Sulfated polysaccharide from brown algae Dictyota caribaea stimulates macrophages to an antitumoral phenotype

Fucoidans are sulfated polysaccharides capable of exerting biological activities such as antitumor and immunomodulatory effects. Previous studies demonstrated the antitumor activity of non-cytotoxic fucoidans from the seaweed Dictyota caribaea (Dc-SP) in vivo. Macrophages (Mfs) are innate immune cells capable of promoting or inhibiting tumor growth depending on the stimulus. This study aimed to evaluate the immunostimulant activity of Dc-SP on a murine Mfs cell line (RAW 264.7) in vitro. Dc-SP was assessed for its ability to modify cell viability and stimulate the production of antitumor markers on RAW 264.7 cells. Dc-SP induced an increase (p < 0.05) in the production of NO and cytokines TNF-α, IL-1β, and IL-10. The exposure of RAW 264.7 to Dc-SP also increased (p < 0.05) the expression of M1 phenotype markers such as iNOS, CD86, and MHC II. Dc-SP did not exhibit direct cytotoxicity on a murine melanoma cell line (B16–F10). However, the conditioned medium (CM) obtained from RAW 264.7 previously stimulated with Dc-SP (CM-Dc-SP) showed antiproliferative activity on tumor cells. B16–F10 incubated with CM-Dc-SP showed a cytostatic profile, tumor cells did not alter membrane integrity, however, they suffered morphological changes such as cell shrinkage and high granularity. In conclusion, Dc-SP stimulated RAW 264.7 to an antitumor phenotype.