Unveiling the structure of sulfated fucose-rich polysaccharides via nuclear magnetic resonance spectroscopy

Fucosylated Chondroitin Sulfates with Rare Disaccharide Branches from the Sea Cucumbers Psolus peronii and Holothuria nobilis: Structures and Influence on Hematopoiesis

Two fucosylated chondroitin sulfates were isolated from the sea cucumbers Psolus peronii and Holothuria nobilis using a conventional extraction procedure in the presence of papain, followed by anion-exchange chromatography on DEAE-Sephacel. Their composition was characterized in terms of quantitative monosaccharide and sulfate content, and structures were mainly elucidated using 1D- and 2D-NMR spectroscopy. As revealed by the data of the NMR spectra, both polysaccharides along with the usual fucosyl branches contained rare disaccharide branches α-D-GalNAc4S6R-(1→2)-α-L-Fuc3S4R → attached to O-3 of the GlcA of the backbone (R = H or SO3-). The polysaccharides were studied as stimulators of hematopoiesis in vitro using mice bone marrow cells as the model. The studied polysaccharides were shown to be able to directly stimulate the proliferation of various progenitors of myelocytes and megakaryocytes as well as lymphocytes and mesenchymal cells in vitro. Therefore, the new fucosylated chondroitin sulfates can be regarded as prototype structures for the further design of GMP-compatible synthetic analogs for the development of new-generation hematopoiesis stimulators.

Approaches to Assure Similarity between Pharmaceutical Heparins from Two Different Manufacturers

Pharmaceutical heparins from different manufacturers may present heterogeneities due to particular extraction and purification procedures or even variations in the raw material manipulation. Heparins obtained from different tissues also differ in their structure and activity. Nevertheless, there is an increased demand for more accurate assessments to ensure the similarities of pharmaceutical heparins. We propose an approach to accurately assess the similarity of these pharmaceutical preparations based on well-defined criteria, which are verified with a variety of refined analytical methods. We evaluate six commercial batches from two different manufacturers which were formulated with Brazilian or Chinese active pharmaceutical ingredients. Biochemical and spectroscopic methods and analysis based on digestion with heparinases were employed to evaluate the purity and structure of the heparins. Specific assays were employed to evaluate the biological activity. We observed minor but significant differences between the constitutive units of the heparins from these two manufacturers, such as the content of N-acetylated α-glucosamine. They also have minor differences in their molecular masses. These physicochemical differences have no impact on the anticoagulant activity but can indicate particularities on their manufacturing processes. The protocol we propose here for analyzing the similarity of unfractionated heparins is analogous to those successfully employed to compare low-molecular-weight heparins.

Nano-Sized Fucoidan Interpolyelectrolyte Complexes: Recent Advances in Design and Prospects for Biomedical Applications

The marine polysaccharide fucoidan (FUC) is a promising polymer for pharmaceutical research and development of novel drug delivery systems with modified release and targeted delivery. The presence of a sulfate group in the polysaccharide makes FUC an excellent candidate for the formation of interpolyelectrolyte complexes (PECs) with various polycations. However, due to the structural diversity of FUC, the design of FUC-based nanoformulations is challenging. This review describes the main strategies for the use of FUC-based PECs to develop drug delivery systems with improved biopharmaceutical properties, including nanocarriers in the form of FUC-chitosan PECs for pH-sensitive oral delivery, targeted delivery systems, and polymeric nanoparticles for improved hydrophobic drug delivery (e.g., FUC-zein PECs, core-shell structures obtained by the layer-by-layer self-assembly method, and self-assembled hydrophobically modified FUC particles). The importance of a complex study of the FUC structure, and the formation process of PECs based on it for obtaining reproducible polymeric nanoformulations with the desired properties, is also discussed.

Comparison of in vitro and in vivo antioxidant activities of commercial fucoidans from Macrocystis pyrifera, Undaria pinnatifida, and Fucus vesiculosus

Antioxidants fucoidans from three seaweeds, Undaria pinnatifida (FUP), Macrocystis pyrifera (FMP) and Fucus vesiculosus (FFV) are sold commercially. However, it is unclear which fucoidan is the most potent antioxidant. Therefore, our objective was to compare the antioxidant activities of these fucoidans. For this purpose, six in vitro antioxidant tests were used, total antioxidant capacity, hydroxyl radical scavenging assay, ferrous and cupric chelating assay, reducing power and H2O2 scavenging assay. The data showed that the fucoidans had a low capacity to donate electrons, and a low capacity to chelate metals. The best activity obtained was in the scavenging of hydroxyl radical. When macrophages were exposed to H2O2 and fucoidans, MTT and live/dead assays showed that all fucoidans protected cells from oxidative damage. The survival rate of zebrafish embryos was significantly higher when exposed to H2O2 and fucoidans than H2O2 alone. In summary, the fucoidans evaluated were ranked according to their antioxidant activity as follows: FMP > FFV > FUP, and the results suggest that these fucoidans, mainly FMP, can be used in the formulation of medicines/foods.

A Fucan Sulfate with Pentasaccharide Repeating Units from the Sea Cucumber Holothuriafloridana and Its Anticoagulant Activity

A fucan sulfate (HfFS) was isolated from the sea cucumber Holothuriafloridana after proteolysis-alkaline treatment and purified with anion-exchange chromatography. The molecular weight (Mw) of HfFS was determined to be 443.4 kDa, and the sulfate content of HfFS was 30.4%. The structural analysis of the peroxidative depolymerized product (dHfFS-1) showed that the primary structure of HfFS was mainly composed of a distinct pentasaccharide repeating unit -[l-Fuc_2S4S-α(1,3)-l-Fuc-α(1,3)-Fuc-α(1,3)-l-Fuc_2S-α(1,3)-l-Fuc_2S-α(1,3)-]_n-. Then, the “bottom-up” strategy was employed to confirm the structure of HfFS, and a series of fucooligosaccharides (disaccharides, trisaccharides, and tetrasaccharides) were purified from the mild acid-hydrolyzed HfFS. The structures identified through 1D/2D NMR spectra showed that these fucooligosaccharides could be derivates from the pentasaccharide units, while the irregular sulfate substituent also exists in the units. Anticoagulant activity assays of native HfFS and its depolymerized products (dHf-1~dHf-6) in vitro suggested that HfFS exhibits potent APTT-prolonging activity and the potencies decreased with the reduction in molecular weights, and HfFS fragments (dHf-4~dHf-6) with Mw less than 11.5 kDa showed no significant anticoagulant effect. Overall, our study enriched the knowledge about the structural diversity of FSs in different sea cucumber species and their biological activities.

NMR spectroscopy for structural elucidation of sulfated polysaccharides from red seaweeds

Some sulfated polysaccharides from red seaweeds are used as hydrocolloids. In addition, it is well known that there are sulfated galactans (carrageenans and agarans) and sulfated mannans, with remarkable biological properties, as antiviral, antitumoral, immunomodulating, antiangiogenic, antioxidant, anticoagulant, and antithrombotic activities, and so on. Knowledge of the detailed structure of the active compound is essential and difficult to acquire. The substitution patterns of the polymer chain, as degree of sulfation and position of sulfate groups, as well as other substituents of the backbone, determine their biological behavior. NMR spectroscopy is a powerful and versatile tool for structural determination. It can be used for elucidation of structures of polysaccharides from new algal sources with novel substitutions or to detect the already known structures from different algal sources, and it could even help to monitor the quality of the active compound on a productive scale. In this review, the available information about NMR spectroscopy of sulfated polysaccharides from red seaweeds is revised and rationalized, to help other researchers working in different fields to study their structures. In addition, considerations about the effects of different structural features, as well as some recording conditions on the chemical shifts of the signals are analyzed.

Structural and kinetic analyses of holothurian sulfated glycans suggest potential treatment for SARS-CoV-2 infection

Certain sulfated glycans, including those from marine sources, can show potential effects against SARS-CoV-2. Here, a new fucosylated chondroitin sulfate (FucCS) from the sea cucumber Pentacta pygmaea (PpFucCS) (MW ∼10-60 kDa) was isolated and structurally characterized by NMR. PpFucCS is composed of {→3)-β-GalNAcX-(1→4)-β-GlcA-[(3→1)Y]-(1→}, where X = 4S (80%), 6S (10%) or nonsulfated (10%), Y = α-Fuc2,4S (40%), α-Fuc2,4S-(1→4)-α-Fuc (30%), or α-Fuc4S (30%), and S = SO3-. The anti-SARS-CoV-2 activity of PpFucCS and those of the FucCS and sulfated fucan isolated from Isostichopus badionotus (IbFucCS and IbSF) were compared with that of heparin. IC50 values demonstrated the activity of the three holothurian sulfated glycans to be ∼12 times more efficient than heparin, with no cytotoxic effects. The dissociation constant (KD) values obtained by surface plasmon resonance of the wildtype SARS-CoV-2 spike (S)-protein receptor-binding domain (RBD) and N501Y mutant RBD in interactions with the heparin-immobilized sensor chip were 94 and 1.8 × 103 nM, respectively. Competitive surface plasmon resonance inhibition analysis of PpFucCS, IbFucCS, and IbSF against heparin binding to wildtype S-protein showed IC50 values (in the nanomolar range) 6, 25, and 6 times more efficient than heparin, respectively. Data from computational simulations suggest an influence of the sulfation patterns of the Fuc units on hydrogen bonding with GlcA and that conformational change of some of the oligosaccharide structures occurs upon S-protein RBD binding. Compared with heparin, negligible anticoagulant action was observed for IbSF. Our results suggest that IbSF may represent a promising molecule for future investigations against SARS-CoV-2.

Exploiting the Amazing Diversity of Natural Source-Derived Polysaccharides: Modern Procedures of Isolation, Engineering, and Optimization of Antiviral Activities

Naturally occurring polysaccharide sulfates are highly diverse, owning variations in the backbone structure, linkage pattern and stereochemistry, branching diversity, sulfate content and positions of sulfate group(s). These structural characteristics bring about diverse sulfated polymers with dissimilar negative charge densities and structure-activity relationships. Herein, we start with a short discussion of techniques needed for extraction, purification, chemical sulfation, and structural characterization of polysaccharides. Processes of isolation and sulfation of plant-derived polysaccharides are challenging and usually involve two steps. In this context, we describe an integrated extraction-sulfation procedure that produces polysaccharide sulfates from natural products in one step, thereby generating additional pharmacological activities. Finally, we provide examples of the spectrum of natural source-derived polysaccharides possessing specific features of bioactivity, in particular focusing on current aspects of antiviral drug development and drug-target interaction. Thus, the review presents a detailed view on chemically engineered polysaccharides, especially sulfated derivatives, and underlines their promising biomedical perspectives.

(Semi)-Synthetic Fucosylated Chondroitin Sulfate Oligo- and Polysaccharides

Fucosylated chondroitin sulfate (fCS) is a glycosaminoglycan (GAG) polysaccharide with a unique structure, displaying a backbone composed of alternating N-acetyl-d-galactosamine (GalNAc) and d-glucuronic acid (GlcA) units on which l-fucose (Fuc) branches are installed. fCS shows several potential biomedical applications, with the anticoagulant activity standing as the most promising and widely investigated one. Natural fCS polysaccharides extracted from marine organisms (Echinoidea, Holothuroidea) present some advantages over a largely employed antithrombotic drug such as heparin, but some adverse effects as well as a frequently found structural heterogeneity hamper its development as a new drug. To circumvent these drawbacks, several efforts have been made in the last decade to obtain synthetic and semi-synthetic fCS oligosaccharides and low molecular weight polysaccharides. In this Review we have for the first time collected these reports together, dividing them in two topics: (i) total syntheses of fCS oligosaccharides and (ii) semi-synthetic approaches to fCS oligosaccharides and low molecular weight polysaccharides as well as glycoclusters displaying multiple copies of fCS species.

Insights on chemical-biological correlations learned from investigations on the sulfated galactan from the marine alga Bothryocladia occidentalis

Marine organisms have been proven to be a valuable source of bioactive compounds. Among them, we highlight the sulfated galactans (SGs) from seaweeds, which besides being massively exploited as industrial thickening and gelling agents (agarans and carrageenans), have also shown promising pharmacological properties. Investigations on the non-agaran/-carrageenan SG from the red algae Bothryocladia occidentalis (SGBo) have demonstrated clear correlations between physical-chemical features and biological activities. SGBo is composed of 2,3-disulfated (~33%) or 2-sulfated (33%) α-D-galactose linked to non- or 2-sulfated β-D-galactose repetitive disaccharide units. The notable serpin-dependent/-independent anticoagulant activity of SGBo (~130 international units [IU]/mg) is higher than those of other SGs containing less 2,3-disulfated α-D-galactose units and their low-molecular-weight derivatives, and thus is directly correlated to its high molecular mass (>200 kDa) and sulfation pattern. Although SGBo has antithrombotic efficacy equivalent to heparin and decreased bleeding potential at low-doses, high-doses substantially increase thrombus formation in animal models. Such an odd dose-dependent dual antithrombotic/prothrombotic activity has been attributed to the ability of SGBo to activate factor XII. In addition to anticoagulant properties, SGBo also exerts antimalarial, antileishmanial and antiophidic activities, and, therefore, has a remarkable potential for the research and development of novel drugs.

Adhesion of freshwater sponge cells mediated by carbohydrate-carbohydrate interactions requires low environmental calcium

Marine ancestors of freshwater sponges had to undergo a series of physiological adaptations to colonize harsh and heterogeneous limnic environments. Besides reduced salinity, river-lake systems also have calcium concentrations far lower than seawater. Cell adhesion in sponges is mediated by calcium-dependent multivalent self-interactions of sulfated polysaccharide components of membrane-bound proteoglycans named aggregation factors. Cells of marine sponges require seawater average calcium concentration (10 mM) to sustain adhesion promoted by aggregation factors. We demonstrate here that the freshwater sponge Spongilla alba can thrive in a calcium-poor aquatic environment and that their cells are able to aggregate and form primmorphs with calcium concentrations 40-fold lower than that required by marine sponges cells. We also find that their gemmules need calcium and other micronutrients to hatch and generate new sponges. The sulfated polysaccharide purified from S. alba has sulfate content and molecular size notably lower than those from marine sponges. Nuclear magnetic resonance analyses indicated that it is composed of a central backbone of non- and 2-sulfated α- and β-glucose units decorated with branches of α-glucose. Assessments with atomic force microscopy/single-molecule force spectroscopy show that S. alba glucan requires 10-fold less calcium than sulfated polysaccharides from marine sponges to self-interact efficiently. Such an ability to retain multicellular morphology with low environmental calcium must have been a crucial evolutionary step for freshwater sponges to successfully colonize inland waters.

The Potential of Fucose-Containing Sulfated Polysaccharides As Scaffolds for Biomedical Applications

Marine environments have a high quantity and diversity of sulfated polysaccharides. In coastal regions brown algae are the most abundant biomass producers and their cell walls have fucosecontaining sulfated polysaccharides (FCSP), known as fucans and/or fucoidans. These sulfated compounds have been widely researched for their biomedical properties, namely the immunomodulatory, haemostasis, pathogen inhibition, anti-inflammatory capacity, and antitumoral. These activities are probably due to their ability to mimic the carbohydrate moieties of mammalian glycosaminoglycans. Therefore, the FCSP are interesting compounds for application in health-related subjects, mainly for developing scaffolds for delivery systems or tissue regeneration. FCSP showed potential for these applications also due to their ability to form stable 3D structures with other polymers able to entrap therapeutic agents or cell and growth factors, besides their biocompatibility and biodegradability. However, for the clinical use of these biopolymers well-defined reproducible molecules are required in order to accurately establish relationships between structural features and human health applications.

Two different fucosylated chondroitin sulfates: Structural elucidation, stimulating hematopoiesis and immune-enhancing effects

Two fucosylated chondroitin sulfates FCS_hp and FCS_ht were isolated from the sea cucumber Holothuria polii and Holothuria tubulosa, respectively. The NMR spectroscopy and HILIC-FTMS methods were applied for their detailed structural characterization. Chemical analysis indicated that the two FCSs all contained a chondroitin sulfate backbone chondroitin sulfate-like core and fucosyl branches of α-L-Fuc2,4S, α-L-Fuc4S or α-L-Fuc3,4S linked to O-3 of glucuronic acid residues. The main branches of FCS_hp and FCS_ht were monofucose, and the small amounts of di-, tri- and tetrafucose with α-1,3-linkage type were also detected. Finally, we investigated the immunomodulatory function of FCS_hp and FCS_ht in cyclophosphamide (CTX)-induced immunosuppressed mouse models. The results showed that FCS_hp and FCS_ht had beneficial effects on hematopoietic function recovery in CTX-induced bone marrow suppression mice. Notably, the α-L-Fuc2,4S was more important to the activity than α-L-Fuc3,4S. These results provided basis for developing the drugs to reduce side effects of chemotherapy.

Separation, purification, structural analysis and immune-enhancing activity of sulfated polysaccharide isolated from sea cucumber viscera

A novel sulfated polysaccharide (SCVP-1) was isolated from sea cucumber viscera and purified to elucidate its structure and immune-enhancing ability. SCVP-1 was found to be a homogeneous polysaccharide with a relative molecular weight of 180.8 kDa and composed of total sugars (60.2 ± 2.6%), uronic acid (15.3 ± 1.8%), proteins (6.8 ± 0.8%), and sulfate groups (18.1 ± 0.9%). SCVP-1 consisted of mannose, glucosamine, glucuronic acid, N-acetyl-galactosamine, glucose, galactose and fucose at an approximate molar ratio of 1.00:1.41:0.88:2.14:1.90:1.12:1.24. The fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (NMR) analyses showed that SCVP-1 was a kind of glycosaminoglycan. And the sulfation patterns of the fucose branches were Fuc2,4S, Fuc3,4S and Fuc0S. The surface morphology of SCVP-1 presented loose and irregular sheet structure formed by aggregation of polysaccharide molecules with spherical structure. Moreover, SCVP-1 promoted the production of nitric oxide (NO) and cytokines (IL-1β, IL-6 and TNF-α) by RAW264.7 cells as well as the expression of related genes (iNOS, IL-1β, IL-6 and TNF-α) and also enhanced their phagocytic activity through TLR4-mediated activation of the MAPKs and NF-κB signaling pathways. This study suggests that sea cucumber viscera are good sources of polysaccharides and SCVP-1 might be a novel immunomodulator.

Tunicate Heparan Sulfate Enriched in 2-Sulfated β-Glucuronic Acid: Structure, Anticoagulant Activity, and Inhibitory Effect on the Binding of Human Colon Adenocarcinoma Cells to Immobilized P-Selectin

Heparin or highly sulfated heparan sulfate (HS) has been described in different invertebrates. In ascidians (Chordata-Tunicata), these glycosaminoglycans occur in intracellular granules of oocyte accessory cells and circulating basophil-like cells, resembling mammalian mast cells and basophils, respectively. HS is also a component of the basement membrane of different ascidian organs. We have analyzed an HS isolated from the internal organs of the ascidian Phallusia nigra, using solution ¹H/¹³C NMR spectroscopy, which allowed us to identify and quantify the monosaccharides found in this glycosaminoglycan. A variety of α-glucosamine units with distinct degrees of sulfation and N-acetylation were revealed. The hexuronic acid units occur both as α-iduronic acid and β-glucuronic acid, with variable sulfation at the 2-position. A peculiar structural aspect of the tunicate HS is the high content of 2-sulfated β-glucuronic acid, which accounts for one-third of the total hexuronic acid units. Another distinct aspect of this HS is the occurrence of high content of N-acetylated α-glucosamine units bearing a sulfate group at position 6. The unique ascidian HS is a potent inhibitor of the binding of human colon adenocarcinoma cells to immobilized P-selectin, being 11-fold more potent than mammalian heparin, but almost ineffective as an anticoagulant. Thus, the components of the HS structure required to inhibit coagulation and binding of tumor cells to P-selectin are distinct. Our results also suggest that the regulation of the pathway involved in the biosynthesis of glycosaminoglycans suffered variations during the evolution of chordates.

Methods for Isolation and Characterization of Sulfated Glycosaminoglycans from Marine Invertebrates

Marine invertebrates produce different kinds of sulfated polysaccharides. These glycans play essential roles in several biological processes and the study of these molecules is promising in a variety of fields. In the following sections, we describe the materials and methods used for the extraction, purification, and characterization of marine invertebrate-derived glycosaminoglycans.

A sulfated galactofucan from the brown alga Hormophysa cuneiformis (Fucales, Sargassaceae)

The brown alga Hormophysa cuneiformis collected from the coastal waters of Vietnam was used to isolate a mixture of sulfated polysaccharides FHC, which was fractionated further by anion-exchange chromatography on DEAE-Sephacel. The main fraction F3 eluted with 1.5 M NaCl contained essentially l-fucose, d-galactose and sulfate and has very complex NMR spectra. Desulfation to obtain F3deS followed by Smith degradation to obtain F3deS-Sm was used to simplify the structure of F3, and all these preparations were characterized by methylation analysis and NMR spectra. A linear (1 → 3)-linked backbone built up of α-l-fucopyranose residues was identified as the main structural motif of molecules. Some fucose residues attached to position 4 of its 3-linked neighbor were found as branches. Galactose residues having both α- and β-configurations were found mostly at the periphery of molecules. They are present as (1 → 6)-linked disaccharide of two β-d-Galp attached to position 4 of the backbone or as single α-d-Galp attached to the same position. Sulfate groups in F3 may probably occupy any positions of the molecule. F3 acts as anticoagulant and is about half as active as the standard low-molecular mass heparin (enoxaparin). FHC was practically inactive in cytotoxicity test against six human cancer cell lines.

Structure and Anti-Inflammatory Activity of a New Unusual Fucosylated Chondroitin Sulfate from Cucumaria djakonovi

Fucosylated chondroitin sulfate CD was isolated from the sea cucumber Cucumaria djakonovi collected from the Avachinsky Gulf of the eastern coast of Kamchatka. Structural characterization of CD was performed using a series of non-destructive NMR spectroscopic procedures. The polysaccharide was shown to contain a chondroitin core [→3)-β-d-GalNAc-(1→4)-β-d-GlcA-(1→]n where about 60% of GlcA residues were 3-O-fucosylated, while another part of GlcA units did not contain any substituents. The presence of unsubstituted both at O-2 and O-3 glucuronic acid residues in a structure of holothurian chondroitin sulfate is unusual and has not been reported previously. Three different fucosyl branches Fucp2S4S, Fucp3S4S and Fucp4S were found in the ratio of 2:1:1. The GalNAc units were mono- or disulfated at positions 4 and 6. Anti-inflammatory activity of CD was assessed on a model of acute peritoneal inflammation in rats. About 45% inhibition was found for CD, while a structurally related linear chondroitin sulfate SS from cartilage of the fish Salmo salar demonstrated only 31% inhibition, indicating that the presence of sulfated fucosyl branches is essential for anti-inflammatory effect of chondroitin sulfates of marine origin.

Glycans and glycosaminoglycans in neurobiology: key regulators of neuronal cell function and fate

The aim of the present study was to examine the roles of l-fucose and the glycosaminoglycans (GAGs) keratan sulfate (KS) and chondroitin sulfate/dermatan sulfate (CS/DS) with selected functional molecules in neural tissues. Cell surface glycans and GAGs have evolved over millions of years to become cellular mediators which regulate fundamental aspects of cellular survival. The glycocalyx, which surrounds all cells, actuates responses to growth factors, cytokines and morphogens at the cellular boundary, silencing or activating downstream signaling pathways and gene expression. In this review, we have focused on interactions mediated by l-fucose, KS and CS/DS in the central and peripheral nervous systems. Fucose makes critical contributions in the area of molecular recognition and information transfer in the blood group substances, cytotoxic immunoglobulins, cell fate-mediated Notch-1 interactions, regulation of selectin-mediated neutrophil extravasation in innate immunity and CD-34-mediated new blood vessel development, and the targeting of neuroprogenitor cells to damaged neural tissue. Fucosylated glycoproteins regulate delivery of synaptic neurotransmitters and neural function. Neural KS proteoglycans (PGs) were examined in terms of cellular regulation and their interactive properties with neuroregulatory molecules. The paradoxical properties of CS/DS isomers decorating matrix and transmembrane PGs and the positive and negative regulatory cues they provide to neurons are also discussed.