Bimalendu Ray

Focus on antivirally active sulfated polysaccharides: From structure-activity analysis to clinical evaluation

In recent years, many compounds having potent antiviral activity in cell culture have been detected and some of these compounds are currently undergoing either preclinical or clinical evaluation. Among these antiviral substances, naturally occurring sulfated polysaccharides and those from synthetic origin are noteworthy. Recently, several controversies over the molecular structures of sulfated polysaccharides, viral glycoproteins, and cell-surface receptors have been resolved, and many aspects of their antiviral activity have been elucidated. It has become clear that the antiviral properties of sulfated polysaccharides are not only a simple function of their charge density and chain length but also their detailed structural features. The in vivo efficacy of these compounds mostly corresponds to their ability to inhibit the attachment of the virion to the host cell surface although in some cases virucidal activity plays an additional role. This review summarizes experimental evidence indicating that sulfated polysaccharides might become increasingly important in drug development for the prevention of sexually transmitted diseases in the near future.

Isolation, chemical investigation and antiviral activity of polysaccharides from Gracilaria corticata (Gracilariaceae, Rhodophyta).

Polysaccharides were sequentially extracted from the agarophyte Gracilaria corticata. Chemical analysis combined with infrared spectroscopy showed that the cold water extracted material consists mainly of a high molecular weight sulfated galactan. Most of the sulfate groups are alkali labile and are located at C-4 of the 1,3-linked D-galactose units and C-6 of the 1,4-linked L-galactose residues. The autoclaved extracts contain agar type polysaccharide having a high pyruvate content and a variable degree of methylation, but were contaminated with floridean starch. 1H-NMR studies indicate that methoxyl groups, when present, occur at C-6 of the 1,3-linked D-galactose units and C-2 of the 1,4-linked L-galactose residues of agar polymer. Bioassays showed that a high molecular weight galactan sulfate, exhibited selective antiviral activity against herpes simplex virus types 1 and 2, likely due to an inhibition of the initial virus attachment to the host cell.

Structural features and antiviral activity of sulphated fucans from the brown seaweed Cystoseira indica

Natural compounds offer interesting pharmacological perspectives for antiviral drug development. In this study, we have analysed sulphated-fucan-containing fractions isolated from the brown seaweed Cystoseira indica. The crude water extract (CiWE) and the main fraction (CiF3) obtained by anion exchange chromatography had potent antiviral activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) without cytotoxicity for Vero cell cultures. Furthermore, they had no direct inactivating effect on virions in a virucidal assay, and lacked anticoagulant activity. The mode of action of these compounds could be mainly ascribed to an inhibitory effect on virus adsorption. Chemical, chromatographic and spectroscopic methods showed that the major polysaccharide had an apparent molecular mass of 35 kDa and contained a backbone of α-(1→3)-linked fucopyranosyl residues substituted at C-2 with fucopyranosyl and xylopyranosyl residues. This sulphated fucan, considered the active principle of the C. indica water extract, also contained variously linked xylose and galactose units and glucuronic acid residues. Sulphate groups, if present, are located mostly at C-4 of (1→3)-linked fucopyranosyl units, and appeared to be very important for the anti-herpetic activity of this polymer.

Polysaccharides from Sargassum tenerrimum: structural features, chemical modification and anti-viral activity.

Herpes simplex viruses (HSVs) display affinity for cell-surface heparan sulfate proteoglycans with biological relevance in virus entry. Here, we exploit an approach to inhibiting HSV infection by using a sulfated fucoidan, and a guluronic acid-rich alginate derived from Sargassum tenerrimum, mimicking the active domain of the entry receptor. These macromolecules have apparent molecular masses of 30+/-5 and 26+/-5 kDa, respectively. They and their chemically sulfated derivatives showed activity against herpes simplex virus type 1 (HSV-1). Their inhibitory concentration 50% (IC(50)) values were in the range 0.5-15 microg/ml and they lacked cytotoxicity at concentrations up to 1000 microg/ml. The anti-HSV activity increased with increasing sulfate ester content. Our results suggest the feasibility of inhibiting HSV infection by blocking viral entry with polysaccharide having specific structure.

Anti-herpetic activity of a sulfated xylomannan from Scinaia hatei

Many viruses display affinity for cell surface heparan sulfate proteoglycans with biological relevance in virus entry. This raises the possibility of the application of sulfated polysaccharides in antiviral therapy. In this study we have analyzed polysaccharide fractions isolated from Scinaia hatei. The crude water extract (ShWE) as well as one fraction (F1) obtained by size exclusion chromatography had potent anti-HSV activity. Their inhibitory concentration 50% (IC50) values ranging from 0.5 to 4.6 microg/ml were much lower than the cytotoxic concentration 50% (CC50) values (1000 microg/ml). These fractions had very low anticoagulant activity. Furthermore, they had a weak inactivating effect on virions in a virucidal assay at concentrations in the range of 60-100 microg/ml. Chemical, chromatographic and spectroscopic methods showed that the major polysaccharide, which had 0.4 sulfate group per monomer unit and an apparent molecular mass of 160 kDa, contained a backbone of alpha-(1-->3)-linked D-mannopyranosyl residues substituted at C-6, C-4 and C-2 with single stub of beta-d-xylopyranosyl residues. Sulfate groups, when present, are located at C-4 of alpha-(1-->3)-linked D-mannopyranosyl units, and appeared to be very important for the anti-herpetic activity of this polymer.

Polysaccharides from Gracilaria corticata: sulfation, chemical characterization and anti-HSV activities.

In this study, we have analyzed water-extracted polysaccharides of Gracilaria corticata. The water extract (WE), a galactan-containing sub-fraction (F3) and their hyper sulfated derivatives (WES1, WES2, F3S1 and F3S2) had anti-HSV activity with inhibitory concentration 50% (IC50) from 1.1 to 27.4 microg/ml. Sub-fraction F3, which has a molecular mass of 30 kDa, consists of a backbone of beta-(1-->3) and alpha-(1-->4)-linked-galactopyranosyl residues. This linear galactan contained Gal2Xyl1, Gal2AnGal2, Gal4 and Me-Gal3AnGal2 as oligomeric building subunits. Sulfate group was located at C-4 of (1-->3)-linked galactopyranosyl residues of the native galactan, and appeared to be very important for the anti-herpetic activity.

Sulfated Xylomannans from the Red Seaweed Sebdenia Polydactyla: Structural Features, Chemical Modification and Antiviral Activity

Background: Many viruses display affinity for cell surface heparan sulfate proteoglycans with biological relevance in virus entry. This raises the possibility of the application of sulfated polysaccharides in antiviral therapy. Methods: In this study, we analysed polysaccharide fractions isolated from Sebdenia polydactyla. Results: The purified xylomannan sulfate and its further sulfated derivatives showed strong activity against herpes simplex virus type-1 (HSV-1). Their 50% inhibitory concentration values were in the range 0.35–2.8 µg/ml and they lacked cytotoxicity at concentrations up to 1,000 µg/ml. The major polysaccharide, which had 0.6 sulfate groups per monomer unit and an apparent molecular mass of 150 kDa, contained a backbone of α-(1→3)-linked D-mannopyranosyl residues substituted at position 6 with a single stub of ß-D-xylopyranosyl residues. Conclusions: The degree of sulfation seemed to play an important role because desulfation and/or further sulfation of the isolated macromolecules largely influenced their in vitro anti-HSV-1 activity.

Antiviral activity against dengue virus of diverse classes of algal sulfated polysaccharides.

Diverse classes of sulfated polysaccharides obtained from the red seaweeds (Rhodophyta) Grateloupia indica, Scinaia hatei and Gracilaria corticata, the brown seaweeds (Phaeophyta) Stoechospermum marginatum and Cystoseira indica and the green seaweed (Chlorophyta) Caulerpa racemosa were assayed for antiviral activity against the four serotypes of dengue virus (DENV). DENV-2 was the most susceptible serotype to all polysulfates, with inhibitory concentration 50% values in the range 0.12-20 μg/mL. The antiviral potency of the sulfated polysaccharides depended on the sulfate content, the position of sulfate group, the sugar composition, and the molar mass. Independently of the sugar composition, the antiviral effect was mainly exerted during DENV-2 adsorption and internalization.

Structural features and in vitro antiviral activities of sulfated polysaccharides from Sphacelaria indica

Many viruses display affinity for cell surface heparan sulfate proteoglycans with biological relevance to virus entry. This raises the possibility of the application of sulfated polysaccharides in antiviral therapy. In this study, we have analyzed xylogalactofucan- and alginic acid-containing fractions from Sphacelaria indica, a marine alga. The xylogalactofucan that has apparent molecular mass of 26±5 kDa and negative specific rotation [α](D)(32) -71° (c 0.2, H(2)O) contains, inter alia, (1→3)-linked L-fucopyranosyl and D-galactopyranosyl residues. The algin (molecular mass: 21±5kDa) contains 41% guluronic and 59% mannuronic acid residues. The 50% inhibitory concentration (IC(50)) values of these macromolecules and their chemically sulfated derivatives against herpes simplex virus type 1 (HSV-1) were in the range of 0.6-10 μg ml(-1) and they lacked cytotoxicity at concentrations up to 200 μg ml(-1). The antiviral activity was dependent on the sulfate contents of the polysaccharides. The results support the feasibility of inhibiting HSV infection by direct interaction of polysaccharides with viral particles.

Chemical characterisation and gelling properties of cell wall polysaccharides from species of Ulva (Ulvales, Chlorophyta)

Two alkali-soluble polysaccharide fractions from the cell wall of Ulva ‘rigida’ were determined to be ,β-1,4-linked glucoxylans and a β-1,4-linked glucuronan by chemical and NMR spectroscopic analysis. The 13C NMR spectrum of water-soluble xyloglucuronorhamnan sulfate from Ulva ‘rigida’ referred to as ulvan is reported and the 13C and 1H NMR chemical shifts of its major repeating unit, the aldobiuronic acid β-D-GlcA-(1,4)-L-Rha, are given. The composition and gelling properties of ulvan from Ulva species from ‘green tides’ are also reported. The thermoreversible gel required both calcium and borate ions and the shear storage modulus G′ was ion concentration dependent. The mechanism of gelation and the associations of the different Ulva cell wall soluble polysaccharides are discussed.