Fucoidans from the brown seaweed Adenocystis utricularis: extraction methods, antiviral activity and structural studies
The brown seaweed Adenocystis utricularis biosynthesizes at least two different types of fucoidans: the galactofucans and the uronofucoidans. The galactofucans show high antiviral activities.
Introduction
Brown seaweeds (Phaeophycophyta) are known to produce different polysaccharides, namely alginates, laminarans and fucoidans.1., 2. The latter polysaccharides usually contain large proportions of l-fucose and sulfate, together with minor amounts of other sugars like xylose, galactose, mannose and glucuronic acid.1., 3. Several biological activities4., 5. have been attributed to the fucoidans: anticoagulant,6., 7., 8., 9., 10., 11., 12. antithrombotic,13 antiinflammatory,14 antitumoral,5., 15. contraceptive,16., 17. and antiviral.18., 19., 20. They have particularly been described as inhibitors of the replication of several enveloped viruses, as human immunodeficiency virus, herpes simplex virus and human cytomegalovirus.20., 21., 22. In spite of the many studies attempting to determine the fine structure of the fucoidans, only few examples of regularity were found: linkages, branching, sulfate position, other sugars appear to be variable and thus the relationship between structure and biological activity was not established. Different techniques for extracting the fucoidans free from contaminants have been used.23., 24. They included the action of calcium-containing solvents, acid media, or plain water.3., 24., 25., 26., 27., 28.
Adenocystis utricularis is a brown seaweed from the cold waters of the Southern Hemisphere. It is found close to the Antarctica, as well as on the coasts of Chile, Argentina, New Zealand and Australia.29 Its classification was revised many times, although it is now considered within the family Adenocystaceae,30 of the order Ectocarpales sensu lato.30., 31. Herein the extraction of the polysaccharides from this seaweed by different methods is reported, together with their purification, analysis, fractionation, assessment of their antiviral activity, and structural analysis of the fractions with antiviral properties.
Section snippets
Algal material
The brown, globular seaweed Adenocystis utricularis was collected in summer at the shores near Comodoro Rivadavia (Chubut Province). The thalli were air-dried and milled to a fine powder.
Analytical methods
Total carbohydrates were determined by the phenol–H2SO4 method using fucose as standard.32 Uronic acids were determined using the method of Filisetti-Cozzi and Carpita33 using glucuronolactone as standard. The percentages of sulfate were measured by turbidimetry34 after hydrolysis with 1 M HCl, while the
Extraction
The milled seaweed was extracted as depicted in Scheme 1. Yields and general analyses of the extracts are shown on Table 1, while the monosaccharide composition is shown on Table 2. Treatment of the seaweed with 80% aqueous ethanol at room temperature and 70 °C removed large amounts of materials. Their analysis revealed small proportions of carbohydrates and proteins, while the monosaccharide composition indicated that mannitol was nearly the only carbohydrate present. Hydrolysis yielded traces
Discussion
Several different procedures have been used for the extraction of fucoidans.24., 26., 27., 28. The main concern in their isolation procedures was to avoid contamination with other polysaccharides, like laminaran and especially alginic acid.49 First extraction attempts were carried out by the use of plain water, often acidified, or other solvents.49 The first attempt to carry out a systematic approach to extraction was effected by Mian and Percival.24 They developed a sequential extraction that
Acknowledgements
N.M.A.P. was recipient of a fellowship from FOMEC-UBA. E.B.D. and C.A.S. are Research Members of the National Research Council of Argentina (CONICET). M.L.F. is member of RIPRONAMED (Iberoamerican Network on Medicinal Natural Products), Sub-Program X (Pharmaceutical Fine Chemistry) of CYTED. This work was supported by grants from UBA, CONICET, and UNPSJB.
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