title: Partial characterization and antioxidant and antiproliferative activities of the aqueous extracellular polysaccharides from the thermophilic microalgae Graesiella sp.
abstract: BACKGROUND
  For thousands of years, Tunisian geothermal water has been used in bathing. Indeed, thermal baths "Hammam" were recommended in the treatment of different type of illnesses as, for instance, for relaxing joints and soothing. The ability of microalgae to sustain at the high temperature makes them potential producers of high value thermostable bio-products. This study aimed to explore the therapeutic potential of the aqueous extracellular polysaccharides (AEPS) of the Tunisian thermophilic microalgae Graesiella sp. and to evaluate its physico-chemical characteristics.
  
  
  METHODS
  Different parameters were used to characterize the AEPS. The dry weight, volatile dry weight, elemental analysis, monosaccharide composition and IR-spectroscopy analysis. Carbohydrate, uronic acid, ester sulfate and protein concentrations were also determined using colorimetric assay. AEPS was analyzed for its antioxidant propriety by means of total antioxidant capacity, DPPH radicals scavenging assay, ferrous chelating ability and hydroxyl and superoxide radical scavenging activity. The antiproliferative activity of AEPS was evaluated for HepG2 and Caco-2 cells using the MTT assay.
  
  
  RESULTS
  The Graesiella sp. AEPS is found to be a hetero-sulfated-anionic polysaccharides that contain carbohydrate (52 %), uronic acids (23 %), ester sulfate (11 %) and protein (12 %). The carbohydrate fraction was formed by eight neutral sugars glucose, galactose, mannose, fucose, rhamnose, xylose, arabinose and ribose. The FT-IR revealed the presence of carboxyl, hydroxyl, amine and sulfate groups. AEPS showed high activity as reducing agent, high ferrous chelating capacity and caused a significant decrease in a concentration-dependent manner of hydroxyl radical. A moderate DPPH scavenging activity and a poor superoxide radical scavenging ability were also observed. AEPS treatment (from 0.01 to 2.5 mg/ml) caused also a clear decrease of cell viabilities in a dose-dependent manner. The IC50 values obtained in HepG2 and Caco-2 cells were 1.06 mg/ml and 0.3 mg/ml respectively.
  
  
  CONCLUSIONS
  This study evidenced that the Graesiella sp. AEPS exhibits antioxidant and antiproliferative activities. The biological activities of this extract depend on its fine structural features. Further work will identify and purify the active polysaccharides to enhance our understanding of their complete structure and relationships with its function.
authors.affiliation: Laboratory of Marine Biodiversity and Biotechnology, National Institute of Marine Sciences and Technology, BP 59, 5000, Monastir, Tunisia.
authors.forename: Lamia
authors.identifier: http://orcid.org/0000-0001-5168-691X
authors.initials: L
authors.lastname: Trabelsi
authors.affiliation: Laboratory of Marine Biodiversity and Biotechnology, National Institute of Marine Sciences and Technology, BP 59, 5000, Monastir, Tunisia.
authors.forename: Olfa
authors.initials: O
authors.lastname: Chaieb
authors.affiliation: Biochemistry Laboratory, Research Laboratory in "Nutrition- Functional Food & Vascular Health" Faculty of Medicine of Monastir, 5019, Monastir, Tunisia.
authors.forename: Amira
authors.initials: A
authors.lastname: Mnari
authors.affiliation: Laboratory of Research on Biologically Compatible Compounds, Faculty of Dentisty, 5019, Monastir, Tunisia.
authors.forename: Salwa
authors.initials: S
authors.lastname: Abid-Essafi
authors.affiliation: Université de Bourgogne Franche-Comté, Laboratoire de Chrono-Environnement, UMR CNRS 6249, Besançon, France. lotfi.aleya@univ-fcomte.fr.
authors.forename: Lotfi
authors.initials: L
authors.lastname: Aleya
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D018938:Caco-2 Cells; D049109:Cell Proliferation / Q000187:drug effects; D000460:Chlorophyta / Q000737:chemistry*; D056945:Hep G2 Cells; D045482:Hot Springs / Q000382:microbiology; D006801:Humans; D058086:Microalgae / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000494:pharmacology*; D014416:Tunisia
chemical_list: D000970:Antineoplastic Agents; D000975:Antioxidants; D010936:Plant Extracts; D011135:Polysaccharides, Bacterial
keywords: Biological activities; Graesiella sp.; Microalgae; Sulfated exopolysaccharides; Tunisian hot spring