Extraction and Evaluation of Outer Membrane Vesicles from Two Important Gut Microbiota Members, Bacteroides fragilis and Bacteroides thetaiotaomicron

The emerging role of bacterial extracellular vesicles in human cancers

Bacterial extracellular vesicles (BEVs) have emerged as pivotal mediators between bacteria and host. In addition to being crucial players in host homeostasis, they have recently been implicated in disease pathologies such as cancer. Hence, the study of BEVs represents an intriguing and rapidly evolving field with substantial translational potential. In this review, we briefly introduce the fundamentals of BEV characteristics, cargo and biogenesis. We emphatically summarize the current relationship between BEVs across various cancer types, illustrating their role in tumorigenesis, treatment responses and patient survival. We further discuss the inherent advantages of BEVs, such as stability, abundance and specific cargo profiles, that make them attractive candidates for non-invasive diagnostic and prognostic approaches. The review also explores the potential of BEVs as a strategy for cancer therapy, considering their ability to deliver therapeutic agents, modulate the tumour microenvironment (TME) and elicit immunomodulatory responses. Understanding the clinical significance of BEVs may lead to the development of better-targeted and personalized treatment strategies. This comprehensive review evaluates the current progress surrounding BEVs and poses questions to encourage further research in this emerging field to harness the benefits of BEVs for their full potential in clinical applications against cancer.

The effect of Bacteroides fragilis and its postbiotics on the expression of genes involved in the endocannabinoid system and intestinal epithelial integrity in Caco-2 cells

Purpose

Gut microbiota and its derivatives by constantly interacting with the host, regulate the host function. Intestinal epithelium integrity is under the control of various factors including the endocannabinoid system (ECS). Accordingly, we aimed at investigating the effect of Bacteroides fragilis and its postbiotics (i.e., heat-inactivated, cell-free supernatants (CFS) and outer membrane vesicles (OMVs)) on the expression of genes involved in ECS (cnr1, faah, pparg) and the epithelial barrier permeability (ocln, tjp1) in a Caco-2 cell line.

Methods

Caco-2 cell line was treated with live or heat-inactivated B. fragilis at MOIs of 50 and 100, or stimulated with 7% V/V CFS and B. fragilis OMVs at a dose of 50 and 100 µg/ml overnight. RT-qPCR was applied for expression analysis.

Results

Heat-inactivated B. fragilis induced cnr1, pparg, tjp1, and suppressed faah expression, while live B. fragilis had the opposite effect. OMVs increased pparg, and tjp1 expression by reducing the activity of ECS through an increase in faah and a reduction in cnr1 expression. Finally, an increase in the expression of pparg and ocln, and a reduction in the expression of cnr1 was detected in Caco-2 cells treated with CFS.

Conclusion

The live and heat-inactivated B. fragilis inversely affected cnr1, faah, pparg, and tjp1 expression in Caco-2 cells. Increased tjp1 mRNA levels by affecting the expression of ECS related genes is taken as an indication of the potential beneficial effects of B. fragilis postbiotics and making them potential candidates for improving permeability in the leaky gut syndrome.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-023-01264-8.

Emerging role of bacterial outer membrane vesicle in gastrointestinal tract

Bacteria form a highly complex ecosystem in the gastrointestinal (GI) tract. In recent years, mounting evidence has shown that bacteria can release nanoscale phospholipid bilayer particles that encapsulate nucleic acids, proteins, lipids, and other molecules. Extracellular vesicles (EVs) are secreted by microorganisms and can transport a variety of important factors, such as virulence factors, antibiotics, HGT, and defensive factors produced by host eukaryotic cells. In addition, these EVs are vital in facilitating communication between microbiota and the host. Therefore, bacterial EVs play a crucial role in maintaining the GI tract's health and proper functioning. In this review, we outlined the structure and composition of bacterial EVs. Additionally, we highlighted the critical role that bacterial EVs play in immune regulation and in maintaining the balance of the gut microbiota. To further elucidate progress in the field of intestinal research and to provide a reference for future EV studies, we also discussed the clinical and pharmacological potential of bacterial EVs, as well as the necessary efforts required to understand the mechanisms of interaction between bacterial EVs and gut pathogenesis.

Microbiota-derived extracellular vesicles in interkingdom communication in the gut

The intestine is fundamental in controlling human health. Intestinal epithelial and immune cells are continuously exposed to millions of microbes that greatly impact on intestinal epithelial barrier and immune function. This microbial community, known as gut microbiota, is now recognized as an important partner of the human being that actively contribute to essential functions of the intestine but also of distal organs. In the gut ecosystem, bidirectional microbiota-host communication does not involve direct cell contacts. Both microbiota and host-derived extracellular vesicles (EVs) are key players of such interkingdom crosstalk. There is now accumulating body of evidence that bacterial secreted vesicles mediate microbiota functions by transporting and delivering into host cells effector molecules that modulate host signalling pathways and cell processes. Consequently, vesicles released by the gut microbiota may have great influence on health and disease. Here we review current knowledge on microbiota EVs and specifically highlight their role in controlling host metabolism, intestinal barrier integrity and immune training.

Epigallocatechin Gallate (EGCG) Promotes the Immune Function of Ileum in High Fat Diet Fed Mice by Regulating Gut Microbiome Profiling and Immunoglobulin Production

This study aimed to investigate the regulatory effect of epigallocatechin gallate (EGCG) on the composition of the gut microbiome, the transcriptomic profiling of ileum, and their interplay in high fat diet (HFD) induced obese mice. Intragastric administration of EGCG to C57BL/6J mice for 14 consecutive weeks remarkably decreased HFD induced excessive fat deposition (p < 0.001), and the increment of serum TG, TC, HDL-C (p < 0.05), as well as improved glucose tolerance (p < 0.001). EGCG shifted the gut microbiota mainly by elevating the relative abundance of Parasutterrlla, Bacteroides, and Akkermansia (p < 0.01), decreasing that of norank_f_Erysipelotrichaceae, unclassified_f_Ruminococcaceae, Anaerotruncus, Roseburia, norank_Lachnospiraceae, and Lachnospiraceae_UCG_006 (p < 0.01) at the genus level. In addition, EGCG affected the transcriptomic profiling of ileum, and the differentially expressed (DE) genes after HFD or/and EGCG treatment were mostly enriched in the immune reaction of ileum, such as the GO term of “immune effector process” and “phagocytosis, recognition.” Furthermore, the KEGG category of “immune diseases,” “immune system,” and “infection diseases: bacterial” were commonly enriched by the DE genes of the two treatments. Among those DE genes, 16 immunoglobulins heavy chain variable region encoded genes (Ighvs) and other immunity-related genes, such as complement component 2 (C2), interferon-induced transmembrane protein 1 (Iftm1), polymeric immunoglobulin receptor (pigR), and alanyl aminopeptidase (Anpep), were highly correlated with the shifted microbes in the gut (p < 0.05, absolute r > 0.5). Overall, the results suggested that EGCG ameliorated the HFD induced metabolic disorder mainly by regulating gut microbiome profiling and the immunoglobulin production of ileum, while the genes expressed in the ileum, especially Ighvs, C2, Iftm1, pigR, and Anpep, might play important roles in coordinating the immunity of mice regarding the gut microbes and the host interactions.

The effect of Faecalibacterium prausnitzii and its extracellular vesicles on the permeability of intestinal epithelial cells and expression of PPARs and ANGPTL4 in the Caco-2 cell culture model

Background and Objectives

Gut microbiota such as Faecalibacterium prausnitzii play a major role in the regulation of gut barrier, inflammation and metabolic functions. Microbiota-derived extracellular vehicles (EVs) have been recently introduced as functional units mediating the eukaryotic and prokaryotic cell-microbiota interactions. In this paper, the effect of F. prausnitzii and its EVs on mRNA expression levels of tight junction genes (ZO1 and OCLN) as well as PPARs and ANGPTL4 genes in the human epithelial colorectal adenocarcinoma (Caco-2) cell line was evaluated.

Methods

F. prausnitzii was cultured on the Brain Heart Infusion (BHI) broth medium under anaerobic conditions, and its EVs were extracted by ultracentrifugation. This bacterium and its EVs were treated on the Caco-2 cells. After 24 h, the expression of the genes encoding TJ proteins such as ZO1 and OCLN, PPARs and ANGPTL4 was evaluated by quantitative real-time PCR.

Results

Unlike F. prausnitzii, its EVs significantly increased the expression of ZO1 and OCLN genes, and PPARα, PPARγ and PPARβ/δ genes (except at a concentration of 100 µg/ml) as well as ANGPTL4 gene.

Conclusions

The results of this study demonstrated that F. prausnitzii-derived EVs increased the intestinal barrier permeability via TJs (ZO1 and OCLN) as well as PPAR-α, PPAR-γ and PPAR β/δ genes and their targeted gene (ANGPTL4) in the Caco-2 cell line. Accordingly, it is suggested that F. prausnitzii-derived EVs can be considered as a new bacterial postbiotic to cure dysbiosis-associated diseases including obesity and its related metabolic dysfunctions, according to the leaky gut hypothesis.