Investigation of the regulatory mechanism of lijie capsules on gut microbiota in rheumatoid arthritis

Lijie Capsules (LJJN) are a classical Chinese herbal formula adopted to treat rheumatoid arthritis (RA) clinically, yet the regulatory mechanism underlying the protection of LJJN against RA has not been fully elucidated. Here, the animal model of RA was established by complete Freund's adjuvant administration in mice. About 60 mg/ml of LJJN was used for treatment. The histological change of ankle joint was measured by hematoxylin and eosin staining. The inflammatory cytokines were detected using ELISA kits. The protein associated with inflammation and GLUD2 was detected using Western blot. The mice feces were analyzed by 16S rRNA sequencing. The levels of glutamate (Glu) and alpha-ketoglutarate (alpha-KG) were detected using their detection kits. In addition, fibroblast-like synoviocytes (FLSs) were stimulated by Glu to induce an injured synoviocytes model in vitro, with or without LJJN treatment for 48 h. It was demonstrated that LJJN alleviated ankle joint swelling and synovial injury in RA mice. Meanwhile, LJJN inactivated nuclear factor kappa B signaling and suppressed inflammation of RA mice. The disordered gut microbiota composition in RA mice was partly restored by LJJN. Bacteroides-mediated Glu metabolism was impacted in RA mice, and LJJN contributed to the conversion of Glu to alpha-KG in RA mice. In addition, the in vitro results revealed that LJJN could block Glu-induced inflammation in FLSs but had no direct influence on alpha-KG and GLUD2 levels. In summary, LJJN exerted a protective role against ankle joint injury and inflammation in RA, which might be partly associated with gut microbiota-mediated Glu metabolism.