Er Miao San Attenuates Collagen-Induced Arthritis Mice by Regulating Gut Microbiota and Its Metabolites

Dysbiosis of the gut microbiota plays a key role in the pathogenesis of rheumatoid arthritis (RA). However, it is still unclear whether the classic prescription Er Miao San (EMS) can exert therapeutic effects on RA by regulating the gut microbiota. In this study, we investigated whether EMS alleviates collagen-induced arthritis (CIA) by modulating the gut microbiota and its metabolites. We demonstrated that EMS significantly reduced arthritis severity, paw swelling, and systemic inflammation in CIA mice. In addition, 16S rRNA sequencing analysis revealed that EMS restored gut microbiota homeostasis, as evidenced by an increased abundance of Bacteroidetes, and a decreased Bacteroidetes/Firmicutes ratio. Crucially, antibiotic depletion of the gut microbiota abolished the protective effects of EMS, whereas fecal microbiota transplantation (FMT) from EMS-treated donors replicated its anti-arthritic efficacy, confirming the indispensable role of the microbiota. Measurement of short-chain fatty acids (SCFAs) further revealed a significant increase in the microbial metabolite butyrate following EMS treatment. Subsequent supplementation with sodium butyrate mimicked the therapeutic effects of EMS, ameliorating joint inflammation and cartilage damage. Mechanistically, butyrate enhanced the expression of intestinal tight junction proteins (ZO-1 and occludin), thereby restoring intestinal barrier integrity. Collectively, our results demonstrate that EMS exerts its anti-arthritic effects by modulating the gut microbiota-butyrate-intestinal barrier axis, highlighting the critical value of microbial metabolites in RA treatment. This study provides novel insights into the mechanism of EMS and suggests the therapeutic potential of butyrate for RA.