Causal Link between Human Blood Metabolites and Asthma: An Investigation Using Mendelian Randomization

Background: Asthma, a chronic inflammatory respiratory ailment, is characterized by variable airflow obstruction and heightened bronchial reactivity. Despite therapeutic advancements, a comprehensive comprehension of its underlying metabolic mechanisms remains elusive. Metabolomics has emerged as a powerful approach to investigating the complex connections between serum metabolites and disease pathogenesis. However, exploring the causal relationship between serum metabolites and asthma susceptibility demands meticulous examination to unveil potential therapeutic targets. Methods: Mendelian randomization (MR) approach was explored to investigate the potential causal associations between serum metabolites and asthma risk. The main analysis employed the inverse variance weighted method, supported by supplementary approaches such as MR-Egger, weighted median, weighted mode, and sample mode. To enhance the strength and credibility of our results, we conducted sensitivity analyses encompassing heterogeneity testing, assessment of horizontal pleiotropy, and leave-one-out analysis. Additionally, pathway enrichment analysis was performed to further elucidate the results. Results: We identified 18 known and 12 unknown metabolites with potential associations with asthma risk. Among known metabolites, seven exhibited protective effects (e.g., 4-acetamidobutanoate, allantoin, kynurenine, oxidized bilirubin*), while eleven were considered risk factors (e.g., ornithine, N-acetylornithine, alanine). Through the integration of four additional MR models and sensitivity analyses, we revealed a connection between 4-acetamidobutanoate and approximately 6% lower asthma risk (OR = 0.94, 95% CI: 0.90–0.98). Conclusions: Our MR analysis uncovered protective and risk-associated metabolites, alongside 12 unknown metabolites linked to asthma. Notably, 4-acetamidobutanoate demonstrated a nominal 6% reduction in asthma risk, highlighting its potential significance. Abbreviations: MR: Mendelian Randomization; IVs: Instrumental Variables; IVW: Inverse Variance Weighted; SNPs: Single Nucleotide Polymorphisms; LD: Linkage Disequilibrium; β: Effect Size; SE: Standard Error; EAF: Effect Allele Frequency; R2: Instrumental Variable; N: Sample Size; k: SNP Count