Direct Action of Non-Digestible Oligosaccharides against a Leaky Gut

Role of Akkermansia muciniphila in insulin resistance

Insulin resistance (IR) is a pathogenic factor in numerous metabolic diseases. The gut microbiota plays a crucial role in maintaining the function of the intestinal barrier and overall human health, thereby influencing IR. Dysbiosis of the gut microbiota can contribute to the development of IR. Therefore, it is essential to maintain a balanced and diverse gut microbiota for optimal health. Akkermansia muciniphila, a widely present microorganism in the human intestine, has been shown to regulate gastrointestinal mucosal barrier integrity, reduce endotoxin penetration, decrease systemic inflammation levels, and improve insulin sensitivity. Reduced abundance of A. muciniphila is associated with an increased risk of IR and other metabolic diseases, highlighting its correlation with IR. Understanding the role and regulatory mechanism of A. muciniphila is crucial for comprehending IR pathogenesis and developing novel strategies for preventing and treating related metabolic disorders. Individual variations may exist in both the gut microbiota composition and its impact on IR among different individuals. Further investigation into individual differences between A. muciniphila and IR will facilitate advancements in personalized medicine by promoting tailored interventions based on the gut microbiota composition, which is a potential future direction that would optimize insulin sensitivity while preventing metabolic disease occurrence. In this review, we describe the physiological characteristics of A. muciniphila, emphasize its roles in underlying mechanisms contributing to IR pathology, and summarize how alterations in its abundance affect IR development, thereby providing valuable insights for further research on A. muciniphila, as well as new drug development targeting diabetes.

Oral mucosal changes in tight junction proteins in patients with oral lichen planus

OBJECTIVE

This study aimed to investigate the expression of tight junction, its distribution pattern in oral lichen planus samples and its potential association with the severity of oral lichen planus.

MATERIALS AND METHODS

Cross-sectional study designs were conducted. Transcriptome sequencing was conducted using oral mucosal tissues from 22 patients with oral lichen planus and 11 healthy controls. Immunohistochemistry and quantitative reverse transcription PCR were performed to verify the expression of claudin-1, claudin-4, occludin and zonula occludens-1 in oral mucosal tissues from another 30 patients with oral lichen planus and 26 healthy controls. The relationship between tight junction protein expression and oral lichen planus severity was explored using correlation analysis.

RESULTS

5603 and 2475 differentially expressed genes were upregulated and downregulated respectively, in oral lichen planus tissues. KEGG analysis showed that tight junctions including CLDN1, CLDN4, OCLN and TJP1 were downregulated in oral lichen planus. Claudin-1, claudin-4, occludin and zonula occludens-1 expression was verified to be significantly lower in oral lichen planus. Furthermore, correlation analyses showed that decreased occludin expression was positively related to oral lichen planus severity.

CONCLUSION

Decreased expression of TJ barrier proteins may be associated with the development of oral lichen planus.

Beneficial effect of heat-killed Lactiplantibacillus plantarum L-137 on intestinal barrier function of rat small intestinal epithelial cells

Heat-killed Lactiplantibacillus plantarum L-137 (HK L-137) has been suggested to enhance the intestinal barrier in obese mice, leading to improvement of metabolic abnormalities and adipose tissue inflammation, and in healthy humans with overweight, leading to improvement of systemic inflammation. However, its detailed mechanism of action has not been clarified. Therefore, this study investigated the effects of HK L-137 on the permeability of rat small intestinal epithelial IEC-6 cells, tight junction-related gene and protein expression and localization, and intracellular signaling pathways involved in barrier function. Treatment of IEC-6 cells with HK L-137 for 26 h significantly reduced the permeability to fluorescein isothiocyanate-dextran (FD-4). HK L-137 also increased gene and protein expression of zonula occludens-1 (ZO-1), an important tight junction protein, without affecting the localization. Furthermore, inhibition of the extracellular signal-regulated kinase (ERK)1/2 pathway in IEC-6 cells canceled the HK L-137-related reduction in permeability to FD-4. Phosphorylation of ERK in IEC-6 cells was induced 15 min after the addition of HK L-137. These results suggest that HK L-137 reduces intestinal permeability partly through activating the ERK pathway and increasing expression of the ZO-1 gene and protein. Enhancement of intestinal barrier function with HK L-137 might be effective in preventing and treating leaky gut, for which no specific therapeutic tool has been established.

Effects of β-mannanase supplementation on intestinal health and growth of nursery pigs

Two experiments were conducted using 120 pigs to test the hypothesis that supplementation of β-mannanase could reduce digesta viscosity, enhance nutrient digestion, and improve intestinal health and growth of nursery pigs. In experiment 1, 48 crossbred barrows were randomly allotted to four treatments with increasing levels of β-mannanase at 0, 200, 400, and 600 U/kg in feeds. All pigs were euthanized on day 12 to collect jejunal digesta to measure digesta viscosity and ileal digesta to measure apparent ileal digestibility (AID) of dry matter (DM), gross energy (GE), neutral detergent fiber (NDF), and acid detergent fiber (ADF). In experiment 2, 72 nursery pigs were randomly allotted to three treatments with increasing levels of β-mannanase at 0, 400, and 600 U/kg in feeds. Plasma collected on day 9 was used to measure tumor necrosis factor-α (TNF-α), immunoglobulin G (IgG), malondialdehyde (MDA), and protein carbonyl (PC). All pigs were euthanized on day 10 to collect duodenal and jejunal tissues to evaluate the production of TNF-α, IL-6, and MDA, morphology, crypt cell proliferation, and expression of tight junction proteins in the jejunum. Data were analyzed using the MIXED procedure for polynomial contrasts and the NLMIXED procedure for broken-line analysis of SAS. In experiment 1, β-mannanase supplementation tended to have quadratic effects on digesta viscosity (P = 0.085) and AID of GE (P = 0.093) in the pigs. In experiment 2, jejunal digesta viscosity of the pigs was reduced (P < 0.05) when β-mannanase was supplemented at 360 U/kg of feed. β-Mannanase supplementation linearly reduced (P < 0.05) TNF-α, IgG, MDA, and PC in the duodenum, and TNF-α, IgG, and MDA in the jejunum of the pigs. β-Mannanase supplementation linearly increased (P < 0.05) villus height to crypt depth ratio and crypt cell proliferation in the jejunum. β-Mannanase supplementation tended to linearly improve (P = 0.083) expression of zonula occludens-1 in the jejunum. In conclusion, supplementation of β-mannanase at 360 U/kg reduced the digesta viscosity and up to 600 U/kg positively affected intestinal health and growth of pigs by reducing inflammation and oxidative stress whilst enhancing structure and barrier function in the jejunum.

Modulating a prebiotic food source influences inflammation and immune-regulating gut microbes and metabolites: insights from the BE GONE trial

BACKGROUND

Accessible prebiotic foods hold strong potential to jointly target gut health and metabolic health in high-risk patients. The BE GONE trial targeted the gut microbiota of obese surveillance patients with a history of colorectal neoplasia through a straightforward bean intervention.

METHODS

This low-risk, non-invasive dietary intervention trial was conducted at MD Anderson Cancer Center (Houston, TX, USA). Following a 4-week equilibration, patients were randomized to continue their usual diet without beans (control) or to add a daily cup of study beans to their usual diet (intervention) with immediate crossover at 8-weeks. Stool and fasting blood were collected every 4 weeks to assess the primary outcome of intra and inter-individual changes in the gut microbiome and in circulating markers and metabolites within 8 weeks. This study was registered on ClinicalTrials.gov as NCT02843425, recruitment is complete and long-term follow-up continues.

FINDINGS

Of the 55 patients randomized by intervention sequence, 87% completed the 16-week trial, demonstrating an increase on-intervention in diversity [n = 48; linear mixed effect and 95% CI for inverse Simpson index: 0.16 (0.02, 0.30); p = 0.02] and shifts in multiple bacteria indicative of prebiotic efficacy, including increased Faecalibacterium, Eubacterium and Bifidobacterium (all p < 0.05). The circulating metabolome showed parallel shifts in nutrient and microbiome-derived metabolites, including increased pipecolic acid and decreased indole (all p < 0.002) that regressed upon returning to the usual diet. No significant changes were observed in circulating lipoproteins within 8 weeks; however, proteomic biomarkers of intestinal and systemic inflammatory response, fibroblast-growth factor-19 increased, and interleukin-10 receptor-α decreased (p = 0.01).

INTERPRETATION

These findings underscore the prebiotic and potential therapeutic role of beans to enhance the gut microbiome and to regulate host markers associated with metabolic obesity and colorectal cancer, while further emphasizing the need for consistent and sustainable dietary adjustments in high-risk patients.

FUNDING

This study was funded by the American Cancer Society.

Immunostimulating Commensal Bacteria and Their Potential Use as Therapeutics

The gut microbiome is intimately intertwined with the host immune system, having effects on the systemic immune system. Dysbiosis of the gut microbiome has been linked not only to gastrointestinal disorders but also conditions of the skin, lungs, and brain. Commensal bacteria can affect the immune status of the host through a stimulation of the innate immune system, training of the adaptive immune system, and competitive exclusion of pathogens. Commensal bacteria improve immune response through the production of immunomodulating compounds such as microbe-associated molecular patterns (MAMPs), short-chain fatty acids (SCFAs), and secondary bile acids. The microbiome, especially when in dysbiosis, is plastic and can be manipulated through the introduction of beneficial bacteria or the adjustment of nutrients to stimulate the expansion of beneficial taxa. The complex nature of the gastrointestinal tract (GIT) ecosystem complicates the use of these methods, as similar treatments have various results in individuals with different residential microbiomes and differential health statuses. A more complete understanding of the interaction between commensal species, host genetics, and the host immune system is needed for effective microbiome interventions to be developed and implemented in a clinical setting.

Protective Effects of Alginate and Chitosan Oligosaccharides against Clostridioides difficile Bacteria and Toxin

Clostridioides difficile infection is expected to become the most common healthcare-associated infection worldwide. C. difficile-induced pathogenicity is significantly attributed to its enterotoxin, TcdA, which primarily targets Rho-GTPases involved in regulating cytoskeletal and tight junction (TJ) dynamics, thus leading to cytoskeleton breakdown and ultimately increased intestinal permeability. This study investigated whether two non-digestible oligosaccharides (NDOs), alginate (AOS) and chitosan (COS) oligosaccharides, possess antipathogenic and barrier-protective properties against C. difficile bacteria and TcdA toxin, respectively. Both NDOs significantly reduced C. difficile growth, while cell cytotoxicity assays demonstrated that neither COS nor AOS significantly attenuated the TcdA-induced cell death 24 h post-exposure. The challenge of Caco-2 monolayers with increasing TcdA concentrations increased paracellular permeability, as measured by TEER and LY flux assays. In this experimental setup, COS completely abolished, and AOS mitigated, the deleterious effects of TcdA on the monolayer's integrity. These events were not accompanied by alterations in ZO-1 and occludin protein levels; however, immunofluorescence microscopy revealed that both AOS and COS prevented the TcdA-induced occludin mislocalization. Finally, both NDOs accelerated TJ reassembly upon a calcium-switch assay. Overall, this study established the antipathogenic and barrier-protective capacity of AOS and COS against C. difficile and its toxin, TcdA, while revealing their ability to promote TJ reassembly in Caco-2 cells.

Specific Human Milk Oligosaccharides Differentially Promote Th1 and Regulatory Responses in a CpG-Activated Epithelial/Immune Cell Coculture

Proper early life immune development creates a basis for a healthy and resilient immune system, which balances immune tolerance and activation. Deviations in neonatal immune maturation can have life-long effects, such as development of allergic diseases. Evidence suggests that human milk oligosaccharides (HMOS) possess immunomodulatory properties essential for neonatal immune maturation. To understand the immunomodulatory properties of enzymatic or bacterial produced HMOS, the effects of five HMOS (2'FL, 3FL, 3'SL, 6'SL and LNnT), present in human milk have been studied. A PBMC immune model, the IEC barrier model and IEC/PBMC transwell coculture models were used, representing critical steps in mucosal immune development. HMOS were applied to IEC cocultured with activated PBMC. In the presence of CpG, 2'FL and 3FL enhanced IFNγ (p < 0.01), IL10 (p < 0.0001) and galectin-9 (p < 0.001) secretion when added to IEC; 2'FL and 3FL decreased Th2 cell development while 3FL enhanced Treg polarization (p < 0.05). IEC were required for this 3FL mediated Treg polarization, which was not explained by epithelial-derived galectin-9, TGFβ nor retinoic acid secretion. The most pronounced immunomodulatory effects, linking to enhanced type 1 and regulatory mediator secretion, were observed for 2'FL and 3FL. Future studies are needed to further understand the complex interplay between HMO and early life mucosal immune development.