| Sumario: | Background It is crucial to pinpoint the metabolites that cause Crohn's disease (CD) and ulcerative colitis (UC) to comprehend their pathogenesis and identify possible targets for therapy. To achieve this goal, we performed the first metabolome-wide Mendelian randomization (MR) study of Japanese patients with CD and UC. Methods As exposure datasets, genetic instruments with blood-circulating metabolites were obtained from the Tohoku Medical Megabank Organization, which includes 204 metabolites from the genome-wide association study data of 7843 Japanese individuals. As outcome datasets, we enrolled Japanese patients with CD (n = 1803), Japanese patients with UC (n = 1992), and healthy controls (n = 2022). The main analysis utilized the inverse variance–weighted method, while stability of the findings was evaluated through sensitivity analyses. Results After single nucleotide polymorphism (SNP) filtering, 169 SNPs for 45 metabolites were available for MR. Genetically predicted elevated circulating trans-glutaconic acid and tryptophan were associated with a lower CD risk (odds ratio [OR], 0.68; P = 5.95 × 10−3; and OR, 0.64; P = 1.90 × 10−2, respectively). Genetically predicted elevated caffeic acid was associated with a lower UC risk (OR, 0.67; P = 4.2 × 10−4), which remained significant after multiple testing correction. We identified a causal link between UC and 3-hydroxybutyrate (OR, 2.21; P = 1.41 × 10−2), trans-glutaconic acid (OR, 0.72; P = 1.77 × 10−2), and 2-hydroxyvaleric acid (OR, 1.31; P = 4.23 × 10−2). There was no evidence of pleiotropy or reverse causal effects for these candidate metabolites. Conclusions In our metabolome-wide MR study, we discovered a notable protective effect of caffeic acid against UC.
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