Polysaccharides isolated from Nostoc commune Vaucher inhibit colitis-associated colon tumorigenesis in mice and modulate gut microbiota

Accumulating evidences have reported that the gut microbiota plays an important role in the occurrence and progression of colorectal cancer. Commonly known as a kind of constituent macromolecules, non-digestible polysaccharides have always been fermented by the intestinal microbiota. Nostoc commune Vaucher (N. commune) has always been appreciated as a healthy food and supplementation worldwide as it is rich in nutrients. Particularly, polysaccharides account for 60% of the dry weight of N. commune. In this study, we examined the protective effects of the polysaccharides isolated from N. commune (NVPS) against colitis-associated colon tumorigenesis in mice treated with azoxymethane (AOM) and dextran sulfate sodium salt (DSS) and the impact of these polysaccharides on the intestinal microbiota. NVPS were administered to mice through an intragastric gavage for 14 weeks. Our results demonstrated that the treatment with NVPS significantly decreased the number and sizes of tumors and reduced the incidence of intestinal tumors. Using 16S rRNA gene sequencing and qPCR, we analyzed the bacterial composition of the fecal samples obtained from mice. The results demonstrated that the alterations in the abundance of Firmicutes and Bacteroidetes caused by the AOM/DSS treatment were significantly reversed in response to the NVPS treatment. Moreover, the short-chain fatty acid (SCFA)-producing genera, including butyric acid-producing genera (Butyricicoccus, Butyrivibrio and Butyricimonas) and acetic acid-producing genera (Lachnospiraceae UCG 001, Lachnospiraceae UCG 006, and Blautia), were drastically enriched following the NVPS intervention. These compositional alterations induced by the NVPS were associated with the suppressed colonic inflammation and carcinogenesis. In conclusion, our results demonstrated an appreciable capability of NVPS to restore the gut microbiota profile altered by AOM/DSS, indicating the potential of NVPS as a promising prebiotic candidate for the prevention and treatment of colorectal cancer.