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Fucoidan, a sulfated polysaccharide rich in fucose, is derived from brown algae and marine invertebrates. Multiple bioactivities have been shown with fucoidan, while growing attraction has emerged in its low-molecular-weight (Mw) hydrolysates. Here, the anti-inflammatory effect of fucoidan, low-Mw acidolyzed fucoidan (LMAF, <1.5 kDa), and high-Mw acidolyzed fucoidan (HMAF, 1.5–20 kDa) were investigated in vitro using lipopolysaccharide (LPS)-stimulated Caco-2 and RAW264.7 co-cultures. Fucoidan, LMAF, and HMAF with different structures exhibited varied anti-inflammatory effects. LMAF and HMAF effectively decreased the nitric oxide release of RAW264.7 cells. LMAF exhibited a competitive effect in reducing tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6 levels compared to HMAF and fucoidan. Transcriptome of RAW264.7 revealed that LPS and LMAF mainly regulated the transcriptional expression of genes, including Tnf, Il6, Il1b, Junb, and Nfkb1 in the TNF signaling pathway, NF-kappa B signaling pathway, and cytokine–cytokine receptor interaction. RT-PCR results indicated that LMAF markedly reduced the LPS-elevated expression of Cxcl2, Tnf, Ccl2, Il1b, and Csf2. Moreover, LMAF effectively increased the proteins expression of Claudin-1, Occludin, and Zonula occluden-1 in Caco-2 cells. This study highlights the potential of LMAF to improve inflammation and intestinal barrier integrity, offering a foundation for further application of low-Mw fucoidan hydrolysates. [ABSTRACT FROM AUTHOR]

Firmicutes and Bacteroidetes are the predominant bacterial phyla colonizing the healthy human gut. Accumulating evidence suggests that dietary fiber plays a crucial role in host health, yet most studies have focused on how the dietary fiber affects health through gut Bacteroides. More recently, gut Firmicutes have been found to possess many genes responsible for fermenting dietary fiber, and could also interact with the intestinal mucosa and thereby contribute to homeostasis. Consequently, the relationship between dietary fiber and Firmicutes is of interest, as well as the role of Firmicutes in host health. In this review, we summarize the current knowledge regarding the molecular mechanism of dietary fiber degradation by gut Firmicutes and explain the communication pathway of the dietary fiber-Firmicutes-host axis, and the beneficial effects of dietary fiber-induced Firmicutes and their metabolites on health. A better understanding of the dialogue sustained by the dietary fiber-Firmicutes axis and the host could provide new insights into probiotic therapy and novel dietary interventions aimed at increasing the abundance of Firmicutes (such as Faecalibacterium, Lactobacillus, and Roseburia) to promote health. Dietary fiber-induced gut Firmicutes and their metabolites exhibit relevant health-promoting functions. Most of dietary fiber have a great effect on gut Firmicutes. Mechanisms of dietary fiber uptake by gut Firmicutes are outlined. Mechanisms of dietary fiber- gut Firmicutes-host interactions require more investigation for the development of dietary fiber in food production and host health. [ABSTRACT FROM AUTHOR]