Cleavage of the antithrombin III binding site in heparin by heparinases and its implication in the generation of low molecular weight heparin

Expanding the Role of Heparin Derivatives in Oncology: From Anticoagulation to Antitumor Activity

Current research demonstrates the expanding therapeutic potential of heparin derivatives in oncology, extending beyond traditional anticoagulation mechanisms. This systematic analysis examines the structural characteristics, molecular mechanisms, and therapeutic applications of heparin-based compounds in malignancy treatment. The essential antithrombin binding pentasaccharide sequence has enabled development of specialized molecular variants, particularly fractionated heparins and their non-anticoagulant counterparts. These agents exert antineoplastic effects via multiple pathways, particularly through modulation of heparanase enzymatic activity and specific protein-glycosaminoglycan interactions. Evidence from pivotal clinical trials (FRAGMATIC, MAGNOLIA, GASTRANOX) confirms efficacy in managing cancer-associated thrombosis while indicating potential enhancement of chemotherapeutic outcomes. The preparation methods utilize enzymatic cleavage reactions and selective chemical derivatization to generate structurally modified heparins exhibiting unique molecular characteristics and biological activities. Analysis of the glycosaminoglycan analog dociparstat sodium reveals significant activity in myeloid malignancies, mediated by specific interference with CXCL12/CXCR4 signaling cascades. Significant challenges remain in manufacturing scale-up, analytical validation, and long-term safety assessment. Future studies must address dose optimization, combination strategies, and controlled clinical trials to determine the full therapeutic potential of these compounds in clinical oncology.

Classification and characteristics of bacterial glycosaminoglycan lyases, and their therapeutic and experimental applications

Glycosaminoglycans (GAGs), as animal polysaccharides, are linked to proteins to form various types of proteoglycans. Bacterial GAG lyases are not only essential enzymes that spoilage bacteria use for the degradation of GAGs, but also valuable tools for investigating the biological function and potential therapeutic applications of GAGs. The ongoing discovery and characterization of novel GAG lyases has identified an increasing number of lyases suitable for functional studies and other applications involving GAGs, which include oligosaccharide sequencing, detection and removal of specific glycan chains, clinical drug development and the design of novel biomaterials and sensors, some of which have not yet been comprehensively summarized. GAG lyases can be classified into hyaluronate lyases, chondroitinases and heparinases based on their substrate spectra, and their functional applications are mainly determined by their substrates, with different lyases exhibiting differing substrate selectivity and preferences. It is thus necessary to understand the properties of the available enzymes to determine strategies for their functional application. Building on previous studies and reviews, this Review highlights small yet crucial differences among or within the various GAG lyases to aid in optimizing their use in future studies. To clarify ideas and strategies for further research, we also discuss several traditional and novel applications of GAG lyases.

Adsorbed polymer conjugates to adaptively inhibit blood coagulation activation by medical membranes

Adaptive drug release can combat coagulation and inflammation activation at the blood-material interface with minimized side effects. For that purpose, poly(styrene-alt-maleic-anhydride) copolymers were conjugated to heparin via coagulation-responsive linker peptides and shown to tightly adsorb onto poly(ethersulfone) (PES)-surfaces from aqueous solutions as monolayers. Coagulation-responsive release of unfractionated as well as low molecular weight heparins from the respective coatings was demonstrated to be functionally beneficial in human plasma and whole blood incubation with faster release kinetics resulting in stronger anticoagulant effects. Coated poly(ethersulfone)/poly(vinylpyrrolidone) (PES/PVP) flat membranes proved the technology to offer an easy, effective and robust anticoagulant interfacial functionalization of hemodialysis membranes. In perspective, the modularity of the adaptive release system will be used for inhibiting multiple activation processes.

Chemical Synthesis of Δ-4,5 Unsaturated Heparan Sulfate Oligosaccharides for Biomarker Discovery

A methodology is described that can provide heparan sulfate oligosaccharides having a Δ4,5-double bond, which are needed as analytical standards and biomarkers for mucopolysaccharidoses. It is based on chemical oligosaccharide synthesis followed by modification of the C-4 hydroxyl of the terminal uronic acid moiety as methanesulfonate. This leaving group is stable under conditions used to remove temporary protecting groups, O-sulfation, and hydrogenolysis. Treatment with NaOH results in elimination of the methanesulfonate and formation of a Δ4,5-double bond.

Heparinase Digestion of 3-O-Sulfated Sequences: Selective Heparinase II Digestion for Separation and Identification of Binding Sequences Present in ATIII Affinity Fractions of Bovine Intestinal Heparins

Binding to antithrombin-III (ATIII) determines the anticoagulant activity of heparin. The complexes formed between heparin and ATIII result from a specific pentasaccharide sequence containing a 3-O-sulfated glucosamine in medium position. Building block analysis of heparins, following heparinase digestion, is a critical method in quality control that provides a simple structural characterization of a complex product. Hence, in these applications, study of the digestion of 3-O-sulfated moieties merits special attention. With heparinase II, specific inhibition of cleavage of the non-reducing bond of 3-O-sulfated units is observed. This specificity was erroneously generalized to other heparinases when it was observed that in exhaustive digests of heparins with the heparinase mixture, resistant 3-O-sulfated tetrasaccharides were also obtained from the specific ATIII-binding pentasaccharides. In fact, the detection of unsaturated 3-O-sulfated disaccharides in digests of heparin by heparinases I+II+III, resulting from the cleavage of the 3-O sulfated unit by heparinase I in non-conventional sequences, shows that this inhibition has exceptions. Thus, in experiments where heparinase II is selectively applied, these sequences can only be digested into tetra- or hexasaccharides where the 3-O-sulfated glucosamine is shifted on the reducing end. Heparinase I+II+III and heparinase II digests with additional tagging by reductive amination with sulfanilic acid were used to study the structural neighborhood of 3-O-sulfated disaccharides in bovine mucosal heparin fractions with increasing affinity for ATIII. The 3-O-sulfated disaccharides detected in heparinase I+II+III digests turn into numerous specific 3-O-sulfated tetrasaccharides in heparinase II digests. Additionally, ATIII-binding pentasaccharides with an extra 3-O-sulfate at the reducing glucosamine are detected in fractions of highest affinity as heparinase II-resistant hexasaccharides with two consecutive 3-O-sulfated units.

Heparin and Its Derivatives: Challenges and Advances in Therapeutic Biomolecules

Heparin has been extensively studied as a safe medicine and biomolecule over the past few decades. Heparin derivatives, including low-molecular-weight heparins (LMWH) and heparin pentasaccharide, are effective anticoagulants currently used in clinical settings. They have also been studied as functional biomolecules or biomaterials for various therapeutic uses to treat diseases. Heparin, which has a similar molecular structure to heparan sulfate, can be used as a remarkable biomedicine due to its uniquely high safety and biocompatibility. In particular, it has recently drawn attention for use in drug-delivery systems, biomaterial-based tissue engineering, nanoformulations, and new drug-development systems through molecular formulas. A variety of new heparin-based biomolecules and conjugates have been developed in recent years and are currently being evaluated for use in clinical applications. This article reviews heparin derivatives recently studied in the field of drug development for the treatment of various diseases.

A rechargeable anti-thrombotic coating for blood-contacting devices

Despite the potential of anti-thrombogenic coatings, including heparinized surfaces, to improve the performance of blood-contacting devices, the inevitable deterioration of bioactivity remains an important factor in device failure and related thrombotic complications. As a consequence, the ability to restore the bioactivity of a surface coating after implantation of a blood-contacting device provides a potentially important strategy to enhance its clinical performance. Here, we report the regeneration of a multicomponent anti-thrombogenic coating through use of an evolved sortase A to mediate reversible transpeptidation. Both recombinant thrombomodulin and a chemoenzymatically synthesized ultra-low molecular weight heparin were repeatedly and selectively immobilized or removed in a sequential, alternating, or simultaneous manner. The generation of activated protein C (aPC) and inhibition of activated factor X (FXa) was consistent with the molecular composition of the surface. The fabrication of a rechargeable anti-thrombogenic surface was demonstrated on an expanded polytetrafluoroethylene (ePTFE) vascular graft with reconstitution of the surface bound coating 4 weeks after in vivo implantation in a rat model.

The 3-O-sulfation of heparan sulfate modulates protein binding and lyase degradation

Humans express seven heparan sulfate (HS) 3-O-sulfotransferases that differ in substrate specificity and tissue expression. Although genetic studies have indicated that 3-O-sulfated HS modulates many biological processes, ligand requirements for proteins engaging with HS modified by 3-O-sulfate (3-OS) have been difficult to determine. In particular, the context in which the 3-OS group needs to be presented for binding is largely unknown. We describe herein a modular synthetic approach that can provide structurally diverse HS oligosaccharides with and without 3-OS. The methodology was employed to prepare 27 hexasaccharides that were printed as a glycan microarray to examine ligand requirements of a wide range of HS-binding proteins. The binding selectivity of antithrombin-III (AT-III) compared well with anti-Factor Xa activity supporting robustness of the array technology. Many of the other examined HS-binding proteins required an IdoA2S-GlcNS3S6S sequon for binding but exhibited variable dependence for the 2-OS and 6-OS moieties, and a GlcA or IdoA2S residue neighboring the central GlcNS3S. The HS oligosaccharides were also examined as inhibitors of cell entry by herpes simplex virus type 1, which, surprisingly, showed a lack of dependence of 3-OS, indicating that, instead of glycoprotein D (gD), they competitively bind to gB and gC. The compounds were also used to examine substrate specificities of heparin lyases, which are enzymes used for depolymerization of HS/heparin for sequence determination and production of therapeutic heparins. It was found that cleavage by lyase II is influenced by 3-OS, while digestion by lyase I is only affected by 2-OS. Lyase III exhibited sensitivity to both 3-OS and 2-OS.

Influence of saccharide modifications on heparin lyase III substrate specificities

A library of 23 synthetic heparan sulfate (HS) oligosaccharides, varying in chain length, types and positions of modifications, was used to analyze the substrate specificities of heparin lyase III enzymes from both Flavobacterium heparinum and Bacteroides eggerthii. The influence of specific modifications, including N-substitution, 2-O sulfation, 6-O sulfation and 3-O sulfation on lyase III digestion was examined systematically. It was demonstrated that lyase III from both sources can completely digest oligosaccharides lacking O-sulfates. 2-O Sulfation completely blocked cleavage at the corresponding site; 6-O and 3-O sulfation on glucosamine residues inhibited enzyme activity. We also observed that there are differences in substrate specificities between the two lyase III enzymes for highly sulfated oligosaccharides. These findings will facilitate obtaining and analyzing the functional sulfated domains from large HS polymer, to better understand their structure/function relationships in biological processes.

Identification of Protein Recognition Elements within Heparin Chains Using Enzymatic Foot-Printing in Solution and Online SEC/MS

Understanding molecular mechanisms governing interactions of glycosaminoglycans (such as heparin) with proteins remains challenging due to their enormous structural heterogeneity. Commonly accepted approaches seek to reduce the structural complexity by searching for "binding epitopes" within the limited subsets of short heparin oligomers produced either enzymatically or synthetically. A top-down approach presented in this work seeks to preserve the chemical diversity displayed by heparin by allowing the longer and structurally diverse chains to interact with the client protein. Enzymatic lysis of the protein-bound heparin chains followed by the product analysis using size exclusion chromatography with online mass spectrometry detection (SEC/MS) reveals the oligomers that are protected from lysis due to their tight association with the protein, and enables their characterization (both the oligomer length, and the number of incorporated sulfate and acetyl groups). When applied to a paradigmatic heparin/antithrombin system, the new method generates a series of oligomers with surprisingly distinct sulfation levels. The extent of sulfation of the minimal-length binder (hexamer) is relatively modest yet persistent, consistent with the notion of six sulfate groups being both essential and sufficient for antithrombin binding. However, the masses of longer surviving chains indicate complete sulfation of disaccharides beyond the hexasaccharide core. Molecular dynamics simulations confirm the existence of favorable electrostatic interactions between the high charge-density saccharide residues flanking the "canonical" antithrombin-binding hexasaccharide and the positive patch on the surface of the overall negatively charged protein. Furthermore, electrostatics may rescue the heparin/protein interaction in the absence of the canonical binding element.

Draft genome sequences of Hirudo medicinalis and salivary transcriptome of three closely related medicinal leeches

BACKGROUND

Salivary cell secretion (SCS) plays a critical role in blood feeding by medicinal leeches, making them of use for certain medical purposes even today.

RESULTS

We annotated the Hirudo medicinalis genome and performed RNA-seq on salivary cells isolated from three closely related leech species, H. medicinalis, Hirudo orientalis, and Hirudo verbana. Differential expression analysis verified by proteomics identified salivary cell-specific gene expression, many of which encode previously unknown salivary components. However, the genes encoding known anticoagulants have been found to be expressed not only in salivary cells. The function-related analysis of the unique salivary cell genes enabled an update of the concept of interactions between salivary proteins and components of haemostasis.

CONCLUSIONS

Here we report a genome draft of Hirudo medicinalis and describe identification of novel salivary proteins and new homologs of genes encoding known anticoagulants in transcriptomes of three medicinal leech species. Our data provide new insights in genetics of blood-feeding lifestyle in leeches.

Identification of a heparosan heptasaccharide as an effective anti-inflammatory agent by partial desulfation of low molecular weight heparin

Low molecular weight heparin (LMWH) possesses a dual function of anticoagulation and anti-inflammation. While the structures and mechanisms on its anticoagulation have been widely studied, the structural features responsible for the anti-inflammatory activity of LMWH remain to be explored. In the present study, guided by an anti-inflammation assay, a non-anticoagulant species was generated from partial desulfation of LMWH to fully retain the anti-inflammatory activity, from which five fractions were further separated and three of them were characterized by enzymatic degradation, hydrophobic labeling, C18-based HPLC and LC-MS/MS analyses. The structure-activity relationship revealed that the sulfate groups in LMWH are critical to distinguish and separate the activities of anticoagulation and anti-inflammation, leading to the identification of a synthetic heparosan-type heptasaccharide as a potent anti-inflammatory agent. The present strategy enables the simplification of complex polysaccharides to bioactive synthetic oligosaccharides for therapeutic utility.

Derangement of the endothelial glycocalyx in sepsis

The vascular endothelial surface is coated by the glycocalyx, a ubiquitous gel-like layer composed of a membrane-binding domain that contains proteoglycans, glycosaminoglycan side-chains, and plasma proteins such as albumin and antithrombin. The endothelial glycocalyx plays a critical role in maintaining vascular homeostasis. However, this component is highly vulnerable to damage and is also difficult to examine. Recent advances in analytical techniques have enabled biochemical, visual and computational investigation of this vascular component. The glycocalyx modulates leukocyte-endothelial interactions, thrombus formation and other processes that lead to microcirculatory dysfunction and critical organ injury in sepsis. It also acts as a regulator of vascular permeability and contains mechanosensors as well as receptors for growth factors and anticoagulants. During the initial onset of sepsis, the glycocalyx is damaged and circulating levels of glycocalyx components, including syndecans, heparan sulfate and hyaluronic acid, can be measured and are reportedly useful as biomarkers for sepsis. Also, a new methodology using side-stream dark-field imaging is now clinically available for assessing the glycocalyx. Multiple factors including hypervolemia and hyperglycemia are toxic to the glycocalyx, and several agents have been proposed as therapeutic modalities, although no single treatment has been proven to be clinically effective. In this article, we review the derangement of the glycocalyx in sepsis. Despite the accumulated knowledge regarding the important roles of the glycocalyx, the relationship between derangement of the endothelial glycocalyx and severity of sepsis or disseminated intravascular coagulation has not been adequately elucidated and further work is needed.

SEMA4D-heparin Complexes Immobilized on Titanium Surfaces Have Anticoagulant, Cell-Migration-Promoting, and Immunoregulatory Effects

Soluble semaphorin 4D (SEMA4D) is a 120 kDa transmembrane protein, which belongs to the semaphorin family of axon guidance molecules that act primarily axonal repellents. SEMA4D elicits its migration-promoting and immunomodulatory effects through activation of PLXNB1 and CD72, respectively. In this study, SEMA4D combined with heparin were adsorbed onto cationic surfaces. The biocompatibility evaluation results indicated that the SEMA4D-heparin-modified surfaces displayed less platelet adhesion and activation, prolonged activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) and reduced fibrinogen gamma chain (FGG) exposure and fibrinogen adhesion. Additionally, endothelial cells (ECs) showed improved adhesion density and proliferation activity on the SEMA4D-heparin-modified surfaces. Chemotactic and haptotaxis assays indicated a highly guided migration for ECs on the modified surfaces. The immunological tests revealed that the SEMA4D-heparin complexes had a positive immunomodulatory effect on macrophages and promoted macrophages polarization into M2 phenotypes. Overall, the results suggested that the SEMA4D-heparin complexes can be a potential therapeutic agent to promote tissue healing and accelerate in situ endothelialization with minimal side effects and positive immunomodulatory effect.

Quantitative analysis of antithrombin III binding site in low molecular weight heparins by exhausetive heparinases digestion and capillary electrophoresis

The antithrombin III (ATIII)-binding site, which contains a special 3-O-sulfated, N-sulfated glucosamine residue with or without 6-O-sulfation, is mainly responsible for the anticoagulant activity of heparin. Undergoing the chemical depolymerization process, the preservation of the ATIII-binding site in low molecular weight heparins (LMWHs) are varied leading to the fluctuation of the anticoagulant activity. Herein we report a capillary electrophoresis (CE) method in combination with heparinase digestion and affinity chromatography for the measurement of molar percentage of ATIII-binding site of LMWHs. After exhaustively digesting LMWHs with the mixture of heparinase I, II and III, almost all the resulting oligosaccharide building blocks, including the three 3-O-sulfated tetrasaccharides derived from the ATIII-binding site, were resolved by CE separation. The peak area of each building block permits quantification of the molar percentage of the ATIII-binding site. The peaks corresponding to the 3-O-sulfated tetrasaccharides were assigned based on the linear relationship between the electrophoretic mobilities of the oligosaccharides and their charge to mass ratios. The peak assignment was further confirmed by analysis of the high ATIII affinity fractions, which contains much high 3-O-sulfated tetrasaccharides. With the method, the molar percentage of the ATIII-binding site of enoxaparin from different batches and different manufactures were measured and compared. It was demonstrated that the CE method provides more precise data for assessing the anti-FXa activity than that of the biochemical assay method.

Immobilization of vitronectin-binding heparan sulfates onto surfaces to support human pluripotent stem cells

Functionalizing medical devices with polypeptides to enhance their performance has become important for improved clinical success. The extracellular matrix (ECM) adhesion protein vitronectin (VN) is an effective coating, although the chemistry used to attach VN often reduces its bioactivity. In vivo, VN binds the ECM in a sequence-dependent manner with heparan sulfate (HS) glycosaminoglycans. We reasoned therefore that sequence-based affinity chromatography could be used to isolate a VN-binding HS fraction (HS9) for use as a coating material to capture VN onto implant surfaces. Binding avidity and specificity of HS9 were confirmed by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR)-based assays. Plasma polymerization of allylamine (AA) to tissue culture-treated polystyrene (TCPS) was then used to capture and present HS9 as determined by radiolabeling and ELISA. HS9-coated TCPS avidly bound VN, and this layered surface supported the robust attachment, expansion, and maintenance of human pluripotent stem cells. Compositional analysis demonstrated that 6-O- and N-sulfation, as well as lengths greater than three disaccharide units (dp6) are critical for VN binding to HS-coated surfaces. Importantly, HS9 coating reduced the threshold concentration of VN required to create an optimally bioactive surface for pluripotent stem cells. We conclude that affinity-purified heparan sugars are able to coat materials to efficiently bind adhesive factors for biomedical applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1887-1896, 2018.

Structural Analysis of Heparin-Derived 3-O-Sulfated Tetrasaccharides: Antithrombin Binding Site Variants

Heparin is a polysaccharide that is widely used as an anticoagulant drug. The mechanism for heparin's anticoagulant activity is primarily through its interaction with a serine protease inhibitor, antithrombin III (AT), that enhances its ability to inactivate blood coagulation serine proteases, including thrombin (factor IIa) and factor Xa. The AT-binding site in the heparin is one of the most well-studied carbohydrate-protein binding sites and its structure is the basis for the synthesis of the heparin pentasaccharide drug, fondaparinux. Despite our understanding of the structural requirements for the heparin pentasaccharide AT-binding site, there is a lack of data on the natural variability of these binding sites in heparins extracted from animal tissues. The present work provides a detailed study on the structural variants of the tetrasaccharide fragments of this binding site afforded following treatment of a heparin with heparin lyase II. The 5 most commonly observed tetrasaccharide fragments of the AT-binding site are fully characterized, and a method for their quantification in heparin and low-molecular-weight heparin products is described.

Parenteral administration of factor Xa/IIa inhibitors limits experimental aortic aneurysm and atherosclerosis

Intraluminal thrombus is a consistent feature of human abdominal aortic aneurysm (AAA). Coagulation factor Xa (FXa) catalyses FII to thrombin (FIIa). We examined the effect of FXa/FIIa inhibition on experimental aortic aneurysm in apolipoprotein E-deficient (ApoE^-/-) mice infused with angiotensin II (AngII). The concentration of FXa within the supra-renal aorta (SRA) correlated positively with SRA diameter. Parenteral administration of enoxaparin (FXa/IIa inhibitor) and fondaparinux (FXa inhibitor) over 14 days reduced to severity of aortic aneurysm and atherosclerosis in AngII-infused ApoE^-/- mice. Enteral administration of the FIIa inhibitor dabigatran had no significant effect. Aortic protease-activated receptor (PAR)-2 expression increased in response to AngII infusion. Fondaparinux reduced SRA levels of FXa, FIIa, PAR-2, matrix metalloproteinase (MMP)2, Smad2/3 phosphorylation, and MOMA-2 positive cells in the mouse model. FXa stimulated Smad2/3 phosphorylation and MMP2 expression in aortic vascular smooth muscle cells (VSMC) in vitro. Expression of MMP2 in FXa-stimulated VSMC was downregulated in the presence of a PAR-2 but not a PAR-1 inhibitor. These findings suggest that FXa/FIIa inhibition limits aortic aneurysm and atherosclerosis severity due to down-regulation of vascular PAR-2-mediated Smad2/3 signalling and MMP2 expression. Inhibition of FXa/FIIa may be a potential therapy for limiting aortic aneurysm.

An integrated approach using orthogonal analytical techniques to characterize heparan sulfate structure

Heparan sulfate (HS), a glycosaminoglycan present on the surface of cells, has been postulated to have important roles in driving both normal and pathological physiologies. The chemical structure and sulfation pattern (domain structure) of HS is believed to determine its biological function, to vary across tissue types, and to be modified in the context of disease. Characterization of HS requires isolation and purification of cell surface HS as a complex mixture. This process may introduce additional chemical modification of the native residues. In this study, we describe an approach towards thorough characterization of bovine kidney heparan sulfate (BKHS) that utilizes a variety of orthogonal analytical techniques (e.g. NMR, IP-RPHPLC, LC-MS). These techniques are applied to characterize this mixture at various levels including composition, fragment level, and overall chain properties. The combination of these techniques in many instances provides orthogonal views into the fine structure of HS, and in other instances provides overlapping / confirmatory information from different perspectives. Specifically, this approach enables quantitative determination of natural and modified saccharide residues in the HS chains, and identifies unusual structures. Analysis of partially digested HS chains allows for a better understanding of the domain structures within this mixture, and yields specific insights into the non-reducing end and reducing end structures of the chains. This approach outlines a useful framework that can be applied to elucidate HS structure and thereby provides means to advance understanding of its biological role and potential involvement in disease progression. In addition, the techniques described here can be applied to characterization of heparin from different sources.

Structural features of heparanase-inhibiting non-anticoagulant heparin derivative Roneparstat

Owing to their anti-tumor and anti-inflammatory properties, non-anticoagulant glycol-split (gs) heparins, obtained by periodate oxidation/borohydride reduction, are of growing interest. The present study was focused on the structural characterization of N-acetylated gs-heparin Roneparstat, a promising anti-cancer heparanase-inhibiting drug currently being investigated in clinical trials. The major and minor structural features of structurally complex Roneparstat have been characterized for the first time using conductimetric titration, size-exclusion chromatography with triple detector array, NMR and LC/MS. It has been shown that gs-uronic acids are mainly interspersed by unmodified disaccharide building blocks, but can also be present within sequences with consequent gs-residues. Peculiar gs-sequences, such as those derived from antithrombin binding regions and those containing I_2S-A_NS3S6S, as well as a variety of unnatural terminal groups, markers of preparation processes, have also been identified in Roneparstat. Structural features of Roneparstat that may play an important role in interactions with proteins have been summarized.

New Functional Tools for Antithrombogenic Activity Assessment of Live Surface Glycocalyx

OBJECTIVE

It is widely accepted that the presence of a glycosaminoglycan-rich glycocalyx is essential for endothelialized vasculature health; in fact, a damaged or impaired glycocalyx has been demonstrated in many vascular diseases. Currently, there are no methods that characterize glycocalyx functionality, thus limiting investigators' ability to assess the role of the glycocalyx in vascular health.

APPROACH AND RESULTS

We have developed novel, easy-to-use, in vitro assays that directly quantify live endothelialized surface's functional heparin weights and their anticoagulant capacity to inactivate Factor Xa and thrombin. Using our assays, we characterized 2 commonly used vascular models: native rat aorta and cultured human umbilical vein endothelial cell monolayer. We determined heparin contents to be ≈10 000 ng/cm(2) on the native aorta and ≈10-fold lower on cultured human umbilical vein endothelial cells. Interestingly, human umbilical vein endothelial cells demonstrated a 5-fold lower anticoagulation capacity in inactivating both Factor Xa and thrombin relative to native aortas. We verified the validity and accuracy of the novel assays developed in this work using liquid chromatography-mass spectrometry analysis.

CONCLUSIONS

Our assays are of high relevance in the vascular community because they can be used to establish the antithrombogenic capacity of many different types of surfaces such as vascular grafts and transplants. This work will also advance the capacity for glycocalyx-targeting therapeutics development to treat damaged vasculatures.

Heparin exerts anti-apoptotic effects on uterine explants by targeting the endocannabinoid system

Miscarriage caused by Gram-negative bacteria infecting the female genital tract is one of the most common complications of human pregnancy. Intraperitoneal administration of LPS to 7-days pregnant mice induces embryo resorption after 24 h. Here, we show that LPS induced apoptosis on uterine explants from 7-days pregnant mice and that CB1 receptor was involved in this effect. On the other hand, heparin has been widely used for the prevention of pregnancy loss in women with frequent miscarriage with or without thrombophilia. Besides its anticoagulant properties, heparin exerts anti-inflammatory, immunomodulatory and anti-apoptotic effects. Here, we sought to investigate whether the administration of heparin prevented LPS-induced apoptosis in uterine explants from 7-days pregnant mice. We found that heparin enhanced cell survival in LPS-treated uterine explants and that this effect was mediated by increasing uterine FAAH activity. Taken together, our results point towards a novel mechanism involved in the protective effects of heparin.

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.

Structure Determination of Natural Products by Mass Spectrometry

I review laboratory research on the development of mass spectrometric methodology for the determination of the structure of natural products of biological and medical interest, which I conducted from 1958 to the end of the twentieth century. The methodology was developed by converting small peptides to their corresponding polyamino alcohols to make them amenable to mass spectrometry, thereby making it applicable to whole proteins. The structures of alkaloids were determined by analyzing the fragmentation of a known alkaloid and then using the results to deduce the structures of related compounds. Heparin-like structures were investigated by determining their molecular weights from the mass of protonated molecular ions of complexes with highly basic, synthetic peptides. Mass spectrometry was also employed in the analysis of lunar material returned by the Apollo missions. A miniaturized gas chromatograph mass spectrometer was sent to Mars on board of the two Viking 1976 spacecrafts.

Re-visiting the structure of heparin

The sulfated polysaccharide heparin has been used as a life-saving anticoagulant in clinics well before its detailed structure was known. This mini-review is a survey of the evolution in the discovery of the primary and secondary structure of heparin. Highlights in this history include elucidation and synthesis of the specific sequence that binds to antithrombin, the development of low-molecular-weight heparins currently used as antithrombotic drugs, and the most promising start of chemo-enzymatic synthesis. Special emphasis is given to peculiar conformational properties contributing to interaction with proteins that modulate different biological properties.

Analysis of 3-O-sulfo group-containing heparin tetrasaccharides in heparin by liquid chromatography-mass spectrometry

Complete heparin digestion with heparin lyase 2 affords a mixture of disaccharides and resistant tetrasaccharides with 3-O-sulfo group-containing glucosamine residues at their reducing ends. Quantitative online liquid chromatography-mass spectrometric analysis of these resistant tetrasaccharides is described in this article. The disaccharide and tetrasaccharide compositions of seven porcine intestinal heparins and five low-molecular-weight heparins were analyzed by this method. These resistant tetrasaccharides account for from 5.3 to 7.3wt% of heparin and from 6.2 to 8.3wt% of low-molecular-weight heparin. Because these tetrasaccharides are derived from heparin's antithrombin III-binding sites, we examined whether this method could be applied to estimate the anticoagulant activity of heparin. The content of 3-O-sulfo group-containing tetrasaccharides in a heparin correlated positively (r=0.8294) to heparin's anticoagulant activity.

De novo synthesis of a narrow size distribution low-molecular-weight heparin

Heparin, a commonly used anticoagulant drug, is a mixture of highly sulfated polysaccharides with various molecular weights (MWs). The unique sulfation pattern dictates the anticoagulant activity of heparin. Commercial heparins are categorized into three forms according to their average MW: unfractionated heparin (UFH, MWavg 14,000), low-MW heparin (LMWH, MWavg 3500-6500) and the synthetic pentasaccharide (fondaparinux, MW 1508.3). UFH is isolated from porcine intestine while LMWH is derived from UFH by various methods of depolymerization, which generate a wide range of oligosaccharide chain lengths. Different degradation methods result in structurally distinct LMWH products, displaying different pharmacological and pharmacokinetic properties. In this report, we utilized a chemoenzymatic method to synthesize LMWH with the emphasis on controlling the size distribution of the oligosaccharides. A tetrasaccharide primer and a controlled enzyme-based polymerization were employed to build a narrow size oligosaccharide backbone. The oligosaccharide backbones were further modified by a series of sulfation and epimerization steps in order to obtain a full anticoagulation activity. Determination of the anticoagulation activity in vitro and ex vivo indicated that the synthetic LMWH has higher potency than enoxaparin, a commercial LMWH drug in clinical usage.

Testing of potential glycan-based heparanase inhibitors in a fluorescence activity assay using either bacterial heparinase II or human heparanase

Heparanase, an endo-β-glucuronidase cleaving heparan sulfate (HS) chains at cell surfaces and in the extracellular matrix (ECM), is involved in angiogenesis, tumor progression and metastasis as well as in inflammation and kidney dysfunction. Therefore, heparanase is considered a promising therapeutic target and diagnostic marker. Recently, we have developed a simple, rapid, fully automatable fluorimetric activity assay using the synthetic sulfated pentasaccharide fondaparinux as substrate and bacterial heparinase II (HEP-II) instead of human heparanase (hHEP). The aim of this study was to evaluate this assay for inhibitor testing as well as to check whether the assay principle is applicable to measure the activity and inhibition, respectively, of the actual target enzyme hHEP. Besides the known hHEP inhibitor suramin and the antiinflammatory and antimetastatic PS3, two series of β-1,3-glucan sulfates differing in their chain length and degree of sulfation, further semisynthetic sulfated glycans, and two sulfated polysaccharides isolated from algae were included to examine structure-activity relationships. The inhibitory activity of sulfated glycans showed to be greatly dependent on both their degree of sulfation and their basic glycan structure, but independent of their molecular size. The β-1,3-glucan sulfates were superior to suramin as well as to the other glycans with similar degree of sulfations. The most active inhibitor was found to be the β-1,3-glucan sulfate PS3 (IC₅₀=0.017 μM). By using hHEP instead of HEP-II comparable results were obtained. With an IC₅₀ being about 160 times lower than that of suramin, PS3 exhibited again the strongest inhibitory effects. Inhibition of hHEP may therefore contribute to the potent antiinflammatory and antimetastatic activities of PS3 in vivo. In conclusion, the fluorimetric hHEP activity assay proved to be a simple, fully automatable tool for testing potential inhibitors. In case of HS mimetic inhibitors, the assay variant with HEP-II may provide a fast and inexpensive option for initial screening purposes.

Heparan sulfate 3-O-sulfation: a rare modification in search of a function

Many protein ligands bind to heparan sulfate, which results in their presentation, protection, oligomerization or conformational activation. Binding depends on the pattern of sulfation and arrangement of uronic acid epimers along the chains. Sulfation at the C3 position of glucosamine is a relatively rare, yet biologically significant modification, initially described as a key determinant for binding and activation of antithrombin and later for infection by type I herpes simplex virus. In mammals, a family of seven heparan sulfate 3-O-sulfotransferases installs sulfate groups at this position and constitutes the largest group of sulfotransferases involved in heparan sulfate formation. However, to date very few proteins or biological systems have been described that are influenced by 3-O-sulfation. This review describes our current understanding of the prevalence and structure of 3-O-sulfation sites, expression and substrate specificity of the 3-O-sulfotransferase family and the emerging roles of 3-O-sulfation in biology.

Structural features of glycol-split low-molecular-weight heparins and their heparin lyase generated fragments

Periodate oxidation followed by borohydride reduction converts the well-known antithrombotics heparin and low-molecular-weight heparins (LMWHs) into their "glycol-split" (gs) derivatives of the "reduced oxyheparin" (RO) type, some of which are currently being developed as potential anti-cancer and anti-inflammatory drugs. Whereas the structure of gs-heparins has been recently studied, details of the more complex and more bioavailable gs-LMWHs have not been yet reported. We obtained RO derivatives of the three most common LMWHs (tinzaparin, enoxaparin, and dalteparin) and studied their structures by two-dimensional nuclear magnetic resonance spectroscopy and ion-pair reversed-phase high-performance liquid chromatography coupled with electrospray ionization mass spectrometry. The liquid chromatography-mass spectrometry (LC-MS) analysis was extended to their heparinase-generated oligosaccharides. The combined NMR/LC-MS analysis of RO-LMWHs provided evidence for glycol-splitting-induced transformations mainly involving internal nonsulfated glucuronic and iduronic acid residues (including partial hydrolysis with formation of "remnants") and for the hydrolysis of the gs uronic acid residues when formed at the non-reducing ends (mainly, in RO-dalteparin). Evidence for minor modifications, such as ring contraction of some dalteparin internal aminosugar residues, was also obtained. Unexpectedly, the N-sulfated 1,6-anhydromannosamine residues at the enoxaparin reducing end were found to be susceptible to the periodate oxidation. In addition, in tinzaparin and enoxaparin, the borohydride reduction converts the hemiacetalic aminosugars at the reducing end to alditols. Typical LC-MS signatures of RO-derivatives of individual LMWH both before and after digestion with heparinases included oligosaccharides generated from the original antithrombin-binding and "linkage" regions.

Controllable production of low molecular weight heparins by combinations of heparinase I/II/III

Enzymatic depolymerization of heparin by heparinases is promising for production of low molecular weight heparins (LMWHs) as anticoagulants, due to its mild reaction conditions and high selectivity. Here, different heparinase combinations were used to depolymerize heparin. Heparinase I and heparinase II can depolymerize heparin more efficiently than heparinase III, respectively, but heparinase III was the best able to protect the anticoagulant activities of LMWHs. Heparinase III and heparinase I/II combinations were able to efficiently depolymerize heparin to LMWHs with higher anticoagulant activity than the LMWHs produced by the respective heparinase I and heparinase II. HepIII and HepI is the best combination for maintaining high anti-IIa activity (75.7 ± 4.21 IU/mg) at the same Mw value. Furthermore, considering both the changes in molecular weight and anticoagulant activity, the action patterns of heparinase I and heparinase II were found not to follow the exolytic and processive depolymerizing mechanism from the reducing end of heparin.

New targets for glycosaminoglycans and glycosaminoglycans as novel targets

Biological functions of a variety of proteins are mediated via their interaction with glycosaminoglycans (GAGs). The structural diversity within the wide GAG landscape provides individual interaction sites for a multitude of proteins involved in several pathophysiological processes. This 'GAG angle' of such proteins as well as their specific GAG ligands give rise to novel therapeutic concepts for drug development. Current glycomic technologies to elucidate the glycan structure-function relationships, methods to investigate the selectivity and specificity of glycan-protein interactions and existing therapeutic approaches to interfere with GAG-protein interactions are discussed.

Heparin dodecasaccharide containing two antithrombin-binding pentasaccharides: structural features and biological properties

The antithrombin (AT) binding properties of heparin and low molecular weight heparins are strongly associated to the presence of the pentasaccharide sequence AGA*IA (A(NAc,6S)-GlcUA-A(NS,3,6S)-I(2S)-A(NS,6S)). By using the highly chemoselective depolymerization to prepare new ultra low molecular weight heparin and coupling it with the original separation techniques, it was possible to isolate a polysaccharide with a biosynthetically unexpected structure and excellent antithrombotic properties. It consisted of a dodecasaccharide containing an unsaturated uronate unit at the nonreducing end and two contiguous AT-binding sequences separated by a nonsulfated iduronate residue. This novel oligosaccharide was characterized by NMR spectroscopy, and its binding with AT was determined by fluorescence titration, NMR, and LC-MS. The dodecasaccharide displayed a significantly increased anti-FXa activity compared with those of the pentasaccharide, fondaparinux, and low molecular weight heparin enoxaparin.

Profiling glycol-split heparins by high-performance liquid chromatography/mass spectrometry analysis of their heparinase-generated oligosaccharides

Glycol-split (gs) heparins, obtained by periodate oxidation/borohydride reduction of heparin currently used as an anticoagulant and antithrombotic drug, are arousing increasing interest in anticancer and anti-inflammation therapies. These new medical uses are favored by the loss of anticoagulant activity associated with glycol-splitting-induced inactivation of the antithrombin III (AT) binding site. The structure of gs heparins has not been studied yet in detail. In this work, ion pair reversed-phase high-performance liquid chromatography (IPRP-HPLC) coupled with electrospray ionization mass spectrometry (ESI-MS) widely used for unmodified heparin has been adapted to the analysis of oligosaccharides generated by digestion with heparinases of gs heparins usually prepared from porcine mucosal heparin. The method was also found to be very effective in analyzing gs derivatives obtained from heparins of different animal and tissue origins. Besides the major 2-O-sulfated disaccharides, heparinase digests of gs heparins contain mainly tetra- and hexasaccharides incorporating one or two gs residues, with distribution patterns typical for individual gs heparins. A heptasulfated, mono-N-acetylated hexasaccharide with two gs residues was shown to be a marker of the gs-modified AT binding site within heparin chains.

Glycomics approaches for the bioassay and structural analysis of heparin/heparan sulphates

The glycosaminoglycan heparan sulphate (HS) has a heterogeneous structure; evidence shows that specific structures may be responsible for specific functions in biological processes such as blood coagulation and regulation of growth factor signalling. This review summarises the different experimental tools and methods developed to provide more rapid methods for studying the structure and functions of HS. Rapid and sensitive methods for the facile purification of HS, from tissue and cell sources are reviewed. Data sets for the structural analysis are often complex and include multiple sample sets, therefore different software and tools have been developed for the analysis of different HS data sets. These can be readily applied to chromatographic data sets for the simplification of data (e.g., charge separation using strong anion exchange chromatography and from size separation using gel filtration techniques. Finally, following the sequencing of the human genome, research has rapidly advanced with the introduction of high throughput technologies to carry out simultaneous analyses of many samples. Microarrays to study macromolecular interactions (including glycan arrays) have paved the way for bioassay technologies which utilize cell arrays to study the effects of multiple macromolecules on cells. Glycan bioassay technologies are described in which immobilisation techniques for saccharides are exploited to develop a platform to probe cell responses such as signalling pathway activation. This review aims at reviewing available techniques and tools for the purification, analysis and bioassay of HS saccharides in biological systems using "glycomics" approaches.

Heparins modulate the IFN-γ-induced production of chemokines in human breast cancer cells

Heparins seem to improve survival in patients with advanced malignancies independently of their anticoagulatory function. As the treatment options in advanced and metastatic breast cancer are still very limited, heparins might be an interesting addition to the existing systemic therapies. The interferon (IFN)-γ-inducible chemokines CXCL9 and CXCL10 play an essential role in the regulation of the immune milieu in malignant tumours, thereby being interesting targets for an immunological intervention. We therefore wanted to test whether heparins have an impact on the chemokines CXCL9 and CXCL10 as well as the IFN-γ signalling in human breast cancer cells in vitro. The well-established cell lines BT-474, MCF-7, SK-BR-3 and MDA-MB-231 were incubated with IFN-γ, unfractionated heparin (UFH), different low molecular weight heparins (LMWHs) and the heparin-related polyanions danaparoid and dextran sulphate. The production of CXCL9 and CXCL10 was measured by ELISA and real-time RT-PCR, the phosphorylation of signal transducer and activator of transcription (STAT) 1 was detected by an in-cell western assay and the amount of cellular bound IFN-γ was analysed by a high sensitivity ELISA. We observed that IFN-γ induced CXCL9 and CXCL10 production in MCF-7, SK-BR-3 and MDA-MB-231 cells but not in BT-474. UFH dose dependently inhibited the effect of IFN-γ on the secretion and expression of CXCL9 and CXCL10. LMWHs and heparin-related compounds differentially modulated IFN-γ-effects-the results depended on their molecular size and charge, but were independent of their anticoagulatory properties. As a reason for these heparin effects, we could show that the IFN-γ-induced phosphorylation of STAT1 was modulated by heparins, caused by an interaction with the cellular binding of IFN-γ. In conclusion, these results support the significance of the immunomodulatory properties of heparins independently of their classical anticoagulatory function. Heparin-derived sulphated polysaccharides with distinct molecular properties might thus be interesting candidates for new therapeutic strategies in breast cancer.

Low-molecular-weight heparins: differential characterization/physical characterization

Low-molecular-weight heparins (LMWHs), derived from unfractionated heparin (UFH) through different depolymerization processes, have advantages with respect to the parent heparin in terms of pharmacokinetics, convenience of administration, and reduced side effects. Each LMWH can be considered as an independent drug with its own activity profile, placing significance on their biophysical characterization, which will also enable a better understanding of their structure-function relationship. Several chemical and physical methods, some involving sample modification, are now available and are reviewed.

The anticoagulant and antithrombotic mechanisms of heparin

The molecular basis for the anticoagulant action of heparin lies in its ability to bind to and enhance the inhibitory activity of the plasma protein antithrombin against several serine proteases of the coagulation system, most importantly factors IIa (thrombin), Xa and IXa. Two major mechanisms underlie heparin's potentiation of antithrombin. The conformational changes induced by heparin binding cause both expulsion of the reactive loop and exposure of exosites of the surface of antithrombin, which bind directly to the enzyme target; and a template mechanism exists in which both inhibitor and enzyme bind to the same heparin molecule. The relative importance of these two modes of action varies between enzymes. In addition, heparin can act through other serine protease inhibitors such as heparin co-factor II, protein C inhibitor and tissue factor plasminogen inhibitor. The antithrombotic action of heparin in vivo, though dominated by anticoagulant mechanisms, is more complex, and interactions with other plasma proteins and cells play significant roles in the living vasculature.