Scientific considerations in the regulatory approval of generic (or biosimilar) version of enoxaparin sodium - A lifesaving carbohydrate polymer

Enoxaparin sodium (Clexane®/Klexane®/Lovenox®) is one amongst the few drugs that have assumed a central role as drug of treatment and/or prevention against thromboembolic complications during COVID-19. The increase in demand resulting in many generic (or biosimilar) versions entering the market has increased the risks of quality and safety (including immunogenicity) related issues. Under the circumstances, development of stringent regulatory approaches has received much attention as investigation of new drug delivery systems for improved therapeutic activity. As one of the measures to increase quality testing and ensure uninterrupted supply of this life-saving drug globally, determination of enoxaparin molecular weight (MW) has been added in the United States Pharmacopoeia (USP) monograph for enoxaparin sodium. In addition, the presence of a unique 1,6-anhydro-ring structure at the reducing end of about 15-25% of the poly (oligo) saccharide chains of the generic (or biosimilar) product has been set as a mandatory requirement. This article presents an overview of the scientific considerations in the quality manufacturing and testing of the generic (or biosimilar) enoxaparin for regulatory review and approval. In certain cases of strong analytical similarity (structural and functional), abandonment of in vivo testing in animals and humans represents a major advancement in the approval of generic (or biosimilar) version of innovator enoxaparin sodium (lovenox®, injections).

Comparison of Low-Molecular-Weight Heparins Prepared From Ovine Heparins With Enoxaparin

Heparin and its low-molecular-weight heparin derivatives are widely used clinical anticoagulants. These drugs are critical for the practice of medicine in applications, including kidney dialysis, cardiopulmonary bypass, and in the management of venous thromboembolism. Currently, these drugs are derived from livestock, primarily porcine intestine and less frequently bovine intestine and bovine lung. The worldwide dependence on the pig as a single dominant animal species has made the supply chain for this critical drug quite fragile, leading to the search for other sources of these drugs, including the expanded use of bovine tissues. A number of laboratories are now also examining the similarities between heparin and low-molecular-weight heparins prepared from porcine and ovine tissues. This study was designed to compare low-molecular-weight heparin prepared from ovine heparin through chemical β-elimination, a process currently used to prepare the low-molecular-weight heparin, enoxaparin. Using top-down, bottom-up, and compositional analyses as well as bioassays, low-molecular-weight heparin derived from ovine intestine was shown to closely resemble enoxaparin. Moreover, the compositions of daughter low-molecular-weight heparins prepared from three unfractionated ovine parent heparins were compared. Ovine enoxaparins had similar molecular weight and in vitro anticoagulant activities as Lovenox. Some disaccharide compositional, oligosaccharide composition at the reducing and nonreducing ends and intact chain compositional differences could be observed between porcine enoxaparin and ovine low-molecular-weight heparin. The similarity of these ovine and porcine heparin products suggests that their preclinical evaluation and ultimately clinical assessment is warranted.

Polymeric Nanoparticles of Enoxaparin as a Delivery System: In Vivo Evaluation in Normal Rats and in a Venous Thrombosis Rat Model

Enoxaparin is an anticoagulant widely used in the treatment and prophylaxis of deep vein thrombosis (DVT). The subcutaneous route of administration, sometimes in repeated doses during 24 hours, represents a limitation to its use. Thus, the development of a product that can be administered either subcutaneously, in a smaller number of applications becomes a major challenge, with interesting clinical applications. The use of a system for sustained release of drugs can help to meet that goal, by protecting and enabling a gradual released of the agent. This study consisted of the evaluation of in vivo anticoagulant and antithrombotic activity of biodegradable nanoparticles of poly (ε-caprolactone) (PCL) with enoxaparin after subcutaneous injection. The nanoparticles were prepared by the method of double emulsion (w/o/w) and solvent evaporation. Subcutaneous enoxaparin encapsulated in PCL nanoparticles (1000 IU/kg) showed a sustained release in vivo for up to 12 hours (Cmax 0.62 IU/mL) a significantly longer period (P < 0.01) when compared to free enoxaparin (1000 IU/Kg) that disappeared after 9 hours (Cmax 1.50 IU/mL), however with lower anti-Xa activity. The antithrombotic action of enoxaparin-nanoparticles was tested in a DVT model by stasis in rats. There were virtually no formation of venous thrombosis in any of the rats that received enoxaparin encapsulated in nanoparticles (0.03 mg), with a significant difference when compared to groups that received saline (17.2 mg, P < 0.001) and free enoxaparin (2.87 mg, P = 0.001). In summary, enoxaparin-encapsulated in polymeric nanoparticles showed a sustained release for a greater period than that of enoxaparin, and with excellent antithrombotic action. These results corroborate the promising use of pharmacological nanoparticles in clinical practice.

In-vitro suppression of IL-6 and IL-8 release from human pulmonary epithelial cells by non-anticoagulant fraction of enoxaparin

BACKGROUND

Enoxaparin, a mixture of anticoagulant and non-anticoagulant fractions, is widely used as an anticoagulant agent. However, it is also reported to possess anti-inflammatory properties. Our study indicated that enoxaparin inhibits the release of IL-6 and IL-8 from A549 pulmonary epithelial cells. Their release causes extensive lung tissue damage. The use of enoxaparin as an anti-inflammatory agent is hampered due to the risk of bleeding associated with its anticoagulant fractions. Therefore, we aimed to identify the fraction responsible for the observed anti-inflammatory effect of enoxaparin and to determine the relationship between its structure and biological activities.

METHODS

A549 pulmonary epithelial cells were pre-treated in the presence of enoxaparin and its fractions. The levels of IL-6 and IL-8 released from the trypsin-stimulated cells were measured by ELISA. The anticoagulant activity of the fraction responsible for the effect of enoxaparin was determined using an anti-factor-Xa assay. The fraction was structurally characterised using nuclear magnetic resonance. The fraction was 2-O, 6-O or N-desulfated to determine the position of sulfate groups required for the inhibition of interleukins. High-performance size-exclusion chromatography was performed to rule out that the observed effect was due to the interaction between the fraction and trypsin or interleukins.

RESULTS

Enoxaparin (60 μg/mL) inhibited the release of IL-6 and IL-8 by >30%. The fraction responsible for this effect of enoxaparin was found to be a disaccharide composed of α-L-iduronic-acid and α-D-glucosamine-6-sulfate. It (15 μg/mL) inhibited the release of interleukins by >70%. The 6-O sulphate groups were responsible for its anti-inflammatory effect. The fraction did not bind to trypsin or interleukins, suggesting the effect was not due to an artefact of the experimental model.

CONCLUSION

The identified disaccharide has no anticoagulant activity and therefore eliminates the risk of bleeding associated with enoxaparin. Future in-vivo studies should be designed to validate findings of the current study.

Lack of anti-factor Xa assay standardization results in significant low molecular weight heparin (enoxaparin) dose variation in neonates and children

INTRODUCTION

Enoxaparin is a frequently used anticoagulant in children. Unlike in adults, consensus guidelines recommend therapeutic monitoring to a target anti-factor Xa level of 0.5-1 U mL(-1) . Therapeutic ranges are not well correlated with clinical outcomes (e.g. thrombosis or hemorrhage), and assays are not standardized. Owing to limited reagent supplies, our clinical laboratory conducted a validation process and switched anti-FXa assays. Although the assays correlated well with each other, anti-FXa values were, on average, 33% higher with the new assay. The target anti-FXa range was not altered. We evaluated how this change in anti-FXa assays influenced enoxaparin dosing (mg kg(-1) ).

METHODS

Enoxaparin dosing and anti-FXa values for all patients started on enoxaparin for the 6 months before and after assay change were retrospectively compiled and analyzed with a Student's t-test.

RESULTS

One hundred and nine children were started on enoxaparin before assay change, and 104 after assay change. The mean therapeutic enoxaparin dose (mg kg(-1) ) was significantly lower in subjects aged < 3 months (P = 0.01) and 3 months to 2 years (P < 0.0001), but not in subjects aged > 2 years (P = 0.18), after assay change. The median number of enoxaparin dose changes required to achieve the target range was significantly reduced after assay change, from 1 to 0 (P = 0.004).

CONCLUSIONS

The current pediatric practice of dose adjustment to achieve and maintain a target anti-FXa range is vulnerable to assay determination, which may provide false reassurance of efficacy and safety and represent misappropriation of time and resources. These data support a pediatric randomized controlled clinical trial comparing the safety and efficacy of enoxaparin weight-based dosing with or without dose titration based on anti-FXa.

[Comparison of structural characteristics and anticoagulation activity of enoxaparin sodium with different degree of 1,6-anhydro derivatives]

The fine structure of enoxaparin sodium samples with different degree of 1,6-anhydro derivatives were analyzed with polyacrylamide gel electrophoresis, high performance liquid chromatography, ultraviolet spectroscopy, infrared spectroscopy and nuclear magnetic resonance spectroscopy. A further study of anticoagulation activity of enoxaparins was performed, including those on their inhibition activities of coagulation factor Xa (FXa) and thrombin (FIIa). The results showed that the anti-FXa and -FIIa activities of enoxaparins with different degree of 1,6-anhydro derivatives (20.0%-39.7%) with similar structure characteristics, had decreasing tendency when the degree of 1,6-anhydro derivatives increased. Especially, the anti-FXa activity was sensitive to the change of the degree of 1,6-anhydro derivatives.

The interaction of enoxaparin and fondaparinux with calcium

The main sites of calcium binding were determined for the low molecular weight heparin drug enoxaparin and the synthetic pentasaccharide Arixtra (fondaparinux). [(1)H,(13)C] HSQC pH titrations were carried out to characterize the acid-base properties of these samples both in the presence and absence of calcium. The differences in the titration curves were used to determine the structural components of enoxaparin and fondaparinux responsible for Ca(2+) binding. In enoxaparin both unsubstituted and 2-O-sulfated iduronic acid residues are important in calcium binding and the presence of the 2-O-sulfo group does not seem to influence the Ca(2+) binding capability of the iduronate ring. In fondaparinux changes in chemical shifts upon Ca(2+) binding were smaller than observed for enoxaparin, and were observed for both the glucuronic acid and 2-O-sulfated iduronic acid residues. In enoxaparin significant perturbations of the chemical shift of the N-sulfoglucosamine anomeric carbon in residues connected to 2-O-sulfated iduronic acid were detected on Ca(2+) binding, however it was not possible to determine whether these changes reflect direct involvement in calcium complexation or result from through space interactions or conformational changes.

Binding of heparin-dependent antibodies to PF4 modified by enoxaparin oligosaccharides: evaluation by surface plasmon resonance and serotonin release assay

BACKGROUND

The minimal structural requirements of low-molecular-weight heparins that determine the risk of developing heparin-induced thrombocytopenia (HIT) are not fully defined.

OBJECTIVES

The ability of enoxaparin-derived oligosaccharides (OS) to induce platelet activation and exposure of platelet-factor 4 (PF4) epitopes recognized by antibodies developed in HIT was studied by surface plasmon resonance (SPR) and serotonin release assay.

RESULTS

Decasaccharides with ≥ 11 sulfate groups induced platelet activation in the presence of plasma from patients with confirmed HIT. Serotonin release of > 80% without full inhibition at 100 μg mL(-1) was achieved with decasaccharides containing 14 or 15 sulfate groups, 2 dodecasaccharides and 2 tetradecasaccharides. An SPR method was developed using purified PF4 immobilized on carboxymethylated dextran. Antibodies from all HIT samples bound to PF4/heparin in SPR assays with resonance units (RU) ratio of 109-173 with HIT plasma vs. 88-93 with control plasma. RU ratios > 100 were measured when PF4 was pre-incubated with OS with ≥ 10 saccharide units and one octasaccharide containing 10 sulfate groups. RU ratios > 140, similar to those measured when PF4 was pre-incubated with unfractionated heparin or enoxaparin, were obtained with purified dodeca- and tetradecasaccharides. RU values strongly correlated with the number of sulfate groups in the decasaccharides tested (r = 0.93, P = 0.02).

CONCLUSIONS

LMWHs with fragments > 10 saccharides and a large number of sulfate groups are more likely to be associated with a higher risk of HIT. These structure-activity relationships were independent of the ability of the OS to bind antithrombin.

Linear polyalkylamines as fingerprinting agents in capillary electrophoresis of low-molecular-weight heparins and glycosaminoglycans

Glycosaminoglycan (GAG) analysis represents a challenging frontier despite the advent of many high-resolution technologies because of their unparalleled structural complexity. We previously developed a resolving agent-aided capillary electrophoretic approach for fingerprinting low-molecular-weight heparins (LMWHs) to profile their microscopic differences and assess batch-to-batch variability. In this report, we study the application of this approach for fingerprinting other GAGs and analyze the basis for the fingerprints observed in CE. Although the resolving agents, linear polyalkylamines, could resolve the broad featureless electropherogram of LMWH into a large number of distinct, highly reproducible peaks, longer GAGs such as chondroitin sulfate, dermatan sulfate, and heparin responded in a highly individualistic manner. Full-length heparin interacted with linear polyalkylamines very strongly followed by dermatan sulfate, whereas chondroitin sulfate remained essentially unaffected. Oversulfated chondroitin sulfate could be easily identified from full-length heparin. Scatchard analysis of the binding profile of enoxaparin with three linear polyalkylamines displayed a biphasic binding profile suggesting two distinctly different types of interactions. Some LMWH chains were found to interact with linear polyalkylamines with affinities as high as 10 nM, whereas others displayed nearly 5000-fold weaker affinities. These observations provide fundamental insight into the basis for fingerprinting of LMWHs by linear polyalkylamine-based resolving agents, which could be utilized in the design of advanced resolving agents for compositional profiling, direct sequencing, and chemoinformatics studies.

Ozonolysis of the double bond of the unsaturated uronate residue in low-molecular-weight heparin and K5 heparosan

Ozone is known to add across and cleave carbon-carbon double bonds. Ozonolysis is widely used for the preparation of pharmaceuticals, for bleaching substances and for killing microorganisms in air and water sources. Some polysaccharides and oligosaccharides, such as those prepared using chemical or enzymatic β-elimination, contain a site of unsaturation. We examined ozonolysis of low-molecular-weight heparins (LMWHs), enoxaparin and logiparin, and heparosan oligo- and polysaccharides for the removal of the nonreducing terminal unsaturated uronate residue. 1D (1)H NMR showed that these ozone-treated polysaccharides retained the same structure as the starting polysaccharide, except that the C4-C5 double bond in the nonreducing end unsaturated uronate had been removed. The anticoagulant activity of the resulting product from enoxaparin and logiparin was comparable to that of the starting material. These results demonstrate that ozonolysis is an important tool for the removal of unsaturated uronate residues from LMWHs and heparosan without modification of the core polysaccharide structure or diminution of anticoagulant activity. This reaction also has potential applications in the chemoenzymatic synthesis of bioengineered heparin from Escherichia coli-derived K5 heparosan.

Rat and human HARE/stabilin-2 are clearance receptors for high- and low-molecular-weight heparins

The human hyaluronic acid (HA) receptor for endocytosis (HARE/stabilin-2) is the primary clearance receptor for systemic HA, chondroitin sulfates, and heparin, but not for heparan sulfate or keratan sulfate (Harris EN, Weigel JA, Weigel PH. J Biol Chem 283: 17341-17350, 2008). HARE is expressed in the sinusoidal endothelial cells (SECs) of liver and lymph nodes where it acts as a scavenger for uptake and degradation of glycosaminoglycans, both as free chains and proteoglycan fragments. Unfractionated heparin (UFH; approximately 14 kDa) and low-molecular-weight heparin (LMWH; approximately 4 kDa) are commonly used in treatments for thrombosis and cancer and in surgical and dialysis procedures. The reported half-lives of UFH and LMWH in the blood are approximately 1 h and 2-6 h, respectively. In this study, we demonstrate that anti-HARE antibodies specifically block the uptake of LMWH and UFH by isolated rat liver SECs and by human 293 cells expressing recombinant human HARE (hHARE). hHARE has a significant affinity (K(d) = 10 microM) for LMWH, and higher affinity (K(d) = 0.06 microM) for the larger UFH. Rat liver SECs or cells expressing the recombinant 190-kDa HARE isoform internalized both UFH and LMWH, and both heparins cross-compete with each other, suggesting that they share the same binding sites. These cellular results were confirmed in ELISA-like assays using purified soluble 190-hHARE ectodomain. We conclude that both UFH and LMWH are cleared by HARE/Stab2 and that the differences in the affinities of HARE binding to LMWH and UFH likely explain the longer in vivo circulating half-life of LMWH compared with UFH.

Affinity and Kinetics of Different Heparins Binding to P- and L-Selectin

Selectins are adhesion receptors that participate in inflammation and tumor cell metastasis. The anti-inflammatory and antimetastatic activities of heparins have been related partly to their ability to interact with P- and L-selectin. The recent findings that various heparins differ in antimetastatic activity were explained by differences in their P- and L-selectin binding ability. To obtain data to illustrate the binding characteristics, we detected for the first time the binding kinetics and affinity of the two low molecular weight heparins (LMWHs) enoxaparin and nadroparin, and of the unfractionated heparin Liquemin N to P- and L-selectin using a quartz crystal microbalance biosensor. Enoxaparin and nadroparin behave nearly identical in their binding affinity to both P-selectin ( KD 4.60 x 10 (- 6) M versus 7.61 x 10 (- 6) M) and L-selectin ( KD 2.01 x 10 (- 6) M versus 2.84 x 10 (- 6) M). Liquemin N displayed slightly higher affinities to both selectins ( KD 6.07 x 10 (- 7) M versus 1.07 x 10 (- 7) M). The differences are caused by a higher association rate compared with that of the LMWHs. These data support recent findings of antimetastatic activities, but illustrate that the intrinsic selectin binding does not entirely reflect the antimetastatic activities in vivo.

Low molecular weight heparin loaded pH-sensitive microparticles

Low molecular weight heparins (LMWH) have shown efficacy in the treatment of inflammatory bowel disease after parenteral administration however risking severe hemorrhagic adverse effects. Therefore, an oral colonic targeted heparin dosage form allowing the release of LMWH directly in the inflamed tissue would be of major interest. Enoxaparin was entrapped into pH-sensitive microspheres using Eudragit P4135F that dissolves at pH>7.2. Particle preparation was based on a double emulsion technique with either solvent extraction or evaporation. In order to increase the entrapment efficacy several preparation parameters were optimized, such as inner phase volume, polymer concentration, stabilization of the internal interface by surfactants. Solvent evaporation led to higher entrapment rates (evaporation: 70.1+/-9.9%; extraction: 46.5+/-6.4%). When increasing the volume of the inner aqueous heparin phase, lower encapsulation rates and larger microspheres ( approximately 100-400 microm) were obtained. Sorbitan monostearate (1.75-28% of the total particle mass) had a stabilizing effect on the primary water/oil emulsion. Indeed, higher encapsulation rates (7%: 78.2+/-3.5%; 14%: 76.4+/-10.1%) and smaller particles ( approximately 120-160 microm) were obtained whereas hexadecyltrimethylammonium bromide destabilized the primary emulsion. Interfacial tension studies at a simulated internal water/oil interface confirmed these results. As expected, in vitro drug release was found to be strongly pH-dependent; LMWH was retained in microspheres at pH<6 (<20% release within 4h) whereas a fast drug release was obtained at pH 7.4. The developed microspheres exhibited a particle size adapted to the needs of inflammatory bowel disease therapy, an efficient LMWH encapsulation, and a pH-controlled drug release. These microspheres represent a promising tool for the selective oral delivery of heparin to the colon, especially interesting in the treatment of inflammatory bowel disease.

In vitro and in vivo evaluation of enoxaparin removal by continuous renal replacement therapies with acrylonitrile and polysulfone membranes

BACKGROUND

Enoxaparin is a low-molecular-weight heparin for which the degree of elimination through hemofilters during continuous renal replacement therapy (CRRT) is not well established.

OBJECTIVE

The elimination of enoxaparin by CRRT, using acrylonitrile (AN69) or polysulfone (PS) membranes, was studied in vitro and among critically ill patients.

METHODS

In vitro procedures were carried out using Ringer's lactate, bovine albumin-containing Ringer's lactate, or fresh human plasma as enoxaparin vehicle, using AN69 or PS membranes, and following continuous veno-venous hemofiltration (CVVH) or continuous veno-venous hemodialysis (CVVHD). Prefilter and ultrafiltrate samples were collected over 60 minutes. All procedures were carried out in triplicate. Patients undergoing CRRT entered the in vivo study. Enoxaparin was administered subcutaneously once daily. The sieving coefficient (Sc) and saturation coefficient (Sa) were calculated as the relation between anti-factor Xa activity in simultaneously collected dialysate/ultrafiltrate samples and plasma samples.

RESULTS

Mean Sc (for CVVH) or Sa (for CVVHD) values in the in vitro procedures ranged from 0.16 to 0.57. Sc values during CVVH were significantly higher than Sa values during CVVHD in the Ringer's lactate procedures for both membranes (AN69 membrane, P = 0.014; PS membrane, P < 0.001) and in the plasma procedures with the PS membrane (P < 0.001). Six male and 2 female patients (all white) participated in the in vivo study. Their mean body weight ranged from 55 to 80 kg, and their age ranged from 71 to 82 years. In patients, Sc or Sa achieved values between 0.26 and 0.67. No significant differences were found in vivo in the permeability of the 2 membranes to enoxaparin.

CONCLUSIONS

In these studies, the Sc and Sa values suggested that enoxaparin passed through AN69 and PS membranes during CRRT. Further pharmacokinetic and clinical studies are needed to determine whether a dose adjustment for enoxaparin is needed for patients undergoing CRRT.

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.

Heparin modulates the 99-loop of factor IXa: effects on reactivity with isolated Kunitz-type inhibitor domains

Reactivity of factor IXa with basic pancreatic trypsin inhibitor is enhanced by low molecular weight heparin (enoxaparin). Previous studies by us have suggested that this effect involves allosteric modulation of factor IXa. We examined the reactivity of factor IXa with several isolated Kunitz-type inhibitor domains: basic pancreatic trypsin inhibitor, the Kunitz inhibitor domain of protease Nexin-2, and the first two inhibitor domains of tissue factor pathway inhibitor. We find that enhancement of factor IXa reactivity by enoxaparin is greatest for basic pancreatic trypsin inhibitor (>10-fold), followed by the second tissue factor pathway inhibitor domain (1.7-fold) and the Kunitz inhibitor domain of protease Nexin-2 (1.4-fold). Modeling studies of factor IXa with basic pancreatic trypsin inhibitor suggest that binding of this inhibitor is sterically hindered by the 99-loop of factor IXa, specifically residue Lys(98). Slow-binding kinetic studies support the formation of a weak initial enzyme-inhibitor complex between factor IXa and basic pancreatic trypsin inhibitor that is facilitated by enoxaparin binding. Mutation of Lys(98) to Ala in factor IXa results in enhanced reactivity with all inhibitors examined, whereas almost completely abrogating the enhancing effects of enoxaparin. The results implicate Lys(98) and the 99-loop of factor IXa in defining enzyme inhibitor specificity. More importantly, these results demonstrate the ability of factor IXa to be allosterically modulated by occupation of the heparin-binding exosite.

[Is there a difference between low-molecular-weight heparins?]

Low-molecular-weight heparins share many properties and are commonly referred to as a group, but structurally and pharmacologically they are dissimilar. The size spectrum of the heparin molecules varies between the different products and as assessed in vitro, their anticoagulant properties differ. In particular, the ratio anti-factor Xa : anti-factor IIa activities varies. The clinical consequences of these differences are unknown. The efficacy and safety of two different low-molecular-weight heparins have been compared in only a few clinical studies; no significant differences in outcome were shown. However, low-molecular-weight heparins should be used according to the approved indication for each product and in doses shown effective and safe in clinical studies. A change from one low-molecular-weight heparin to another in the same patient should be avoided. Fondaparinux is a synthetic penta-saccharide which may be regarded as an extreme low-molecular-weight heparin with a ratio of anti-factor Xa : anti-factor IIa activity as 1 : 0, and with a promising efficacy/safety profile. So far, the approved clinical indication for its use is limited to prophylaxis in orthopaedic surgery.

Few bicyclic acetals at reducing end of low-molecular-weight heparins: might they restrict specification of pharmacopoeia?

The alkaline hydrolysis of heparin benzyl ester originates enoxaparin. The depolymerization by beta-elimination is the primary effect of reaction; but side reactions can happen and the bicyclic acetal at the reducing end of glucosamine N,6-disulphate, called 1,6-anhydro ring, is a product of a side reaction. The amount of this predictable moiety of enoxaparin can be controlled to a lowest extent (6%) and to extent higher than 40% by modulating the alkalinity and duration of the reaction of hydrolysis. With the exclusion of the beta-elimination effects and of these non significative side reactions, the chemical structure of the parent heparin is entirely maintained in enoxaparin as it results by the same profiles of constituent disaccharides. The content of 1,6-anhydro rings is assessed by a not yet validated NMR method. The chains of enoxaparin bearing, at their reducing end, 1,6-anhydro rings could be regarded as Related Substances of enoxaparin. If present, even in an amount less than, or equal to, 30% of chains, these "related substances" affect neither activities nor safety of enoxaparin.

Clinical use of enoxaparin in the management of non-ST segment elevation acute coronary syndromes

Enoxaparin (Lovenox; Roule-Poulenc Rorer, Inc.), a low molecular weight heparin (LMWH), is commonly used in the management of non-ST-segment elevation acute coronary syndromes (NSTE ACS) based on clinical trial outcomes. It is one of a group of glycosaminoglycan compounds that accelerate the inactivation of factor Xa by inducing a conformational change in antithrombin. In contrast to unfractionated heparin (UFH), LMWH have greater bioavailability, a more predictable anticoagulant response, longer half-life and a higher proportion of anti-factor Xa to anti-factor IIa activity. As a consequence, laboratory monitoring of the anticoagulant effect is typically unnecessary. Antithrombin therapy with LMWH or UFH has the highest-level recommendation (IA) in the 2002 professional guidelines for the management of unstable angina and non-ST-elevation myocardial infarction, where enoxaparin has a IIA recommendation over UFH unless early coronary artery bypass surgery is planned. In a recent systematic overview of > 20,000 patients with NSTE ACS from six clinical trials, including conservative and invasively managed patients, enoxaparin provided a statistically significant reduction in 30-day death or nonfatal myocardial infarction (MI) compared with UFH with no significant excess in transfusions, or major bleeding. These data support the role of enoxaparin as an anti-coagulant in patients with NSTE ACS.

Effect of low molecular weight heparin and different heparin molecular weight fractions on the activity of the matrix-degrading enzyme aggrecanase: Structure-function relationship

The matrix-degrading enzyme aggrecanase has been identified in cartilage and is largely responsible for cartilage breakdown. The present study determined the efficacy of different heparin molecular weight fractions (HMWFs) and low molecular weight heparins (LMWHs) on aggrecanase activity. Aggrecanase activity was determined using biotinylated peptide substrate, which was immobilized onto streptavidin-coated 96-well plates; aggrecanase enzyme was then added. Proteolysis of the substrate at the specific amide bond was detected using specific antibody for the neoepitope generated. HMWFs ranging from 1,700 to 12,000 Da demonstrated a concentration-dependent inhibitory efficacy of aggrecanase activity, with a Ki ranging from 5,000 nM down to 1 nM as a function of the molecular weight. The higher the molecular weight distribution, the greater the inhibitory efficacy of the heparin fragments toward aggrecanase activity. The absence or presence of antithrombin did not alter the affinity of heparin in inhibiting aggrecanase. Additionally, tissue factor pathway inhibitor at various levels did not alter the activity of aggrecanase. LMWHs demonstrated different levels of potency in inhibiting aggrecanase activity as a function of their average molecular weight distribution. Tinzaparin (average molecular weight = 6,500 Da) and enoxaparin (average molecular weight = 4,500 Da) demonstrated a Ki of 20 and 80 nM, respectively. The aggrecanase inhibitory effect of LMWH might contribute to blocking inflammation and tumor invasion by inhibiting aggrecanase activity and maintaining an intact extracellular matrix barrier.

Generic Low-Molecular-Weight Heparins: Some Practical Considerations

It is now widely accepted that various low-molecular-weight heparins (LMWHs) exhibit specific molecular and structural attributes that are determined by the type of manufacturing process used. For example, enoxaparin, which is prepared by benzylation followed by alkaline hydrolysis of unfractionated heparin (UFH), exhibits a double bond at the nonreducing end and the presence of a unique bicyclic structure namely 1,6 anhydromanno glucose or mannose, or both, at the reducing end. Similarly, the other LMWHs, such as dalteparin, nadroparin, tinzaparin, and parnaparin, exhibit specific structural characteristics that may contribute to their own unique biochemical and pharmacological profiles. These unique features may not exhibit any major influence on the routinely determined anti-Xa and anti-IIa activities. However, these may have an impact on the pharmacokinetics and other biological actions such as the interactions with growth factors, blood components, and vascular cells. This is the reason for the initial caution for the noninterchangeability of the anti-Xa adjusted dosing of the different LMWHs. Although the nonanticoagulant biological effects of these drugs are poorly understood at this time, they are now recognized as contributing significantly to the overall therapeutic effects of these drugs. Because some of these drugs have proved to be effective in the management of cancer-associated thrombosis and exhibit improvements in mortality outcome, these LMWHs may also produce several other effects by modulating inflammatory processes, apoptosis, and other regulatory functions related to cellular functions at different levels. Thus, the interactions of these LMWHs with antithrombin and heparin cofactor II are not the only determinants of their biological actions. Release of tissue factor pathway inhibitor (TFPI), regulation of cytokines, nitric oxide, and eicosanoids contribute to their individuality. Such properties are not only dependent on the oligosaccharide sequence and consensus sites but also depend mainly on microchemical and structural attributes in these drugs. European Pharmacopoeia (EP) and the World Health Organization (WHO) have developed guidelines to characterize these agents in terms of their molecular and biological profile. Regulatory agencies such as the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMEA) consider each of these drugs as distinct pharmacological agents. This has prompted the requirement for product-specific clinical data for the approval of their use in various clinical indications. There is a clear concern regarding the development of potential generic versions of branded products and the submissions by generic manufacturers for the regulatory approval of generic interchangeability that refers to the substitution of an apparent chemically identical and bioequivalent versions of the branded LMWHs. Currently, there are no regulatory guidelines or consensus opinions on the acceptance of generic versions of the branded products. Because the LMWHs represent not only a biological entity but also product-specific molecular and structural attributes, the acceptance of a generic version must be based on clearly defined guidelines stipulating minimal molecular and structural, biological, and clinical validation requirements. It is therefore to be stressed that each of the LMWHs is a distinct drug entity that characteristically exhibits a product-based therapeutic spectrum in different thrombotic and nonthrombotic disorders. Thus, until the establishment of valid regulatory guidelines for the generic interchangeability of the commercially available LMWHs is completed, generic substitutes are not recommended.

Chain length-dependent effects of alkylmaltosides on nasal absorption of enoxaparin

The purpose of this study was to investigate whether the hydrophobic chain length of alkylmaltosides affects their efficacy as absorption promoters for nasally administered low-molecular-weight heparin and to study whether these agents enhance nasal absorption in a time-dependent manner without causing irreversible damage to the nasal epithelial membrane. For the nasal absorption studies, enoxaparin formulated with different alkylmaltosides was administered nasally to anesthetized rats and absorption of the drug was determined by measuring plasma anti-factor Xa activity. Reversibility studies were performed by administering enoxaparin at different time points after administration of alkylmaltosides. The AUC(0-360) for plasma anti-factor Xa-time curves increased with the increase in alkylmaltoside concentration in the formulations. Absolute and relative bioavailability of enoxaparin were increased by two-fold when the alkyl chain length of maltosides was increased from 8 to 14 carbons. Alkylmaltosides therefore increase nasal absorption of enoxaparin in a dose- and chain length-dependent manner. Of the alkylmaltosides tested, tetradecylmaltoside is the most potent enhancer of nasal absorption of enoxaparin. Longer chain alkylmaltosides produce a more prolonged effect on nasal mucosa compared with those with shorter alkyl chain.

Biospecific extraction and neutralization of anticoagulant heparin with fibroblast growth factors (FGF)

The polyanionic sulfated carbohydrate heparin is a mixture of anticoagulant and nonanticoagulant activity that is best known for its pharmacological benefit as an anticoagulant. The objective of this study was to design and evaluate a simple purification method for an anticoagulant fraction of heparin from a crude heparin mixture as an alternative to antithrombin. Similar to blood clotting, the fibroblast growth factor signaling system is heparan sulfate-regulated and comprised of components with structurally distinct heparin-binding domains. A rare and highly specific motif within a single heparan sulfate chain has been proposed to tether both FGF and the FGFR ectodomain together. The diversity of heparin-binding motifs within the large FGF family of polypeptides and receptors provides a repertoire of diverse templates for capture of diverse heparin/heparan sulfate motifs in biology. We show here that, similar to antithrombin, a member of the FGF family, FGF7, selectively captures anti-Factor Xa and anti-Factor IIa activity from commercially and clinically applied heparin mixtures. In the presence of purified anticoagulant heparin and derivative, FGF7 has the similar activity as protamine sulfate for reversal of anticoagulant effect, while FGF1 is much less potent than FGF7. This may provide a novel cost-effective, bioaffinity-based alternative to antithrombin for concurrent enrichment and recovery of anticoagulant and nonanticoagulant heparin from the same heparin mixture. In addition, FGF7 and homologues may be useful in pharmaceutical neutralization of anticoagulant heparin and heparan sulfate.

Alkanoylsucroses in nasal delivery of low molecular weight heparins: in-vivo absorption and reversibility studies in rats

The efficacy of alkanoylsucroses in enhancing nasal absorption of low molecular weight heparin (LMWH) and the time span of action of these agents on the nasal membrane has been investigated. In this regard, LMWH formulated with alkanoylsucroses was administered nasally to anaesthetized male Sprague-Dawley rats and the absorption of LMWH was determined by measuring plasma antifactor Xa activity. The duration of action of these agents at the site of administration was investigated by an in-vivo reversibility study. The potency and efficacy of dodecanoylsucrose was compared with that of sodium glycocholate. Alkanoylsucroses used in this study include dodecanoylsucrose, decanoylsucrose and octanoylsucrose. These agents enhance nasal absorption of enoxaparin in a dose-dependent and chain-length-dependent manner. Of the agents tested, dodecanoylsucrose was found to be the most potent in enhancing nasal absorption of LMWH. The bioavailability of enoxaparin formulated with alkanoylsucroses was increased by several folds compared with enoxaparin formulated in saline. The reversibility study with dodecanoylsucrose showed that the effect of alkanoylsucroses faded away with time and the duration of action of this agent at the site of administration was 120-140 min. Dodecanoylsucrose was found to be twice as potent as sodium glycocholate. Overall, the nasal absorption of LMWH was effectively enhanced by co-administration of alkanoylsucroses and the effect of alkanoylsucroses on nasal epithelium was found to be reversible. The potency of these agents depends on their hydrophobic chain lengths.

Anti-Xa Stability of Diluted Enoxaparin for Use in Pediatrics

BACKGROUND

The use of enoxaparin in low-weight pediatric patients is becoming common practice. Anti-Xa stability of unit-dose syringes prepared after dilution beyond one day is presently unknown.

OBJECTIVE

To evaluate the anti-Xa stability of diluted enoxaparin stored in glass vials and tuberculin syringes.

METHODS

Four separate batches of enoxaparin were diluted with sterile water to a final concentration of 20 mg/mL (2000 IU/mL) and aliquoted into plastic 1-mL syringes containing 6 mg (0.3 mL) or maintained in the glass vial. Syringes were stored at room temperature or under refrigeration. The glass vial used for diluting was stored at room temperature. The anti-Xa activity was measured on the date of preparation to 4 weeks. Statistical comparisons determined whether differences in anti-Xa activity in diluted enoxaparin are affected by the storage medium or temperature. A paired t-test was used to determine any significant differences between the anti-Xa activity on date of preparation (baseline) and subsequent time periods, with p < 0.05 considered statistically significant.

RESULTS

The mean baseline anti-Xa activity was 2607 IU/mL (95% CI 2300 to 2914). No measurable decrease occurred in diluted enoxaparin anti-Xa activity in the glass vial maintained over the 4-week period. Compared with the glass vial, room temperature and refrigerated syringe samples had trending decreases of anti-Xa activity at weeks 3 and 4, but did not reach statistical significance.

CONCLUSIONS

A nonsignificant decrease in anti-Xa activity occurred starting at day 22 for the diluted enoxaparin in tuberculin syringes, regardless of storage temperature. Storage up to 4 weeks of diluted enoxaparin in glass or prefilled syringes does not result in a statistically significant loss of anticoagulant potential, as measured by anti-Xa activity.

Variability of Plasma Anti-Xa Activities with Different Lots of Enoxaparin

BACKGROUND

Previous studies have indicated the variability of anti-Xa activity in different sources of heparin and the variability of different methods used for measuring anti-Xa activity. Manufacturers of low-molecular-weight heparins (LMWHs) determine each lot's anti-Xa activity against the World Health Organization standard, but little information is known about anti-Xa activity variation between lots of LMWH and the impact on reported anti-Xa activity in patient samples.

OBJECTIVE

To determine the variation of plasma anti-Xa activity in patients receiving enoxaparin when different lots of enoxaparin are used for test calibration.

METHODS

We obtained 7 lots of enoxaparin containing approximately 10 000 IU/mL and one lot containing approximately 15 000 IU/mL of anti-Xa activity. For each lot, a 2.0 anti-Xa IU/mL dilution was prepared and a calibration curve performed using a chromogenic method. To test the variation in reported results between the different calibration lots, 20 patient samples were tested. Nineteen patients receiving enoxaparin and one patient not receiving enoxaparin (negative control) were tested in a blinded fashion, and the changes in light absorbance recorded. Anti-Xa activity results from tested plasmas were then extrapolated from each enoxaparin lot calibration curve.

RESULTS

Using Student's paired t-test, there were statistically significant differences between the plasma anti-Xa activities generated from the various enoxaparin lots. In the range of 0.5–1.0 IU/mL of anti-Xa activity, 3 (4.2%) samples had a >0.2 IU/mL difference (maximum difference 0.33 IU/mL) in anti-Xa activity between 2 lots of enoxaparin. For samples that had supratherapeutic anti-Xa activities (1.0–1.5 IU/mL anti-Xa activity), there was a wider variation (>0.2 IU/mL) in anti-Xa activity, which may have resulted in a dosing change.

CONCLUSIONS

The statistical differences in plasma anti-Xa activities noted between enoxaparin lots are not clinically significant. However, anti-Xa activities in the upper therapeutic and supratherapeutic ranges (>1.0 IU/mL of anti-Xa activity) resulted in a deviation of >0.3 IU/mL in reported anti-Xa activity, which may result in dosing changes.

Novel concatameric heparin-binding peptides reverse heparin and low-molecular-weight heparin anticoagulant activities in patient plasma in vitro and in rats in vivo

Patients given unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) for prophylaxis or treatment of thrombosis sometimes suffer serious bleeding. We showed previously that peptides containing 3 or more tandem repeats of heparin-binding consensus sequences have high affinity for LMWH and neutralize LMWH (enoxaparin) in vivo in rats and in vitro in citrate. We have now modified the (ARKKAAKA)n tandem repeat peptides by cyclization or by inclusion of hydrophobic tails or cysteines to promote multimerization. These peptides exhibit high-affinity binding to LMWH (dissociation constant [Kd], ≈ 50 nM), similar potencies in neutralizing anti–Factor Xa activity of UFH and enoxaparin added to normal plasma in vitro, and efficacy equivalent to or greater than protamine. Peptide (ARKKAAKA)3VLVLVLVL was most effective in all plasmas from enoxaparin-treated patients, and was 4- to 20-fold more effective than protamine. Several other peptide structures were effective in some patients' plasmas. All high-affinity peptides reversed inhibition of thrombin-induced clot formation by UFH. These peptides (1 mg/300 g rat) neutralized 1 U/mL anti–Factor Xa activity of enoxaparin in rats within 1 to 2 minutes. Direct blood pressure and heart rate measurements showed little or no hemodynamic effect. These heparin-binding peptides, singly or in combination, are potential candidates for clinical reversal of UFH and LMWH in humans.

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.

Antithrombin binding of low molecular weight heparins and inhibition of factor Xa

Fluorescence and stopped flow methods were used to compare clinically used heparins with regard to their ability to bind to antithrombin and to accelerate the inactivation of factor Xa. Titration of antithrombin with both low molecular weight heparin (LMWH) (enoxaparin, fragmin and ardeparin) and unfractionated heparin (UFH) produced an equivalent fluorescence increase and indicates similar affinity of all heparin preparations to antithrombin. However, relative to UFH enoxaparin, the LMWH with the smallest average molecular mass, contained only 12% material with high affinity for antithrombin. The rate of factor Xa inhibition by antithrombin increased with the concentration of the examined heparins to the same limiting value, but the concentration required for maximal acceleration depended on the preparation. According to these data the high affinity fraction of the heparin preparations increased the intrinsic fluorescence and inhibitory activity equally without additional effects by variations in chain length and chemical composition. In contrast, in the presence of Ca UFH accelerated the inhibition of factor Xa by antithrombin 10-fold more efficiently than comparable concentrations of the high affinity fractions of enoxaparin and fragmin. The bell-shaped dependence of this accelerating effect suggests simultaneous binding of both proteins to heparin. In conclusion, under physiologic conditions the anti-factor Xa activity of heparin results from a composite effect of chain length and the content of material with high affinity to antithrombin. Thus, the reduced antithrombotic activity of LMWH relative to UFH results from a smaller content of high affinity material and the absence of a stimulating effect of calcium.

Compatibility and activity of enoxaparin sodium in 0.9% sodium chloride injection for 48 hours

The stability of enoxaparin sodium in 0.9% sodium chloride injection in polyvinyl chloride (PVC) containers was studied. Triplicate solutions of 120 mg (1.2 mL) of enoxaparin (as the sodium salt) and 98.8 mL of 0.9% sodium chloride injection were prepared in 250-mL PVC containers and stored at room temperature (20-22 degrees C). Samples were taken immediately after preparation and at 0.25, 0.5, 0.75, 1, 4, 12, 16, 24, and 48 hours. Inspections for color change and precipitation were performed with a clarity inspection station and a magnifying glass. Samples of the three admixtures were evaluated in duplicate for pharmacologic activity by an automated coagulation heparin assay. Throughout the 48-hour study period, the enoxaparin admixtures were free of color change, evolution of gas, and precipitates. The pharmacologic activity of enoxaparin in the PVC containers remained > 94% of the initial measured activity for 48 hours. Enoxaparin 1.2 mg/mL (as the sodium salt) in 0.9% sodium chloride injection in PVC containers was stable for up to 48 hours at 20-22 degrees C.