Chemical structure and snake antivenom properties of sulfated agarans obtained from Laurencia dendroidea (Ceramiales, Rhodophyta)

[Display omitted] •A family of sulfated and methylated agarans was obtained from Laurencia dendroidea.•Fine chemical structure of a purified agaran fraction was determined.•Most β-d-galactose units are 2-sulfated, non sulfated or 6-O-methylated.•L-Galactose units are 6-sulfate, 3,6-anhydro, or 6-sulfate 3-xylose.•KCl-soluble agaran inhibited toxic effects of the snake venoms (L. muta, B. jararaca). Aqueous and KCl-soluble polysaccharides were extracted from Laurencia dendroidea (Rhodomelaceae, Ceramiales) and their chemical profile was accessed by anion-exchange chromatography, chemical and spectroscopic analyses. The homogeneous agaran DHS-4 (181.3 × 103 g. mol−1, 21.3% of NaSO3) presents A units mostly 2-sulfated (18.9 mol%), nonsubstituted (15.3 mol%) and 6-O-methylated (10.1 mol%), while B units are l-sugars composed predominantly by galactose 6-sulfate precursor units (19.2 mol%) and 3,6-anhydrogalactose (13.8 mol%), besides non-precursor galactose 6-sulfate units bearing d-xylose substituents on C-3 (8.1 mol%). The crude KCl-soluble DHS agaran (20.5% of NaSO3) inhibited proteolysis and hemolysis induced by Lachesis muta and Bothrops jararaca venoms. DHS was able to inhibit up to 75% the L. muta venom hemorrhagic effect and to reduce the lethality displayed by B. jararaca venom, increasing the mice survival time up to 3 times. Therefore, this agaran has high potential to be used as an additional tool to treat snakebite envenomation.