Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread around the world at an unprecedented rate. In the present study, 4 marine sulfated polysaccharides were screened for their inhibitory activity against SARS-CoV-2, including sea cucumber sulfated polysaccharide (SCSP), fucoidan from brown algae, iota-carrageenan from red algae, and chondroitin sulfate C from sharks (CS). Of them, SCSP, fucoidan, and carrageenan showed significant antiviral activities at concentrations of 3.90–500 μg mL⁻¹. SCSP exhibited the strongest inhibitory activity with IC₅₀ of 9.10 μg mL⁻¹. Furthermore, a test using pseudotype virus with S glycoprotein confirmed that SCSP could bind to the S glycoprotein to prevent SARS-CoV-2 host cell entry. The three antiviral polysaccharides could be employed to treat and prevent COVID-19.

In this study, the immunostimulatory activity of Caulerpa lentillifera polysaccharides (CLP) was elucidated in cytoxan (CTX)-induced immunosuppressed BALB/c mice. The results showed that CLP ameliorated the CTX-evoked damage to body weight, colon length and thymus/spleen indexes and enhanced the secretions of interleukin (IL)-1β, tumor necrosis factor (TNF)-α and superoxidase dismutase (SOD) in serum and thymic, splenic and colonic tissues of the immunosuppressed mice. Besides, CLP promoted the production of secretory immunoglobulin A (SIgA) and mucin2 in the colonic tissue of the immunosuppressed mice. Associated with the above immunostimulatory effects, CLP positively affected the production of short chain fatty acids (SCFAs) and microbiota diversity and composition, such as improvement in the growth of Lactobacillus, Coriobacteriaceae, Ruminococcaceae, Clostridium_XVIII and Helicobacter, whereas it suppressed the microbial populations of Bacteroides, Barnesiella and Lachnospiraceae. These findings suggested that CLP modulated SCFA production and gut microbiota in the immunosuppressed mice, evoking the colonic mucosal immunity, which might activate the systemic immunity in blood, thymus and spleen. The results could be helpful for understanding the functions of CLP, supporting their potential as novel prebiotics and immunostimulators.

Gut microbes and untargeted/targeted metabolomics were combined to comprehensively understand the therapeutic effect and the underlying mechanism of Lycium barbarum arabinogalactan (LBP-3) in DSS-induced colitis mice.