A new heparan sulfate from the mollusk Nodipecten nodosus inhibits merozoite invasion and disrupts rosetting and cytoadherence of Plasmodium falciparum

BACKGROUND

Despite treatment with effective antimalarial drugs, the mortality rate is still high in severe cases of the disease, highlighting the need to find adjunct therapies that can inhibit the adhesion of Plasmodium falciparum-infected erythrocytes (Pf-iEs).

OBJECTIVES

In this context, we evaluated a new heparan sulfate (HS) from Nodipecten nodosus for antimalarial activity and inhibition of P. falciparum cytoadhesion and rosetting.

METHODS

Parasite inhibition was measured by SYBR green using a cytometer. HS was assessed in rosetting and cytoadhesion assays under static and flow conditions using Chinese hamster ovary (CHO) and human lymphatic endothelial cell (HLEC) cells expressing intercellular adhesion molecule-1 (ICAM1) and chondroitin sulfate A (CSA), respectively.

FINDINGS

This HS inhibited merozoite invasion similar to heparin. Moreover, mollusk HS decreased cytoadherence of P. falciparum to CSA and ICAM-1 on the surface of endothelial cells under static and flow conditions. In addition, this glycan efficiently disrupted rosettes.

CONCLUSIONS

These findings support a potential use for mollusk HS as adjunct therapy for severe malaria.

Unbalanced effects of dermatan sulfates with different sulfation patterns on coagulation, thrombosis and bleeding

We compared the anticoagulant, antithrombotic and bleeding effects of highly sulfated dermatan sulfates from invertebrates and their mammalian counterpart. An invertebrate dermatan sulfate containing 2-O-sulfated alpha-L-iduronic acid and 4-O-sulfated N-acetyl-beta-D-galactosamine residues is a potent anticoagulant due to a high heparin cofactor II activity. It inhibits thrombin due to the formation of a covalent complex with heparin cofactor II, as in the case of mammalian dermatan sulfate, but the effect occurs at lower concentrations for the invertebrate polysaccharide. Surprisingly, the invertebrate dermatan sulfate has a lower potency to prevent thrombus formation on an experimental model and a lower bleeding effect in rats than the mammalian dermatan sulfate. In contrast, another invertebrate dermatan sulfate, also enriched in 2-O-sulfated alpha-L-iduronic acid, but in this case sulfated at O-6 position of the N-acetyl-beta-D-galactosamine units, has no in vitro or in vivo anticoagulant activity, does not prevent thrombus formation but shows a bleeding effect similar to the mammalian glycosaminoglycan. Overall, these results demonstrate unbalanced effects of dermatan sulfates with different sulfation patterns on coagulation, thrombosis and bleeding, and raise interesting questions concerning the relationship among these three biological actions of sulfated polysaccharides.

Occurrence of heparin in the invertebrate styela plicata (Tunicata) is restricted to cell layers facing the outside environment. An ancient role in defense?

Heparin is an intracellular product of vertebrate mast cell currently used as exogenous anticoagulant. Despite of the potent biological activities of exogenous heparin, its physiological function has not been clearly established yet. Here, a heparin with similar structure and anticoagulant properties to the mammalian counterpart was shown to occur as the intracellular product of test cells, a cell monolayer that surrounds egg of the invertebrate Styela plicata (Chordata-Tunicata). As in the case of mammalian mast cells, heparin from the ascidian test cells is removed from the intracellular granules after incubation with compound 48/80. Following fertilization, the test cells surrounding the developing larva still retain heparin as metachromatic granulation. In the adult invertebrate, heparin occurs as intracellular granules at the apical tip of epithelial cells surrounding the lumen of both intestine and pharynx, in close contact with the external environment. This is the first description of the presence of heparin in cytoplasmic granules of epithelial-like cells around the lumen of sites exposed to external agents. This arrangement may reflect the participation of heparin in defense mechanisms in this invertebrate.

Isolation and characterization of a highly sulfated heparan sulfate from ascidian test cells

Several sulfated polysaccharides have been isolated from the test cells of the ascidian Styela plicata. The preponderant polysaccharide is a highly sulfated heparan sulfate with the following disaccharide composition: (1) UA(2SO4)-1-->4 GlcN(SO4)(6SO4), 53%; (2) UA(2SO4)-1-->4-GlcN(SO4), 22%; (3) UA-1-->4-GlcNAc(6SO4), 14% and (4) UA-1-->4-GlcN(SO4), 11%. Two others unidentified sulfated polysaccharides and a glycogen polymer are also present in the ascidian eggs. Histochemistry with the cationic dye 1,9-dimethyl-methylene blue and biochemical analysis of the 35S-sulfate incorporation into the eggs reveal that the sulfated glycans are present exclusively in the test cells. Possibly these sulfated polysaccharides are involved in important functions of these cells, such as to confer an external and hydrophilic layer which protect the eggs and the larvae of ascidians.

Highly sulfated dermatan sulfates from Ascidians. Structure versus anticoagulant activity of these glycosaminoglycans

Dermatan sulfates with the same backbone structure [4-alpha-L-IdceA-1-->3-beta-D-GalNAc-1]n but with different patterns of sulfation substitutions have been isolated from the ascidian body. All the ascidian dermatan sulfates have a high content of 2-O-sulfated alpha-L-iduronic acid residues but differ in the pattern of sulfation of the N-acetyl-beta-D-galactosamine units. Styela plicata and Halocynthia pyriformis have 4-O-sulfated units, but in Ascidian nigra they are 6-O-sulfated. This collection of ascidian dermatan sulfates (together with native and oversulfated mammalian dermatan sulfate), where the extent and position of sulfate substitution have been fully characterized, were tested in anticoagulant assays. Dermatan sulfate from A. nigra has no discernible anticoagulant activity, which indicates that 4-O-sulfation of the N-acetyl-beta-D-galactosamine is essential for the anticoagulant activity of this glycosaminoglycan. In contrast dermatan sulfates from S. plicata and H. pyriformis are potent anticoagulants due to potentiation of thrombin inhibition by heparin cofactor II. These ascidian dermatan sulfates have approximately 10-fold and approximately 6-fold higher activity with heparin cofactor II than native and an oversulfated mammalian dermatan sulfate, respectively. They have no effect on thrombin or factor Xa inhibition by antithrombin. These naturally oversulfated ascidian dermatan sulfates are sulfated at selected sites required for interaction with heparin cofactor II and thus have specific and potent anticoagulant activity.

Chondroitin ABC lyase digestion of an ascidian dermatan sulfate. Occurrence of unusual 6-O-sulfo-2-acetamido-2-deoxy-3-O-(2-O-sulfo-alpha-L-idopyranosyluronic acid)-beta-D-galactose units

A dermatan sulfate-like glycosaminoglycan was isolated from the body of the ascidian Ascidia nigra (J. Biol. Chem. 270: 31027-31036, 1995). 1H NMR and fast atom bombardment mass spectrometry (FAB-MS) spectra of the tetra and disaccharides formed by chondroitin ABC lyase digestion support the proposed repeating disaccharide structure for this glycosaminoglycan, [-->4)-alpha-L-IdoA(2SO4)-(1-->3)-beta-D-GalNAc(6SO4)-(1-->] , which differ from mammalian dermatan sulfate in its sulfation at both 2-position of the alpha-L-iduronic acid and the 6-position of the N-acetyl-beta-D-galactosamine residue.

Structure and anticoagulant activity of a fucosylated chondroitin sulfate from echinoderm. Sulfated fucose branches on the polysaccharide account for its high anticoagulant action

A polysaccharide isolated from the body wall of the sea cucumber Ludwigothurea grisea has a backbone like that of mammalian chondroitin sulfate: [4-beta-D-GlcA-1-->3-beta-D-GalNAc-1]n but substituted at the 3-position of the beta--glucuronic acid residues with sulfated alpha--fucopyranosyl branches (Vieira, R. P., Mulloy, B., and Mourão, P. A. S. (1991) J. Biol. Chem. 266, 13530-13536). Mild acid hydrolysis removes the sulfated alpha--fucose branches, and cleaved residues have been characterized by 1H NMR spectroscopy; the most abundant species is fucose 4-O-monosulfate, but 2,4- and 3, 4-di-O-sulfated residues are also present. Degradation of the remaining polysaccharide with chondroitin ABC lyase shows that the sulfated alpha-L-fucose residues released by mild acid hydrolysis are concentrated toward the non-reducing end of the polysaccharide chains; enzyme-resistant polysaccharide material includes the reducing terminal and carries acid-resistant -fucose substitution. The sulfated alpha-L-fucose branches confer anticoagulant activity on the polysaccharide. The specific activity of fucosylated chondroitin sulfate in the activated partial thromboplastin time assay is greater than that of a linear homopolymeric alpha-L-fucan with about the same level of sulfation; this activity is lost on defucosylation or desulfation but not on carboxyl-reduction of the polymer. Assays with purified reagents show that the fucosylated chondroitin sulfate can potentiate the thrombin inhibition activity of both antithrombin and heparin cofactor II.

Unique sulfated polysaccharides from ascidians (Chordata, Tunicata)

Unique sulfated polysaccharides have been identified in ascidian tissues. A high-molecular-weight sulfated L-galactan consisting mainly of alpha-L-galactopyranose glycosidically linked through positions 1-->4, and sulfated at carbon 3 is present in the tunic of all species studied. Methylation, periodate oxidation, as well as 1H and 13C NMR analysis revealed that despite their homogeneous chemical composition, these L-galactans differ in type of glycosidic linkage, number of branches, and in the extent and position of sulfation. These L-galactans are synthesized by epidermal cells that epimerize D-glucose, possibly from a trehalose precursor, into L-galactose. In addition, a dermatan sulfate composed of a backbone of repeating [4-alpha-L-IdoA-1-->3-beta-D-GalNAc-1]n units similar to mammalian dermatan sulfate, but differing in the extent and position of sulfation has been isolated from the body of the ascidian, Ascidia nigra. Degradation of the ascidian dermatan with specific glycosidases and sulfatases, together with 1H and 13C NMR data, indicated that the disaccharide units are sulfated at the 2-position of alpha-L-induronate residues and at the 6-position of the N-acetyl-beta-D-galactosamine units. In contrast to mammalian dermatan sulfate, the ascidian molecule has no discenrible anticoagulant activity, as measured by the APTT assay, and has a low ability to potentiate heparin cofactor II. These data suggest that the 4-O-sulfation of N-acetyl-beta-D-galactosamine residues is essential for the anticoagulant activity of dermatan sulfate polymers.

A unique dermatan sulfate-like glycosaminoglycan from ascidian. Its structure and the effect of its unusual sulfation pattern on anticoagulant activity

A dermatan sulfate, similar to the mammalian glycosaminoglycans but not identical with any of them, has been isolated from the body of the ascidian Ascidia nigra. Degradation with chondroitin ABC lyase, analysis of the disaccharide products by digestion with chondro-4- and -6-sulfatases, and 1H and 13C NMR data confirm that the predominant structure is [4-alpha-L-IdoA-(2SO4)-1-->3-beta-D-GalNAc(6SO4)-1]n. Mammalian dermatan sulfate is an anticoagulant due to its ability to potentiate inhibition of thrombin by heparin cofactor II. The structure in dermatan sulfate which binds to heparin cofactor II is [4-alpha-L-IdoA-(2SO4)-1-->3-beta-D-GalNAc(4SO4)-1]n, where n > or = 3. We have compared the ascidian dermatan sulfate with mammalian dermatan sulfate and with chemically oversulfated mammalian dermatan sulfate for anticoagulant activity as measured by the activated partial thromboplastin time assay and for its ability to potentiate heparin cofactor II. In spite of its high content of 2-O-sulfated alpha-L-iduronic acid residues, the ascidian compound had no discernible anticoagulant activity and had low ability to potentiate heparin cofactor II. These results suggest that 4-O-sulfation of the N-acetyl-beta-D-galactosamine residues is essential for the anticoagulant activity of dermatan sulfate.

Acidic polysaccharides of the ascidian Styela plicata. Biosynthetic studies on the sulfated L-galactans of the tunic, and preliminary characterization of a dermatan sulfate-like polymer in body tissues

Histochemical and chemical analyses reveal important differences between tunic and body of the ascidian Styela plicata. The body contains hydroxyproline, nucleic acid and hexuronic acid. Analyses of the hexuronic acid-containing molecules indicates the presence of dermatan sulfate and heparan sulfate. The tunic, on the other hand, contains no hydroxyproline and small amounts of nucleic acid and hexuronic acid. Large amounts of sulfated polysaccharides, identified by agarose gel electrophoresis, are also present in the tunic. In vitro, incorporation of 35S-sulfate and 14C-glucose and 35S-sulfate pulse-chase experiments show that sulfate and glucose are incorporated into the sulfated polysaccharides of the tunic. The radioactivity is associated mainly with the region of the tunic containing the epidermal cells; however, a small amount of radioactivity is also detected in other regions of the tunic, suggesting that the sulfated polysaccharides are synthesized mainly by the epidermal cells and, to a small extent, by other cell types present in the tunic. Conversion of D-glucose to L-galactose, previously observed in the tunic of Styela plicata (Biochemistry 30, 3458-3464, 1990) is more intense in the region of the tunic containing the epidermal cells.

Structure of a unique sulfated alpha-L-galactofucan from the tunicate Clavelina

A purified sulfated alpha-L-galactofucan from Clavelina sp. has been studied before and after desulfation, using periodate oxidation, methylation analysis, and n.m.r. spectroscopy, and shown to be composed mainly of 3-sulfated 4-linked alpha-L-galactopyranosyl residues. There was also a small proportion of 3-sulfated 4-linked alpha-L-fucose residues.

Structural studies of a sulfated L-galactan from Styela plicata (Tunicate): analysis of the Smith-degraded polysaccharide

The tunic of the ascidian Styela plicata is rich in a high molecular weight sulfated-L-galactan called the F-1 fraction. This polysaccharide is of complex structure and is highly branched. In this study we undertook detailed structural analysis of the F-1 fraction that was submitted to the Smith degradation procedure which, for this polysaccharide, results mainly in the elimination of the branches. By methylation, and one- and two-dimensional n.m.r. analysis of the Smith-degraded and desulfated Smith-degraded F-1 fraction, we determined the main structure of this polymer. It is composed of a core of alpha-L-galactopyranose units, sulfated at C-3 and glycosidically linked through position 1----4. The nonsulfated, nonreducing end units are branched at C-2 of the sulfated L-galactoses.

Structural heterogeneity among unique sulfated L-galactans from different species of ascidians (tunicates)

The sulfated polysaccharides that occur in the tunic of ascidians differ markedly in molecular weight and chemical composition. A high molecular weight fraction (F-1), which has a high galactose content and a strong negative optical rotation, is present in all species. Several structural differences were observed among the F-1 fractions obtained from three species of ascidians that were studied in detail. Large numbers of alpha-L-galactopyranose residues sulfated at position 3 and linked glycosidically through position 1----4 are present in F-1 from all three ascidians. However, alpha-L-galactopyranose units, 1----3-linked and partially sulfated at position 4, comprise about half of the sugar units in the central core of F-1 from Ascidian nigra. In addition, L-galactopyranose nonreducing end units occur in F-1 from Styela plicata and A. nigra, but comprise only a minor fraction of F-1 from Clavelina sp. The combination of these various component units gives a complex structure for F-1 from S. plicata and A. nigra, whereas F-1 from Clavelina sp. possesses a simpler structure. The structures of these ascidian glycans are unique among all previously described sulfated polysaccharides, since they are highly branched (except that from Clavelina sp), sulfated at position 3, and contain large amounts of L-galactose without its D-enantiomorph. These data show unusual examples of polyanionic glycans with structural function in animal tissues.