Further evidence that periodate cleavage of heparin occurs primarily through the antithrombin binding site

Chemical Modification of Glycosaminoglycan Polysaccharides

The linear anionic class of polysaccharides, glycosaminoglycans (GAGs), are critical throughout the animal kingdom for developmental processes and the maintenance of healthy tissues. They are also of interest as a means of influencing biochemical processes. One member of the GAG family, heparin, is exploited globally as a major anticoagulant pharmaceutical and there is a growing interest in the potential of other GAGs for diverse applications ranging from skin care to the treatment of neurodegenerative conditions, and from the treatment and prevention of microbial infection to biotechnology. To realize the potential of GAGs, however, it is necessary to develop effective tools that are able to exploit the chemical manipulations to which GAGs are susceptible. Here, the current knowledge concerning the chemical modification of GAGs, one of the principal approaches for the study of the structure-function relationships in these molecules, is reviewed. Some additional methods that were applied successfully to the analysis and/or processing of other carbohydrates, but which could be suitable in GAG chemistry, are also discussed.

Heparan Sulfate Proteoglycans as Attachment Factor for SARS-CoV-2

Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) is causing an unprecedented global pandemic demanding the urgent development of therapeutic strategies. Microarray binding experiments, using an extensive heparan sulfate (HS) oligosaccharide library, showed that the receptor binding domain (RBD) of the spike of SARS-CoV-2 can bind HS in a length- and sequence-dependent manner. A hexasaccharide composed of IdoA2S-GlcNS6S repeating units was identified as the minimal binding epitope. Surface plasmon resonance showed the SARS-CoV-2 spike protein binds with a much higher affinity to heparin (K D = 55 nM) compared to the RBD (K D = 1 μM) alone. It was also found that heparin does not interfere in angiotensin-converting enzyme 2 (ACE2) binding or proteolytic processing of the spike. However, exogenous administered heparin or a highly sulfated HS oligosaccharide inhibited RBD binding to cells. Furthermore, an enzymatic removal of HS proteoglycan from physiological relevant tissue resulted in a loss of RBD binding. The data support a model in which HS functions as the point of initial attachment allowing the virus to travel through the glycocalyx by low-affinity high-avidity interactions to reach the cell membrane, where it can engage with ACE2 for cell entry. Microarray binding experiments showed that ACE2 and HS can simultaneously engage with the RBD, and it is likely no dissociation between HS and RBD is required for binding to ACE2. The results highlight the potential of using HS oligosaccharides as a starting material for therapeutic agent development.

Characterization of heparin and severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) spike glycoprotein binding interactions

Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has resulted in a pandemic and continues to spread around the globe at an unprecedented rate. To date, no effective therapeutic is available to fight its associated disease, COVID-19. Our discovery of a novel insertion of glycosaminoglycan (GAG)-binding motif at S1/S2 proteolytic cleavage site (681-686 (PRRARS)) and two other GAG-binding-like motifs within SARS-CoV-2 spike glycoprotein (SGP) led us to hypothesize that host cell surface GAGs may interact SARS-CoV-2 SGPs to facilitate host cell entry. Using a surface plasmon resonance direct binding assay, we found that both monomeric and trimeric SARS-CoV-2 SGP bind more tightly to immobilized heparin (K_D = 40 pM and 73 pM, respectively) than the SARS-CoV and MERS-CoV SGPs (500 nM and 1 nM, respectively). In competitive binding studies, the IC₅₀ of heparin, tri-sulfated non-anticoagulant heparan sulfate, and non-anticoagulant low molecular weight heparin against SARS-CoV-2 SGP binding to immobilized heparin were 0.056 μM, 0.12 μM, and 26.4 μM, respectively. Finally, unbiased computational ligand docking indicates that heparan sulfate interacts with the GAG-binding motif at the S1/S2 site on each monomer interface in the trimeric SARS-CoV-2 SGP, and at another site (453-459 (YRLFRKS)) when the receptor-binding domain is in an open conformation. The current study serves a foundation to further investigate biological roles of GAGs in SARS-CoV-2 pathogenesis. Furthermore, our findings may provide additional basis for further heparin-based interventions for COVID-19 patients exhibiting thrombotic complications.

Non-anticoagulant Heparin as a Pre-exposure Prophylaxis Prevents Lyme Disease Infection

Lyme disease (LD) is caused by the spirochete Borrelia burgdorferi sensu lato (Bbsl). After transmission to humans by ticks, Bbsl spreads to multiple organs, leading to arthritis, carditis, and neuroborreliosis. No effective prophylaxis against human LD prior to tick exposure is currently available. Thus, a pre-exposure prophylaxis (PrEP) against LD is needed. The establishment of LD bacteria at diverse sites is dictated partly by the binding of Bbsl to proteoglycans (PGs) and glycosaminoglycans (GAGs) in tissues. The drug heparin is structurally similar to these GAGs and inhibits Bbsl attachment to PGs, GAGs, cells, and tissues, suggesting its potential to prevent LD. However, the anticoagulant activity of heparin often results in hemorrhage, hampering the development of this compound as LD PrEP. We have previously synthesized a non-anticoagulant version of heparin (NACH), which was verified for safety in mice and humans. Here, we showed that NACH blocks Bbsl attachment to PGs, GAGs, and mammalian cells. We also found that treating mice with NACH prior to the exposure of ticks carrying Bbsl followed by continuous administration of this compound prevents tissue colonization by Bbsl. Furthermore, NACH-treated mice develop greater levels of IgG and IgM against Bbsl at early stages of infection, suggesting that the upregulation of antibody immune responses may be one of the mechanisms for NACH-mediated LD prevention. This is one of the first studies examining the ability of a heparin-based compound to prevent LD prior to tick exposure. The information presented might also be extended to prevent other infectious diseases agents.

Non-Anticoagulant Heparins as Heparanase Inhibitors

The chapter will review early and more recent seminal contributions to the discovery and characterization of heparanase and non-anticoagulant heparins inhibiting its peculiar enzymatic activity. Indeed, heparanase displays a unique versatility in degrading heparan sulfate chains of several proteoglycans expressed in all mammalian cells. This endo-β-D-glucuronidase is overexpressed in cancer, inflammation, diabetes, atherosclerosis, nephropathies and other pathologies. Starting from known low- or non-anticoagulant heparins, the search for heparanase inhibitors evolved focusing on structure-activity relationship studies and taking advantage of new chemical-physical analytical methods which have allowed characterization and sequencing of polysaccharide chains. New methods to screen heparanase inhibitors and to evaluate their mechanism of action and in vivo activity in experimental models prompted their development. New non-anticoagulant heparin derivatives endowed with anti-heparanase activity are reported. Some leads are under clinical evaluation in the oncology field (e.g., acute myeloid leukemia, multiple myeloma, pancreatic carcinoma) and in other pathological conditions (e.g., sickle cell disease, malaria, labor arrest).

Heparinoid Complex-Based Heparin-Binding Cytokines and Cell Delivery Carriers

Heparinoid is the generic term that is used for heparin, heparan sulfate (HS), and heparin-like molecules of animal or plant origin and synthetic derivatives of sulfated polysaccharides. Various biological activities of heparin/HS are attributed to their specific interaction and regulation with various heparin-binding cytokines, antithrombin (AT), and extracellular matrix (ECM) biomolecules. Specific domains with distinct saccharide sequences in heparin/HS mediate these interactions are mediated and require different highly sulfated saccharide sequences with different combinations of sulfated groups. Multivalent and cluster effects of the specific sulfated sequences in heparinoids are also important factors that control their interactions and biological activities. This review provides an overview of heparinoid-based biomaterials that offer novel means of engineering of various heparin-binding cytokine-delivery systems for biomedical applications and it focuses on our original studies on non-anticoagulant heparin-carrying polystyrene (NAC-HCPS) and polyelectrolyte complex-nano/microparticles (N/MPs), in addition to heparin-coating devices.

Glycosaminoglycan Compositional Analysis of Relevant Tissues in Zika Virus Pathogenesis and in Vitro Evaluation of Heparin as an Antiviral against Zika Virus Infection

Zika virus (ZIKV) is an enveloped RNA virus from the flavivirus family that can cause fetal neural abnormalities in pregnant women. Previously, we established that ZIKV-EP (envelope protein) binds to human placental chondroitin sulfate (CS), suggesting that CS may be a potential host cell surface receptor in ZIKV pathogenesis. In this study, we further characterized the GAG disaccharide composition of other biological tissues (i.e., mosquitoes, fetal brain cells, and eye tissues) in ZIKV pathogenesis to investigate the role of tissue specific GAGs. Heparan sulfate (HS) was the major GAG, and levels of HS-6-sulfo, HS 0S (unsulfated HS), and CS 4S disaccharides were the main differences in the GAG composition of Aedes aegypti and Aedes albopictus mosquitoes. In human fetal neural progenitor and differentiated cells, HS 0S and CS 4S were the main disaccharides. A change in disaccharide composition levels was observed between undifferentiated and differentiated cells. In different regions of the bovine eyes, CS was the major GAG, and the amounts of hyaluronic acid or keratan sulfate varied depending on the region of the eye. Next, we examined heparin (HP) of various structures to investigate their potential in vitro antiviral activity against ZIKV and Dengue virus (DENV) infection in Vero cells. All compounds effectively inhibited DENV replication; however, they surprisingly promoted ZIKV replication. HP of longer chain lengths more strongly promoted activity in ZIKV replication. This study further expands our understanding of role of GAGs in ZIKV pathogenesis and carbohydrate-based antivirals against flaviviral infection.

Non-Anticoagulant Low Molecular Weight Heparins for Pharmaceutical Applications

Heparin is a polypharmacological agent with anticoagulant activity. Periodate oxidation of the nonsulfated glucuronic acid residue results in non-anticoagulant heparin derivative (NACH) of reduced molecular weight. Similar treatment of a low molecular weight heparin, dalteparin, also removes its anticoagulant activity, affording a second heparin derivative (D-NACH). A full structural characterization of these two derivatives reveals their structural differences. SPR studies display their ability to bind to several important heparin-binding proteins, suggesting potential new therapeutic applications.

Borrelia burgdorferi glycosaminoglycan-binding proteins: a potential target for new therapeutics against Lyme disease

The spirochete bacterium Borrelia burgdorferi sensu lato is the causative agent of Lyme disease, the most common vector-borne disease in Europe and the United States. The spirochetes can be transmitted to humans via ticks, and then spread to different tissues, leading to arthritis, carditis and neuroborreliosis. Although antibiotics have commonly been used to treat infected individuals, some treated patients do not respond to antibiotics and experience persistent, long-term arthritis. Thus, there is a need to investigate alternative therapeutics against Lyme disease. The spirochete bacterium colonization is partly attributed to the binding of the bacterial outer-surface proteins to the glycosaminoglycan (GAG) chains of host proteoglycans. Blocking the binding of these proteins to GAGs is a potential strategy to prevent infection. In this review, we have summarized the recent reports of B. burgdorferi sensu lato GAG-binding proteins and discussed the potential use of synthetic and semi-synthetic compounds, including GAG analogues, to block pathogen interaction with GAGs. Such information should motivate the discovery and development of novel GAG analogues as new therapeutics for Lyme disease. New therapeutic approaches should eventually reduce the burden of Lyme disease and improve human health.

Identification of Heparin Modifications and Polysaccharide Inhibitors of Plasmodium falciparum Merozoite Invasion That Have Potential for Novel Drug Development

Despite recent successful control efforts, malaria remains a leading global health burden. Alarmingly, resistance to current antimalarials is increasing and the development of new drug families is needed to maintain malaria control. Current antimalarials target the intraerythrocytic developmental stage of the Plasmodium falciparum life cycle. However, the invasive extracellular parasite form, the merozoite, is also an attractive target for drug development. We have previously demonstrated that heparin-like molecules, including those with low molecular weights and low anticoagulant activities, are potent and specific inhibitors of merozoite invasion and blood-stage replication. Here we tested a large panel of heparin-like molecules and sulfated polysaccharides together with various modified chemical forms for their inhibitory activity against P. falciparum merozoite invasion. We identified chemical modifications that improve inhibitory activity and identified several additional sulfated polysaccharides with strong inhibitory activity. These studies have important implications for the further development of heparin-like molecules as antimalarial drugs and for understanding merozoite invasion.

Old and new applications of non-anticoagulant heparin

The aim of this chapter is to provide an overview of non-anticoagulant effects of heparins and their potential use in new therapeutic applications. Heparin and heparin derivatives have been tested in inflammatory, pulmonary and reproductive diseases, in cardiovascular, nephro- and neuro-tissue protection and repair, but also as agents against angiogenesis, atheroschlerosis, metastasis, protozoa and viruses. Targeting and inhibition of specific mediators involved in the inflammatory process, promoting some of the above mentioned pathologies, are reported along with recent studies of heparin conjugates and oral delivery systems. Some reports from the institute of the authors, such as those devoted to glycol-split heparins are also included. Among the members and derivatives of this class, several are undergoing clinical trials as antimetastatic and antimalarial agents and for the treatment of labour pain and severe hereditary anaemia. Other heparins, whose therapeutic targets are non-anticoagulant such as nephropathies, retinopathies and cystic fibrosis are also under investigation.

Pathogenesis and Inhibition of Flaviviruses from a Carbohydrate Perspective

Flaviviruses are enveloped, positive single stranded ribonucleic acid (RNA) viruses with various routes of transmission. While the type and severity of symptoms caused by pathogenic flaviviruses vary from hemorrhagic fever to fetal abnormalities, their general mechanism of host cell entry is similar. All pathogenic flaviviruses, such as dengue virus, yellow fever virus, West Nile virus, Japanese encephalitis virus, and Zika virus, bind to glycosaminglycans (GAGs) through the putative GAG binding sites within their envelope proteins to gain access to the surface of host cells. GAGs are long, linear, anionic polysaccharides with a repeating disaccharide unit and are involved in many biological processes, such as cellular signaling, cell adhesion, and pathogenesis. Flavivirus envelope proteins are N-glycosylated surface proteins, which interact with C-type lectins, dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) through their glycans. In this review, we discuss both host and viral surface receptors that have the carbohydrate components, focusing on the surface interactions in the early stage of flavivirus entry. GAG-flavivirus envelope protein interactions as well as interactions between flavivirus envelope proteins and DC-SIGN are discussed in detail. This review also examines natural and synthetic inhibitors of flaviviruses that are carbohydrate-based or carbohydrate-targeting. Both advantages and drawbacks of these inhibitors are explored, as are potential strategies to improve their efficacy to ultimately help eradicate flavivirus infections.

Heparin coatings for improving blood compatibility of medical devices

Blood contact with biomaterials triggers activation of multiple reactive mechanisms that can impair the performance of implantable medical devices and potentially cause serious adverse clinical events. This includes thrombosis and thromboembolic complications due to activation of platelets and the coagulation cascade, activation of the complement system, and inflammation. Numerous surface coatings have been developed to improve blood compatibility of biomaterials. For more than thirty years, the anticoagulant drug heparin has been employed as a covalently immobilized surface coating on a variety of medical devices. This review describes the fundamental principles of non-eluting heparin coatings, mechanisms of action, and clinical applications with focus on those technologies which have been commercialized. Because of its extensive publication history, there is emphasis on the CARMEDA^® BioActive Surface (CBAS^® Heparin Surface), a widely used commercialized technology for the covalent bonding of heparin.

Susceptibility of enoxaparin reducing end amino sugars to periodate oxidation

There is a growing interest on glycol-split low-molecular weight heparins (gs-LMWHs), obtained by periodate oxidation of LMWHs, optionally followed by borohydride reduction, as potential anticancer and anti-inflammatory drugs. However, their structural characterization is still a challenging task, mainly because of the high microheterogeneity of the starting material. In addition, susceptibility to oxidation of some end-groups of LMWHs induces additional heterogeneity, making analysis of gs-LMWHs more complex. In our previous study we showed that 1,6-anhydro-d-mannosamine N-sulfate was affected by periodate, while its epimer 1,6-anhydro-d-glucosamine N-sulfate was resistant. In order to understand the apparently anomalous behavior of terminal 1,6-anhydro-d-mannosamine N-sulfate residues, in the present work we have studied by NMR spectroscopy and LC/MS the behavior of the reducing end amino sugar residues of the tetrasaccharides, isolated from the LMWH enoxaparin, in the presence of periodate. Their molecular mechanics conformational characterization has been also performed. We have shown that the C(2)-C(3) bond of the 1,6-anhydro-d-mannosamine residue can be split by periodate despite the N-substitution. Moreover, we have found that both terminal d-mannosamine N-sulfate and d-glucosamine N-sulfate, lacking the 1,6-anhydro-bridge, can be also oxidized by periodate but with a significantly lower rate. The present results suggest that the cis-e-/a-position of OH and NHSO3(-) groups of N-sulfated 1,6-anhydro-d-mannosamine is not the only factor that makes these end residues susceptible to the oxidation. The 1,6-anhydro-bridge that 'blocks' the ring conformation appears another crucial factor for oxidation to occur. Moreover, we have shown that controlling the reaction time could permit to selectively split non-sulfated iduronic acids of enoxaparin chains without oxidizing terminal amino sugar residues, a finding that may be useful to obtain more structurally homogeneous gs-LMHWs.

Assays for determining heparan sulfate and heparin O-sulfotransferase activity and specificity

O-sulfotransferases (OSTs) are critical enzymes in the cellular biosynthesis of the biologically and pharmacologically important heparan sulfate and heparin. Recently, these enzymes have been cloned and expressed in bacteria for application in the chemoenzymatic synthesis of glycosaminoglycan-based drugs. OST activity assays have largely relied on the use of radioisotopic methods using [(35)S] 3'-phosphoadenosine-5'-phosphosulfate and scintillation counting. Herein, we examine alternative assays that are more compatible with a biomanufacturing environment. A high throughput microtiter-based approach is reported that relies on a coupled bienzymic colorimetric assay for heparan sulfate and heparin OSTs acting on polysaccharide substrates using arylsulfotransferase-IV and p-nitrophenylsulfate as a sacrificial sulfogroup donor. A second liquid chromatography-mass spectrometric assay, for heparan sulfate and heparin OSTs acting on structurally defined oligosaccharide substrates, is also reported that provides additional information on the number and positions of the transferred sulfo groups within the product. Together, these assays allow quantitative and mechanistic information to be obtained on OSTs that act on heparan sulfate and heparin precursors.

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.

Unravelling structural information from complex mixtures utilizing correlation spectroscopy applied to HSQC spectra

The first use of statistical correlation spectroscopy to extract chemical information from 2D-HSQC spectra, termed HSQC correlation spectroscopy (HSQCcos), is reported. HSQCcos is illustrated using heparin, a heterogeneous polysaccharide, whose diverse composition causes signals in HSQC spectra to disperse. HSQCcos has been used to probe the chain modifications that cause this effect and reveals hitherto unreported structural details. An interesting finding was that the signal for position 2 of trisulfated glucosamine [N-, 3-O-, and 6-O-sulfated] (A*) is bifurcated, owing to the presence of A* residues in both the "normal" antithrombin binding site and also at the nonreducing end of the molecule, which is reported in intact heparin for the first time. The method was also applied to investigating the environment around other rare sequences/disaccharides, suggesting that the disaccharide; 2-O-sulfated iduronic acid linked to 6-O-sulfated N-glucosamine, which contains a free amine at position 2, is adjacent to the heparin linkage region. HSQCcos can extract chemically related signals from information-rich spectra obtained from complex mixtures such as heparin.

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.

Anti-proliferative effects of O-acyl-low-molecular-weight heparin derivatives on bovine pulmonary artery smooth muscle cells

Heparin (HP) inhibits the growth of several cell types in vitro including bovine pulmonary artery (BPA) smooth muscle cells (SMCs). In initial studies we discovered that an O-hexanoylated low-molecular-weight (LMW) HP derivative having acyl groups with 6-carbon chain length was more potent inhibitor of BPA-SMCs than the starting HP. We prepared several O-acylated LMWHP derivatives having 4-, 6-, 8-, 10-, 12-, and 18- carbon acyl chain lengths to determine the optimal acyl chain length for maximum anti-proliferative properties of BPA-SMCs. The starting LMWHP was prepared from unfractionated HP by sodium periodate treatment followed by sodium borohydride reduction. The tri-n-butylammonium salt of this LMWHP was O-acylated with butanoic, hexanoic, octanoic, decanoic, dodecanoic, and stearyl anhydrides separately to give respective O-acylated LMWHP derivatives. Gradient polyacrylamide gel electrophoresis (PAGE) was used to examine the average molecular weights of those O-acylated LMWHP derivatives. NMR analysis indicated the presence of one O-acyl group per disaccharide residue. Measurement of the inhibition of BPA-SMCS as a function of O-acyl chain length shows two optima, at a carbon chain length of 6 (O-hexanoylated LMWHP) and at a carbon chain length 12-18 (O-dodecanoyl and O-stearyl LMWHPs). A solution competition SPR study was performed to test the ability of different O-acylated LMWHP derivatives to inhibit fibroblast growth factor (FGF) 1 and FGF2 binding to surface-immobilized heparin. All the LMWHP derivatives bound to FGF1 and FGF2 but each exhibited slightly different binding affinity.

NMR methods to monitor the enzymatic depolymerization of heparin

Heparin and the related glycosaminoglycan, heparan sulfate, are polydisperse linear polysaccharides that mediate numerous biological processes due to their interaction with proteins. Because of the structural complexity and heterogeneity of heparin and heparan sulfate, digestion to produce smaller oligosaccharides is commonly performed prior to separation and analysis. Current techniques used to monitor the extent of heparin depolymerization include UV absorption to follow product formation and size exclusion or strong anion exchange chromatography to monitor the size distribution of the components in the digest solution. In this study, we used ¹H nuclear magnetic resonance (NMR) survey spectra and NMR diffusion experiments in conjunction with UV absorption measurements to monitor heparin depolymerization using the enzyme heparinase I. Diffusion NMR does not require the physical separation of the components in the reaction mixture and instead can be used to monitor the reaction solution directly in the NMR tube. Using diffusion NMR, the enzymatic reaction can be stopped at the desired time point, maximizing the abundance of larger oligosaccharides for protein-binding studies or completion of the reaction if the goal of the study is exhaustive digestion for characterization of the disaccharide composition. In this study, porcine intestinal mucosa heparin was depolymerized using the enzyme heparinase I. The unsaturated bond formed by enzymatic cleavage serves as a UV chromophore that can be used to monitor the progress of the depolymerization and for the detection and quantification of oligosaccharides in subsequent separations. The double bond also introduces a unique multiplet with peaks at 5.973, 5.981, 5.990, and 5.998 ppm in the ¹H-NMR spectrum downfield of the anomeric region. This multiplet is produced by the proton of the C-4 double bond of the non-reducing end uronic acid at the cleavage site. Changes in this resonance were used to monitor the progression of the enzymatic digestion and compared to the profile obtained from UV absorbance measurements. In addition, in situ NMR diffusion measurements were explored for their ability to profile the different-sized components generated over the course of the digestion.

Figure

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

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

Increase in the growth inhibition of bovine pulmonary artery smooth muscle cells by an O-hexanoyl low-molecular-weight heparin derivative

Proliferation of pulmonary artery smooth muscle cells (PASMCs) appears to play a significant role in chronic pulmonary hypertension. The proliferation of PASMCs is strongly inhibited by some commercial heparin preparations. Heparin fragments were prepared by periodate treatment, followed by sodium borohydride reduction, to enhance potency. The tributylammonium salt of this fragmented heparin was O-acylated with hexanoic anhydride. Gradient polyacrylamide gel electrophoresis showed that the major heparin fragment contained eight disaccharide units. NMR analysis showed that approximately one hexanoyl group per disaccharide residue was present. The O-hexanoyl heparin fragments were assayed for growth inhibitory effect on bovine PASMCs in culture. This derivative was found to be more effective in growth inhibition of bovine PASMCs in culture than the heparin from which it was derived. In the future, it is envisioned that this or similar derivatives may be an effective treatment for pulmonary hypertension.

Structural Effects of a Covalent Linkage Between Antithrombin and Heparin: Covalent N-Terminus Attachment of Heparin Enhances the Maintenance of Antithrombin's Activated State

We have produced a molecule comprising of permanently-activated covalently linked antithrombin and heparin (ATH). This study was designed to elucidate the covalent linkage point(s) for heparin on antithrombin and conformational properties of the ATH molecule. ATH was produced using Schiff base/Amadori rearrangement by incubating antithrombin with unfractionated heparin for 14 d at 40 degrees C. ATH was then digested using Proteinase K, and the heparin-peptide was reacted with NaIO4/NaBH4/mild acid to degrade the heparin moiety. Sequencing of the remaining peptide was performed by Edman degradation with linkage point confirmation by LC-MS. The degree of insertion of the reactive center loop (RCL) of antithrombin into the A-sheet of ATH was examined using synthesized antithrombin RCL peptides. Binding between the peptides and ATH, and the formation of ATH in the presence of the peptides were tested. CD was used to further examine the secondary and tertiary structures of ATH. The results suggest that heparin is conjugated to the amino terminal of antithrombin in the majority of ATH molecules, proximal to the previously determined heparin binding domain of antithrombin. From the linkage data, a model is proposed for the structure of ATH. Studies using the RCL peptides and CD analysis of ATH support this model.

Imparting bone mineral affinity to osteogenic proteins through heparin-bisphosphonate conjugates

Although numerous growth factors can promote the regeneration of bone upon parenteral administration, all exhibit undesirable side-effects that prevent their clinical utility. These side-effects arise due to the growth factors' inherent lack of bone affinity. The goal of this study was to develop a means to enhance the bone mineral affinity of osteogenic growth factors so as to minimize their extra-skeletal distribution. Heparin, a glycosaminoglycan that exhibits a high affinity to numerous growth factors, was modified with bisphosphonates to enhance its affinity to bone mineral (i.e. hydroxyapatite, HA). To this end, conjugation of 1-amino-1,1-diphosphonate methane (aminoBP) onto periodate-oxidized heparin using 4-(maleimidomethyl)cyclohexane-1-carboxyl-hydrazide was attempted. Using this chemistry, the number of aminoBPs conjugated onto heparin was modulated by varying the reacting reagent concentrations (to a maximum of 7 aminoBPs per heparin). Increasing the number of aminoBPs resulted in a more than twofold increase in heparin's affinity for HA in vitro. Subsequently, the ability of aminoBP-heparin conjugates to enhance the mineral affinity of basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) was explored. The results revealed that the complexation between the conjugates and growth factors had occurred and that the conjugates increased the bone mineral affinity of bFGF and BMP-2 in an aminoBP-dependent manner. In conclusion, the conjugation of aminoBP onto heparin is a feasible approach to enhance the affinity of heparin-binding, osteogenic growth factors to HA.