Plasma Sphingomyelin Levels Mediate the Causal Relationship Between Gut Microbiota and Myocardial Interstitial Fibrosis: A Mendelian Randomization Study

BACKGROUND: Prior studies established associations between gut microbiota and myocardial interstitial fibrosis. Nevertheless, the causal relationships and potential intermediaries remain unknown. Thus, we employed a Mendelian randomization strategy to explore whether gut microbiota causally influence myocardial interstitial fibrosis and to assess whether plasma metabolites serve as potential intermediaries in this pathway. METHODS: A two-sample Mendelian randomization approach was performed, utilizing genome-wide association studies to examine the causal relationship between gut microbiota (n= 18,340) and myocardial interstitial fibrosis (n=41,505). Additionally, an investigation was conducted to determine the potential mediation by four plasma metabolites (n=8,299) via a two-step Mendelian randomization analysis. Inverse variance weighted method was the primary method employed in Mendelian randomization, and complementary analyses were conducted alongside to enhance the robustness of the results. RESULTS: Mendelian randomization analysis indicated suggestive associations of three microbial taxa with myocardial interstitial fibrosis. The most significant taxon was the genus Faecalibacterium (β [SE], -0.1272 [0.0347], P = 0.0002). Reverse Mendelian randomization analyses revealed no evidence of myocardial interstitial fibrosis affecting these three microbial taxa. In the two-step Mendelian randomization analysis involving four plasma metabolites, it was found that plasma sphingomyelin levels mediated the causal effects of genus Faecalibacterium on myocardial interstitial fibrosis (proportion mediated = 14.2%, 95% CI = 1.4-27.0%). CONCLUSION: The study validates the causality between particular gut microbial taxa and myocardial interstitial fibrosis, and suggests that plasma sphingomyelin might mediate this association. These findings offer a novel perspective on myocardial interstitial fibrosis prevention, and underscore the significance of plasma sphingomyelin in human health and disease.