Dietary nitrate drives gastritis by modulating gastric microbiota and metabolites

Objective: Dietary nitrate has been increasingly recognized as a potential carcinogen associated with gastritis. In this study the mechanistic role of a high-nitrate diet (NaD) in driving gastritis was elucidated with a focus on modulation of the gastric microbiota composition and metabolomic profiles. Methods: Animals were randomly assigned to two dietary intervention groups using a C57BL/6 mouse model: a NaD containing 7.5% nitrate; or a standard normal diet (ND). Gastric microbiota composition was characterized based on full-length 16S rRNA sequencing and gastric metabolite profiles were analyzed using high-performance liquid chromatography-mass spectrometry (HPLC/MS). Finally, the roles of the microbiome and metabolites in gastritis development were validated using the human gastric epithelial cell line (GES-1), as well as conventional and germ-free mouse models. Results: NaD induced gastritis in conventional mice compared to ND-fed mice. In addition, NaD incited the infiltration of macrophages and neutrophils with elevated levels of inflammatory cytokine genes (IL-17a, Ccl20, Cxcl5, IL-6, and Ccl2). A significant shift in the composition of the gastric microbiota occurred with an increase in pathogenic bacteria (Enterococcus gallinarum, Prevotella timonensis, and Mycobacterium gordona) and a decrease in probiotics (Roseburia hominis, Clostriduim scindens, and Faecalibacterium prausnitzii). Furthermore, NaD induced alterations in the metabolic profile, marked by an elevated level of 5-hydroxyindoleacetate (5-HIAA), a key downstream metabolite of the tryptophan metabolic pathway. Notably, 5-HIAA also upregulated the levels of inflammatory cytokines in the human gastric epithelial GES-1 cell line. In addition, both E. gallinarum colonization and 5-HIAA exposure significantly increased inflammatory responses in conventional and germ-free mouse models. Conclusions: NaD drives gastritis in mice by inducing gastric microbial dysbiosis and metabolomic dysregulation with elevated 5-HIAA.