Salivary metabolomics of burning mouth syndrome: A cross-sectional study.

OBJECTIVE: There is a lack of systematic studies on salivary metabolomic profiles in burning mouth syndrome (BMS); metabolomics could help explore BMS pathogenesis. We aimed to explore the salivary metabolomic profile of patients with BMS using untargeted metabolomics techniques. DESIGN: A cross-sectional study was designed to analyze the characteristics of unstimulated whole salivary metabolomics of patients with BMS (n = 34) and healthy participants (n = 30). Ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry, principal component, orthogonal partial least-squares-discriminant, hierarchical clustering, and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed to identify differentially expressed metabolites and metabolic pathways in which they were enriched. RESULTS: We identified 12,982 metabolite ions. Among them, 394 differentially expressed metabolites were identified with variable importance in projection scores of > 1 (P < 0.05) compared with those in the controls. Based on the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis, 30 metabolites were identified, and 16 of them were enriched in 25 metabolic pathways. The levels of caffeine (log2-fold change = -2.91) and its metabolites, paraxanthine (-2.01) and theophylline (-2.03), were low, and the caffeine metabolism pathway was downregulated in the BMS group compared with those in the controls (P < 0.05). CONCLUSIONS: The salivary metabolomic profile of patients with BMS presented characteristics distinct from those of the controls. A low caffeine level may be associated with BMS. This study provides a novel insight for further exploration of the pathogenesis of and potential therapeutic approaches for BMS.