Seaweed has raised great interest as an excellent source of bioactive components, including vitamins, minerals, polysaccharides, polyphenols, and unique secondary metabolites which reveal a broad-spectrum biological activity. In particular, the complex polysaccharides from brown, red and green seaweed possess numerous therapeutic properties. The galactan is routinely used in biomedical research. This study investigates the bioactive properties of sulfated galactan (Hd-SG) derived from the red macroalgae Halymenia dilatata, including its anticancer, antibacterial, anti-biofilm and antioxidant effects. The isolated Hd-SG exhibited potent cytotoxicity against MDA-MB-231 cells with a half-maximum inhibitory concentration (IC50) of 75 μg/mL. It was found that Hd-SG had antibacterial activity against Vibrio alginolyticus, a coastal aquaculture pathogen, with a minimum inhibitory concentration of 300 μg/ml. Toxicology analysis revealed that the isolated Hd-SG was not toxic to zebrafish embryos, even at higher concentrations (100 μg/ml). Moreover, zebrafish embryos treated with Hd-SG at a concentration of 100 μg/ml exhibited a 118.8% reduction in oxidative damage caused by H2O2-induced reactive oxygen species (ROS) production compared to the H2O2 alone treated embryos (562%). In summary, this study demonstrated that the sulfated galactan of H. dilatata has a wide range of therapeutic properties, making it a viable option for biomedical and aquaculture preventive medicine.
