Phycocolloids from Sargassum microcystum: Immunomodulatory and antioxidant activities of alginic acid and fucoidan

This study focused on isolating and characterizing phycocolloids, particularly alginic acid and fucoidan, from the brown seaweed Sargassum microcystum. Sequential extraction using acetone, chloroform, and methanol yielded various fractions (AIP, ASP, ASPF1, ASPF2, ASPF3). Comprehensive analyses via HPLC, HRGPC, FTIR, and ¹H NMR identified distinct compositions of mannuronic acid, guluronic acid, total sugars, uronic acids, and sulfates across the fractions. Further fractionation of ASP through Q-Sepharose and Sephadex G-100 chromatography revealed homogeneous polymers with molecular weights of 55, 40, and 25 kDa for ASPF1, ASPF2, and ASPF3, respectively. Spectroscopic analyses confirmed AIP as alginic acid, while ASPF2 and ASPF3 were identified as fucoidan. Immunomodulatory assays showed significant IL-10 induction by ASPF3 and concentration-dependent IFN-γ production by ASPF2 and ASPF3 in PBMCs. Additionally, ASPF2 and ASPF3 stimulated NO production in RAW 264.7 cells, with ASPF3 showing the highest induction. ASPF3 demonstrated the highest antioxidant activity in DPPH, FRAP, HRS, and RP assays, achieving dose-dependent scavenging efficiencies of 73.6 %, 62.6 %, 60.4 %, and 52.4 % at 100 µg/mL. Cell viability assays confirmed the biocompatibility of these phycocolloids. Overall, this study highlights the immunomodulatory, antioxidant, and biocompatible properties of phycocolloids from S. microcystum, suggesting their potential for diverse industrial applications.