Standardization of prothrombin time for laboratory control of oral anticoagulant therapy

Acute Ischemic Stroke and Heart Failure: Stroke Risk Factors Associated with Exclusion from Thrombolytic Therapy

Objective: Acute ischemic stroke (AIS) patients with congestive heart failure (HF) that present with various risk factors are less likely to receive recombinant tissue plasminogen activator (rtPA). The risk factors associated with excluding AIS patients with congestive heart failure (AIS-HF) from rtPA therapy have not been fully established. Methods: Retrospective data for 5469 AIS patients comprised of 590 AIS patients with HF and 4879 AIS patients without HF were collected from a regional stroke registry between January 2010 and June 2016. Baseline risk factors were analyzed using logistic regression analysis to determine the risk factors associated with rtPA exclusion in AIS-HF patients. Results: In the adjusted analysis, AIS-HF patients that that did not receive rtPA were more likely to be older (OR = 0.982, 95% CI, 0.966-1, P = .020), presented with coronary artery disease (OR = 0.618, 95% CI, 0.391-0.98, P = .040), and with an elevated INR (OR = 0.326, 95% CI, 0.129-0.82, P = .018). AIS-HF patients that were included for rtPA therapy were more likely to show improvement in ambulatory status (OR = 1.69, 95% CI, 1.058-2.7, P = .028). The discriminating power of the model was strong with an area under the curve (AUROC) = 0.668 (95% CI, 0.611-0.724, P < .001). Conclusion: Our study establishes the associations between stroke risk factors and exclusion from rtPA therapy. This finding suggests the need to develop management strategies for older HF patients with carotid artery disease and an elevated INR to improve their eligibility for rtPA treatment following an acute ischemic stroke.

A review of the two major regulatory pathways for non-proprietary low-molecular-weight heparins

With the expiry or pending expiry of originator low-molecular-weight heparin (LMWH) patents, pharmaceutical companies have invested in developing non-proprietary versions of LMWHs. LMWHs are manufactured by depolymerising highly purified unfractionated heparin. In contrast to traditional synthetic drugs with well-defined chemical structures, LMWHs contain complex oligosaccharide mixtures and the different manufacturing processes for LMWHs add to the heterogeneity in their physicochemical properties such that the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) consider existing originator LMWHs to be distinct medicinal entities that are not clinically interchangeable. The FDA views LMWHs as drugs and has approved two non-proprietary (generic) LMWHs, using the Abbreviated New Drug Application pathway. In contrast, the World Health Organization and the EMA view LMWHs as biological medicines. Therefore, the EMA and also the Scientific and Standardization Subcommittee on Anticoagulation of the International Society on Thrombosis and Haemostasis and the South Asian Society of Atherosclerosis and Thrombosis have all published specific guidelines for assessing non-proprietary (biosimilar) LMWHs. This manuscript reviews why there are two distinct pathways for approving non-proprietary LMWHs. Available literature on non-proprietary LMWHs approved in some jurisdictions is also reviewed in order to assess whether they satisfy the requirements for LMWHs in the three guidance documents. The review also highlights some of the significant difficulties the two pathways pose for manufacturers and an urgent need to develop a consensus governing the manufacture and regulation of non-proprietary LMWHs to make them more widely available.

Isolation and Characterization of Heparin From Tuna Skins

This study characterized heparin isolated from tuna skins. Glycosaminoglycans were isolated from tuna skin after digestion using anion exchange resin. Heparin was eluted from the resin by sodium chloride gradient and was further fractionated by acetone fractionation. Anticoagulant activity was determined using the activated partial thromboplastin time and Heptest assays. Potency was determined using amidolytic antifactor IIa and antifactor Xa assays. The presence of heparin in the extracted tuna skin glycosaminoglycans was confirmed using13C-nuclear magnetic resonance. The activated partial thromboplastin time and Heptest clotting times were doubled at concentrations of about 4 and 1 µg/mL, respectively. The clotting time prolongation and antiprotease activity induced by tuna heparin was readily neutralized by 25 µg/mL protamine sulfate. These results demonstrate that biologically active heparin with properties similar to clinical grade heparin can be derived from tuna skin, a raw material with otherwise relatively little economic value.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Antithrombin-binding oligosaccharides: structural diversities in a unique function?

Heparin-antithrombin interaction is one of the most documented examples of heparin/protein complexes. The specific heparin sequence responsible for the binding corresponds to a pentasaccharide sequence with an internal 3-O-sulfated glucosamine residue. Moreover, the position of the pentasaccharide along the chain as well as the structure of the neighbor units affects the affinity to antithrombin. The development of separation and purification techniques, in conjunction with physico-chemical approaches (mostly NMR), allowed to characterize several structural variants of antithrombin-binding oligosaccharides, both in the free state and in complex with antithrombin. The article provides an overview of the studies that lead to the elucidation of the mechanism of interaction as well as acquiring new knowledge in heparin biosynthesis.

Differentiating chondroitin sulfate glycosaminoglycans using collision-induced dissociation; uronic acid cross-ring diagnostic fragments in a single stage of tandem mass spectrometry

The stereochemistry of the hexuronic acid residues of the structure of glycosaminoglycans (GAGs) is a key feature that affects their interactions with proteins and other biological functions. Electron based tandem mass spectrometry methods, in particular electron detachment dissociation (EDD), have been able to distinguish glucuronic acid (GlcA) from iduronic acid (IdoA) residues in some heparan sulfate tetrasaccharides by producing epimer-specific fragments. Similarly, the relative abundance of glycosidic fragment ions produced by collision-induced dissociation (CID) or EDD has been shown to correlate with the type of hexuronic acid present in chondroitin sulfate GAGs. The present work examines the effect of charge state and degree of sodium cationization on the CID fragmentation products that can be used to distinguish GlcA and IdoA containing chondroitin sulfate A and dermatan sulfate chains. The cross-ring fragments (2,4)A(n) and (0,2)X(n) formed within the hexuronic acid residues are highly preferential for chains containing GlcA, distinguishing it from IdoA. The diagnostic capability of the fragments requires the selection of a molecular ion and fragment ions with specific ionization characteristics, namely charge state and number of ionizable protons. The ions with the appropriate characteristics display diagnostic properties for all the chondroitin sulfate and dermatan sulfate chains (degree of polymerization of 4-10) studied.

Diagnosis and treatment of disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is a condition in which systemic activation of coagulation without a specific localization occurs, resulting in extensive formation of intravascular fibrin, particularly in small and midsize vessels. Disseminated intravascular coagulation may lead to several altered coagulation parameters, including a low platelet count, abnormal global clotting assays, low levels of physiological anticoagulant proteases, or increased fibrin degradation products. Also, more complex assays for activation of coagulation factors or pathways may indicate involvement of these molecules in DIC. None of these tests alone, however, can accurately ascertain or rebuff a diagnosis of DIC. Nonetheless, a combination of readily available routine assays may be instrumental in establishing a diagnosis of DIC and can also be useful to point to a subset of patients with DIC that may need definite, often costly, interventions in the hemostatic system. Current insights on relevant etiological pathways that may contribute to the occurrence of DIC have led to innovative therapeutic and adjunctive approaches to patient with DIC. Management options directed at the amelioration of hemostatic activation may tentatively be indicated and were found to be advantageous in experimental and clinical investigations. These treatments encompass elimination of tissue factor-mediated thrombin generation or restitution of normal anticoagulant function.

Four factor prothrombin complex concentrate (human): review of the pharmacology and clinical application for vitamin K antagonist reversal

Vitamin K antagonists (VKAs) have been used for decades for the treatment and prophylaxis of thromboembolic events. Due to their wide range of therapeutic indications, they are the most prescribed oral anticoagulant worldwide. However, they are associated with bleeding complications due to their narrow therapeutic range, variability in individual dose responses and laboratory monitoring, and overdoses. Despite off-label use of 3-factor prothrombin complex concentrates and recombinant activated factor VII, until recently, vitamin K and plasma were the only recommended therapeutic options for reversing VKAs in the USA. In 2013, a 4-factor prothrombin complex concentrate (4F-PCC) was approved in the USA for VKA reversal in patients with bleeding or requiring emergency surgery and invasive procedure. Recent randomized controlled clinical trials have shown that 4F-PCC (Kcentra™) is non-inferior for hemostatic efficacy and superior for international normalized ratio correction as compared to plasma and has a similar safety profile.

Comparison between the conventional method and a portable device for determination of INR

CONTEXT: Anticoagulation with warfarin is considered the appropriate treatment for venous thromboembolism and other thrombotic pathologies. Regular INR control is required for dosage adjustment and therapeutic control. Use of portable monitoring systems optimizes management of these patients. OBJECTIVE: To compare INR measurements taken using the portable Coaguchek XS system in capillary blood with the standard laboratory method using venous blood. METHOD: Fifty-two samples each of venous and capillary blood were collected from nineteen patients on warfarin, who had been admitted to the Hospital da Beneficência Portuguesa de São Paulo, and analyzed using the conventional method and the Coaguchek XS system, respectively. RESULTS: Spearman's correlation coefficient ® for the overall performance of the two methods was 0.978 (p<0.0001; 95%CI 0.961-0.988). The Kappa measure of agreement for all patients was 76.8% (p<0.001; IC: 95% 0.975-0.561). Mean INR according to the Coaguchek XS system underestimated the values provided by the conventional method by -0.01 INR points, with a standard error of 0.342. Results for INR values greater than 3.5 were satisfactory with a correlation coefficient of 0.71, but without statistical significance (p>0.714). CONCLUSIONS: The Coaguchek XS system can be used to monitor prothrombin time in patients on oral anticoagulants, provided INR values greater than 3.5 are confirmed using the conventional laboratory method.

The utility of a diagnostic scoring system for disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is an acquired syndrome characterized by microvascular thrombosis resulting from systemic activation of coagulation, and it should be diagnosed and treated as early as possible. No single test is sufficiently accurate to establish or rule out a diagnosis of DIC. Therefore, diagnostic scoring uses a combination of several laboratory tests. Three diagnostic scoring systems are now available and validated. Because it is not easy to assess the superiority or inferiority of these scoring systems, it may be better to select the scoring system depending on the need for an early or affirmative diagnosis of DIC.

Evaluation of the Prothrombin Time for Measuring Rivaroxaban Plasma Concentrations Using Calibrators and Controls

This study evaluated the prothrombin time (PT) assay for the measurement of plasma concentrations of rivaroxaban using calibrators and controls. The intra- and interlaboratory precision of the measurement was investigated in a field trial involving 21 laboratories. Each laboratory was provided with rivaroxaban calibrators and control plasma samples containing different concentrations of rivaroxaban, and PT reagents. The evaluation was carried out over 2 consecutive weeks using centrally provided and local PT reagents. A calibration curve was produced each day (for inter-run precision), and day-to-day precision was evaluated by testing 3 control plasma samples. A large interlaboratory variation (in seconds) was observed with local PT reagents. The results were less variable when expressed as rivaroxaban concentrations (ng/mL) or when central PT reagent was used (STA Neoplastine CI Plus). The widely available PT assay, in conjunction with rivaroxaban calibrators, may be useful for the measurement of peak plasma levels of rivaroxaban.

Coagulation biomarkers in critically ill patients

This article discusses coagulation biomarkers in critically ill patients where coagulation abnormalities occur frequently and may have a major impact on the outcome. An adequate explanation for the cause is important, since many underlying disorders may require specific treatment and supportive therapy directed at the underlying condition. Deficiencies in platelets and coagulation factors in bleeding patients or patients at risk for bleeding can be achieved by transfusion of platelet concentrate or plasma products, respectively. Prohemostatic treatment may be beneficial in case of severe bleeding, whereas restoring physiological anticoagulant pathways may be helpful in patients with sepsis and disseminated intravascular coagulation.

[Conditions causing copious bleeding important for dental medicine practice]

<Zakljucak> Dobro poznavanje mogucih uzoraka prekomernog krvarenja, kao i stomatoloskih postupaka u toku oralnohirurskih intervencija kod obolelih od trombocitopenije, hemofilije, u slucaju snizene koncentracije faktora zavisnih od vitamina K i predozirane antitrombotske terapije, omogucava adekvatnu i blagovremenu oralnohirursku hemostazu u skladu sa predvidjenim protokolom lecenja. Ukoliko je, medjutim, oralnohirurska intervencija propracena produzenim krvarenjem u trajanju od nekoliko sati ili dana, bez pouzdanih anamnestickih podataka i pismene medicinske dokumentacije, problem postaje veliki. U takvim situacijama, podsecanje na stanja koja izazivaju prekomerno krvarenje, kao i na stomatoloske postupke u toku oralnohirurskih intervencija kod takvih bolesnika, moze biti dragocen doprinos dobroj stomatoloskoj praksi.

Antithrombin-binding octasaccharides and role of extensions of the active pentasaccharide sequence in the specificity and strength of interaction. Evidence for very high affinity induced by an unusual glucuronic acid residue

The antithrombotic activity of low molecular weight heparins (LMWHs) is largely associated with the antithrombin (AT)-binding pentasaccharide sequence AGA(*)IA (GlcN(NAc/NS,6S)-GlcA-GlcN(NS,3,6S)-IdoUA(2S)-GlcN(NS,6S)). The location of the AGA(*)IA sequences along the LMWH chains is also expected to influence binding to AT. This study was aimed at investigating the role of the structure and molecular conformation of different disaccharide extensions on both sides of the AGA(*)IA sequence in modulating the affinity for AT. Four high purity octasaccharides isolated by size exclusion chromatography, high pressure liquid chromatography, and AT-affinity chromatography from the LMWH enoxaparin were selected for the study. All the four octasaccharides terminate at their nonreducing end with 4,5-unsaturated uronic acid residues (DeltaU). In two octasaccharides, AGA(*)IA was elongated at the reducing end by units IdoUA(2S)-GlcN(NS,6S) (OCTA-1) or IdoUA-GlcN(NAc,6S) (OCTA-2). In the other two octasaccharides (OCTA-3 and OCTA-4), AGA(*)IA was elongated at the nonreducing side by units GlcN(NS,6S)-IdoUA and GlcN(NS,6S)-GlcA, respectively. Extensions increased the affinity for AT of octasaccharides with respect to pentasaccharide AGA(*)IA, as also confirmed by fluorescence titration. Two-dimensional NMR and docking studies clearly indicated that, although elongation of the AGA(*)IA sequence does not substantially modify the bound conformation of the AGA(*)IA segment, extensions promote additional contacts with the protein. It should be noted that, as not previously reported, the unusual GlcA residue that precedes the AGA(*)IA sequence in OCTA-4 induced an unexpected 1 order of magnitude increase in the affinity to AT with respect to its IdoUA-containing homolog OCTA-3. Such a residue was found to orientate its two hydroxyl groups at close distance to residues of the protein. Besides the well established ionic interactions, nonionic interactions may thus contribute to strengthen oligosaccharide-AT complexes.

Proteoglycanomics: tools to unravel the biological function of glycosaminoglycans

Glycosylation is the most frequent PTM and contributes significantly to the function of proteins depending on the type of glycosylation. Especially glycan structures like the glycosaminoglycans are considered to constitute themselves the major function of the glycoconjugate which is therefore termed proteoglycan. Here we review recent views on and novel tools for analysing the proteoglycanome, which are directly related to the type of glycanation under investigation. We define the major function of the proteoglycanome to be its interaction with various proteins in many different (patho-)physiological conditions. This is exemplified by the differential glycosaminoglycan-interactome of healthy versus arthritic patient sera.

Characterization of di- and monosulfated, unsaturated heparin disaccharides with terminal N-sulfated 1,6-anhydro-β-d-glucosamine or N-sulfated 1,6-anhydro-β-d-mannosamine residues

Modified heparin disaccharides were obtained by the alkaline treatment of a solution containing the disulfated heparin disaccharide DeltaHexA-alpha-(1-->4)-D-GlcNSO(3),6SO(3). Their structures were characterized by one- and two-dimensional NMR spectroscopy: DeltaHexA-alpha-(1-->4)-1,6-anhydro-GlcNSO(3), DeltaHexA-alpha-(1-->4)-1,6-anhydro-ManNSO(3) and DeltaHexA-alpha-(1-->4)-ManNSO(3),6OSO(3). NMR spectroscopy, in combination with HPLC, provided the composition of the mixture. Characteristic NMR signals of the disaccharides were identified, even at low levels, in a high field of (1)H-(13)C correlation NMR spectra (HSQC) of a low molecular weight heparin (LMWH) obtained by beta-elimination (alkaline hydrolysis) of heparin benzyl ester, providing a more complete structural profile of this class of compounds.

Quantitative determination of disaccharide content in digested unfragmented heparin and low molecular weight heparin by direct-infusion electrospray mass spectrometry

Heparins and low molecular weight heparins (LMWHs) are heterogeneous glycosaminoglycans derived from natural sources that are prescribed as anticoagulants. In this work, a direct-infusion electrospray ionization mass spectrometry (ESI-MS) method was applied to the quantitative analysis of known disaccharides in various native heparins and LMWHs after digestion with heparinase enzymes. Disaccharide deltaUA2S-->GlcNS6S was found to compose the majority of all samples analyzed (81-88%). The values were significantly higher than those reported by previously published methods. The disaccharide isomer pair deltaUA-->GlcNS6S/deltaUA2S-->GlcNS was also detected in all samples at lower levels (11-19%). While digestion with heparinases I and II revealed a limited number of disaccharides, the addition of heparinase III to digests led to the detection of disaccharide deltaUA2S-->GlcNAc6S in native porcine heparin. This result indicated the importance of utilizing all three heparinases to gain maximum information when analyzing heparin and LMWH digests. This method displayed good between-day (4-6%) and between-digest (1-2%) reproducibility in separate experiments. To determine if the digestion matrix was suppressing the signal of low-abundance disaccharides, several disaccharides were exogenously added at low levels (1-10 pmol/mg) to a quenched digest reaction. Analysis revealed that low level disaccharides were detectable in this matrix above the limits of detection (0.1-0.2 pmol/mg) and quantitation (0.2-0.7 pmol/mg). While this method was unable to distinguish between disaccharide isomers, it utilized simple mass spectrometry instrumentation to provide useful quantitative data for characterizing preparations of native heparin and LMWH, which could be used to compare various marketed preparations of these popular anticoagulants.

Coagulation abnormalities in critically ill patients

Many critically ill patients develop hemostatic abnormalities, ranging from isolated thrombocytopenia or prolonged global clotting tests to complex defects, such as disseminated intravascular coagulation. There are many causes for a deranged coagulation in critically ill patients and each of these underlying disorders may require specific therapeutic or supportive management. In recent years, new insights into the pathogenesis and clinical management of many coagulation defects in critically ill patients have been accumulated and this knowledge is helpful in determining the optimal diagnostic and therapeutic strategy.

Monitoring of heparin and its low-molecular-weight analogs by silicon field effect

Heparin is a highly sulfated glycosaminoglycan that is used as an important clinical anticoagulant. Monitoring and control of the heparin level in a patient's blood during and after surgery is essential, but current clinical methods are limited to indirect and off-line assays. We have developed a silicon field-effect sensor for direct detection of heparin by its intrinsic negative charge. The sensor consists of a simple microfabricated electrolyte-insulator-silicon structure encapsulated within microfluidic channels. As heparin-specific surface probes the clinical heparin antagonist protamine or the physiological partner antithrombin III were used. The dose-response curves in 10% PBS revealed a detection limit of 0.001 units/ml, which is orders of magnitude lower than clinically relevant concentrations. We also detected heparin-based drugs such as the low-molecular-weight heparin enoxaparin (Lovenox) and the synthetic pentasaccharide heparin analog fondaparinux (Arixtra), which cannot be monitored by the existing near-patient clinical methods. We demonstrated the specificity of the antithrombin III functionalized sensor for the physiologically active pentasaccharide sequence. As a validation, we showed correlation of our measurements to those from a colorimetric assay for heparin-mediated anti-Xa activity. These results demonstrate that silicon field-effect sensors could be used in the clinic for routine monitoring and maintenance of therapeutic levels of heparin and heparin-based drugs and in the laboratory for quantitation of total amount and specific epitopes of heparin and other glycosaminoglycans.

GLYCOMICS APPROACH TO STRUCTURE-FUNCTION RELATIONSHIPS OF GLYCOSAMINOGLYCANS

Extracellular modulation of phenotype is an emerging paradigm in this current postgenomics age of molecular and cell biology. Glycosaminoglycans (GAGs) are primary components of the cell surface and the cell-extracellular matrix (ECM) interface. Advances in the technology to analyze GAGs and in whole-organism genetics have led to a dramatic increase in the known important biological role of these complex polysaccharides. Owing to their ubiquitous distribution at the cell-ECM interface, GAGs interact with numerous proteins and modulate their activity, thus impinging on fundamental biological processes such as cell growth and development. Many recent reviews have captured important aspects of GAG structure and biosynthesis, GAG-protein interactions, and GAG biology. GAG research is currently at a stage where there is a need for an integrated systems or glycomics approach, which involves an integration of all of the above concepts to define their structure-function relationships. Focusing on heparin/heparan (HSGAGs) and chondroitin/dermatan sulfate (CSGAGs), this review highlights the important aspects of GAGs and summarizes these aspects in the context of taking a glycomics approach that integrates the different technologies to define structure-function relationships of GAGs.

Properties of recombinant human thromboplastin that determine the International Sensitivity Index (ISI)

Prothrombin Time (PT) clotting tests are widely used to monitor oral anticoagulation therapy and to screen for clotting factor deficiencies. The active ingredient in PT reagents (thromboplastins) is tissue factor, the integral membrane protein that triggers the clotting cascade through the extrinsic pathway. Several years ago, a system for calibrating and using thromboplastin reagents, known as the International Sensitivity Index (ISI) and the International Normalized Ratio (INR), was developed to standardize monitoring of oral anticoagulant therapy. The ISI/INR method, while revolutionizing the monitoring of coumarin therapy, has been criticized for a number of perceived shortcomings. We have undertaken a series of studies aimed at achieving a detailed understanding of which parameters influence the ISI values of thromboplastin reagents, with an ultimate goal of creating 'designer thromboplastins' whose sensitivities to the various clotting factors can be individually tailored. In this study, we demonstrate that ISI values of thromboplastin reagents based on relipidated, recombinant human tissue factor can be controlled by a combination of changes in the phospholipid content (in particular, the levels of phosphatidylserine and phosphatidylethanolamine) and ionic strength. The sensitivity of a given thromboplastin reagent can be increased (i.e. its ISI value decreased) by decreasing the content of phosphatidylserine and/or increasing the ionic strength. The molar ratio of phospholipid to tissue factor, on the other hand, had essentially no impact on ISI value.

Rational design of low-molecular weight heparins with improved in vivo activity

Heparin and low-molecular weight heparins (LMWHs), complex, sulfated polysaccharides isolated from endogenous sources, are potent modulators of hemostasis. Heparin and LMWHs interact with multiple components of the coagulation cascade to inhibit the clotting process. Pharmaceutical preparations of these complex polysaccharides, typically isolated from porcine intestinal mucosa, are heterogeneous in length and composition and, hence, highly polydisperse. Because of the structural heterogeneity of heparin and LMWHs, correlating their activity with a particular structure or structural motif has been a challenging task. Herein, we demonstrate a practical analytical method that enables the measurement of a structural correlate to in vivo anticoagulant function. With this understanding we have developed LMWHs with increased anticoagulant activity and decreased polydispersity. In addition to the pronounced anti-Xa and anti-IIa activity of these LMWHs, we also demonstrate that they possess desirable in vivo pharmacokinetic properties, the ability to cause the release of tissue factor pathway inhibitor (TFPI) from the endothelium, complete bioavailability through s.c. delivery, and the ability to inhibit both venous and arterial thromboses. Importantly, from a clinical safety point of view, unlike LMWHs presently used in the clinic, we show that these LMWHs are rapidly and completely neutralized by protamine. Together, the findings presented herein demonstrate a facile approach for the creation of designer LMWHs with optimal activity profiles.

A novel computational approach to integrate NMR spectroscopy and capillary electrophoresis for structure assignment of heparin and heparan sulfate oligosaccharides

Heparin and heparan sulfate (HS) glycosaminoglycans (GAGs) are cell surface polysaccharides that bind to a multitude of signaling molecules, enzymes, and pathogens and modulate critical biological processes ranging from cell growth and development to anticoagulation and viral invasion. Heparin has been widely used as an anticoagulant in a variety of clinical applications for several decades. The heterogeneity and complexity of HS GAGs pose significant challenges to their purification and characterization of structure-function relationships. Nuclear magnetic resonance (NMR) spectroscopy is a promising tool that provides abundant sequence and structure information for characterization of HS GAGs. However, complex NMR spectra and low sensitivity often make analysis of HS GAGs a daunting task. We report the development of a novel methodology that incorporates distinct linkage information between adjacent monosaccharides obtained from NMR and capillary electrophoresis (CE) data using a property encoded nomenclature (PEN) computational framework to facilitate a rapid and unbiased procedure for sequencing HS GAG oligosaccharides. We demonstrate that the integration of NMR and CE data sets with the help of the PEN framework dramatically reduces the number of experimental constraints required to arrive at an HS GAG oligosaccharide sequence.

Disagreement between bedside and laboratory activated partial thromboplastin time and international normalized ratio for various novel anticoagulants

During studies on warfarin, heparin and various anticoagulants with novel mechanisms of action, the activated partial thromboplastin time (aPTT) and the (apparent) international normalized ratio (INR) from a bedside monitor (Coagucheck Plus(R)) were compared with laboratory assay results. Data were compared using the Bland and Altman method of comparison where systematic differences result in significant slopes of the regression line. During heparin treatment, the bedside monitor largely underestimated the aPTT (slope = -0.80). During treatment with the direct thrombin inhibitor napsagatran (slope = 0.99), the pentasaccharides Org31540/SR90107A (slope = 0.77) and SanOrg34006 (slope = 0.35), and warfarin (slope = 0.60), the bedside monitor underestimated the aPTT at lower aPTT levels, while at higher aPTT levels it overestimated the laboratory values. The bedside monitor slightly overestimated the INR during treatment with warfarin (slope = 0.33). Apparent INR was largely overestimated during treatment with Org31540/SR90107A (slope = 1.38), SanOrg34006 (slope = 0.97), Napsagatran (slope = 1.23), and recombinant tissue factor pathway inhibitor (slope = 1.48, P < 0.001 for all regression lines). These results indicate that a substantial disagreement in aPTT or (apparent) INR exists between the bedside monitor and laboratory assay during treatment with the studied 'classic' and novel anticoagulants. The amount of disagreement depended on the anticoagulant given.

Differentiation of the low-molecular-weight heparins

The three low-molecular-weight heparins (LMWHs) available in the United States have been extensively evaluated for a wide array of indications. Properties associated with one LMWH cannot be assumed to be the same as those associated with another LMWH, as they are different pharmacologic entities. Therefore, therapeutic interchange of these agents is inappropriate. The pharmacokinetic and pharmacodynamic differences among LMWHs can be explained by comparing methods of preparation, molecular structures, half-lives, antithrombin- and non-antithrombin-mediated actions, effect on thrombus, and dosing interval. The Food and Drug Administration-approved indications and their respective levels of clinical evidence further differentiate these agents. A dichotomy in the results of clinical trials has been observed with the LMWHs. As the LMWHs are distinct compounds that each possess unique pharmacokinetic and pharmacodynamic profiles, treatment decisions should be based on the available safety and efficacy data for each LMWH. Agents should be prescribed only for those indications for which they have been shown to be effective and only at dosages that have been studied.

Dosing and monitoring of low-molecular-weight heparins in special populations

As a result of numerous clinical trials and meta-analyses supporting the superior efficacy and relative safety of low-molecular-weight heparins (LMWHs) compared with unfractionated heparin (UFH), LMWHs are emerging as the antithrombotic agents of choice for the prevention and treatment of deep vein thrombosis and pulmonary embolism. In addition, data indicate that enoxaparin given with low-dosage aspirin is more effective than UFH in treating acute coronary syndromes. Anti-Xa activity can be used as a biologic marker of LMWH activity. Because of the more predictable anticoagulant response to subcutaneous administration of LMWHs compared with UFH, routine monitoring of anti-Xa activity in clinically stable adults with uncomplicated disease is not recommended. Because the optimal dosage of LMWHs has not been established for patients with renal insufficiency or extremes of body weight, during pregnancy, or for children, anti-Xa activity monitoring may be warranted in these subsets.

Clinical utilization of the international normalized ratio (INR)

The prothrombin time (PT) is one of the most important laboratory tests to determine the functionality of the blood coagulation system. It is used in patient care to diagnose diseases of coagulation, assess the risk of bleeding in patients undergoing operative procedures, monitor patients being treated with oral anticoagulant (coumadin) therapy, and evaluate liver function. The PT is performed by measuring the clotting time of platelet-poor plasma after the addition of calcium and thromboplastin, a combination of tissue factor and phospholipid. Intra- and interlaboratory variation in the PT was a significant problem for clinical laboratories in the past, when crude extracts of rabbit brain or human placenta were the only source of thromboplastin. The international normalized ratio (INR), developed by the World Health Organization in the early 1980s, is designed to eliminate problems in oral anticoagulant therapy caused by variability in the sensitivity of different commercial sources and different lots of thromboplastin to blood coagulation factor VII. The INR is used worldwide by most laboratories performing oral anticoagulation monitoring, and is routinely incorporated into dosage planning for patients receiving warfarin. Although the recent availability of sensitive PT reagents prepared from recombinant human tissue factor (rHTF) and synthetic phospholipids eliminated many of the earlier problems associated with the use of crude thromboplastin preparations, local instrument variability in the INR still remains a problem. Presently, the use of plasma calibrants seems the best solution to this problem. Standardizing the point-of-care instruments for INR monitoring is another dilemma faced by the industry. Ultimately, new generations of anticoagulant drugs may eliminate the need for laboratory monitoring of anticoagulant therapy.

Low molecular weight heparins and heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) and HIT thrombosis syndrome (HITTS) are immune-mediated complications of clinical use of unfractionated heparin (UFH). The antibody/antigen complex is composed of heparin and platelet factor 4. This complex not only activates platelets but also the clotting system leading to thrombin generation. This explains the thrombosing tendency of these patients, and venous and arterial thromboembolisms are encountered with a morbidity and mortality of about 25-37%. The incidence of HIT is about 3% when UFH is administered therapeutically. The diagnosis is at this time based on clinical observations, especially a sudden, unexplained drop in platelet counts without other reasons. Laboratory tests can be used to confirm the clinical diagnosis, but none of the available tests is 100% reliable. There is no test that will predict HIT and no test that will signal the development of HITTS. Treatment consists of discontinuation of UFH in any form and anticoagulation with danaparoid or r-hirudin, if needed. The use of low molecular weight heparins instead of UFH could largely (not totally) alleviate the problem.