New antithrombin-based anticoagulants

Glycosaminoglycan microarrays for studying glycosaminoglycan-protein systems

More than 3000 proteins are now known to bind to glycosaminoglycans (GAGs). Yet, GAG-protein systems are rather poorly understood in terms of selectivity of recognition, molecular mechanism of action, and translational promise. High-throughput screening (HTS) technologies are critically needed for studying GAG biology and developing GAG-based therapeutics. Microarrays, developed within the past two decades, have now improved to the point of being the preferred tool in the HTS of biomolecules. GAG microarrays, in which GAG sequences are immobilized on slides, while similar to other microarrays, have their own sets of challenges and considerations. GAG microarrays are rapidly becoming the first choice in studying GAG-protein systems. Here, we review different modalities and applications of GAG microarrays presented to date. We discuss advantages and disadvantages of this technology, explain covalent and non-covalent immobilization strategies using different chemically reactive groups, and present various assay formats for qualitative and quantitative interpretations, including selectivity screening, binding affinity studies, competitive binding studies etc. We also highlight recent advances in implementing this technology, cataloging of data, and project its future promise. Overall, the technology of GAG microarray exhibits enormous potential of evolving into more than a mere screening tool for studying GAG - protein systems.

Mannose 2, 3, 4, 5, 6-O-pentasulfate (MPS): a partial activator of human heparin cofactor II with anticoagulation potential

Thromboembolic diseases are a major cause of mortality in human and the currently available anticoagulants are associated with various drawbacks, therefore the search for anticoagulants that have better safety profile is highly desirable. Compounds that are part of the dietary routine can be modified to possibly increase their anticoagulant potential. We show mannose 2,3,4,5,6-O-pentasulfate (MPS) as a synthetically modified form of mannose that has appreciable anticoagulation properties. An in silico study identified that mannose in sulfated form can bind effectively to the heparin-binding site of antithrombin (ATIII) and heparin cofactor II (HCII). Mannose was sulfated using a simple sulfation strategy-involving triethylamine-sulfur trioxide adduct. HCII and ATIII were purified from human plasma and the binding analysis using fluorometer and isothermal calorimetry showed that MPS binds at a unique site. A thrombin inhibition analysis using the chromogenic substrate showed that MPS partially enhances the activity of HCII. Further an assessment of in vitro blood coagulation assays using human plasma showed that the activated partial thromboplastin time (APTT) and prothrombin time (PT) were prolonged in the presence of MPS. A molecular dynamics simulation analysis of the HCII-MPS complex showed fluctuations in a N-terminal loop and the cofactor binding site of HCII. The results indicate that MPS is a promising lead due to its effect on the in vitro coagulation rate.Communicated by Ramaswamy H. Sarma.

Designing Smaller, Synthetic, Functional Mimetics of Sulfated Glycosaminoglycans as Allosteric Modulators of Coagulation Factors

Natural glycosaminoglycans (GAGs) are arguably the most diverse collection of natural products. Unfortunately, this bounty of structures remains untapped. Decades of research has realized only one GAG-like synthetic, small-molecule drug, fondaparinux. This represents an abysmal output because GAGs present a frontier that few medicinal chemists, and even fewer pharmaceutical companies, dare to undertake. GAGs are heterogeneous, polymeric, polydisperse, highly water soluble, synthetically challenging, too rapidly cleared, and difficult to analyze. Additionally, GAG binding to proteins is not very selective and GAG-binding sites are shallow. This Perspective attempts to transform this negative view into a much more promising one by highlighting recent advances in GAG mimetics. The Perspective focuses on the principles used in the design/discovery of drug-like, synthetic, sulfated small molecules as allosteric modulators of coagulation factors, such as antithrombin, thrombin, and factor XIa. These principles will also aid the design/discovery of sulfated agents against cancer, inflammation, and microbial infection.

Designing Synthetic, Sulfated Glycosaminoglycan Mimetics That Are Orally Bioavailable and Exhibiting In Vivo Anticancer Activity

Sulfated glycosaminoglycans (GAGs), or synthetic mimetics thereof, are not favorably viewed as orally bioavailable drugs owing to their high number of anionic sulfate groups. Devising an approach for oral delivery of such highly sulfated molecules would be very useful. This work presents the concept that conjugating cholesterol to synthetic sulfated GAG mimetics enables oral delivery. A focused library of sulfated GAG mimetics was synthesized and found to inhibit the growth of a colorectal cancer cell line under spheroid conditions with a wide range of potencies ( 0.8 to 46 μM). Specific analogues containing cholesterol, either alone or in combination with clinical utilized drugs, exhibited pronounced in vivo anticancer potential with intraperitoneal as well as oral administration, as assessed by ex vivo tertiary and quaternary spheroid growth, cancer stem cell (CSC) markers, and/or self-renewal factors. Overall, cholesterol derivatization of highly sulfated GAG mimetics affords an excellent approach for engineering oral activity.

Modification of Arabinogalactan Isolated from Larix sibirica Ledeb. into Sulfated Derivatives with the Controlled Molecular Weights

The process of sulfation of arabinogalactan—a natural polysaccharide from Larix sibirica Ledeb.—with sulfamic acid in 1,4-dioxane using different activators has been studied for the first time. The dynamics of the molecular weight of sulfated arabinogalactan upon variation in the temperature and time of sulfation of arabinogalactan with sulfamic acid in 1,4-dioxane has been investigated. It has been found that, as the sulfation time increases from 10 to 90 min, the molecular weights of the reaction products grow due to the introduction of sulfate groups without significant destruction of the initial polymer and sulfation products. Sulfation at 95 °C for 20 min yields the products with a higher molecular weight than in the case of sulfation at 85 °C, which is related to an increase in the sulfation rate; however, during the further process occurring under these conditions, sulfation is accompanied by the destruction and the molecular weight of the sulfated polymer decreases. The numerical optimization of arabinogalactan sulfation process has been performed. It has been shown that the optimal parameters for obtaining a product with a high sulfur content are a sulfamic acid amount of 20 mmol per 1 g of arabinogalactan, a process temperature of 85 °C, and a process time of 2.5 h.

Small-molecule modulators of serine protease inhibitor proteins (serpins)

Serine protease inhibitors (serpins) are a large family of proteins that regulate and control crucial physiological processes, such as inflammation, coagulation, thrombosis and thrombolysis, and immune responses. The extraordinary impact that these proteins have on numerous crucial pathways makes them an attractive target for drug discovery. In this review, we discuss recent advances in research on small-molecule modulators of serpins, examine their mode of action, analyse the structural data from crystallised protein-ligand complexes, and highlight the potential obstacles and possible therapeutic perspectives. The application of in silico methods for rational drug discovery is also summarised. In addition, we stress the need for continued research in this field.

A Review on Chitosan's Uses as Biomaterial: Tissue Engineering, Drug Delivery Systems and Cancer Treatment

Chitosan, derived from chitin, is a biopolymer consisting of arbitrarily distributed β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine that exhibits outstanding properties- biocompatibility, biodegradability, non-toxicity, antibacterial activity, the capacity to form films, and chelating of metal ions. Most of these peculiar properties are attributed to the presence of free protonable amino groups along the chitosan backbone, which also gives it solubility in acidic conditions. Moreover, this biopolymer can also be physically modified, thereby presenting a variety of forms to be developed. Consequently, this polysaccharide is used in various fields, such as tissue engineering, drug delivery systems, and cancer treatment. In this sense, this review aims to gather the state-of-the-art concerning this polysaccharide when used as a biomaterial, providing information about its characteristics, chemical modifications, and applications. We present the most relevant and new information about this polysaccharide-based biomaterial's applications in distinct fields and also the ability of chitosan and its various derivatives to selectively permeate through the cancer cell membranes and exhibit anticancer activity, and the possibility of adding several therapeutic metal ions as a strategy to improve the therapeutic potential of this polymer.

Pharmaceutical and Nutraceutical Potential Applications of Sargassum fulvellum

Sargassum fulvellum is a brown seaweed of the Sargassaceae family which has been demonstrated to exhibit antipyretic, analgesic, antiedema, antimicrobial, antioxidant, antitumor, neuroprotective, anticoagulative, anti-inflammatory, and hepatoprotective activities. It has been widely used as a food additive and as a medicine in oriental medicine to treat lumps, dropsy, swelling, testicular pains, and urinary problems. S. fulvellum has been identified as a potential producer of a wide spectrum of natural compounds such as carotenoids, fucoidans, and phlorotannins, showing different biological activities in various industrial applications including pharmaceutical, nutraceutical, cosmeceutical, and functional food. However, the promising health effects associated with the extracts and compounds isolated from S. fulvellum have not been reviewed to date. The present review thus focuses on the biological activity of S. fulvellum as reported by previous publications, which include antioxidant, anticoagulant, anti-inflammatory, neuroprotective, immunomodulatory, antidiabetic, and anticancer effects. Thus, this review might serve to increase the utilization of this invaluable natural source as a potential component in pharmaceutical and nutraceutical applications.

Enzyme immobilization offers a robust tool to scale up the production of longer, diverse, natural glycosaminoglycan oligosaccharides

Although structurally diverse, longer glycosaminoglycan (GAG) oligosaccharides are critical to understand human biology, few are available. The major bottleneck has been the predominant production of oligosaccharides, primarily disaccharides, upon enzymatic depolymerization of GAGs. In this work, we employ enzyme immobilization to prepare hexasaccharide and longer sequences of chondroitin sulfate in good yields with reasonable homogeneity. Immobilized chondroitinase ABC displayed good efficiency, robust operational pH range, broad thermal stability, high recycle ability and excellent distribution of products in comparison to the free enzyme. Diverse sequences could be chromatographically resolved into well-defined peaks and characterized using LC-MS. Enzyme immobilization technology could enable easier access to diverse longer GAG sequences.

G-quadruplex-based aptamers targeting human thrombin: Discovery, chemical modifications and antithrombotic effects

First studies on thrombin-inhibiting DNA aptamers were reported in 1992, and since then a large number of anticoagulant aptamers has been discovered. TBA - also named HD1, a 15-mer G-quadruplex (G4)-forming oligonucleotide - is the best characterized thrombin binding aptamer, able to specifically recognize the protein exosite I, thus inhibiting the conversion of soluble fibrinogen into insoluble fibrin strands. Unmodified nucleic acid-based aptamers, in general, and TBA in particular, exhibit limited pharmacokinetic properties and are rapidly degraded in vivo by nucleases. In order to improve the biological performance of aptamers, a widely investigated strategy is the introduction of chemical modifications in their backbone at the level of the nucleobases, sugar moieties or phosphodiester linkages. Besides TBA, also other thrombin binding aptamers, able to adopt a well-defined G4 structure, e.g. mixed duplex/quadruplex sequences, as well as homo- and hetero-bivalent constructs, have been identified and optimized. Considering the growing need of new efficient anticoagulant agents associated with the strong therapeutic potential of these thrombin inhibitors, the research on thrombin binding aptamers is still a very hot and intriguing field. Herein, we comprehensively described the state-of-the-art knowledge on the DNA-based aptamers targeting thrombin, especially focusing on the optimized analogues obtained by chemically modifying the oligonucleotide backbone, and their biological performances in therapeutic applications.

Seafood Waste as Attractive Source of Chitin and Chitosan Production and Their Applications

Chitosan is a cationic polymer obtained by deacetylation of chitin, found abundantly in crustacean, insect, arthropod exoskeletons, and molluscs. The process of obtaining chitin by the chemical extraction method comprises the steps of deproteinization, demineralization, and discoloration. To obtain chitosan, the deacetylation of chitin is necessary. These polymers can also be extracted through the biological extraction method involving the use of microorganisms. Chitosan has biodegradable and biocompatible properties, being applied in the pharmaceutical, cosmetic, food, biomedical, chemical, and textile industries. Chitosan and its derivatives may be used in the form of gels, beads, membranes, films, and sponges, depending on their application. Polymer blending can also be performed to improve the mechanical properties of the bioproduct. This review aims to provide the latest information on existing methods for chitin and chitosan recovery from marine waste as well as their applications.

Combinatorial virtual library screening analysis of antithrombin binding oligosaccharide motif generation by heparan sulfate 3-O-Sulfotransferase 1

Pharmaceutical heparin's activity arises from a key high affinity and high selectivity antithrombin binding motif, which forms the basis for its use as an anticoagulant. The current problems with the supply of pig heparin raises the emphasis of understanding heparin biosynthesis so as to control and advance recombinantly expressed agent that could bypass the need for animals. Unfortunately, much remains to be understood about the generation of the antithrombin-binding motif by the key enzyme involved in its biosynthesis, 3-O-sulfotransferase-1 (3OST-1). In this work, we present a novel computational approach to understand recognition of oligosaccharide sequences by 3OST-1. Application of combinatorial virtual library screening (CVLS) algorithm on hundreds of tetrasaccharide and hexasaccharide sequences shows that 3OST-1 belongs to the growing number of proteins that recognize glycosaminoglycans with very high selectivity. It prefers very well defined pentasaccharide sequences carrying distinct groups in each of the five residues to generate the antithrombin binding motif. CVLS also identifies key residues including His271, Arg72, Arg197 and Lys173, which interact with 6-sulfate, 5-COO¯, 2-/6-sulfates and 2-sulfate at the -2, -1, +2, and +1 positions of the precursor pentasaccharide, respectively. Additionally, uncharged residues, especially Gln163 and Asn167, were also identified as playing important roles in recognition. Overall, the success of CVLS in predicting 3OST-1 recognition characteristics that help engineer selectivity lead to the expectation that recombinant enzymes could be designed to help resolve the current problems in the supply of anticoagulant heparin.

Visualizing antithrombin-binding 3-O-sulfated heparan sulfate motifs on cell surfaces

To map the cellular topography of the rare 3-O-sulfated structural motif of heparan sulfate (HS), we constructed quantum dot-based probes for antithrombin and FGF2, which reveal widely different distribution of the targeted HS motifs.

Sulfated Non-Saccharide Glycosaminoglycan Mimetics as Novel Drug Discovery Platform for Various Pathologies

Glycosaminoglycans (GAGs) are very complex, natural anionic polysaccharides. They are polymers of repeating disaccharide units of uronic acid and hexosamine residues. Owing to their template-free, spatiotemporally-controlled, and enzyme-mediated biosyntheses, GAGs possess enormous polydispersity, heterogeneity, and structural diversity which often translate into multiple biological roles. It is well documented that GAGs contribute to physiological and pathological processes by binding to proteins including serine proteases, serpins, chemokines, growth factors, and microbial proteins. Despite advances in the GAG field, the GAG-protein interface remains largely unexploited by drug discovery programs. Thus, Non-Saccharide Glycosaminoglycan Mimetics (NSGMs) have been rationally developed as a novel class of sulfated molecules that modulate GAG-protein interface to promote various biological outcomes of substantial benefit to human health. In this review, we describe the chemical, biochemical, and pharmacological aspects of recently reported NSGMs and highlight their therapeutic potentials as structurally and mechanistically novel anti-coagulants, anti-cancer agents, anti-emphysema agents, and anti-viral agents. We also describe the challenges that complicate their advancement and describe ongoing efforts to overcome these challenges with the aim of advancing the novel platform of NSGMs to clinical use.

Surfing the Blood Coagulation Cascade: Insight into the Vital Factor Xa

Factor Xa (FXa) plays a key role in haemostasis, it is a central part of the blood coagulation cascade which catalyzes the production of thrombin and leads to clot formation and wound closure. Therefore, FXa is an attractive target for the development of new anticoagulant agents. In this review, we will first describe the molecular features of this fundamental protein in order to understand its mechanism of action, an essential background for the design of novel inhibitors by means of synthetic organic chemistry or using peptides obtained from recombinant methodologies. Then, we will review the current state of the synthesis of novel direct FXa inhibitors along with their mechanisms of action. Finally, approved reversal agents that aid in maintaining blood haemostasis by using these commercial drugs will also be discussed.

Antithrombotic potential of esculin 7, 3', 4', 5', 6'-O-pentasulfate (EPS) for its role in thrombus reduction using rat thrombosis model

Currently available anticoagulants for prevention and treatment of thrombosis have several limitations, thus, small organic scaffolds that can dissolve clots in vivo in a dose dependent manner with lesser side effects are highly desirable. Here we report the synthesis of esculin pentasulfate (EPS) and assessment of its in vitro, in vivo and ex vivo anticoagulant and antithrombotic potential. Assessment of in vitro clotting times showed prolonged activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) in the presence of EPS. EPS also showed remarkable reduction in thrombus formation when administered in occlusion induced thrombotic rats at a low dose (2.5 mg/kg). Further, assessment of clot rate with plasma isolated from EPS treated rats confirmed its anticoagulation potential. EPS at varying concentrations showed no significant cytotoxic effect on HEK293 cell line. Further, molecular docking analysis of EPS with known anticoagulant proteins [(antithrombin (ATIII) and heparin cofactor II (HCF II)] that require heparin revealed good binding affinity (-7.9 kcal/mol) with ATIII but not with HCF II. ATIII when incubated with EPS showed increased fluorescence intensity, with no change in secondary structure. Overall, our results clearly show the in vivo modulation of thrombus formation using a modified natural scaffold EPS.

Biomedical Applications of Chitosan and Its Derivative Nanoparticles

Chitosan is a biodegradable natural polymer with many advantages such as nontoxicity, biocompatibility, and biodegradability. It can be applied in many fields, especially in medicine. As a delivery carrier, it has great potential and cannot be compared with other polymers. Chitosan is extremely difficult to solubilize in water, but it can be solubilized in acidic solution. Its insolubility in water is a major limitation for its use in medical applications. Chitosan derivatives can be obtained by chemical modification using such techniques as acylation, alkylation, sulfation, hydroxylation, quaternization, esterification, graft copolymerization, and etherification. Modified chitosan has chemical properties superior to unmodified chitosan. For example, nanoparticles produced from chitosan derivatives can be used to deliver drugs due to their stability and biocompatibility. This review mainly focuses on the properties of chitosan, chitosan derivatives, and the origin of chitosan-based nanoparticles. In addition, applications of chitosan-based nanoparticles in drug delivery, vaccine delivery, antimicrobial applications, and callus and tissue regeneration are also presented. In summary, nanoparticles based on chitosan have great potential for research and development of new nano vaccines and nano drugs in the future.

Deciphering the Role of Sulfonated Unit in Heparin-Mimicking Polymer to Promote Neural Differentiation of Embryonic Stem Cells

Glycosaminoglycans (GAGs), especially heparin and heparan sulfate (HS), hold great potential for inducing the neural differentiation of embryonic stem cells (ESCs) and have brought new hope for the treatment of neurological diseases. However, the disadvantages of natural heparin/HS, such as difficulty in isolating them with a sufficient amount, highly heterogeneous structure, and the risk of immune responses, have limited their further therapeutic applications. Thus, there is a great demand for stable, controllable, and well-defined synthetic alternatives of heparin/HS with more effective biological functions. In this study, based upon a previously proposed unit-recombination strategy, several heparin-mimicking polymers were synthesized by integrating glucosamine-like 2-methacrylamido glucopyranose monomers (MAG) with three sulfonated units in different structural forms, and their effects on cell proliferation, the pluripotency, and the differentiation of ESCs were carefully studied. The results showed that all the copolymers had good cytocompatibility and displayed much better bioactivity in promoting the neural differentiation of ESCs as compared to natural heparin; copolymers with different sulfonated units exhibited different levels of promoting ability; among them, copolymer with 3-sulfopropyl acrylate (SPA) as a sulfonated unit was the most potent in promoting the neural differentiation of ESCs; the promoting effect is dependent on the molecular weight and concentration of P(MAG-co-SPA), with the highest levels occurring at the intermediate molecular weight and concentration. These results clearly demonstrated that the sulfonated unit in the copolymers played an important role in determining the promoting effect on ESCs' neural differentiation; SPA was identified as the most potent sulfonated unit for copolymer with the strongest promoting ability. The possible reason for sulfonated unit structure as a vital factor influencing the ability of the copolymers may be attributed to the difference in electrostatic and steric hindrance effect. The synthetic heparin-mimicking polymers obtained here can offer an effective alternative to heparin/HS and have great therapeutic potential for nervous system diseases.

A Hexasaccharide Containing Rare 2-O-Sulfate-Glucuronic Acid Residues Selectively Activates Heparin Cofactor II

Glycosaminoglycan (GAG) sequences that selectively target heparin cofactor II (HCII), a key serpin present in human plasma, remain unknown. Using a computational strategy on a library of 46 656 heparan sulfate hexasaccharides we identified a rare sequence consisting of consecutive glucuronic acid 2-O-sulfate residues as selectively targeting HCII. This and four other unique hexasaccharides were chemically synthesized. The designed sequence was found to activate HCII ca. 250-fold, while leaving aside antithrombin, a closely related serpin, essentially unactivated. This group of rare designed hexasaccharides will help understand HCII function. More importantly, our results show for the first time that rigorous use of computational techniques can lead to discovery of unique GAG sequences that can selectively target GAG-binding protein(s), which may lead to chemical biology or drug discovery tools.

Role of heparin and non heparin binding serpins in coagulation and angiogenesis: A complex interplay

Pro-coagulant, anti-coagulant and fibrinolytic pathways are responsible for maintaining hemostatic balance under physiological conditions. Any deviation from these pathways would result in hypercoagulability leading to life threatening diseases like myocardial infarction, stroke, portal vein thrombosis, deep vein thrombosis (DVT) and pulmonary embolism (PE). Angiogenesis is the process of sprouting of new blood vessels from pre-existing ones and plays a critical role in vascular repair, diabetic retinopathy, chronic inflammation and cancer progression. Serpins; a superfamily of protease inhibitors, play a key role in regulating both angiogenesis and coagulation. They are characterized by the presence of highly conserved secondary structure comprising of 3 β-sheets and 7-9 α-helices. Inhibitory role of serpins is modulated by binding to cofactors, specially heparin and heparan sulfate proteoglycans (HSPGs) present on cell surfaces and extracellular matrix. Heparin and HSPGs are the mainstay of anti-coagulant therapy and also have therapeutic potential as anti-angiogenic inhibitors. Many of the heparin binding serpins that regulate coagulation cascade are also potent inhibitors of angiogenesis. Understanding the molecular mechanism of the switch between their specific anti-coagulant and anti-angiogenic role during inflammation, stress and regular hemostasis is important. In this review, we have tried to integrate the role of different serpins, their interaction with cofactors and their interplay in regulating coagulation and angiogenesis.

A Simple Method for Discovering Druggable, Specific Glycosaminoglycan-Protein Systems. Elucidation of Key Principles from Heparin/Heparan Sulfate-Binding Proteins

Glycosaminoglycans (GAGs) affect human physiology and pathology by modulating more than 500 proteins. GAG-protein interactions are generally assumed to be ionic and nonspecific, but specific interactions do exist. Here, we present a simple method to identify the GAG-binding site (GBS) on proteins that in turn helps predict high specific GAG-protein systems. Contrary to contemporary thinking, we found that the electrostatic potential at basic arginine and lysine residues neither identifies the GBS consistently, nor its specificity. GBSs are better identified by considering the potential at neutral hydrogen bond donors such as asparagine or glutamine sidechains. Our studies also reveal that an unusual constellation of ionic and non-ionic residues in the binding site leads to specificity. Nature engineers the local environment of Asn45 of antithrombin, Gln255 of 3-O-sulfotransferase 3, Gln163 and Asn167 of 3-O-sulfotransferase 1 and Asn27 of basic fibroblast growth factor in the respective GBSs to induce specificity. Such residues are distinct from other uncharged residues on the same protein structure in possessing a significantly higher electrostatic potential, resultant from the local topology. In contrast, uncharged residues on nonspecific GBSs such as thrombin and serum albumin possess a diffuse spread of electrostatic potential. Our findings also contradict the paradigm that GAG-binding sites are simply a collection of contiguous Arg/Lys residues. Our work demonstrates the basis for discovering specifically interacting and druggable GAG-protein systems based on the structure of protein alone, without requiring access to any structure-function relationship data.

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

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

Polysulfated trehalose as a novel anticoagulant agent with dual mode of action

Physiological hemostatic balance is a coordinated outcome of counteracting coagulation and fibrinolytic systems. An imbalance of procoagulant and anticoagulant factors may result in life threatening thromboembolism. Presently, anticoagulant administration is the first line of therapy for the treatment of these conditions and several anticoagulants have been approved, including various forms of heparin. However, the polyanionic nature and multispecificity of heparin pose several complications. Generally, the polysulfated compounds with antithrombotic potential are thought to have feasible synthetic procedures with much less bleeding, thus having favourable safety profiles. Here we report the synthesis of a novel compound, trehalose octasulfate and the assessment of its anticoagulation potential. Molecular docking of trehalose and trehalose octasulfate with antithrombin showed a specificity switch in binding affinity on sulfation, where trehalose octasulfate interacts with critical residues of AT that are either directly involved in heparin binding or in the conformational rearrangement of AT on heparin binding. An in vitro analysis of trehalose octasulfate demonstrated prolonged clotting time. Lead compound when intravenously injected in occlusion induced thrombotic rats showed remarkable reduction in the size and weight of the clot at a low dose. Delay in coagulation time was observed by analysing blood plasma isolated from rats preinjected with trehalose octasulfate. A decrease in Adenosine 5′-Diphosphate (ADP) induced platelet aggregation indicated a probable dual anticoagulant and antiplatelet mechanism of action. To summarize, this study presents trehalose octasulfate as a novel, effective, dual acting antithrombotic agent.

The effects of marine carbohydrates and glycosylated compounds on human health

Marine organisms have been recognized as a valuable source of bioactive compounds with industrial and nutraceutical potential. Recently, marine-derived carbohydrates, including polysaccharides and low molecular weight glycosylated oligosaccharides, have attracted much attention because of their numerous health benefits. Moreover, several studies have reported that marine carbohydrates exhibit various biological activities, including antioxidant, anti-infection, anticoagulant, anti-inflammatory, and anti-diabetic effects. The present review discusses the potential industrial applications of bioactive marine carbohydrates for health maintenance and disease prevention. Furthermore, the use of marine carbohydrates in food, cosmetics, agriculture, and environmental protection is discussed.

Investigation of the heparin-thrombin interaction by dynamic force spectroscopy

BACKGROUND

The interaction between heparin and thrombin is a vital step in the blood (anti)coagulation process. Unraveling the molecular basis of the interactions is therefore extremely important in understanding the mechanisms of this complex biological process.

METHODS

In this study, we use a combination of an efficient thiolation chemistry of heparin, a self-assembled monolayer-based single molecule platform, and a dynamic force spectroscopy to provide new insights into the heparin-thrombin interaction from an energy viewpoint at the molecular scale.

RESULTS

Well-separated single molecules of heparin covalently attached to mixed self-assembled monolayers are demonstrated, whereby interaction forces with thrombin can be measured via atomic force microscopy-based spectroscopy. Further these interactions are studied at different loading rates and salt concentrations to directly obtain kinetic parameters.

CONCLUSIONS

An increase in the loading rate shows a higher interaction force between the heparin and thrombin, which can be directly linked to the kinetic dissociation rate constant (koff). The stability of the heparin/thrombin complex decreased with increasing NaCl concentration such that the off-rate was found to be driven primarily by non-ionic forces.

GENERAL SIGNIFICANCE

These results contribute to understanding the role of specific and nonspecific forces that drive heparin-thrombin interactions under applied force or flow conditions.

Synthesis of glycosaminoglycan mimetics through sulfation of polyphenols

In nearly all cases of biological activity of sulfated GAGs, the sulfate group(s) are critical for interacting with target proteins. A growing paradigm is that appropriate small, sulfated, nonsaccharide GAG mimetics can be designed to either mimic or interfere with the biological functions of natural GAG sequences resulting in the discovery of either antagonist or agonist agents. A number of times these sulfated NSGMs can be computationally designed based on the parent GAG-protein interaction. The small sulfated NSGMs may possess considerable aromatic character so as to engineer hydrophobic, hydrogen-bonding, Coulombic or cation-pi forces in their interactions with target protein(s) resulting in higher specificity of action relative to parent GAGs. The sulfated NSGMs can be easily synthesized in one step from appropriate natural polyphenols through chemical sulfation under microwave-based conditions. We describe step-by-step procedures to perform microwave-based sulfation of several small polyphenol scaffolds so as to prepare homogenous NSGMs containing one to more than 10 sulfate groups per molecule in high yields.

6-O-sulfated chitosan promoting the neural differentiation of mouse embryonic stem cells

Embryonic stem cells (ESCs) can be induced to differentiate into nerve cells, endowing them with potential applications in the treatment of neurological diseases and neural repair. In this work, we report for the first time that sulfated chitosan can promote the neural differentiation of ESCs. As a type of sulfated glycosaminoglycan analog, sulfated chitosan with well-defined sulfation sites and a controlled degree of sulfation (DS) were prepared through simple procedures and the influence of sulfated glycosaminoglycan on neural differentiation of ESCs was investigated. Compared with other sulfation sites, 6-O-sulfated chitosan showed the most optimal effects. By monitoring the expression level of neural differentiation markers using immunofluorescence staining and PCR, it was found that neural differentiation was better enhanced by increasing the DS of 6-O-sulfated chitosan. However, increasing the DS by introducing another sulfation site in addition to the 6-O site to chitosan did not promote neural differentiation as much as 6-O-sulfated chitosan, indicating that compared with DS, the sulfation site is more important. Additionally, the optimal concentration and incubation time of 6-O-sulfated chitosan were investigated. Together, our results indicate that the sulfate site and the molecular structure in a sulfated polysaccharide are very important for inducing the differentiation of ESCs. Our findings may help to highlight the role of sulfated polysaccharide in inducing the neural differentiation of ESCs.

A simple, general approach of allosteric coagulation enzyme inhibition through monosulfated hydrophobic scaffolds

Allosteric inhibition of coagulation enzymes offers the advantage of controlled inhibition. In this study, a small library of mono sulfated indole and benzothiazole based molecules was synthesized and screened against the panel of coagulation proteases. The results reveal that selected molecules inhibit the thrombin, factor Xa and factor XIa with moderate potency. Compound 6a was found to have an allosteric mode of inhibition against thrombin. Plasma clotting assays suggest that selected inhibitors 14b, 14c and 14d prolong both prothrombin and activated partial thromboplastin time. Overall, this work presents the newer class of allosteric inhibitors of thrombin and factor XIa with improved aqueous solubility profile.

Therapeutic potential and health benefits of Sargassum species

Sargassum species are tropical and sub-tropical brown macroalgae (seaweed) of shallow marine meadow. These are nutritious and rich source of bioactive compounds such as vitamins, carotenoids, dietary fibers, proteins, and minerals. Also, many biologically active compounds like terpenoids, flavonoids, sterols, sulfated polysaccharides, polyphenols, sargaquinoic acids, sargachromenol, pheophytine were isolated from different Sargassum species. These isolated compounds exhibit diverse biological activities like analgesic, anti-inflammatory, antioxidant, neuroprotective, anti-microbial, anti-tumor, fibrinolytic, immune-modulatory, anti-coagulant, hepatoprotective, anti-viral activity etc., Hence, Sargassum species have great potential to be used in pharmaceutical and neutralceutical areas. This review paper explores the current knowledge of phytochemical, therapeutic potential, and health benefits of different species of genus Sargassum.

Elucidating the specificity of non-heparin-based conformational activators of antithrombin for factor Xa inhibition

Introduction:

Antithrombin, the principal inhibitor of coagulation proteases, requires allosteric activation by its physiological cofactor, heparin or heparin sulfate to achieve physiologically permissible rates. This forms the basis of heparin's use as a clinical anticoagulant. However, heparin therapy is beset with severe complications, giving rise to the need to search new non-heparin activators of antithrombin, devoid of these complications and with favorable safety profiles.

Materials and Methods:

We chose some representative organic compounds that have been shown to be involved in coagulation modulation by affecting antithrombin and applied a blind docking protocol to find the binding energy and interactions of the modified (sulfated) versus unmodified organic scaffolds.

Results and Conclusion:

Increased sulfation plays a key role in shifting the specificity of organic compounds like quercetin, diosmin, rutin, mangiferin, isomangostin, Trapezifolixanthone and benzofuran towards the heparin binding site (HBS). However, in hesperetin and tetrahydroisoquinoline, sulfation shifts the specificity away from HBS. We have further tried to elucidate changes in the binding affinity of quercetin on account of gradual increase in the number of hydroxyl groups being substituted by sulfate groups. The results show gradual increase in binding energy with increase in sulfation. A theoretical screening approach is an ideal mechanism to predict lead molecules as activators of antithrombin and in determining the specificity for antithrombin.

A comparative study of the molecular structure, lipophilicity, solubility, acidity, absorption and polar surface area of coumarinic anticoagulants and direct thrombin inhibitors

The methods of computational chemistry have been used to elucidate the molecular properties of coumarinic anticoagulants (acenocoumarol, phenprocoumon, warfarin and tecarfarin) and direct thrombin inhibitors (melagatran, dabigatran and their prodrug forms).

Single gold nanoparticle localized surface plasmon resonance spectral imaging for quantifying binding constant of carbohydrate-protein interaction

Quantifying carbohydrate-protein (ligand-receptor) interactions is important to understand diverse biological processes and to develop new diagnostic and therapeutic methods. We develop an approach to quantitatively study carbohydrate-protein interactions by Au nanoparticle localized surface plasmon resonance (LSPR) peak position shift at the single particles level. Unlike the previous techniques for single particle LSPR spectral imaging, only the first-order streak of an individual nanoparticle is needed to extract a LSPR spectrum, which has great potential to increase throughput to 500 single particle spectra in each frame. LSPR peak shift of protein modified single Au nanoparticles is found to be a function of its ligand concentration, which can be used to fit the binding constants of the interactions. The moderate interactions of Antithrombin III (AT III) and heparins including low molecular weight heparin (LMWH) are determined as well as the strong interaction of transferrin and antitransferrin and the weak interaction of bovine serum album (BSA) and heparin. The measured binding constants of transferrin to antitransferrin, heparin and LMWH to AT III, and BSA to heparin are (3.0 ± 0.6) × 10(9) M(-1), (3.1 ± 0.3) × 10(6) M(-1), (8.0 ± 0.5) × 10(5) M(-1), and (5.1 ± 0.1) × 10(3) M(-1), respectively, which are in good agreement with the reported values.

Discovery of allosteric modulators of factor XIa by targeting hydrophobic domains adjacent to its heparin-binding site

To discover promising sulfated allosteric modulators (SAMs) of glycosaminoglycan-binding proteins (GBPs), such as human factor XIa (FXIa), we screened a library of 26 synthetic, sulfated quinazolin-4(3H)-ones (QAOs) resulting in the identification of six molecules that reduced the Vmax of substrate hydrolysis without influencing the KM. Mutagenesis of residues of the heparin-binding site (HBS) of FXIa introduced a nearly 5-fold loss in inhibition potency supporting recognition of an allosteric site. Fluorescence studies showed a sigmoidal binding profile indicating highly cooperative binding. Competition with a positively charged, heparin-binding polymer did not fully nullify inhibition suggesting importance of hydrophobic forces to binding. This discovery suggests the operation of a dual-element recognition process, which relies on an initial Coulombic attraction of anionic SAMs to the cationic HBS of FXIa that forms a locked complex through tight interaction with an adjacent hydrophobic patch. The dual-element strategy may be widely applicable for discovering SAMs of other GBPs.

Anticoagulant use in real time

Venous thromboembolism (VTE) encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE). Each year, VTE affects about 300,000 to 600,000 people in the United States, and death is the first manifestation in one-fourth of this population.(1){Beckman, 2010 #79} Moreover, approximately 10% of the US population has genetic factors that increase their risk for developing thrombosis.(1) In addition to inherited disorders, factors that contribute to VTE include prolonged immobilization, trauma, surgery, cancer, and critically ill patients.(2) Routine assessment and prophylaxis are recommended in these groups to avoid DVT-related complications.(2) Anticoagulants are the mainstay of drugs used in DVT/PE prevention and treatment. Despite the availability of evidence-based guidelines for anticoagulant therapy, there is suboptimal implementation of DVT prophylaxis in hospitalized patients.(3) All anticoagulants are "high-alert" drugs, and judicious use is mandatory to prevent bleeding complications.(4) This review discusses treatment guidelines, monitoring, side effects, and reversal agents available for some anticoagulant drugs approved for VTE. Dissemination of the knowledge via pharmacy education programs significantly improves the adherence to VTE prophylaxis.(5) Understanding the clinical aspects of anticoagulant dispensing as presented in this review is hoped to facilitate implementation of the theoretical knowledge as well as evidence-based guidelines in order to maximize patient benefit.

Investigating the role of T7 and T12 residues on the biological properties of thrombin-binding aptamer: enhancement of anticoagulant activity by a single nucleobase modification

An acyclic pyrimidine analogue, containing a five-member cycle fused on the pyrimidine ring, was synthesized and introduced at position 7 or 12 of the 15-mer oligodeoxynucleotide GGTTGGTGTGGTTGG, known as thrombin-binding aptamer (TBA). Characterization by 1H NMR and CD spectroscopies of the resulting aptamers, TBA-T7b and TBA-T12b, showed their ability to fold into the typical antiparallel chairlike G-quadruplex structure formed by TBA. The apparent CD melting temperatures indicated that the introduction of the acyclic residue, mainly at position 7, improves the thermal stability of resulting G-quadruplexes with respect to TBA. The anticoagulant activity of the new molecules was then valued in PT assay, and it resulted that TBA-T7b is more potent than TBA in prolonging clotting time. On the other hand, in purified fibrinogen assay the thrombin inhibitory activity of both modified sequences was lower than that of TBA using human enzyme, whereas the potency trend was again reversed using bovine enzyme. Obtained structure-activity relationships were investigated by structural and computational studies. Taken together, these results reveal the active role of TBA residues T7 and T12 and the relevance of some amino acids located in the anion binding exosite I of the protein in aptamer-thrombin interaction.