TLR2-stimulating contaminants in glycoconjugate fractions prepared from Bacteroides fragilis

Bacteroides vesicles promote functional alterations in the gut microbiota composition

Inflammatory bowel diseases are characterized by chronic intestinal inflammation and alterations in the gut microbiota composition. Bacteroides fragilis, which secretes outer membrane vesicles (OMVs) with polysaccharide A (PSA), can moderate the inflammatory response and possibly alter the microbiota composition. In this study, we created a murine model of chronic sodium dextran sulfate (DSS)-induced intestinal colitis and treated it with B. fragilis OMVs. We monitored the efficiency of OMV therapy by determining the disease activity index (DAI) and performing histological examination (HE) of the intestine before and after vesicle exposure. We also analyzed the microbiota composition using 16S rRNA gene sequencing. Finally, we evaluated the volatile compound composition in the animals' stools by HS-GC/MS to assess the functional activity of the microbiota. We observed more effective intestinal repair after OMV treatment according to the DAI and HE. A metabolomic study also revealed changes in the functional activity of the microbiota, with a predominance of phenol and pentanoic acid in the control group compared to the group treated with DSS and the group treated with OMVs (DSS OMVs). We also observed a positive correlation of these metabolites with Saccharibacteria and Acetivibrio in the control group, whereas in the DSS group, there was a negative correlation of phenol and pentanoic acid with Lactococcus and Romboutsia. According to the metabolome and sequencing data, the microbiota composition of the DSS-treated OMV group was intermediate between that of the control and DSS groups. OMVs not only have an anti-inflammatory effect but also contribute to the recovery of the microbiota composition.IMPORTANCEBacteroides fragilis vesicles contain superficially localized polysaccharide A (PSA), which has unique immune-modulating properties. Isolated PSA can prevent chemically induced colitis in a murine model. Outer membrane vesicles (OMVs) also contain digestive enzymes and volatile metabolites that can complement the anti-inflammatory properties of PSA. OMVs showed high therapeutic activity against sodium dextran sulfate-induced colitis, as confirmed by histological assays. 16S rRNA sequencing of fecal samples from different inflammatory stages, supplemented with comprehensive metabolome analysis of volatile compounds conducted by HS-GC/MS, revealed structural and functional alterations in the microbiota composition under the influence of OMVs. Correlation analysis of the OMV-treated and untreated experimental animal groups revealed associations of phenol and pentanoic acid with Lactococcus, Romboutsia, Saccharibacteria, and Acetivibrio.

Berberine inhibits dendritic cells differentiation in DSS-induced colitis by promoting Bacteroides fragilis

BACKGROUNDS

Berberine (BBR), a compound long used in traditional Chinese medicine, has been reported to have therapeutic effects in treating ulcerative colitis (UC), attributed to its anti-inflammatory properties and restorative potential of tight junctions (TJs). However, the mechanism by which BBR affects intestinal bacteria and immunity is still unclear.

METHODS

This study investigated the effects of BBR on intestinal bacteria and the inflammatory response in dextran sulfate sodium (DSS)-induced colitis mice. Immunohistochemistry (IHC) and electron microscopy were used to detect intestinal TJs. Microflora analysis was used to screen for bacteria regulated by BBR.

RESULTS

The results showed that BBR had increased colonic epithelium zonula occludens proteins-1 (ZO-1) and occludin expression and reduced T-helper 17/T regulatory ratio in DSS-induced mice. Mechanically, BBR eliminated DSS-induced intestinal flora disturbances in mice, particularly increased Bacteroides fragilis (B. fragilis) in vivo and in vitro. B. fragilis decreased the interleukin-6 induced by dendritic cells through some heat-resistant component rather than nucleic acids or proteins.

CONCLUSIONS

Overall, these data suggest that BBR had a moderating effect on DSS-induced colitis. This compound may regulate intestinal immune cell differentiation by affecting the growth of B. fragilis, providing new insights into the potential application of BBR in UC.

Protective effect of Bacteroides fragilis LPS on Escherichia coli LPS-induced inflammatory changes in human monocytic cells and in a rheumatoid arthritis mouse model

It has been reported that patients with rheumatoid arthritis (RA) have significantly less bacteria belonging to the Bacteroides group in their microbiota. We speculate that inhibition of cytokine production is impaired in patients with RA owing to their low levels of intestinal bacteria belonging to the Bacteroidetes group. Here we investigated the effect of Bacteroides fragilis lipopolysaccharide (B-LPS) on cytokine production in vitro and on the development of collagen antibody-induced arthritis (CAIA) in DBA/1 mice, an animal model of RA. in vitro culture experiments showed that Escherichia coli LPS (E-LPS)-induced cytokine production from THP-1 monocytic cells and peripheral blood mononuclear cells was significantly suppressed by B-LPS in a dose-dependent manner. A decrease in TNF-α and IL-1β production was also observed in LPS-tolerized macrophages induced by B-LPS at concentrations equal to and higher than that of E-LPS. Similar results were obtained when autoclaved feces were used to induce cytokine production instead of E-LPS. In in vivo experiments using CAIA models, B-LPS had no adverse effects even when administered at 10 times the concentration of E-LPS, which elicits severe arthritis. In addition, simultaneous administration of high dose B-LPS with E-LPS or administration of B-LPS prior to E-LPS significantly suppressed arthritis development in CAIA model animals when compared with administration of E-LPS alone. These results suggest that increasing certain bacterial groups such as Bacteroides is an effective strategy for preventing arthritis development in patients with RA.

Pairing Bacteroides vulgatus LPS Structure with Its Immunomodulatory Effects on Human Cellular Models

The gut microbiota guide the development of the host immune system by setting a systemic threshold for immune activation. Lipopolysaccharides (LPSs) from gut bacteria are able to trigger systemic and local proinflammatory and immunomodulatory responses, and this capability strongly relies on their fine structures. Up to now, only a few LPS structures from gut commensals have been elucidated; therefore, the molecular motifs that may be important for LPS-mammalian cell interactions at the gut level are still obscure. Here, we report on the full structure of the LPS isolated from one of the prominent species of the genus Bacteroides, Bacteroides vulgatus. The LPS turned out to consist of a particular chemical structure based on hypoacylated and mono-phosphorylated lipid A and with a galactofuranose-containing core oligosaccharide and an O-antigen built up of mannose and rhamnose. The evaluation of the immunological properties of this LPS on human in vitro models revealed a very interesting capability to produce anti-inflammatory cytokines and to induce a synergistic action of MD-2/TLR4- and TLR2-mediated signaling pathways.

Immunomodulatory Roles of Polysaccharide Capsules in the Intestine

The interplay between the immune system and the microbiota in the human intestine dictates states of health vs. disease. Polysaccharide capsules are critical elements of bacteria that protect bacteria against environmental and host factors, including the host immune system. This review summarizes the mechanisms by which polysaccharide capsules from commensal and pathogenic bacteria in the gut microbiota modulate the innate and adaptive immune systems in the intestine. A deeper understanding of the roles of polysaccharide capsules in microbiota-immune interactions will provide a basis to harness their therapeutic potential to advance human health.

Weak Agonistic LPS Restores Intestinal Immune Homeostasis

Generated by gram-negative bacteria, lipopolysaccharides (LPSs) are one of the most abundant and potent immunomodulatory substances present in the intestinal lumen. Interaction of agonistic LPS with the host myeloid-differentiation-2/Toll-like receptor 4 (MD-2/TLR4) receptor complex results in nuclear factor κB (NF-κB) activation, followed by the robust induction of pro-inflammatory immune responses. Here we have isolated LPS from a common gut commensal, Bacteroides vulgatus mpk (BVMPK), which provides only weak agonistic activity. This weak agonistic activity leads to the amelioration of inflammatory immune responses in a mouse model for experimental colitis, and it was in sharp contrast to strong agonists and antagonists. In this context, the administration of BVMPK LPS into mice with severe intestinal inflammation re-established intestinal immune homeostasis within only 2 weeks, resulting in the clearance of all symptoms of inflammation. These inflammation-reducing properties of weak agonistic LPS are grounded in the induction of a special type of endotoxin tolerance via the MD-2/TLR4 receptor complex axis in intestinal lamina propria CD11c⁺ cells. Thus, weak agonistic LPS represents a promising agent to treat diseases involving pathological overactivation of the intestinal immune system, e.g., in inflammatory bowel diseases.