In this study, we have performed that the flavonoid component taxifolin modulated inflammatory response in FCA-induced RA rats. The changes in PV, AI score, and BW have been classically used for evaluating the anti-inflammatory and anti-arthritic effects of certain treatments on RA. We found that taxifolin ameliorated the pathological symptoms of FCA-induced RA rats. Similarly, the spleen and thymus coefficients significantly decreased in taxifolin groups. And the rats in each treatment group showed alleviation of bone destruction and inflammatory cell infiltration in the left hind paw after treatment. The MCP-1, TNF-α, IL-12 and IL-17 expression levels all significantly decreased as the taxifolin dosage increased. IL-8 is a classical prototypical chemokine and responsible for inducing chemotaxis, which directly migrates cells to the inflammatory site. In this study, our results showed that because inflammatory responses were gradually improved in all treatment groups, the IL-8 expression level in plasma returned to normal state.
RA is a T cell-dependent disease; thus, increasing efforts have focused on understanding the phenotype and function of CD4+ T cells in rheumatoid inflammation. Th1 and Th2 cells, two important subtypes of CD4+ Th cells, are associated with RA. Research shows that Th1 effector cells initiate cellular immune responses through proinflammatory cytokines such as IFN-γ, while Th2 cells can produce several types cytokines (e.g., IL-4, IL-10, IL-13 etc.) that are required for humoral immunity. Furthermore, Th1 and Th2 cytokine gene expression is regulated by T-bet and GATA-3, two major Thspecific transcription factors that play a central role in Th cell differentiation. Our results demonstrated that the mechanism of action of taxifolin in the plasma of FCA-induced rats may involve humoral immunity. By contrast, the mode of action in the spleen tissue may involve cellular immune response. Further, the spleen may play a regulatory function on Th1/Th2 cells, but not thymus tissue. Therefore, the spleen plays a crucial role in this study. Taken together, taxifolin exhibited immunoregulatory effect of Th1/Th2 in a dose-dependent manner in vivo.
In the successfully activated Jurkat T cells, the cells mostly polarized into Th1 status; however, this extreme pathological shift was reversed by taxifolin as the dosage increased, suggesting that taxifolin can correct Th1 cell polarization in vitro. These results were in good agreement with previous conclusion of Th1/Th2 phenomenon in the plasma. Combining these in vivo and in vitro results, taxifolin had potential immunomodulatory effects.
The activated sensor protein NLRP3, which triggered ASC through the pyrin domain structure (PYD), and then the CARD domain in ASC recruited the CARD domain in pro-caspase-1 to form the NLRP3–ASC–caspase-1 complex, subsequently secreting IL-1β and IL-18, which plays a malignant role in the development of inflammatory and immune responses. For example, a previous study on a spontaneous arthritis mouse model demonstrated that the pathology of arthritis may be associated with the NLRP3 inflammasome/IL1β axis . In this study, the NLRP3, ASC, caspase-1 expression levels all dramatically increased after the inducement of PHA, and suggest that this NLRP3 inflammasome were activated in vitro. However, taxifolin reduced NLRP3, ASC, caspase-1 expression levels, revealing that taxifolin may exhibited anti-inflammation effect through NLRP3 inflammasome. Simultaneously, ROS accumulation, which is also involved with the NLRP3 inflammasome[6, 1], was also investigated. Our results showed that taxifolin and NAC both reduced the IL-1β and IL-18 expression levels and ROS activity in vitro. These findings demonstrated that the anti-inflammation mechanism of action of taxifolin involved the NLRP3 inflammasome in vitro.
In conclusion, our study demonstrated the Th1/Th2 status plays a significant role in the pharmacologic activity of taxifolin in the FCA-induced RA rats. Further, this study confirmed the role of taxifolin in correcting the activated of NLRP3 inflammasome axis in the classical Jurkat T cell model in vitro. Our findings also corroborate previously published data and validate that taxifolin has both antioxidant and immunomodulatory effects, providing the basis for the development of new drugs for RA treatment with traditional Chinese medicine. Naturally, the specific mechanism of taxifolin improving NLRP3 remains to be further studied and clarified.