Molecular characteristics of sulfated polysaccharides from Monostroma nitidum and their in vitro anticancer and immunomodulatory activities

doi:10.1016/j.ijbiomac.2010.12.002

International Journal of Biological Macromolecules

Volume 48, Issue 2, 1 March 2011, Pages 311-318

https://doi.org/10.1016/j.ijbiomac.2010.12.002 Get rights and content

Abstract

We investigated water-soluble sulfated polysaccharides isolated from Monostroma nitidum using ion-exchange chromatography to determine their molecular characteristics and biological activities. The crude and fractionated polysaccharides (F₁, F₂, and F₃) consisted mostly of carbohydrates (58.3–91.9%), uronic acids (0–21.8%) and sulfates (1.8–17.7%) as well as varying amounts of proteins (1.6–9.4%). Their monosaccharide levels were significantly different including rhamnose (0–95.7%) and glucose (0–98.6%) content with small amounts of xylose (0.8–4.3%). These polysaccharides contained one or two subfractions with average molecular weights (M_w) ranging from 94.4 to 1387 × 10³ g/mol. The in vitro inhibitory activity (≤75%) of the polysaccharides on a human cancer cell line (AGS) suggested that the polysaccharides had direct cytotoxic effects on the cancer cells. In addition, these hetero-polysaccharides (from the crude and F₁ and F₂ fractions) stimulated a macrophage cell line, Raw 264.7 cells, inducing considerable NO and PGE₂, production, which suggested that they could be strong immunomodulators.

Introduction

Naturally occurring sulfated polysaccharides are commonly found in three major groups of marine algae: brown algae (Phaeophyta), red algae (Rhodophyta) and green algae (Chlorophyta). Studies on sulfated polysaccharides from marine algae have mainly focused on fucoidans, ascophyllan, sargassan and glucuronoxylofucan (from brown algae) and agar and carrageenan (from red algae) due to their effective anticoagulant, antitumor, antiviral, immunomodulatory, anti-inflammatory and antioxidant activities [1], [2], [3], [4], [5]. The sulfated polysaccharides from green algae are referred to as ulvans. Recently, ulvans have been found to exhibit various biological and pharmacological activities. For example, sulfated polysaccharides from Monostroma nitidum were potent thrombin inhibitors mediated by heparin cofactor II that showed strong anticoagulant activity [6]. In addition, ulvans from Ulva lactuca inhibited the cancer cell growth by inducing cell reactivity to Ulex europaeus-1 lectins [7]. Additionally, ulvans possess antiviral activity against human and avian influenza viruses by suppressing the viral reproduction [8]. In a hyperlipidemia study using ICR mice, antihyperlipidemia activity was observed with ulvans from Ulva pertusa, which significantly lowered the levels of plasma total cholesterol, low-density lipoprotein cholesterol and triglyceride but increased those of serum high-density lipoprotein cholesterol [9]. Moreover, ulvans were reported to protect against alcohol induced peptic ulcers [10].

Ulvans from green seaweeds, Ulva rigida and Enteromorpha compressa, are mainly composed of rhamnose, xylose and glucuronic acid with major repeating disaccharide units of α-l-Rhap-(1 → 4)-d-Xyl and (→4)-β-d-GlcpA-(1 → 4)-α-l-Rhap and include minor amounts of other sugars, such as galactose, arabinose, mannose and glucose [11], [12]. The type of glycosidic linkages in ulvan backbones is closely related between species of green seaweeds [8], [11], [12]. Sulfate groups were also found at the O-2, O-3 or O-4 positions of the ulvan backbones from U. rigida, E. compressa and Gayralia oxysperma [11], [12], [13]. The biological activities of ulvans have been reported to be closely related to their molecular weight and sulfate content. Kaeffer et al. [7] reported that ulvans with molecular weights (M_w) of less than 5 × 10³ g/mol strongly inhibited proliferation and differentiation of human cancer cells, suggesting a relationship between their molecular weight and anticancer activity. Qi et al. [14] reported that oversulfated ulvans were more effective antioxidant agents than native ulvans. In a study of other polysaccharides, the structure and physico-chemical properties are the major factors affecting the biological activities of the polysaccharides [15]. Therefore, a basic understanding of both the primary and secondary structures of the polysaccharides may lead to successful interpretation of their bioactivities.

Despite the abundance and availability of green seaweeds, relatively few studies have been performed on the molecular structures and bioactivities of their sulfated polysaccharides. In addition, there is little information available on the structures and anticancer and immunomodulatory activities of sulfated polysaccharides from M. nitidum, one of the most popular edible green seaweeds in the Northeast Asian countries. In this study, a sulfated polysaccharide from M. nitidum was extracted in distilled water and subsequently fractionated using ion-exchange chromatography. The purpose of this study was to investigate the chemical and molecular characteristics of the fractionated polysaccharides and to evaluate their anticancer and immunomodulatory activities.

Section snippets

Materials

Green seaweed, M. nitidum, was harvested in the spring of 2009 from the coast of Wando, Chunnam Province, Korea. The raw material was washed with tap water and air-dried at 60 °C. The dried raw material was milled using a blender, sieved (<0.5 mm) and stored at −20 °C before extraction of the polysaccharide. All chemicals and reagents used in this work were analytical grade. RPMI-1640 medium and fetal bovine serum (FBS) were purchased from Lonza (Walkersville, MD, USA).

Extraction of crude polysaccharide

The milled sample (20 g) was

Chemical composition analysis

The chemical composition of the crude polysaccharide from M. nitidum is shown in Table 1. The yield of the crude polysaccharide was 13.1%, which was similar to the value (16.0%) reported by Charles et al. [21]. The extracted polysaccharide consisted of mostly carbohydrates (61.1%), uronic acid (16.8%), sulfate (13.5%) and a small amount of protein (4.0%), which is in good agreement with the constituents of the soluble polysaccharide of Charles et al. [21]. Monosaccharide composition analysis

Conclusion

The molecular characteristics and biological activities of sulfated polysaccharides that were extracted from M. nitidum and fractionated by ion-exchange chromatography were investigated. The extracted polysaccharide consisted of mostly carbohydrates (61.1%), uronic acid (16.8%) and sulfate (13.5%) with a considerable amount of protein (4.0%). Ion-exchange chromatography led to the identification of three polysaccharides having various chemical compositions and M_w. Considerable cytotoxic effects

Acknowledgments

This work was supported by both the Korea Research Foundation Grant funded by the Korean Government (MEST) (The Regional Core Research Program/Medical & Bio-Materials Research Center) and the academic research development grant of Gangneung-Wonju National University (2007).

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Molecular characteristics of sulfated polysaccharides from Monostroma nitidum and their in vitro anticancer and immunomodulatory activities

Abstract

Introduction

Section snippets

Materials

Extraction of crude polysaccharide

Chemical composition analysis

Conclusion

Acknowledgments

Pharmacol. Res.

Carbohydr. Res.

Food Chem.

Carbohydr. Polym.

Food Chem. Toxicol.

Carbohydr. Res.

Carbohydr. Polym.

Carbohydr. Res.

Int. J. Biol. Macromol.

J. Biol. Chem.

Food Chem. Toxicol.

Int. Immunopharmacol.

Carbohydr. Res.

Int. J. Biol. Macromol.

Int. Immunopharmacol.