis (DVT), and Tinzaparin additionally for the treatment of Pulmonary Embolism (PE), but so far none is licensed for use in pregnancy or paediatrics.

Monitoring of low-molecular-weight heparins in cardiovascular disease

Thrombin generation is a key event in the pathophysiology of coronary syndromes and provides the rationale for treatment with anticoagulants. Unlike standard heparin, low-molecular-weight heparin (LMWH) has little effect on activated partial thromboplastin time. LMWH treatment has been monitored by measurement of anti-Factor Xa activity, but this may not accurately reflect the anticoagulant action because LMWHs also inhibit Factor II. The Heptest is a clotting assay that is sensitive to both anti-Xa and anti-IIa activity, as well as inhibition of the extrinsic pathway by LMWH-stimulated release of tissue factor pathway inhibitor. The plasma thrombin neutralization assay has also been used to measure LMWH and to detect low concentrations to which chromogenic assays are insensitive. In the clinical setting, monitoring the anti-Xa activity in patients treated with LMWH after acute deep vein thrombosis offered no advantages over a standard weight-adjusted dose. Moreover, in acute coronary syndromes there is no increase in major hemorrhage rates with weight-adjusted LMWH. Monitoring of LMWH concentrations may be advisable in the presence of comorbid conditions carrying an increased risk of hemorrhage, such as renal disease, advanced age, severe over- or underweight, or a history of previous bleeding episodes.

Mechanism of factor IXa inhibition by antithrombin in the presence of unfractionated and low molecular weight heparins and fucoidan

Heparin exerts its anticoagulant activity by catalysing the inhibition of coagulation proteases by antithrombin (AT). Its main target is thrombin but it also catalyses the inhibition of the other serine-proteases of the coagulation cascade, such as factor IXa (fIXa). The aim of this study was to compare the catalysis of inhibition of blood fIXa by antithrombin in the presence of several sulfated polysaccharides with anticoagulant activity, i.e. heparin, three widely used in therapeutics low molecular weight heparins (LMWH) and fucoidan. Plots of the second-order rate constants of the fIXa-antithrombin reaction vs. the concentration of added heparin and LMWH are bell-shaped and fit the kinetic model established for thrombin-antithrombin reaction by Jordan R., Beeler D., Rosenberg R. (1979) J. Biol. Chem., 254, 2902-2913. In the ascending branch, the catalyst (C) binds quickly to the inhibitor (I) to form a catalyst-inhibitor (CI) complex which is more reactive towards the enzyme (E) than the free inhibitor, leading to the formation of an inactive enzyme-inhibitor complex (EI) and the release of free catalyst, in a rate-limiting second step. After a maximum corresponding to an optimal catalyst concentration, the decrease in the reaction rate was in keeping with the formation of a catalyst-enzyme (CE) complex, whose inactivation by the CI complex was slower than that of the free enzyme. Maximum second-order rate constants for the inhibition of fIXa by AT were 105, 6.8, 12.24 and 22 microM-1 min-1 with heparin, Enoxaparin, Fraxiparin and Fragmin, respectively, leading to 3500-, 225-, 405- and 728-fold increases in the inhibition rate in the absence of polysaccharide, respectively. Fucoidan yielded 23-fold increase in the fIXa-antithrombin interaction rate. The kinetic profiles obtained with this polysaccharide exhibited ascending branch which correlated well with the kinetic model based on the formation of binary complexes (CI or CE). Fucoidan was covalently conjugated with a fluorescent probe (DTAF) and used in conjunction with fluorescence anisotropy to follow its binding to antithrombin, heparin cofactor II (HCII), thrombin and fIXa. The binding of fucoidan to these proteins occurred with low affinities when compared to heparin and LMWH. Fucoidan had higher affinity for the inhibitor HCII compared to antithrombin and enzymes. These data suggest that binding of heparins and fucoidan to the inhibitor (CI) is required for the polysaccharide-dependent enhancement in the rate of neutralization of the enzyme by the inhibitor.

Low-molecular-weight heparins in the treatment of deep-vein thrombosis

OBJECTIVE

To compare the characteristics and clinical efficacy of low-molecular-weight heparins (LMWHs) and unfractionated heparin (UFH) in the treatment of deep-vein thrombosis (DVT). Adverse effects, dosing, and cost issues are also discussed.

DATA SOURCES

A MEDLINE search (January 1984-October 1997) was used to identify pertinent French and English literature, including clinical trials and reviews on LMWHs and their use in DVT.

STUDY SELECTION

Trials comparing dalteparin, enoxaparin, tinzaparin, and nadroparin with UFH were selected. As studies were numerous, only randomized trials including more than 50 patients were reviewed. Moreover, all patients studied had a first episode of symptomatic DVT confirmed by objective tests (i.e., venography, duplex ultrasonography, impedance plethysmography). Clinical efficacy and safety of LMWHs were assessed in these trials.

DATA EXTRACTION

Results pertaining to venographic assessment, recurrent thromboembolism, total mortality, and bleeding complications were extracted from the selected studies.

DATA SYNTHESIS

Compared with UFH, LMWHs have a longer plasma half-life, better subcutaneous bioavailability, more predictable anticoagulant response, and require less intense laboratory monitoring. Most trials demonstrate comparable effects on thrombus extension and incidence of recurrent thromboembolism. Compared with UFH, LMWHs do not alter total mortality. Although animal trials predict a lower hemorrhagic potential for LMWHs, the incidence of bleeding complications is generally similar to that observed with UFH. Outpatient management of DVT with LMWHs has shown comparable safety and efficacy with inpatient UFH use but a shorter hospital stay.

CONCLUSIONS

Because LMWHs are as safe and as effective as UFH, and because of their more convenient method of administration, they can be considered valuable alternatives for the treatment of DVT. Savings generated by less intensive laboratory monitoring and the possibility of early hospital discharge and outpatient therapy may outweight the higher acquisition cost of LMWHs.

Low molecular weight heparin(oid)s. Clinical investigations and practical recommendations

Unfractionated heparin (UFH) is traditionally used for prevention and treatment of thrombosis. However, its use is associated with a clinically relevant bleeding risk. Low molecular weight heparin(oid) [LMWH] preparations have been designed to improve upon the efficacy and safety ratio of UFH. They have been investigated in clinical studies following the favourable outcome of extensive animal experimentation to determine their efficacy in the prevention and treatment of venous thromboembolism and in arterial thrombotic conditions such as ischaemic stroke, percutaneous transluminal coronary angioplasty (PTCA) and unstable angina. Indeed, an improved efficacy/safety ratio of LMWHs in the prevention of postoperative venous thrombosis in high risk orthopaedic surgery patients has been observed as compared to UFH prophylaxis. No significant differences with respect to antithrombotic efficacy and bleeding complications were observed in patients with relatively lower risk such as in those undergoing general surgery. Subsequently, these agents have been investigated for the treatment of venous thromboembolism. The results of a series of clinical trials reveal that LMWHs are at least as safe and effective as UFH for initial treatment, with the additional advantage of the possibility of home treatment without the requirement of laboratory control and with a reduced risk of heparin-induced thrombocytopenia. Preliminary data suggest that LMHWs may be suitable for thromboprophylaxis in neurosurgery and stroke patients; in addition, they may have a place in the treatment of patients with acute stroke, unstable angina and individuals in the post-myocardial infarction stage. However, additional confirmatory data for these potential indications are required before definite recommendations can be given. LMWH compounds have at least a similar efficacy and safety as UFH in haemodialysis. In addition, they simplify the anticoagulant regimen because of the efficacy of a single predialysis bolus injection.