Regulation of gut microbiota substantially contributes to the induction of intestinal Treg cells and consequent anti-arthritis effect of madecassoside.

Previously, we reported that oral administration of madecassoside, the main active triterpene in Centella asiatica L., exerted anti-arthritis effect by inducing the generation of regulatory T (Treg) cells in small intestine. This study investigates the action site and mechanism of madecassoside to induce Treg cells. In collagen-induced arthritis (CIA) of rats, oral administration of madecassoside significantly alleviated arthritis symptoms, but its main metabolite madecassic acid did not, suggesting that madecassoside functions in the parent form. Madecassoside was shown to increase the number of Treg cells and promote the expression of Foxp3 and IL-10 in rat ileum rather than duodenum and jejunum, as detected using the immunohistochemistry assay and quantitative PCR assay, respectively. Unexpectedly, madecassoside was absent of significant effect on in vitro Treg cell differentiation and the expression of Foxp3 and IL-10. A combined use of broad-spectrum antibiotics resulted in significant reduction of the anti-arthritis effect of madecassoside in CIA rats. The 16S rRNA gene sequence showed that madecassoside could reverse the changes of gut microbiota under arthritis condition, and enrich several bacteria such as Lachnospiraceae, Butyricicoccus, Faecalibacterium, Butyricicoccus pullicaecorum and so on. GC-MS assay showed that madecassoside elevated the levels of acetic acid and butyric acid, but not other short chain fatty acids (SCFAs) in the cecum contents of CIA rats. Butyric acid rather than acetic acid could induce the in vitro differentiation of Treg cells and the expression of Foxp3 and IL-10. Accordingly, when madecassoside was co-administered with heptanoyl CoA, the competitive inhibitor of butyrate synthase, its effect on butyric acid production, Treg cell proportion and arthritis nearly disappeared. These findings indicate that oral madecassoside induces the generation of Treg cells and therefore displays anti-arthritis effect in the parent form but not metabolites, and the ileum is the main action site. The mechanism of madecassoside can be summarized as: expansion of the richness of butyrate-producing bacteria-up-regulation of intestinal butyrate level-induction of Treg cell differentiation and IL-10 expression.

The gut microbiota modulator berberine ameliorates collagen-induced arthritis in rats by facilitating the generation of butyrate and adjusting the intestinal hypoxia and nitrate supply.

The commensal microbiota is one of the environmental triggers of rheumatoid arthritis (RA). Recent studies have identified the characteristics of the gut microbiota in patients with RA. However, it is still unclear how the microbiota can be modulated to slow down disease progression. In the present study, berberine, a modulator of gut microbiota with substantial anti-RA effect, was chosen to explore the mechanisms by which the microbiota modulators ameliorate RA. The results showed that oral administration of berberine alleviated collagen-induced arthritis (CIA) in rats in a gut microbiota-dependent manner. Berberine down-regulated the diversity and richness of the gut bacteria, reduced the abundance of Prevotella, and elevated the abundance of butyrate-producing bacteria in CIA rats as determined by the 16S rRNA gene sequence, which might function through limiting the generation of nitrate and stabilizing the physiologic hypoxia in the intestine. Moreover, berberine treatment significantly increased the intestinal butyrate level and promoted the expression and activity of butyryl-CoA:acetate-CoA transferase (BUT). The coadministration of a BUT inhibitor largely diminished the adjustment of intestinal environment and the antiarthritic effect of berberine. In conclusion, modulators of the gut microbiota might serve as therapeutic agents for RA by inducing the butyrate generation through promoting the expression and activity of BUT.-Yue, M., Tao, Y., Fang, Y., Lian, X., Zhang, Q., Xia, Y., Wei, Z., Dai, Y. The gut microbiota modulator berberine ameliorates collagen-induced arthritis in rats by facilitating the generation of butyrate and adjusting the intestinal hypoxia and nitrate supply.