Dissecting Causal Relationships Between Gut Microbiota, 1400 Blood Metabolites, and Intervertebral Disc Degeneration

The precise mechanisms driving intervertebral disc degeneration (IVDD) development remain unclear, but evidence suggests a significant involvement of gut microbiota (GM) and blood metabolites. We aimed to investigate the causal relationships between GM, IVDD, and blood metabolites using Mendelian randomization (MR) analysis.

We utilized the summary statistics of GM from the MiBioGen consortium, 1400 blood metabolites from the genome-wide association studies (GWAS) Catalog, and IVDD data from the FinnGen repository, which are sourced from the largest GWAS conducted to date. Employing bidirectional MR analyses, we investigated the causal relationships between GM and IVDD. Additionally, we conducted 2 mediation analyses, 2-step MR and multivariable MR (MVMR), to identify potential mediating metabolites.

Five bacterial genera were causally associated with IVDD, while IVDD did not show a significant causal effect on GM. In the 2-step MR analysis, Eubacteriumfissicatenagroup, RuminococcaceaeUCG003, Lachnoclostridium, and Marvinbryantia genera, along with metabolites X-24949, Pimeloylcarnitine/3-methyladipoylcarnitine (C7-DC), X-24456, histidine, 2-methylserine, Phosphocholine, and N-delta-acetylornithine, were all significantly associated with IVDD (all p < 0.05). MVMR analysis revealed that the associations between Eubacteriumfissicatenagroup genus and IVDD were mediated by X-24949 (8.1%, p = 0.024); Lachnoclostridium genus and IVDD were mediated by histidine (18.1%, p = 0.013); and RuminococcaceaeUCG003 genus and IVDD were mediated by C7-DC (-7.5%, p = 0.041).

The present MR study offers evidence supporting the causal relationships between several specific GM taxa and IVDD, as well as identifying potential mediating metabolites.