Methotrexate promotes recovery of arthritis-induced alveolar bone loss and modifies the composition of the oral-gut microbiota

The impact of rheumatoid arthritis (RA) on the shaping of the oral and gut microbiome raises the question of whether and how RA treatment modifies microbial communities. We examined changes in the oral and gut microbiota in a mouse model of antigen-induced arthritis (AIA) treated or not with methotrexate (MTX). Maxillae and stools were evaluated by the MiSeq platform of the V4 region of the 16S rRNA gene. Alveolar bone parameters were analysed by micro-computed tomography. Moreover, arthritis-induced changes in hyperalgesia and oedema were assessed, along with the impact on periodontal bone health. Microbial communities in MTX-treated AIA mice revealed distinct clusters compared to the control and AIA groups. Overall, MTX impacted the richness and variability of microorganisms in the oral-gut axis microbiome at the phylum level. Regarding the oral microbiome, while in the control group the most dominant phylum was Firmicutes, in the AIA group there was a shift towards the predominance of Campilobacteriota and Bacteroidetes associated with the disease. MTX treatment led to greater dominance of the health-associated phylum Proteobacteria. In the gut microbiome, AIA induction resulted in increased abundance of the Verrucomicrobiota phylum, and MTX treatment restored its levels compared to control. Importantly, the MTX-treated AIA animals had significantly less periodontal bone loss, as well as decreased hyperalgesia and joint oedema compared to the AIA animals. Data suggest the benefit of MTX treatment in protecting alveolar bone, in addition to providing new insights on the drug-microbiome interaction in the course of RA.