It is well known that dental pulp tissue can evoke some of the most severe acute inflammation observed in the human body. We found that dental pulp cells secrete a factor that induces tumor necrosis factor-α production from macrophages, and designated this factor, dental pulp cell-derived powerful inducer of TNF-α (DPIT). DPIT was induced in dental pulp cells and transported to recipient cells via microvesicles. Treatment of dental pulp cells with a PKR inhibitor markedly suppressed DPIT activity, and weak interferon signals were constitutively activated inside the cells. In recipient macrophages, stimulation with DPIT-containing supernatants from pulp cells resulted in activation of both nuclear factor-κB and MAP kinases like JNK and p38. Proteomics analyses revealed that many stress granule-related proteins were present in supernatants from dental pulp cells as well as microvesicle marker proteins like GAPDH, β-actin, HSPA8, HSPB1, HSPE1, and HSPD1. Furthermore, giant molecule AHNAK and PKR were detected in microvesicles derived from dental pulp cells, and gene silencing of AHNAK in dental pulp cells led to reduced DPIT activity. Thus, it appeared that the core protein of DPIT was PKR, and that PKR was maintained in an active state in stress granule aggregates with AHNAK and transported via microvesicles. The activity of DPIT for TNF-α induction was far superior to that of gram-negative bacterial endotoxin. Therefore, we, report for the first time, that active PKR is transported via microvesicles as stress granule aggregates and induces powerful inflammatory signals in macrophages.

Background: Older people are more susceptible to deterioration of the gut microbiota. Prebiotics help improve the gut microbiota. Inulin, a major prebiotic, stimulates the growth of Bifidobacterium; however, it produces a large amount of gas, which leads to abdominal symptoms. Methods: In this study, in vitro fecal fermentation was performed using fecal samples from seven older people (mean subject age, 73.4 years; five men and two women) to examine whether combining inulin with another prebiotic material, resistant dextrin, could lead to decreased gas production and show prebiotic effects. Results: The Bifidobacterium counts and short-chain fatty acid production did not differ significantly between the inulin 0.5% group and the inulin 0.25% plus resistant dextrin 0.25% combination group. However, the inulin 0.25% plus resistant dextrin 0.25% combination group had lower gas production than the inulin 0.5% group (p < 0.10). Furthermore, compared with the inulin 0.5% group, the 0.25% combination group showed significantly greater gut microbiota diversity and tended toward a lower pH in the fermentation medium at the end of fermentation (p = 0.09). These effects are believed to be due to the combination of inulin, which is highly selective for Bifidobacterium and rapidly utilized by the gut microbiota, and resistant dextrin, which is slowly utilized by various bacterial genera. Conclusions: These findings suggest that the inulin plus resistant dextrin combination has superior prebiotic effects in older people and causes less gas production than inulin alone.

Background/objectives: Aging-related dysbiosis is associated with increased production of harmful gut-derived metabolites. Reducing these metabolites by modulating the gut microbiota is important for maintaining health in older adults. This study aimed to investigate whether a combination of resistant dextrin and inulin suppresses the production of harmful metabolites in the gut microbiota of older adults using in vitro fecal fermentation and a metabolomics approach. Methods: Fecal samples from eight older adults were fermented with resistant dextrin, inulin, their combination, or no saccharides as a control. Potentially harmful metabolites in the fermentation supernatants were assessed by metabolomic analysis. Trimethylamine production was verified by the fecal fermentation with a choline-supplemented medium. Results: The combination group showed a decreasing trend in the production of deoxycholic acid, kynurenine, and trimethylamine compared with the control group. Assessment of trimethylamine production using a choline-supplemented medium revealed that the combination group had a higher proportion of fecal samples with low trimethylamine production (3 of 8 samples) than either prebiotic-alone group. Conclusion: Combining resistant dextrin and inulin could reduce the production of some harmful metabolites by the gut microbiota in older adults.