Genetic associations in the gut–lung axis: a Mendelian randomization study and in vitro assessment of sodium butyrate in non-small cell lung cancer

Abstract

The gut microbiota may influence host immunity, but the relationship between specific microbial genera and non-small cell lung cancer (NSCLC) risk remains uncertain. We evaluated genetically proxied microbial abundance and conducted separate exploratory experiments with sodium butyrate (NaB). Two-sample Mendelian randomization (MR) used genus-level MiBioGen summary statistics and FinnGen/OpenGWAS NSCLC data (finn-b-C3_LUNG_NONSMALL; 1,627 cases and 217,165 controls). Instruments were selected at P < 1 × 10 −5 with linkage disequilibrium clumping (r 2 < 0.001; 10,000 kb) and F > 10. Inverse variance weighting (IVW) was the primary estimator; Benjamini–Hochberg false discovery rate (BH-FDR) correction was applied across 119 genera. Sensitivity analyses included MR-Egger, weighted median, mode-based methods, heterogeneity, pleiotropy and leave-one-out analyses. NaB, used as a representative microbial metabolite rather than a taxon-specific product, was evaluated at 1 mM for 24 h in tumor-conditioned medium (TCM) experiments. Six genera showed nominal inverse IVW associations with NSCLC risk (P = 0.0120–0.0498): Alistipes, Methanobrevibacter, Bacteroides , Ruminococcus gauvreauii group, Ruminococcus 1 and Peptococcus . None survived BH-FDR correction (q = 0.6072–0.9819). Sensitivity tests did not detect heterogeneity or directional pleiotropy for these genera, but alternative estimators and leave-one-out analyses did not consistently retain nominal significance. In THP-1-derived macrophages, NaB treatment altered polarization-associated transcripts, reduced the TCM-associated CCK-8 signal and increased acetylated histone H3 (Ac-H3) relative to TCM alone. The MR analysis identifies six suggestive microbial associations with NSCLC risk that require independent replication. Complementary NaB experiments show changes in macrophage-associated transcripts, metabolic viability and histone acetylation, providing a basis for further study of microbial metabolites in the tumor microenvironment.