Fuzi alleviates cold-related rheumatoid arthritis via regulating gut microbiota and microbial bile acid metabolism

Abstract Background Rheumatoid arthritis (RA) with cold pattern is an important type of RA according to the theory of traditional Chinese medicine. Fuzi (also known as the lateral roots of Aconitum carmichaelii Debx.) represents a typical traditional Chinese medicine that has been clinically used for treatment of the RA especially cold-related RA for thousands of years, yet its mechanism remains unknown. Purpose The purpose of the research was to study the therapeutic effects of Fuzi on cold-related RA, and to investigate the mechanism of its action. Methods Here, we investigated the pharmacological effects of Fuzi on cold-related RA using micro-CT, histopathological analysis, and inflammatory cytokine test. Then, a gut microbiota composition analysis in combination with fecal microbiota transplantation were used to confirm the role of gut microbiota in the therapeutic effects of Fuzi. Further, targeted bile acid metabolomics was used to screen the possible differential microbial bile acids involved in the mechanism of Fuzi. In vitro bioactivity analysis of differential bile acids was used to assess their anti-inflammation activity. Finally, western blot was used to investigate the signaling pathways of Fuzi in reducing the inflammation of cold-related RA. Results The results showed that Fuzi alleviates cold-related RA by improving arthritis index, paw swelling, bone damage, and inflammatory cytokines. In addition, the ameliorative effect of Fuzi is dependent on gut microbiota such as the taxa Lachnospiraceae and Ruminococcaceae. Targeted analysis of fecal and serum bile acids showed that TCA and THDCA were the main differential metabolites. In vitro, TCA and THDCA showed anti-inflammation effects on RAW264.7 cells. Western blot showed that Fuzi regulates TGR5-cAMP-PKA signaling and NLRP3 inflammasome to reduce cold-related arthritis. Conclusion Overall, our results demonstrated that Fuzi could regulate gut microbiota and microbial bile acid metabolism, the microbial metabolite THDCA acts on TGR5-cAMP-PKA signaling pathway and NLRP3 inflammasome to reduce cold-related arthritis. Our study suggests that supplementation of Fuzi or THDCA can be of great value for the prevention and clinical treatment of cold-related RA. Graphical Abstract