| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 105 === Gut-associated lymphoid tissue (GALT) represents approximately 70 % of the entire immune system, and it is the main route of contact with the external antigens. Therefore, regulation of immune response and tolerance of gut mucosal immune system is essential for promoting systemic immune balance. Radix Astragali is an important traditional Chinese medicine widely used in regulating immune system, and it is also approved by the Ministry of Health and Welfare to be used as a food ingredient due to its safety. Since fermentation is often used for processing Chinese herbal medicine to enhance its bioactivity. In this study, we fermented Radix Astragali by using Bifidobacterium infantis (BCRC14602), B. adolescentis (BCRC14606), B. bifidum (BCRC14615), B. longum (BCRC14634) and B. animalis subsp. Lactis (BB-12) to get fermented Radix Astragali (FRA) in comparison with non-fermented Radix Astragali (NRA). The purpose of this study was to investigate whether the gut mucosal immunomodulatory activity of Radix Astragali can be improved by fermentation. In respect of non-specific immunity, the expression of NF-κB in RAW 264.7 was significantly enhanced by BCRC 14615, 14634 and BB-12 FRA compared with NRA, and FRA had a better inhibitory effect on LPS-induced NO production. Then we used differentiated Caco-2 cells to mimic small intestinal epithelial cells. Results showed that BCRC 14606 and BB-12 FRA could significantly increase transepithelial electrical resistance (TEER) without influening cell growth. It appeared that BCRC 14606 and BB-12 FRA can promote tight junction between Caco-2 cells thus enhance the intestinal barrier function. On the other hand, we found that NRA, BCRC 14606 FRA and BB-12 FRA could inhibit the expression of MHC II and co-stimulatory molecules (CD40, CD80, CD86) on THP-1 induced immature dendritic cells, which in term limit the maturation of dendritic cells and prevent the activation of adaptive immune responses. We further constructed an in vitro co-culture model using differentiated Caco-2 cells and THP-1 induced immature dendritic cells. We found that the dendritic cells in the environment of polarized epithelial cells had a higher tolerance, thus the co-culture model is more similar to human gut mucosal immune environment. In this co-culture model, NRA, BCRC 14606 FRA and BB-12 FRA could induce dendritic cells to yield immune tolerance in normal physiological state and inhibit the expression of MHC II, co-stimulatory molecules and pro-inflammatory cytokines (IL-1β and IL-6), which keeps dendritic cells in immature state and prevents the activation of adaptive immune responses. As a result, the fermentation samples we used can restore the immune homeostasis of gut mucosa. Finally, by the analyses of the active compontents of NRA and FRA, we found that the Bifidobacterium spp. could transform the high polarity compounds in Radix Astragali and increase the content of low polarity compounds such as astragalus saponins (asrtragaloside I-IV), and thus enhanced the gut mucosal immunoregulatory activity of Radix Astragali. In conclusion, our Radix Astragali fermentation products may have the potential to be a dietary supplement for gut mucosal immunoregulation. In the future, we should conduct more analyses and compared the changes in the active ingredients before and after fermentation, thus we may be able to identify the key compounds in fermented Radix Astragali, which have gut mucosal immunomodulatory activity.
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