Purification, molecular properties, structural characterization, and immunomodulatory activities of water soluble polysaccharides from Sargassum angustifolium

https://doi.org/10.1016/j.ijbiomac.2017.11.059Get rights and content

Highlights

  • A sulfated polysaccharide (F2) was purified from S. angustifolium.

  • Polysaccharide F2 was found to be the most immunostimulating polysaccharide.

  • Sulfate groups were responsible for bioactivity and located on C-2 and C-4 of fucose as well as C-3 of galactose.

  • Polysaccharide F2 was mainly composed of (1  4)- and (1  3)-linked fucose residues.

Abstract

Sulfated polysaccharides isolated from Sargassum angustifolium and purified to determine their structural characteristics and biological activities. Crude polysaccharides and fractions (F1 and F2) were chiefly composed of neutral sugars (49.4–68.5%) and sulfates (12.5–23.0%) along with small amounts of uronic acids (1.3–13.6%) and proteins (4.1–4.7%). Polysaccharides were mainly constructed of different levels of fucose (23.9–69.9%) and galactose (22.5–29.8%) sugars. Subfractions with molecular weights ranging from 157.2 to 790.8 × 103 g/mol were identified for isolated polysaccharides. Polysaccharides induced RAW264.7 macrophage cells to release noticeable amounts of nitric oxide and cytokines including IL-1β, TNF-α, IL-6, IL-10 and IL-12 through NF-κB and MAPKs signaling pathways. Sulfate esters of fraction F2 were necessary to its bioactivity and they were located on carbons 2, 4 and 6 of the major sugars. Fraction F2 was formed of (1  4)- and (1  3)-linked fucose residues branched at C-2 and C-4 as well as (1  6)-linked galactose residues branched at C-3.

Introduction

Fucose-rich polysaccharides are anionic polymers abundantly found in marine organisms including invertebrates and algae. While the former source contains a simple and homogeneous fucans with linear chain, the latter one synthesizes a polymer with rather more complex and heterogeneous structure [1]. These polysaccharides which are located in the cell wall of brown seaweeds have been given a general name as fucoidans [2]. Besides to fucose, fucoidans are consisted of sulfate esters and one or more small proportions of galactose, mannose, xylose, rhamnose, gluccoronic acid and even acetyl groups [3], [4]. The structure of fucoidans might differ from one species to another and yet can be categorized into two major types. Type I which is consisted of (1–3)-α-l-fucopyranose and type II which contains alternating (1–3)- and (1–4)-α-l-fucopyranose [5]. In addition to the main sequences, there are other glycosidic residues involved in the structure of fucoidans which leads to the formation of structural subclasses such as fucogalactan, fucoglucuronomannan and fucoglucuronan [6], [7].

The composition of these macromolecules may vary according to the species, extraction protocol and growth condition of seaweeds [2]. These variations in the chemical structures of fucoidans have found to be directly responsible for their wide and irregular biological functions. A broad spectrum of therapeutic effects has been reported for fucoidans including antitumor, immunomodulatory, antioxidant, anticoagulant, antithrombotic and anti-inflammatory activities [3], [4]. The exhibition of biological properties by fucoidans is thought to be driven by one or more of their structural features such as molecular weight, amount and position of sulfate, sugar composition, uronic acid and glycosidic linkages [2]. However, these structure-activity relationships (SAR) of fucoidans have been rarely sought and therefore not fully understood resulting in the failure of a proper development of fucoidan products. The relatively undeveloped research and market status of fucoidans have been primarily attributed to the limited number of investigations conducted on SAR of purified fucoidans and the complex nature of their structures [8].

Therefore, the current study was dedicated to the determination of structural and molecular characteristics of purified polysaccharides from Sargassum angustifolium and the valuation of their anticancer and immunomodulatory properties on both cellular and molecular levels.

Section snippets

Samples and reagents

S. angustifolium was collected from the coast of Bushehr, Iran. The seaweed was previously identified by Agricultural and Natural Resources Research Center of Bushehr under the voucher number 2662 [9]. The fresh seaweed was initially washed with tap water and air dried at 60 °C. The dried biomass was milled using a blender, sieved (< 0.5 mm) and kept in plastic bags at −20 °C. All other chemicals and reagents were of analytical grade. RPMI-1640 medium and fetal bovine serum (FBS) used in cell

Chemical analysis

The yields and chemical compositions of the isolated polysaccharides are presented in Table 1. The extraction yield of crude polysaccharide from S. angustifolium was found to be 6.35% which was notably higher than those of S. fusiforme (1.53%) and S. mcclurei (2.7%) [18], [19]. However, compared to current study, a slightly higher yield was obtained for polysaccharide from S. henslowianum (7.0%) [20]. The crude polysaccharide was mainly consisted of neutral sugars (49.45%) and sulfate esters

Conclusion

Two fractions were obtained after fractionation of sulfated polysaccharides from S. angustifolium with significant difference in sulfate contents and uronic acids. While fraction F1 showed a similar sugar composition to crude polysaccharide, fraction F2 only consisted of fucose and galactose. Fraction F2 was a homogeneous polysaccharide with a molecular weight of 364.3 × 106 g/mol. The greatest inhibition of HeLa cancer cells was obtained for fraction F2. The polysaccharides of fraction F2 were

Acknowledgement

The authors would like to thank the Iran National Science Foundation (INSF) for their financial support of this research (Project No. 95818095).

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