Structural characteristics and anticancer activity of fucoidan from the brown alga Sargassum mcclurei

Abstract

Three different fucoidan fractions were isolated and purified from the brown alga, Sargassum mcclurei. The SmF1 and SmF2 fucoidans are sulfated heteropolysaccharides that contain fucose, galactose, mannose, xylose and glucose. The SmF3 fucoidan is highly sulfated (35%) galactofucan, and the main chain of the polysaccharide contains a →3)-α-L-Fucp(2,4SO₃⁻)-(1→3)-α-L-Fucp(2,4SO₃⁻)-(1→ motif with 1,4-linked 3-sulfated α-L-Fucp inserts and 6-linked galactose on reducing end. Possible branching points include the 1,2,6- or 1,3,6-linked galactose and/or 1,3,4-linked fucose residues that could be glycosylated with terminal β-D-Galp residues or chains of alternating sulfated 1,3-linked α-L-Fucp and 1,4-linked β-D-Galp residues, which have been identified in galactofucans for the first time. Both α-L-Fucp and β-D-Galp residues are sulfated at C-2 and/or C-4 (and some C-6 of β-D-Galp) and potentially the C-3 of terminal β-D-Galp, 1,4-linked β-D-Galp and 1,4-linked α-L-Fucp residues. All fucoidans fractions were less cytotoxic and displayed colony formation inhibition in colon cancer DLD-1 cells. Therefore, these fucoidan fractions are potential antitumor agents.

Figure 1

Negative-ion MALDI-TOFMS of LWM oligosaccharide fraction SmF3-AH, obtained from a fucoidan of S. mcclurei by autohydrolysis.

Figure 2

Negative-ion ESIMS/MS of [FucSO₃]⁻ at m/z 243.02 (A), MALDIMS/MS of [FucSO₃]⁻ at m/z 243.0 (B).

Figure 3

Negative-ion tandem MALDI-TOFMS of [Fuc₂(SO₃Na)₂ − Na]⁻ at m/z 491.00 (A), CID ESIMS/MS of [Fuc₂(SO₃)₃]³⁻ at m/z 182.323 (B).

Figure 4

Negative-ion ESIMS/MS of [GalFuc(SO₃)]³⁻ at m/z 187.65.

Figure 5

Negative-ion ESIMS/MS of [Fuc₃Gal(SO₃)]³⁻ at m/z 285.028.

Figure 6

Negative-ion tandem MALDI-TOFMS of [Fuc₃Gal₂(SO₃Na)₂ − Na]⁻ ion at m/z 960.95. Fragment ions, enclosed in brackets are corresponding to the (doubly) sulfated monosaccharide residues, sulfate groups of which are not shown to minimize drawing.

Figure 7

The inhibitory effects of fucoidans from brown seaweeds S. mcclurei on colony formation in human colon cancer cells DLD-1 comparing untreated control cells. Cells (2.4 × 10⁴/mL) treated with/without fucoidans (100 μg/mL) were exposed in 1 mL of 0.3% BME’s agar containing 10% FBS. The culture was maintained at 37 °C in a 5% CO₂ atmosphere for three weeks. The colonies were counted under a microscope with the aid of the ImageJ soft ware program. Data are represented as the means SD of the number of colonies are determined from three independent experiments.

Figure 8

Scheme of isolation and separation of water-soluble polysaccharides from brown alga S. mcclurei.