Metabolomic insights into idiopathic xerostomia: The central role of caffeine metabolism in salivary biochemistry.

OBJECTIVE: This study aims to delineate the salivary metabolomic profile of patients with idiopathic xerostomia using untargeted metabolomics techniques, with the goal of addressing the lack of clear diagnostic markers and providing insights into the pathophysiological mechanisms of the condition. DESIGN: In this observational, cross-sectional study, saliva samples from 33 patients with idiopathic xerostomia and 34 healthy controls were analyzed using Ultra Performance Liquid Chromatography Quadrupole Time of Flight Mass Spectrometry (UPLC-QTOF MS). Metabolomic profiling was complemented by multivariate statistical analysis to differentiate between affected individuals and controls. RESULTS: Metabolomic analysis delineated a pronounced differentiation between patients with idiopathic xerostomia and healthy controls. A total of 195 metabolites displayed significant differential expression, each with a variable importance in projection (VIP) greater than 1 and a P-value less than 0.05. Pathway enrichment analysis, according to the Kyoto Encyclopedia of Genes and Genomes (KEGG), identified 22 metabolites that participated in 18 distinct metabolic pathways. Among these, the caffeine metabolism pathway, characterized by notable alterations in impact values (VIP, P-value, Log2-fold change, Rich factor), emerged as the most significantly disrupted, underscoring its potential role in the pathophysiology of idiopathic xerostomia (P = 0.0000395). CONCLUSIONS: The salivary metabolomic profiling revealed distinct alterations in idiopathic xerostomia, with a significant reduction in caffeine metabolism pathways, underscoring potential neuropathic involvement. This study advances our understanding of the metabolic alterations in xerostomia, suggesting that salivary metabolomics may offer viable biomarkers for diagnosing and understanding the etiology of idiopathic xerostomia. Future research should focus on therapeutic targeting of these metabolic disturbances and evaluating their reversibility with treatment.