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In vitro cytotoxic and immunomodulative activities of low molecular weight ι-carageenans partially methylated and pyruvated
Carrageenan is a kind of sulphated galactan isolated from the cell wall of red algae. This name covers a broad dispersion of structure that has been grouped into several family namelyκ/ι-, µ/v- and λ-carrageenans. These polysaccharides are well know to have biological activities comprising antiviral [1–5], anticoagulant [6,7], antitumoral  and anti-inflammatory  actions. These activities can be enhanced by depolymerisation of the polysaccharide [10–13]. Immunomodulative effects has been also demonstrated on the low molecular weight fractions ofλ- andκ-carrageenan [14–16]. Our study has focused on the carrageenan of the abundant red alga Solieria chordalis (Gigartinales) from Brittany coast. The elucidation structure (GC-MS, 13C NMR and FTIR spectroscopies, LPLC-GPC) revealed a hybrid structure average 900Kda, build up with major amount of iota-type (DA2S-G4S) and minor amount of methylated and pyruvated units. The depolymerisation of this polysaccharide was obtained by two methods: the free radical depolymerisation and acid hydrolysis. The hydrolysats were then fractionated by LPLC-GPC in order to get low molecular weight (LMW) fractions (below 10KDa) and the cytotoxicity of these fractions was evaluated on daudi cells (human B cells, Burkitt Lymphoma). Apoptosis was quantified by detecting surface exposure of phosphatidylserine using Annexin V-FITC/PI (propidium iodide) detection kit. No cytotoxicity was revealed after daudi cells treatment by 10mM of these compounds. On the other hand, these molecules have shown great immunostimulating properties, increasing neutrophil phagocytosis, highlighted by an assay based on cytofluocytometrical measurement of the uptake of fluorescence-labelled E. coli by respective cells of interest. Furthermore we noticed an enhancement of NK cell cytotoxicity, after exposure to low molecular weight carrageenans by a flow cytometric assay based on their ability to kill K562 target cells.
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