Background
Ulcerative colitis (UC) is a chronic inflammatory bowel disease with a multifactorial etiology, including genetic, immunological, and environmental factors, as well as alterations in the gut microbiome and plasma metabolites. The interplay between these factors is complex and not fully elucidated, particularly regarding the potential mediation of metabolites in the relationship between gut microbiota and UC.
Methods
We performed a Mendelian randomization (MR) study to investigate the causal associations between gut microbiota, plasma metabolites, and UC. The study utilized a two-sample MR approach to discern causal relationships among these factors. Genetic variants from genome-wide association studies (GWAS) served as instrumental variables (IVs) in the MR analyses, conducted using the “TwoSampleMR” package in R software. We adhered to the fundamental assumptions of MR analyses, ensuring the validity of our causal inferences. Additionally, we incorporated a mediation analysis to assess the potential mediating role of plasma metabolites in the relationship between gut microbiota and UC.
Results
Our study identified significant associations between specific gut microbial taxa and the risk of UC. We found that six microbial taxa, including Genus Dorea, Phylum Proteobacteria, Species Streptococcus parasanguinis, Species Ruminococcus obeum, Species Roseburia intestinalis, and Order Lactobacillales, were causally associated with UC. Seventy-three metabolites and metabolite ratios were also causally associated with UC, with mediation analysis revealing that metabolites such as Stearoylcarnitine, 3-hydroxyoctanoylcarnitine, 1-arachidonoyl-GPE (20:4n6), 3-(3-hydroxyphenyl)propionate sulfate, and Thioproline mediated the effects of gut microbiota on UC, suggesting a role for these metabolites in the disease's pathogenesis.
Conclusion
This MR study provides evidence for causal relationships between specific gut microbiota and UC, with plasma metabolites potentially mediating these effects. The findings offer new perspectives on the causal nexus between the gut microbiota, plasma metabolites, and UC, suggesting potential intervention targets for the disease. Further research is warranted to validate these results and to explore the underlying mechanisms.