Nadezhda E. Ustyuzhanina

Fucans, but Not Fucomannoglucuronans, Determine the Biological Activities of Sulfated Polysaccharides from Laminaria saccharina Brown Seaweed

Sulfated polysaccharides from Laminaria saccharina (new name: Saccharina latissima) brown seaweed show promising activity for the treatment of inflammation, thrombosis, and cancer; yet the molecular mechanisms underlying these properties remain poorly understood. The aim of this work was to characterize, using in vitro and in vivo strategies, the anti-inflammatory, anti-coagulant, anti-angiogenic, and anti-tumor activities of two main sulfated polysaccharide fractions obtained from L. saccharina: a) L.s.-1.0 fraction mainly consisting of O-sulfated mannoglucuronofucans and b) L.s.-1.25 fraction mainly composed of sulfated fucans. Both fractions inhibited leukocyte recruitment in a model of inflammation in rats, although L.s.-1.25 appeared to be more active than L.s.-1.0. Also, these fractions inhibited neutrophil adhesion to platelets under flow. Only fraction L.s.-1.25, but not L.s.-1.0, displayed anticoagulant activity as measured by the activated partial thromboplastin time. Investigation of these fractions in angiogenesis settings revealed that only L.s.-1.25 strongly inhibited fetal bovine serum (FBS) induced in vitro tubulogenesis. This effect correlated with a reduction in plasminogen activator inhibitor-1 (PAI-1) levels in L.s.-1.25-treated endothelial cells. Furthermore, only parent sulfated polysaccharides from L. saccharina (L.s.-P) and its fraction L.s.-1.25 were powerful inhibitors of basic fibroblast growth factor (bFGF) induced pathways. Consistently, the L.s.-1.25 fraction as well as L.s.-P successfully interfered with fibroblast binding to human bFGF. The incorporation of L.s.-P or L.s.-1.25, but not L.s.-1.0 into Matrigel plugs containing melanoma cells induced a significant reduction in hemoglobin content as well in the frequency of tumor-associated blood vessels. Moreover, i.p. administrations of L.s.-1.25, as well as L.s.-P, but not L.s.-1.0, resulted in a significant reduction of tumor growth when inoculated into syngeneic mice. Finally, L.s.-1.25 markedly inhibited breast cancer cell adhesion to human platelet-coated surfaces. Thus, sulfated fucans are mainly responsible for the anti-inflammatory, anticoagulant, antiangiogenic, and antitumor activities of sulfated polysaccharides from L. saccharina brown seaweed.

Fucoidans: Pro- or antiangiogenic agents?

Sulfated polysaccharides of brown algae (fucoidans) attract great attention due to their high and strongly diversified biological activity. This review summarizes recent data on the structural variability of these polysaccharides and reports their anti- and proangiogenic properties. Recent publications have revealed that fucoidans isolated from different algal species may differ considerably in the structures of their backbones and branches, in both monosaccharide composition and sulfate content. It was found that the degree of sulfation significantly influences the biological properties of fucoidans. Additionally, fucoidan action in angiogenesis is highly dependent on molecular weight: antiangiogenic activity is connected with the high-molecular weight of polysaccharide molecules, whereas the low-molecular-weight fractions may act as proangiogenic agents. The influence of other fine structural details of fucoidans on angiogenesis remains to be established.

Acid-promoted synthesis of per-O-sulfated fucooligosaccharides related to fucoidan fragments.

The synthesis of per-O-sulfated derivatives of di-, tetra-, hexa-, octa-, dodeca-, and hexadecafucosides related to natural fucoidans of different types has been performed with the use of previously reported acid-promoted protocol for per-O-sulfation of polyols by SO(3) complexes. During the treatment of (1→3)-linked oligofucosides under these conditions with the promotion by TfOH, the unusual rearrangement of the reducing pyranose residue into furanose one was observed. To avoid the formation of rearrangement by-products, the use of a series of strong acids as promoters of sulfation of large oligofucosides was studied and the improved protocol was developed based on the use of TFA instead of TfOH. The efficiency of the new method was demonstrated by the syntheses of per-O-sulfated derivatives of dodeca- and hexadecafucosides. The described method of O-sulfation opens access to the preparation of the oligosaccharides related to fucoidan fragments and their per-O-sulfated derivatives interesting for elucidation of the relationship between their structure and biological activity.

Influence of Fucoidans on Hemostatic System

Three structurally different fucoidans from the brown seaweeds Saccharina latissima (SL), Fucus vesiculosus (FV), and Cladosiphon okamuranus (CO), two chemically modified fucoidans with a higher degree of sulfation (SL-S, CO-S), and a synthetic totally sulfated octasaccharide (OS), related to fucoidans, were assessed on anticoagulant and antithrombotic activities in different in vitro experiments. The effects were shown to depend on the structural features of the compounds tested. Native fucoidan SL with a degree of sulfation (DS) of 1.3 was found to be the most active sample, fucoidan FV (DS 0.9) demonstrated moderate activity, while the polysaccharide CO (DS 0.4) was inactive in all performed experiments, even at high concentrations. Additional introduction of sulfate groups into fucoidan SL slightly decreased the anticoagulant effect of SL-S, while sulfation of CO, giving rise to the preparation CO-S, increased the activity dramatically. The high level of anticoagulant activity of polysaccharides SL, SL-S, and CO-S was explained by their ability to form ternary complexes with ATIII-Xa and ATIII-IIa, as well as to bind directly to thrombin. Synthetic per-O-sulfated octasaccharide OS showed moderate anticoagulant effect, determined mainly by the interaction of OS with the factor Xa in the presence of ATIII. Comparable tendencies were observed in the antithrombotic properties of the compounds tested.

Pyranoside‐into‐Furanoside Rearrangement: New Reaction in Carbohydrate Chemistry and Its Application in Oligosaccharide Synthesis

Great interest in natural furanoside-containing compounds has challenged the development of preparative methods for their synthesis. Herein a novel reaction in carbohydrate chemistry, namely a pyranoside-into-furanoside (PIF) rearrangement permitting the transformation of selectively O-substituted pyranosides into the corresponding furanosides is reported. The discovered process includes acid-promoted sulfation accompanied by rearrangement of the pyranoside ring into a furanoside ring followed by solvolytic O-desulfation. This process, which has no analogy in organic chemistry, was shown to be a very useful tool for the synthesis of furanoside-containing complex oligosaccharides, which was demonstrated by synthesizing disaccharide derivatives α-D-Galp-(1→3)-β-D-Galf-OPr, 3-O-s-lactyl-β-D-Galf-(1→3)-β-D-Glcp-OPr, and α-L-Fucf-(1→4)-β-D-GlcpA-OPr related to polysaccharides from the bacteria Klebsiella pneumoniae and Enterococcus faecalis and the brown seaweed Chordaria flagelliformis.

Structural characterization of fucosylated chondroitin sulfates from sea cucumbers Apostichopus japonicus and Actinopyga mauritiana

Two samples of fucosylated chondroitin sulfate (FCS), AJ and AM, were isolated from holothurian species Apostichopus japonicus and Actinopyga mauritiana, respectively. Purification of FCS was performed by ion exchange chromatography followed by gel filtration. Structure of the biopolymers was elucidated using chemical and NMR spectroscopic methods. Both polysaccharides were shown to contain a typical chondroitin core built up of repeating disaccharide units →3)-β-d-GalNAc-(1→4)-β-d-GlcA-(1→ and decorated by sulfate groups and α-l-Fuc branches. Two polysaccharides were different in pattern of sulfation of GalNAc and fucosyl branches connected to O-3 of GlcA. The ratio of GalNAc4S6S:GalNAc4S for AJ was about 2:1, whereas for AM this value was approximately 1:1. AJ contained Fucp2S4S and Fucp3S4S residues linked to O-3 of GlcA in a ratio of 3:1, while for AM this ratio was 1:4. Small portions of Fucp4S units attached to O-3 of GlcA were also found in both polysaccharides. Moreover, in a structure of AM the presence of Fucp3S residues linked to O-6 of GalNAc were determined using the data of NMR spectra.

Structure and biological activity of a fucosylated chondroitin sulfate from the sea cucumber Cucumaria japonica.

A fucosylated chondroitin sulfate (FCS) was isolated from the body wall of Pacific sea cucumber Cucumaria japonicaby extraction in the presence of papain followed by Cetavlon precipitation and anion-exchange chromatography. FCS was shown to contain D-GalNAc, D-GlcA, L-Fuc and sulfate in molar proportions of about 1:1:1:4.5. Structure of FCS was elucidated using NMR spectroscopy and methylation analysis of the native polysaccharide and products of its desulfation and carboxyl reduction. The polysaccharide was shown to contain a typical chondroitin core → 3)-β-D-GalNAc-(1 → 4)-β-D-GlcA-(1 →. Sulfate groups in this core occupy O-4 and the majority of O-6 of GalNAc. Fucosyl branches are represented by 3,4- and 2,4-disulfated units in a ratio of 4:1 and are linked to O-3 of GlcA. In addition, ∼ 33% of GlcA are 3-O-sulfated, and hence, the presence of short fucooligosaccharide chains side by side with monofucosyl branches cannot be excluded. FCS was shown to inhibit platelets aggregation in vitro mediated by collagen and ristocetin, but not adenosine diphosphate, and demonstrated significant anticoagulant activity, which is connected with its ability to enhance inhibition of thrombin and factor Xa by antithrombin III, as well as to influence von Willebrand factor activity. The latest property significantly distinguished FCS from low-molecular-weight heparin.

Anticoagulant activity of fucoidans from brown algae

The anticoagulant activity of polysaccharide fucoidans from 11 species of brown algae was studied. The anticoagulant activity was measured by the activated partial thromboplastin time (APTT), prothrombin time, and thrombin time. Inhibitory action of these fucoidans significantly varied from one species to another. Fucoidans from Laminaria saccharina and Fucus distichus exhibited high anticoagulant activity, while fucoidans from Cladosiphon okamuranus and Analipus japonicus were almost inactive. Other fucoidans exhibited intermediate inhibitory activity. The inhibitory effect of fucoidans on thrombin and factor Xa was investigated in the presence or in the absence of natural thrombin inhibitor, antithrombin III (AT III). In contrast to the best-studied anticoagulant, heparin, most of these fucoidans inhibited thrombin in the absence of AT III. In the presence of AT III the inhibitory effect of fucoidans considerably increased. In contrast to heparin, fucoidans weakly influenced factor Xa activity in the presence of AT III and their inhibitory effect was not observed in the absence of AT III. There was no correlation between the anticoagulant activities of this series of fucoidans and their anti-inflammatory action, studied earlier. It is suggested that these two types of fucoidan activities depend on different structural features of fucoidans. Results of this study demonstrate a possibility of preparation of fucoidans with high anti-inflammatory activity but low anticoagulant activity. Anticoagulant activity of the fucoidans did not exhibit direct dependence on the content of fucose, the other neutral sugars and sulfates; no dependence was also found between the anticoagulant activity and the structure of the backbone of their molecules.

Anticoagulant and antithrombotic activities of modified xylofucan sulfate from the brown alga Punctaria plantaginea.

Selectively and totally sulfated (1 → 3)-linked linear homofucans bearing ∼ 20 monosaccharide residues on average have been prepared from the branched xylofucan sulfate isolated from the brown alga Punctaria plantaginea. Anticoagulant and antithrombotic properties of the parent biopolymer and its derivatives were assessed in vitro. Highly sulfated linear fucan derivatives were shown to inhibit clot formation in APTT assay and ristocetin induced platelets aggregation, while the partially sulfated analogs were inactive. In the experiments with purified proteins, fucan derivatives with degree of sulfation of ∼ 2.0 were found to enhance thrombin and factor Xa inhibition by antithrombin III. The effect of sulfated fucans on thrombin inhibition, which was similar to those of heparinoid Clexane(®) (enoxaparin) and of a fucoidan from the brown alga Saccharina latissima studied previously, can be explained by the multicenter interaction and formation of a ternary complex thrombin-antithrombin III-polysaccharide. The possibility of such complexation was confirmed by computer docking study.

Synthesis of the Oligosaccharides Related to Branching Sites of Fucosylated Chondroitin Sulfates from Sea Cucumbers

Natural anionic polysaccharides fucosylated chondroitin sulfates (FCS) from sea cucumbers attract great attention nowadays due to their ability to influence various biological processes, such as blood coagulation, thrombosis, angiogenesis, inflammation, bacterial and viral adhesion. To determine pharmacophore fragments in FCS we have started systematic synthesis of oligosaccharides with well-defined structure related to various fragments of these polysaccharides. In this communication, the synthesis of non-sulfated and selectively O-sulfated di- and trisaccharides structurally related to branching sites of FCS is described. The target compounds are built up of propyl β-d-glucuronic acid residue bearing at O-3 α-l-fucosyl or α-l-fucosyl-(1→3)-α-l-fucosyl substituents. O-Sulfation pattern in the fucose units of the synthetic targets was selected according to the known to date holothurian FCS structures. Stereospecific α-glycoside bond formation was achieved using 2-O-benzyl-3,4-di-O-chloroacetyl-α-l-fucosyl trichloroacetimidate as a donor. Stereochemical outcome of the glycosylation was explained by the remote participation of the chloroacetyl groups with the formation of the stabilized glycosyl cations, which could be attacked by the glycosyl acceptor only from the α-side. The experimental results were in good agreement with the SCF/MP2 calculated energies of such participation. The synthesized oligosaccharides are regarded as model compounds for the determination of a structure-activity relationship in FCS.