Daily and Circadian Variations in Salivary Metabolome

Objectives: In recent years, the number of patients complaining of symptoms of oral discomfort has been increasing. An increase in the amount of saliva by the recovery of chewing ability is effective in improving oral discomfort. In addition, metabolome analysis shows a difference in the metabolites of stimulated and unstimulated saliva. However, collected criteria of saliva metabolites are unknown. In this study, we investigated whether the saliva collection time affects the salivary metabolomic profile.
Methods: Stimulated and unstimulated salivary samples using the spitting method and gum test were collected from 13 subjects with normal occlusion state. Salivary samples were collected in the morning (9:00), noon (13:00), and evening (17:00), three times for one week (Monday, Wednesday, Friday). The metabolomic profiles of saliva were quantified using capillary electrophoresis time-of-flight mass spectrometry. Principal component analyses (PCA) was performed in order to evaluate the metabolomic profiles. The Wilcoxon matched pairs test was used for the analysis of salivary sample. P-values were corrected by using the false discovery rate (FDR).This study protocol was approved by the ethics committees of Kanagawa Dental University (no.243).
Results: A difference in the metabolomic profile was observed between stimulated and unstimulated saliva. Daily and circadian variations were observed in the metabolomic profile of unstimulated saliva.
Conclusions: Metabolites of stimulated and unstimulated saliva were studied to identify daily and circadian variation. Different saliva collection times affect the salivary metabolomic profile. Future studies on the saliva metabolomic profile should take into account the effect of saliva collection time.