Polymannuronic acid

Polymannuronic acid (PM), also called 1 → 4-linked β-D-mannuronic acid, is structurally similar to mannans. PM is one of numerous alginates isolated from brown seaweeds, and has been shown to possess antioxidant activities and has been exploited for its medicinal potential. In a study on 15 mice, PM was able to restore the High Fat Diet (HFD)-repressed abundance of Actinobacteria to its pre-stressed level as observed in the mice fed a low-fat diet. The butyrate-producing bacteria Roseburia and Anaerofustis were significantly increased by PM, but overall populations of the butyrate-producing bacteria as a functional group impacted by PM were small. This suggests that PM may regulate gut butyrate production via metabolic cross-feeding rather than a direct expansion of butyrate-producing bacteria. PM significantly increased the abundance of R. bromii, from HFD-repressed 0·04 to 1·94%, a level much higher than that observed in the mice fed a low-fat diet. PM treatment resulted in a 5-fold expansion of B. pseudolongum. After the expansion, B. pseudolongum became the most abundant species in the HFD mice supplemented with PM. Oral administration of B. pseudolongum to BALB/c mice results in a higher excretion of viable bifidobacteria and a positive impact on antigen-induced cytokine production. In addition, PM significantly increased the abundance of a probiotic bacterium, L. reuteri. PM may exert its immunoregulatory effects via enhancing proliferation of several bacterial species with probiotic activities. PM as a dietary supplement resulted in a 290-fold reduction in E. coli abundance, to a level ten times lower than that in the mice fed LFD. Similarly, PM significantly decreased the abundance of several key genera that harbor human pathogens, such as Clostridium and Enterococcus. PM was able to reduce HFD-induced body weight gain, adiposity index, fat mass and serum TAG levels in mice. Moreover, PM significantly decreased blood LPS levels and increased the expression of several anti-inflammatory cytokines at the mRNA level. PM had a profound impact on the gut microbiome, significantly altering the abundance of approximately 14% species-level OTU. Furthermore, PM as a dietary supplement resulted in a significant expansion of several probiotic species while repressing the abundance of the genera that harbor pathogens, suggesting that PM may exert its immunoregulatory effects by restoring the structure and function of the gut microbiome altered by HFD. [PMID: 28528593]