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

Quality control, safety assessment and preparation approaches of low molecular weight heparin

Low Molecular Weight Heparins (LMWHs) are well-established for use in the prevention and treatment of thrombotic diseases, and as a substitute for unfractionated heparin (UFH) due to their predictable pharmacokinetics and subcutaneous bioavailability. LMWHs are produced by various depolymerization methods from UFH, resulting in heterogeneous compounds with similar biochemical and pharmacological properties. However, the delicate supply chain of UFH and potential contamination from animal sources require new manufacturing approaches for LMWHs. Various LMWH preparation methods are emerging, such as chemical synthesis, enzymatic or chemical depolymerization and chemoenzymatic synthesis. To establish the sameness of active ingredients in both innovator and generic LMWH products, the Food and Drug Administration has implemented a stringent scientific method of equivalence based on physicochemical properties, heparin source material and depolymerization techniques, disaccharide composition and oligosaccharide mapping, biological and biochemical properties, and in vivo pharmacodynamic profiles. In this review, we discuss currently available LMWHs, potential manufacturing methods, and recent progress for manufacturing quality control of these LMWHs.

Low-molecular weight sulfated marine polysaccharides: Promising molecules to prevent neurodegeneration in mucopolysaccharidosis IIIA?

Mucopolysaccharidosis IIIA is a hereditary disease caused by mutations in the sulfamidase enzyme that participates in catabolism of heparan sulfate (HS), leading to HS fragment accumulation and multisystemic failure. No cure exists and death occurs around the second decade of life. Two low molecular weight highly sulfated compounds derived from marine diabolican and infernan exopolysaccharides (A5_3 and A5_4, respectively) with heparanase inhibiting properties were tested in a MPSIIIA cell line model, resulting in limited degradation of intracellular HS. Next, we observed the effects of intraperitoneal injections of the diabolican derivative A5_3 from 4 to 12 weeks of age on MPSIIIA mice. Brain metabolism and microstructure, levels of proteins and genes involved in MPSIIIA brain pathophysiology were also investigated. 1H-Magnetic Resonance Spectroscopy (MRS) indicated deficits in energetic metabolism, tissue integrity and neurotransmission at both 4 and 12 weeks in MPSIIIA mice, with partial protective effects of A5_3. Ex-vivo Diffusion Tensor Imaging (DTI) showed white matter microstructural damage in MPSIIIA, with noticeable protective effects of A5_3. Protein and gene expression assessments displayed both pro-inflammatory and pro-apoptotic profiles in MPSIIIA mice, with benefits of A5_3 counteracting neuroinflammation. Overall, derivative A5_3 was well tolerated and was shown to be efficient in preventing brain metabolism failure and inflammation, resulting in preserved brain microstructure in the context of MPSIIIA.

Synthetic Heparanase Inhibitors Can Prevent Herpes Simplex Viral Spread

Herpes simplex virus (HSV-1) employs heparan sulfate (HS) as receptor for cell attachment and entry. During late-stage infection, the virus induces the upregulation of human heparanase (Hpse) to remove cell surface HS allowing viral spread. We hypothesized that inhibition of Hpse will prevent viral release thereby representing a new therapeutic strategy for HSV-1. A range of HS-oligosaccharides was prepared to examine the importance of chain length and 2-O-sulfation of iduronic moieties for Hpse inhibition. It was found that hexa- and octasaccharides potently inhibited the enzyme and that 2-O-sulfation of iduronic acid is tolerated. Computational studies provided a rationale for the observed structure-activity relationship. Treatment of human corneal epithelial cells (HCEs) infected with HSV-1 with the hexa- and octasaccharide blocked viral induced shedding of HS which significantly reduced spread of virions. The compounds also inhibited migration and proliferation of immortalized HCEs thereby providing additional therapeutic properties.

Saturated tetrasaccharide profile of enoxaparin. An additional piece to the heparin biosynthesis puzzle

Enoxaparin, widely used antithrombotic drug, is a polydisperse glycosaminoglycan with highly microheterogeneous structure dictated by both parent heparin heterogeneity and depolymerization conditions. While the process-related modifications of internal and terminal sequences of enoxaparin have been extensively studied, very little is known about the authentic non-reducing ends (NRE). In the present study a multi-step isolation and thorough structural elucidation by NMR and LC/MS allowed to identify 16 saturated tetramers along with 23 unsaturated ones in the complex enoxaparin tetrasaccharide fraction. Altogether the elucidated structures represent a unique enoxaparin signature, whereas the composition of saturated tetramers provides a structural readout strictly related to the biosynthesis of parent heparin NRE. In particular, both glucuronic and iduronic acids were detected at the NRE of macromolecular heparin. The tetrasaccharides bearing glucosamine at the NRE are most likely associated with the heparanase hydrolytic action. High sulfation degree and 3-O-sulfation are characteristic for both types of NRE.

Binding ability of methylene blue with heparin dependent on its sulfate level rather than its sulfation location or basic saccharide structure

Methylene blue (MB) is one of the most common cationic dyes to detect heparin. As the sulfate residue presented in heparin was the main contributor to bind with MB, the UV performance of the MB with selectively desulfated heparin derivatives was investigated. It was found that the sulfate residue in different heparin analogues did not show the equal ability to attract MB binding. The stoichiometry of sulfate with MB among the heparin and derivatives was verified as a non-constant number. For the two selectively desulfated heparin derivatives: sulfate elimination at 6-O (6-OdeS) and N-acetylated heparin (N-deS-Acetyl), the MB to sulfate ratios were significantly higher than for heparin. For the not fully diminished sulfate at 2-O heparin derivative (2-OdeS), the MB-SO₃^- ratio of 2-OdeS was between 6-OdeS, N-deS-Acetlyl and heparin. Although in a distinct sulfation position, the MB-SO₃^- ratio of 6-OdeS and N-deS-Acetyl was almost equal, which agreed with the comparable total desulfation degree between 6-OdeS and N-deS-Acetyl. In addition, compared to heparin groups, the non-desulfated gs-HP showed no significantly different MB-SO₃^- ratio with heparin. The above results demonstrated that compared with the sulfate location and glycan composition of heparin, the content of sulfate was the most essential factor for the MB binding.

Heparanase Inhibitors in Cancer Progression: Recent Advances

BACKGROUND

An endo-β-glucuronidase enzyme, Heparanase (HPSE), degrades the side chains of polymeric heparan sulfate (HS), a glycosaminoglycan formed by alternate repetitive units of D-glucosamine and D-glucuronic acid/L-iduronic acid. HS is a major component of the extracellular matrix and basement membranes and has been implicated in processes of the tissue's integrity and functional state. The degradation of HS by HPSE enzyme leads to conditions like inflammation, angiogenesis, and metastasis. An elevated HPSE expression with a poor prognosis and its multiple roles in tumor growth and metastasis has attracted significant interest for its inhibition as a potential anti-neoplastic target.

METHODS

We reviewed the literature from journal publication websites and electronic databases such as Bentham, Science Direct, PubMed, Scopus, USFDA, etc., about HPSE, its structure, functions, and role in cancer.

RESULTS

The present review is focused on Heparanase inhibitors (HPIns) that have been isolated from natural resources or chemically synthesized as new therapeutics for metastatic tumors and chronic inflammatory diseases in recent years. The recent developments made in the HPSE structure and function are also discussed, which can lead to the future design of HPIns with more potency and specificity for the target.

CONCLUSION

HPIns can be a better target to be explored against various cancers.

A heparin derivatives library constructed by chemical modification and enzymatic depolymerization for exploitation of non-anticoagulant functions

Non-anticoagulant biological functions of heparin-based drugs have drawn increasing attention. However, the exploration into the non-anticoagulant activities of various low molecular weight heparins was associated with bleeding risks in clinical practice and often led to controversial conclusions due to the structural differences. In this study, we aimed to establish a process to produce a library of heparin derivatives with structural diversity and reduced/abolished anticoagulant activity through the combination of chemical modifications and enzymatic cleavage of heparins. The depolymerization characteristics of various selectively modified heparin derivatives by three heparinases were comprehensively analyzed. The order of periodate treatment and heparinase-I depolymerization was proved to significantly change the structural characteristics of the oligosaccharide products. Finally, among several heparin derivatives that screened in the bleomycin-induced cell apoptosis model, the low molecular weight partially 6-O-/N-desulfated heparins showed the strongest anti-apoptotic activities. This study provided a useful approach for future development of novel heparin-derivative medications.

Heparanase as an Additional Tool for Detecting Structural Peculiarities of Heparin Oligosaccharides

Due to the biological properties of heparin and low-molecular-weight heparin (LMWH), continuous advances in elucidation of their microheterogeneous structure and discovery of novel structural peculiarities are crucial. Effective strategies for monitoring manufacturing processes and assessment of more restrictive specifications, as imposed by the current regulatory agencies, need to be developed. Hereby, we apply an efficient heparanase-based strategy to assert the structure of two major isomeric octasaccharides of dalteparin and investigate the tetrasaccharides arising from antithrombin binding region (ATBR) of bovine mucosal heparin. Heparanase, especially when combined with other sample preparation methods (e.g., size exclusion, affinity chromatography, heparinase depolymerization), was shown to be a powerful tool providing relevant information about heparin structural peculiarities. The applied approach provided direct evidence that oligomers bearing glucuronic acid–glucosamine-3-O-sulfate at their nonreducing end represent an important structural signature of dalteparin. When extended to ATBR-related tetramers of bovine heparin, the heparanase-based approach allowed for elucidation of the structure of minor sequences that have not been reported yet. The obtained results are of high importance in the view of the growing interest of regulatory agencies and manufacturers in the development of low-molecular-weight heparin generics as well as bovine heparin as alternative source.

Targeting Heparanase in Cancer: Inhibition by Synthetic, Chemically Modified, and Natural Compounds

Heparanase is an endoglycosidase involved in remodeling the extracellular matrix and thereby in regulating multiple cellular processes and biological activities. It cleaves heparan sulfate (HS) side chains of HS proteoglycans into smaller fragments and hence regulates tissue morphogenesis, differentiation, and homeostasis. Heparanase is overexpressed in various carcinomas, sarcomas, and hematological malignancies, and its upregulation correlates with increased tumor size, tumor angiogenesis, enhanced metastasis, and poor prognosis. In contrast, knockdown or inhibition of heparanase markedly attenuates tumor progression, further underscoring the potential of anti-heparanase therapy. Heparanase inhibitors were employed to interfere with tumor progression in preclinical studies, and selected heparin mimetics are being examined in clinical trials. However, despite tremendous efforts, the discovery of heparanase inhibitors with high clinical benefit and minimal adverse effects remains a therapeutic challenge. This review discusses the key roles of heparanase in cancer progression focusing on the status of natural, chemically modified, and synthetic heparanase inhibitors in various types of malignancies.

λ-Carrageenan Oligosaccharides of Distinct Anti-Heparanase and Anticoagulant Activities Inhibit MDA-MB-231 Breast Cancer Cell Migration

In tumor development, the degradation of heparan sulfate (HS) by heparanase (HPSE) is associated with cell-surface and extracellular matrix remodeling as well as the release of HS-bound signaling molecules, allowing cancer cell migration, invasion and angiogenesis. Because of their structural similarity with HS, sulfated polysaccharides are considered a promising source of molecules to control these activities. In this study, we used a depolymerisation method for producing λ-carrageenan oligosaccharides (λ-CO), with progressive desulfation over time. These were then used to investigate the influence of polymeric chain length and degree of sulfation (DS) on their anti-HPSE activity. The effects of these two features on λ-CO anticoagulant properties were also investigated to eliminate a potential limitation on the use of a candidate λ-CO as a chemotherapeutic agent. HPSE inhibition was mainly related to the DS of λ-CO, however this correlation was not complete. On the other hand, both chain length and DS modulated λ-CO activity for factor Xa and thrombin IIa inhibition, two enzymes that are involved in the coagulation cascade, and different mechanisms of inhibition were observed. A λ-carrageenan oligosaccharide of 5.9 KDa was identified as a suitable anticancer candidate because it displayed one of the lowest anticoagulant properties among the λ-CO produced, while showing a remarkable inhibitory effect on MDA-MB-231 breast cancer cell migration.

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.

The Low Molecular Weight Heparin Tinzaparin Attenuates Platelet Activation in Terms of Metastatic Niche Formation by Coagulation-Dependent and Independent Pathways

An intimate interplay with platelets is an initial key issue for tumor cells in terms of hematogenous metastasis. Tumor cells activate platelets by different pathways and receive, upon forming a platelet cloak, protection from immune surveillance and support in metastatic niche creation. Therapeutic intervention with this early interaction is promising to antagonize the whole metastatic cascade. Here we aimed to investigate the capability of low molecular weight heparin (LMWH), unfractionated heparin (UFH), and a non-anticoagulant heparin derivative or FXa inhibitor fondaparinux to interfere with platelet activation by tumor cells. Coagulation-dependent and independent pathways of platelet activation by three tumor cell lines, and interference therewith were analyzed by fluorigenic thrombin formation assay, platelet aggregometry, ATP and VEGF release and endothelial tube formation assay. LMWH and UFH were found to repress various routes of platelet activation, reflected by attenuated endothelial tube formation. This confirms the duality of anti-coagulative and anti-adhesive properties of heparin. While non-anticoagulative heparin (RO-heparin) depressed platelets’ ATP and VEGF release by contact inhibition sufficiently, fondaparinux just attenuated tissue factor mediated thrombin generation. Concluding, these data suggest that LMWH as a guideline-based drug for anticoagulative strategies in oncology is promising to provide additional benefit for interference with metastatic activities.

Binding and structure-kinetic relationship analysis of selective TLR4-targeted immunosuppressive self-assembling heparin nanoparticles

Self-assembling aliphatic heparin derivatives were shown to inhibit the immune system by antagonizing Toll-like receptor 4/myeloid differentiation protein 2 (TLR4/MD2). In the present study, glycol split heparin-d-erythro-sphingosine conjugates (NAHNP) and its regioselectively desulfated derivatives with shortened aliphatic chains were investigated regarding their biophysical properties in the interaction with TLR4/MD2. Two-dimensional nuclear Overhauser effect spectroscopy studies showed that upon glycol splitting, the heparin backbone gains extra adaptability that facilitates binding to proteins. However, unlike native heparin or glycol split non-anticoagulant heparin (NAH), hydrophobic derivatization of NAH forces sulfated iduronic acid residues to change configuration from a ²S₀ skew-boat to a ¹C₄ chair form. Whereas neither heparin nor NAH had any appreciable effect, NAHNP significantly inhibited lipopolysaccharide-induced activation of the NF-κB transcription factor. We showed that NAHNP binds to TLR4/MD2 with an affinity of 62.3 nM. In line with computational studies, biosensor-based structure-kinetic relationship studies demonstrated that 6-O-sulfo groups of d-glucosamine residue were essential in binding to arginines of both TLR4 and MD2 domains of the receptor complex. The desulfation of 6-O-sulfo groups decreases the association kinetics from 4.2 × 10⁴ M^-1 s^-1 to 3.8 × 10³ M^-1 s^-1, which results in a decreased affinity of 800 nM. Two aliphatic chains of NAHNP bound to the MD2 pocket similarly to lipopolysaccharide. A decrease in chain length resulted in a loss of inhibitory activity on NF-κB transcription and binding affinity to TLR4/MD2. In conclusion, the present study characterizes the immunosuppressive effect of aliphatic heparin derivatives and provides a promising strategy to develop selective immunosuppressants for acute and chronic inflammatory disorders.

Characterization of therapeutic protein AvidinOX by an integrated analytical approach

AvidinOX, the oxidized derivative of Avidin, is a chemically modified glycoprotein, being currently under clinical investigation for targeted delivery of radioactive biotin to inoperable tumors. AvidinOX is produced by 4-hydroxyazobenzene-2-carboxylic acid (HABA)-assisted sodium periodate oxidation of Avidin. The peculiar property of the periodate-generated glycol-split carbohydrate moieties to form Schiff's bases with amino groups of the tissue proteins allows to achieve a tissue half-life of 2 weeks compared to 2 h of native Avidin. Carbohydrate oxidation, along with possible minor amino acid modifications, introduces additional microheterogeneity in the glycoprotein structure, making its characterization even more demanding than for native glycoproteins. Aiming at the elucidation of the effects of oxidation conditions on the AvidinOX protein backbone and sugars, this microheterogeneous glycoprotein derivative was characterized for the first time using a combination of different analytical methods, including colorimetric methods, mass spectrometry, hollow-fiber flow field-flow fractionation with UV and multi-angle laser scattering detection (HF5-UV-MALS), and NMR. The proposed integrated approach reveals structural features of AvidinOX relevant for its biological activity, e.g., oxidized sites within both carbohydrate moieties and protein backbone and conformational stability, and will be considered as an analytical tool for AvidinOX industrial preparations. It is worth noting that this study enriches also the structural data of native Avidin published up-to-date (e.g., glycan structure and distribution, peptide fingerprint, etc.). Graphical abstract Scheme of phenylacetic hydrazide/MALDI-TOF approach for quantification of aldehydes in AvidinOX based on the determination of the number of hydrazone adducts between hydrazide reagent and aldehyde groups of protein.

Targeting heparin and heparan sulfate protein interactions

Heparin and heparan sulfate glycosaminoglycans are long, linear polysaccharides that are made up of alternating dissacharide sequences of sulfated uronic acid and amino sugars. Unlike heparin, which is only found in mast cells, heparan sulfate is ubiquitously expressed on the cell surface and in the extracellular matrix of all animal cells. These negatively-charged glycans play essential roles in important cellular functions such as cell growth, adhesion, angiogenesis, and blood coagulation. These biomolecules are also involved in pathophysiological conditions such as pathogen infection and human disease. This review discusses past and current methods for targeting these complex biomolecules as a novel therapeutic strategy to treating disorders such as cancer, neurodegenerative diseases, and infection.

Characterization of Danaparoid Complex Extractive Drug by an Orthogonal Analytical Approach

Danaparoid sodium salt, is the active component of ORGARAN, an anticoagulant and antithrombotic drug constituted of three glycosaminoglycans (GAGs) obtained from porcine intestinal mucosa extracts. Heparan sulfate is the major component, dermatan sulfate and chondroitin sulfate being the minor ones. Currently dermatan sulfate and chondroitin sulfate are quantified by UV detection of their unsaturated disaccharides obtained by enzymatic depolymerization. Due to the complexity of danaparoid biopolymers and the presence of shared components, an orthogonal approach has been applied using more advanced tools and methods. To integrate the analytical profile, 2D heteronuclear single quantum coherence (HSQC) NMR spectroscopy was applied and found effective to identify and quantify GAG component signals as well as those of some process signatures of danaparoid active pharmaceutical ingredient (API) batches. Analyses of components of both API samples and size separated fractions proceeded through the determination and distribution of the molecular weight (Mw) by high performance size exclusion chromatographic triple detector array (HP-SEC-TDA), chain mapping by LC/MS, and mono- (¹H and ¹³C) and bi-dimensional (HSQC) NMR spectroscopy. Finally, large scale chromatographic isolation and depolymerization of each GAG followed by LC/MS and 2D-NMR analysis, allowed the sequences to be defined and components to be evaluated of each GAG including oxidized residues of hexosamines and uronic acids at the reducing ends.

Structural Characterization of the Low-Molecular-Weight Heparin Dalteparin by Combining Different Analytical Strategies

A number of low molecular weight heparin (LMWH) products are available for clinical use and although all share a similar mechanism of action, they are classified as distinct drugs because of the different depolymerisation processes of the native heparin resulting in substantial pharmacokinetic and pharmacodynamics differences. While enoxaparin has been extensively investigated, little information is available regarding the LMWH dalteparin. The present study is focused on the detailed structural characterization of Fragmin^® by LC-MS and NMR applied both to the whole drug and to its enzymatic products. For a more in-depth approach, size homogeneous octasaccharide and decasaccharide components together with their fractions endowed with high or no affinity toward antithrombin were also isolated and their structural profiles characterized. The combination of different analytical strategies here described represents a useful tool for the assessment of batch-to-batch structural variability and for comparative evaluation of structural features of biosimilar products.

Past, present, and future perspectives of heparins in clinical settings and the role of impaired renal function

Heparin, whose discovery goes back one hundred years, was first detected as a thromboplastin from liver tissue, and its anticoagulant action was only identified later. The procoagulant action of heparin, which was later characterized as an immunologic reaction by binding to platelet-factor IV, presenting as heparin-induced thrombocytopenia, remains as a side effect. For more than 60 years heparin has been the immediate anticoagulant of choice in many clinical indications. Further development of heparins resulted in the production of low-molecular weight heparins and Fondaparinux, which substituted heparin for many indications and has received many more new indications, including administration for non-anticoagulant purposes. This development is still ongoing and has resulted in more than 300 registered clinical trials at the end of 2015. All types of heparins are still investigated in patients with impairment of renal function to improve the safety of treatment. New therapeutic strategies for the prevention and treatment of thromboembolism, as well as of the non-anticoagulant actions of natural and modified types of heparins, are studied intensively. The clinical study designs include treatment with vitamin-K and non-vitamin K oral anticoagulants. Consequently, heparins, low-molecular weight heparins and Fondaparinux play an important role in the human health care system.

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.

Structural peculiarity and antithrombin binding region profile of mucosal bovine and porcine heparins

The major compositional differences between bovine mucosal heparin (BMH) and the currently employed porcine mucosal heparin (PMH) have been reported to essentially consist of reduced 6-O-sulfation of the glucosamine residues in BMH and somewhat lower 2-O-sulfation of the iduronate residues in PMH. The present work is based on direct comparison of several BMH and PMH commercial preparations. A combined study by 2D (heteronuclear single quantum coherence, HSQC) NMR and ion-pair reversed-phase high performance liquid chromatography (IPRP-HPLC) coupled with electrospray ionization mass spectrometry (ESI-MS) on the heparins, extended to the analysis of their heparinases digests and fractions separated by affinity chromatography on antithrombin (AT), confirmed the previously reported lower degree of 6-O-sulfation and showed lower 3-O-sulfated glucosamine content in BMH. More detailed studies allowed the identification of structural variants of AT-binding region (ATBR) structural variants, showing higher content of the N-sulfated components in BMH than in PMH.

Determination of the molecular weight of low-molecular-weight heparins by using high-pressure size exclusion chromatography on line with a triple detector array and conventional methods

The evaluation of weight average molecular weight (Mw) and molecular weight distribution represents one of the most controversial aspects concerning the characterization of low molecular weight heparins (LMWHs). As the most commonly used method for the measurement of such parameters is high performance size exclusion chromatography (HP-SEC), the soundness of results mainly depends on the appropriate calibration of the chromatographic columns used. With the aim of meeting the requirement of proper Mw standards for LMWHs, in the present work the determination of molecular weight parameters (Mw and Mn) by HP-SEC combined with a triple detector array (TDA) was performed. The HP-SEC/TDA technique permits the evaluation of polymeric samples by exploiting the combined and simultaneous action of three on-line detectors: light scattering detectors (LALLS/RALLS); refractometer and viscometer. Three commercial LMWH samples, enoxaparin, tinzaparin and dalteparin, a γ-ray depolymerized heparin (γ-Hep) and its chromatographic fractions, and a synthetic pentasaccharide were analysed by HP-SEC/TDA. The same samples were analysed also with a conventional HP-SEC method employing refractive index (RI) and UV detectors and two different chromatographic column set, silica gel and polymeric gel columns. In both chromatographic systems, two different calibration curves were built up by using (i) γ-Hep chromatographic fractions and the corresponding Mw parameters obtained via HP-SEC/TDA; (ii) the whole γ-Hep preparation with broad Mw dispersion and the corresponding cumulative distribution function calculated via HP-SEC/TDA. In addition, also a chromatographic column calibration according to European Pharmacopoeia indication was built up. By comparing all the obtained results, some important differences among Mw and size distribution values of the three LMWHs were found with the five different calibration methods and with HP-SEC/TDA method. In particular, the detection of the lower molecular weight components turned out to be the most critical aspect. Whereas HP-SEC/TDA may underestimate species under 2 KDa when present in low concentration, other methods appeared to emphasize their content.

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.

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.