Sulfation of Agarose from Subantarctic Ahnfeltia Plicata (Ahnfeltiales, Rhodophyta): Studies of Its Antioxidant and Anticoagulan
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J Appl Phycol DOI 10.1007/s10811-014-0297-3 IV LATIN AMERICAN CONGRESS OF ALGAE BIOTECHNOLOGY (CLABA) AND IV REDEALGAS WORKSHOP Sulfation of agarose from subantarctic Ahnfeltia plicata (Ahnfeltiales, Rhodophyta): studies of its antioxidant and anticoagulant properties in vitro and its copolymerization with acrylamide Betty Matsuhiro & Ta m a r a B a r a h o n a & María V. Encinas & Andrés Mansilla & Jonathan A. Ortiz Received: 19 December 2013 /Revised and accepted: 17 March 2014 # Springer Science+Business Media Dordrecht 2014 Abstract Aqueous extraction of Ahnfeltia plicata collected in Introduction the Magellan ecoregion afforded agarose devoid of sulfate groups. This neutral agarose was subjected to sulfation with Agarans are a family of polysaccharides extracted with hot SO3-pyridine complex, giving an aqueous soluble derivative water from several species of red algae. They are composed of with 35.5 % sulfate groups. Analysis by Fourier transform alternating 3-linked β-D-galactopyranosyl and 4-linked α-L- 1 13 infrared spectroscopy (FT-IR) and by Hand C NMR spec- galactopyranosyl or 3,6-anhydro-α-L-galactopyranosyl resi- troscopy indicated that this derivative was sulfated at positions dues, substituted with sulfate, methyl, and/or pyruvate groups C-6 of the β-galactopyranosyl residue and C-2 of the α-3,6- (Duckworth and Yaphe 1971;Izumi1971;Usov2011). anhydrogalactopyranosyl residue and partially sulfated at po- Agarose, a →3-β-D-galactopyranosy-1→4-3,6-anhydro-α- sition C-2 of the β residue. The antioxidant capacity of sulfated L-galactopyranosyl-1→ polymer is the most important mem- agarose was evaluated by the oxygen radical absorbance ca- ber of this family due to its application in many biochemical pacity (ORAC) method, ABTS radical cation, hydroxyl radi- separation processes (Guiseley 1987; Matsuhashi 1998). cals, and chelating assays. This capacity of sulfated agarose Agarans contain a small amount of hemiester sulfate toward peroxyl radicals was higher than that of commercial λ- (~3.0%)comparedwithcarrageenans(22–38 %), carrageenan, while native agarose presented good activity, with (Duckworth and Yaphe 1971; Campo et al. 2009). The bio- an ORAC value similar to that of commercial κ-carrageenan. logical properties of sulfated polysaccharides from marine Sulfated agarose presented good antioxidant capacity toward algae are known (Usov 2011; Wijesekara et al. 2011). other radicals. Copolymerization of sulfated agarose with ac- Studies on the antioxidant capacity of sulfated polysaccharides rylamide was achieved using ceric ammonium nitrate as initi- from brown and red seaweeds indicated the influence of ator. NMR spectroscopy indicated grafting of polyacrylamide sulfate content, molecular weight, and structure of the glycosyl at position C-4 of β-galactopyranosyl residues. residues (Ruperez et al. 2002; Zhang et al. 2003;Zhaoetal. 2004; 2008; Rocha de Souza et al. 2007; Barahona et al. 2011, 2012). On the other hand, it was found that sulfation of Keywords Agarose . Sulfation . Anticoagulant activity . polysaccharides increased their biological properties, such as Antioxidant capacity . Copolymerization antioxidant, antitumor, and anticoagulant activity (Sun et al. 2009;Wangetal.2009a; 2009b; 2010; Zhang et al. 2010; Telles et al. 2011). Also, over the last two decades, there has been increasing interest in the copolymerization of polysac- * : : : B. Matsuhiro ( ) T. Barahona M. V. Encinas J. A. Ortiz charides with vinyl monomers, a modification that allowed the Departamento de Ciencias del Ambiente, Facultad de Química y Biología, Universidad de Santiago de Chile, Av. L. B. O’Higgins, preparation of graft copolymers with new properties for indus- 3363 Santiago, Chile trial applications (Jenkins and Hudson 2001;Ranaetal.2011). e-mail: [email protected] Various vinyl monomers such as acrylamide, acrylic acid, acrylonitrile, N-vinyl-2-pyrrolidone, 2-acrylamidoglycolic ac- A. Mansilla κ Laboratorio de Macroalgas Antárticas y Subantárticas, id, and vinylsulfonic acid were grafted onto -carrageenan via Universidad de Magallanes, Av. Bulnes, 1465 Punta Arenas, Chile free radical polymerization (Meena et al. 2006; Pourjavadi J Appl Phycol et al. 2008; Hosseinzadeh 2009;Mishraetal.2010; Sand et al. the extraction was re-extracted twice with water under the 2012; Yadav et al. 2012). same conditions. Recently, it was found that Ahnfeltia plicata (Hudson) E.M. Fries (Ahnfeltiales, Rhodophyta) forms extensive Chemical analysis Reducing sugars were determined by the natural beds with high biomass production in the phenol-sulfuric acid method using D-galactose as standard Magellan ecoregion of southernmost Chile (Mansilla (Chaplin 1986). The 3,6-anhydrogalactose content was deter- et al. 2012, 2013). Its phycocolloid would be a very mined according to Matsuhiro and Zanlungo (1983)usingD- interesting starting material for the preparation of deriva- fructose as standard. The amount of sulfate was determined by tives with potential biological applications. The aim of this a modification of the Dodgson and Price method, using glyc- work is the structural characterization of the aqueous erin instead of gelatin (Barahona et al. 2012). The molecular extract from A. plicata, the preparation, characterization, weight of the polysaccharide was determined by the reducing and studies of the biological properties of a sulfated end method (Cáceres et al. 2000). Sulfur content was deter- derivative and its conjugation with acrylamide. mined by microanalysis at the Facultad de Química, Universidad Católica de Chile. Acid hydrolysis The purified extract (0.005 g) was heated with Materials and methods 0.75 mL of 2 M trifluoroacetic acid for 2 h at 120 °C and the acid was removed by co-evaporations with distilled water. The Analytical grade solvents were purchased from Merck product of hydrolysis was dissolved in 2 mL of distilled water, (Germany); reagent grade chemicals were purchased from treated with sodium borohydride during 2 h and concentrated Sigma (USA). Absorbance was measured in a Genesys 5 in vacuo. The resulting syrup was acetylated with acetic Thermospectronic spectrophotometer (Thermo Fisher anhydride in dry pyridine and analyzed by GLC. Per-O-ace- Scientific, USA). Fourier transform infrared (FT-IR) spectra tates of D-galactitol, D-glucitol, D-mannitol, L-rhamnitol, L- in KBr pellets of seaweeds and polysaccharides were recorded fucitol and D-xylitol were used as standards. in the 4,000–400 cm−1 region in a Bruker IFS 66v instrument (Bruker, UK) according to Leal et al. (2008). All the samples Sulfation Sulfation was performed with SO3-pyridine com- were previously milled under liquid nitrogen and dried for 8 h plex (Vogl et al. 2000). Freeze-dried agarose (0.200 g) was invacuoat56°C.1HNMR(400.13MHz)and13C dissolved in 5 mL of formamide and 2 mL of dry pyridine, and (100.62 MHz) spectra were recorded in D2O, after isotopic 2.0 g of the SO3-pyridine complex were added with stirring. exchange (3×0.75 mL) at 70ºC in a Bruker Avance DRX 400 The resulting mixture was heated at 90 °C under a nitrogen spectrometer (Bruker, UK) using the sodium salt of atmosphere for 4 h, cooled to room temperature, and poured 3-(trimethylsilyl)-1-propionic-2,2,3,3-d4 acid as internal refer- over 20 mL of ice water. The resultant solution was neutral- ence. The two-dimensional experiments were performed ized with 0.1 N NaOH and precipitated over 150 mL of using a pulse field gradient incorporated into an NMR pulse ethanol and centrifuged. The pellet was dissolved in distilled sequence. The number of scans in each experiment was de- water, dialyzed using Spectra/Por membranes (MWCO 3500) pendent on sample concentration. Gas–liquid chromatogra- (Spectrum Laboratories, USA) against 0.1 M sodium acetate phy (GC) was performed on a Shimadzu GC-14B chromato- for 3 days, followed by distilled water, concentrated in vacuo, graph (Shimadzu, Japan) equipped with a flame ionization and freeze-dried. detector using an SP 2330 column (0.25 mm×30 m), and it was carried out with an initial 5-min hold at 150ºC and then at 5ºC min−1 to 210ºC for 10 min. The helium flow was Antioxidant capacity assays 20 mL min−1. A. plicata (Ahnfeltiales, Rhodophyta) was collected at Riesco Island, Magellan ecoregion (Mansilla Oxygen radical absorbance capacity assay et al. 2013). The consumption of fluorescein due to incubation with AAPH Extraction The dried ground seaweed (100 g) was heated [2,2’-azo-bis(2-amidinopropane) dihydrochloride] at different with distilled water (2 L) at 95 °C for 3 h, cooled to 45 °C times was estimated from fluorescence measurements and centrifuged at 3,500 xg. The supernatant was allowed to (Alarcón et al. 2008; Barahona et al. 2011). A reaction mixture gel for 12 h and frozen overnight. The frozen gel was allowed containing 10 mM AAPH with and without the native agarose to thaw on a piece of muslin and was washed with distilled or the sulfated agarose at different concentrations (0.1– water until the filtrate became colorless. Purification of the gel 1.0 mg mL−1) in distilled water was incubated in a phosphate was performed by three freeze-thaw cycles and the gel was buffer (10 mM, pH 7.0) at 37 °C. Fluorescein (1.5 μM) dissolved in distilled water and freeze-dried. The residue of consumption was evaluated from the decrease of the J Appl Phycol fluorescence intensity (exCitation 491 nm, emission 512 nm) samples were incubated with 0.005 mL of STA-Cephascreen in the presence of polysaccharide. Fluorescence measure- solution (Diagnostica Stago Inc., USA) at 37ºC for 4 min. ments were made in a Fluorolog-Spex 1681/0.22 spectroflu- Then, 0.005 mL of 0.025 M CaCl2 solution was added and the orometer (Spex, USA). Bandwidths of 1.25 nm were used for clotting time was measured in triplicate on STA Compact the excitation and emission slits. The fluorescence intensity (Diagnostica Stago Inc.) equipment and repeated on three values, F, were plotted with respect to the initial value F/Fo as different days.