The mechanism of a humid climate on the joints of normal rats and collagen- induced arthritis rats: mutual effects on faecal metabolism and microbial diversity

Abstract

Abstract Studies have shown that high humidity is a condition that aggravates the pain of rheumatoid arthritis (RA), but the relevant mechanism is controversial. Currently, there is a lack of animal experimental studies on high humidity as an adverse factor related to the pathogenesis of RA. We used healthy SD rats and collagen-induced arthritis (CIA) rats to investigate the effects of high humidity on arthritis in healthy rats and CIA rats. Integrated metabolomics analyses of faeces and 16S rRNA sequencing of the faecal microbiota were performed to comprehensively analyse the results and diversity of the faecal microbiota and metabolites in healthy rats and CIA rats. In this study, high humidity aggravated arthritis in CIA rats, including articular cartilage lesions, arthritis scores, and proinflammatory cytokines. High humidity had a certain effect on articular cartilage extent, arthritis score and proinflammatory cytokines of healthy rats. Furthermore, high humidity caused significant changes in faecal microbes and faecal metabolites in healthy and CIA rats. Sequencing of the 16S rRNA unit in faecal samples showed that high humidity aggravated inflammation-related bacteria in healthy and CIA rats. Faecal metabolomics results showed that high humidity significantly altered faecal metabolites in healthy rats and CIA rats, and the changes in biological functions were mainly related to the inflammatory response and oxidative stress. Combined analysis showed that there was a strong correlation between the faecal microbiota and faecal metabolites. High humidity is an adverse factor for the onset and development of RA, and its mechanism is related to the inflammatory response and oxidative stress. However, how high humidity leads to the pathogenesis of RA needs to be further determined.